WorldWideScience

Sample records for active galactic nuclei

  1. Active galactic nuclei

    Blandford, RD; Woltjer, L

    1990-01-01

    Starting with this volume, the Lecture Notes of the renowned Advanced Courses of the Swiss Society for Astrophysics and Astronomy will be published annually. In each course, three extensive lectures given by leading experts in their respective fields cover different and essential aspects of the subject. The 20th course, held at Les Diablerets in April 1990, dealt with current research on active galactic nuclei; it represents the most up-to-date views on the subject, presented with particular regard for clarity. The previous courses considered a wide variety of subjects, beginning with ""Theory

  2. Active galactic nuclei

    Beckmann, Volker

    2012-01-01

    This AGN textbook includes phenomena based on new results in the X-Ray domain from new telescopes such as Chandra and XMM Newton not mentioned in any other book. Furthermore, it considers also the Fermi Gamma Ray Space Telescope with its revolutionary advances of unprecedented sensitivity, field of view and all-sky monitoring. Those and other new developments as well as simulations of AGN merging events and formations, enabled through latest super-computing capabilities. The book gives an overview on the current knowledge of the Active Galacitc Nuclei phenomenon. The spectral energy d

  3. Variability of Active Galactic Nuclei

    Peterson, Bradley M.

    2001-01-01

    Continuum and emission-line variability of active galactic nuclei provides a powerful probe of microarcsecond scale structures in the central regions of these sources. In this contribution, we review basic concepts and methodologies used in analyzing AGN variability. We develop from first principles the basics of reverberation mapping, and pay special attention to emission-line transfer functions. We discuss application of cross-correlation analysis to AGN light curves. Finally, we provide a ...

  4. Evolution of active galactic nuclei

    Merloni, Andrea

    2012-01-01

    [Abriged] Supermassive black holes (SMBH) lurk in the nuclei of most massive galaxies, perhaps in all of them. The tight observed scaling relations between SMBH masses and structural properties of their host spheroids likely indicate that the processes fostering the growth of both components are physically linked, despite the many orders of magnitude difference in their physical size. This chapter discusses how we constrain the evolution of SMBH, probed by their actively growing phases, when they shine as active galactic nuclei (AGN) with luminosities often in excess of that of the entire stellar population of their host galaxies. Following loosely the chronological developments of the field, we begin by discussing early evolutionary studies, when AGN represented beacons of light probing the most distant reaches of the universe and were used as tracers of the large scale structure. This early study turned into AGN "Demography", once it was realized that the strong evolution (in luminosity, number density) of ...

  5. Energy Radiation of the Active Galactic Nuclei

    TANG Zhi-Ming; WANG Yong-Jiu

    2004-01-01

    In the Hellings-Nordtvedt theory, we obtain some expressions of energy radiation and mass defect effect for a kind of the active galactic nuclei, which is meaningful to calculating the energy radiation in the procession of forming this kind of celestial bodies. This calculation can give some interpretation for energy source of the jet from the active galactic nuclei.

  6. Power spectra of active galactic nuclei

    2009-01-01

    The power spectral densities(PSDs)for a sample of active galactic nuclei(AGNs)are analyzed in both the frequency domain and the time domain.We find for each object that for broadband noise a character timescale-bifurcation timescale of Fourier and time-domain PSD exists in the 10 3 -10 6 s range, below which the time-domain power spectrum is systematically higher than the corresponding Fourier spectrum.The relationship between bifurcation timescale,AGN mass and luminosity is studied.Compared with the fact that similar phenomena have been found for Galactic black hole candidates(GBHs) with bifurcation timescale~0.1 s but not for accreting neutron stars,our finding indicates that AGNs and GBHs have common intrinsic nature in rapid X-ray variability with a character time parameter scaled with their masses.

  7. Power spectra of active galactic nuclei

    WANG TaiShan; WU YuXiang; LIU Yuan

    2009-01-01

    The power spectral densities (PSDs) for a sample of active galactic nuclei (AGNs) are analyzed in both the frequency domain and the time domain. We find for each object that for broadband noise a character timescale-bifurcation timescale of Fourier and time-domain PSD exists in the 103-106 s range,below which the time-domain power spectrum is systematically higher than the corresponding Fourier spectrum. The relationship between bifurcation timescale, AGN mass and luminosity is studied. Compared with the fact that similar phenomena have been found for Galactic black hole candidates (GBHs)with bifurcation timescale ~0.1 s but not for accreting neutron stars, our finding indicates that AGNs and GBHs have common intrinsic nature in rapid X-ray variability with a character time parameter scaled with their masses.

  8. Stellar transits in active galactic nuclei

    Béky, Bence

    2012-01-01

    Supermassive black holes (SMBH) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGN) produce a characteristic transit lightcurve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit lightcurves using the Novikov--Thorne thin accretion disk model, including general relatistic effects. Based on the expected properties of stellar cusps, we find that around 10^6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low mass AGNs to 1% photometric accuracy in optical, or ~ 10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Su...

  9. Stellar Transits in Active Galactic Nuclei

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 106 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ~10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  10. Einstein Observatory results on active galactic nuclei

    Mushotzky, R. F.; Holt, S. S.

    1982-01-01

    The results of Einstein Observatory surveys of active galactic nuclei (AGN) are reviewed. The ubiquity of X-ray emission from AGNs was confirmed. The relations between X-ray and optical luminosities, between X-ray and radio properties, and between X-ray and optical-UV line emission found by the surveys are summarized and briefly discussed. The possible causes of observed X-ray emission from jets in Cen-A, 3C273, and M87 are considered. The active nucleus discovered in the optically 'dull' galaxy NGC 4156 is covered, and a model for NGC 4151 based on detailed spectral studies is briefly discussed. This model establishes the global symmetry of the AGN clouds, their approximate sizes, and their ionization state. Difficulties encountered in attempting to explain the cosmic X-ray background in terms of AGN contributions are addressed.

  11. Active Galactic Nuclei Feedback and Clusters

    Biman B. Nath

    2011-12-01

    The Intracluster Medium (ICM) is believed to have been affected by feedback from Active Galactic Nuclei (AGN) and/or supernovae-driven winds. These sources are supposed to have injected entropy into the ICM gas. The recently determined universal pressure profile of the ICM gas has been used and after comparing with the entropy profile of the gas from gravitational effects of the dark matter halo, the additional entropy injected by non-gravitational sources, as a function of the total cluster mass is determined. The current observational data of red-shift evolution of cluster scaling relation is shown that allow models in which the entropy injection decreases at high red-shift.

  12. Broad iron lines in Active Galactic Nuclei

    Fabian, A C; Reynolds, C S; Young, A J

    2000-01-01

    An intrinsically narrow line emitted by an accretion disk around a black hole appears broadened and skewed as a result of the Doppler effect and gravitational redshift. The fluorescent iron line in the X-ray band at 6.4-6.9keV is the strongest such line and is seen in the X-ray spectrum of many active galactic nuclei and, in particular, Seyfert galaxies. It is an important diagnostic with which to study the geometry and other properties of the accretion flow very close to the central black hole. The broad iron line indicates the presence of a standard thin accretion disk in those objects, often seen at low inclination. The broad iron line has opened up strong gravitational effects around black holes to observational study with wide-reaching consequences for both astrophysics and physics.

  13. Cluster magnetic fields from active galactic nuclei

    Sutter, P M; Yang, H -Y

    2009-01-01

    Active galactic nuclei (AGN) found at the centers of clusters of galaxies are a possible source for weak cluster-wide magnetic fields. To evaluate this scenario, we present 3D adaptive mesh refinement MHD simulations of a cool-core cluster that include injection of kinetic, thermal, and magnetic energy via an AGN-powered jet. Using the MHD solver in FLASH 2, we compare several sub-resolution approaches that link the estimated accretion rate as measured on the simulation mesh to the accretion rate onto the central black hole and the resulting feedback. We examine the effects of magnetized outflows on the accretion history of the black hole and discuss the ability of these models to magnetize the cluster medium.

  14. Suzaku observations of 'bare' active galactic nuclei

    Walton, D J; Fabian, A C; Gallo, L C; Reis, R C

    2012-01-01

    We present a X-ray spectral analysis of a large sample of 25 'bare' active galactic nuclei, sources with little or no complicating intrinsic absorption, observed with Suzaku. Our work focuses on studying the potential contribution from relativistic disc reflection, and examining the implications of this interpretation for the intrinsic spectral complexities frequently displayed by AGN in the X-ray bandpass. During the analysis, we take the unique approach of attempting to simultaneously undertake a systematic analysis of the whole sample, as well as a detailed treatment of each individual source, and find that disc reflection has the required flexibility to successfully reproduce the broadband spectrum observed for all of the sources considered. Where possible, we use the reflected emission to place constraints on the black hole spin for this sample of sources. Our analysis suggests a general preference for rapidly rotating black holes, which if taken at face value is most consistent with the scenario in whic...

  15. Launching of Active Galactic Nuclei Jets

    Tchekhovskoy, Alexander

    As black holes accrete gas, they often produce relativistic, collimated outflows, or jets. Jets are expected to form in the vicinity of a black hole, making them powerful probes of strong-field gravity. However, how jet properties (e.g., jet power) connect to those of the accretion flow (e.g., mass accretion rate) and the black hole (e.g., black hole spin) remains an area of active research. This is because what determines a crucial parameter that controls jet properties—the strength of large-scale magnetic flux threading the black hole—remains largely unknown. First-principles computer simulations show that due to this, even if black hole spin and mass accretion rate are held constant, the simulated jet powers span a wide range, with no clear winner. This limits our ability to use jets as a quantitative diagnostic tool of accreting black holes. Recent advances in computer simulations demonstrated that accretion disks can accumulate large-scale magnetic flux on the black hole, until the magnetic flux becomes so strong that it obstructs gas infall and leads to a magnetically-arrested disk (MAD). Recent evidence suggests that central black holes in jetted active galactic nuclei and tidal disruptions are surrounded by MADs. Since in MADs both the black hole magnetic flux and the jet power are at their maximum, well-defined values, this opens up a new vista in the measurements of black hole masses and spins and quantitative tests of accretion and jet theory.

  16. Quasi periodic oscillations in active galactic nuclei

    Alston, W.; Fabian, A.; Markevičiutė, J.; Parker, M.; Middleton, M.; Kara, E.

    2016-05-01

    Quasi-periodic oscillations (QPOs) are coherent peaks of variability power observed in the X-ray power spectra (PSDs) of stellar mass X-ray binaries (XRBs). A scale invariance of the accretion process implies they should be present in the active galactic nuclei. The first robust detection was a ∼ 1 h periodicity in the Seyfert galaxy RE J1034+396 from a ∼ 90 ks XMM-Newton observation; however, subsequent observations failed to detect the QPO in the 0.3-10.0 keV band. In this talk we present the recent detection of the ∼ 1 h periodicity in the 1.0-4.0 keV band of 4 further low-flux/spectrally-harder observations of RE J1034+396 (see Alston et al. 2014). We also present recent work on the discovery of a QPO in the Seyfert galaxy, MS 2254.9-3712, which again is only detected in energy bands associated with the primary power-law continuum emission (Alston et al. 2015). We conclude these features are most likely analogous to the high-frequency QPOs observed in XRBs. In both sources, we also see evidence for X-ray reverberation at the QPO frequency, where soft X-ray bands and Iron Kα emission lag the primary X-ray continuum. These time delays may provide another diagnostic for understanding the underlying QPO mechanism observed in accreting black holes.

  17. Warped circumbinary disks in active galactic nuclei

    We study a warping instability of a geometrically thin, non-self-gravitating disk surrounding binary supermassive black holes on a circular orbit. Such a circumbinary disk is subject to not only tidal torques due to the binary gravitational potential but also radiative torques due to radiation emitted from an accretion disk around each black hole. We find that a circumbinary disk initially aligned with the binary orbital plane is unstable to radiation-driven warping beyond the marginally stable warping radius, which is sensitive to both the ratio of vertical to horizontal shear viscosities and the mass-to-energy conversion efficiency. As expected, the tidal torques give no contribution to the growth of warping modes but tend to align the circumbinary disk with the orbital plane. Since the tidal torques can suppress the warping modes in the inner part of circumbinary disk, the circumbinary disk starts to be warped at radii larger than the marginally stable warping radius. If the warping radius is of the order of 0.1 pc, a resultant semi-major axis is estimated to be of the order of 10–2 pc to 10–4 pc for 107 M☉ black hole. We also discuss the possibility that the central objects of observed warped maser disks in active galactic nuclei are binary supermassive black holes with a triple disk: two accretion disks around the individual black holes and one circumbinary disk surrounding them.

  18. TANAMI - Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry

    Mueller, Cornelia; Kadler, Matthias; Ojha, Roopesh; De Boeck, M.; Booth, R.; Dutka, M. S.; Edwardsk, P.; Fey, A. L.; Fuhrmann, L.; Hase, H.; Horiuchi, S.; Jauncey, D. L.; Johnston, K.J.; Katz, U.; Lister, M.

    2009-01-01

    We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Australian Long Baseline Array (LBA) and the trans-oceanic antennas Hartebeesthoek, TIGO, and O'Higgins. TANAMI is focusing on extragalactic sources south of -30 degrees declination with observations a...

  19. LINERs as Low-Luminosity Active Galactic Nuclei

    Ho, L C

    1998-01-01

    Many nearby galaxies contain optical signatures of nuclear activity in the form of LINER nuclei. LINERs may be the weakest and most common manifestation of the quasar phenomenon. The physical origin of this class of objects, however, has been ambiguous. I draw upon a number of recent observations to argue that a significant fraction of LINERs are low-luminosity active galactic nuclei.

  20. Recurrent Activity in Active Galactic Nuclei

    Saikia, D J

    2010-01-01

    There has been a growing body of evidence to suggest that AGN activity, which is powered by mass accretion on to a supermasive black hole, could be episodic, although the range of time scales involved needs to be explored further. The structure and spectra of radio emission from radio galaxies, whose sizes range up to $\\sim$5 Mpc, contain information on the history of AGN activity in the source. They thus provide a unique opportunity to study the time scales of recurrent AGN activity. The most striking examples of recurrent activity in radio galaxies and quasars are the double-double or triple-double radio sources which contain two or three pairs of distinct lobes on opposite sides of the parent optical object. Spectral and dynamical ages of these lobes could be used to constrain time scales of episodic activity. Inverse-Compton scattered cosmic microwave background radiation could in principle probe lower Lorentz-factor particles than radio observations of synchrotron emission, and thereby reveal an older po...

  1. ACTIVE GALACTIC NUCLEI WITH DOUBLE-PEAKED NARROW LINES: ARE THEY DUAL ACTIVE GALACTIC NUCLEI?

    Double-peaked [O III] profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from ∼7000 active galaxies in Sloan Digital Sky Survey DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O III] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at ∼1 kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about ∼10-2, impacting on the current observational deficit of binary supermassive black holes with a probability of ∼10-4 (Boroson and Lauer).

  2. Active Galactic Nuclei Discovered in the Kepler Mission

    Shaya, Edward J.; Olling, Robert; Mushotzky, Richard

    2015-12-01

    We report on candidate active galactic nuclei (AGNs) discovered during the monitoring of ∼500 bright (r variability over three month periods, as seen in the SFs and power spectral densities (PSDs), can dramatically change for many of these AGN candidates. Four of the candidates have features in their SFs that may indicate quasi-periodic behavior, although other possibilities are discussed.

  3. Environment and properties of obscured and unobscured active galactic nuclei

    Taormina, M.; Bornancini, C.

    We analyze the properties of obscured and unobscured active galactic nuclei selected using mid-infrared colors in the redshift range 1 < z < 3. We find that obscured objects are located in a denser local galaxy environment compared to the unobscured sample.

  4. Active galactic nuclei shed light on axion-like-particles

    Burrage, Clare [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Davis, Anne-Christine [Centre for Mathematical Sciences, Cambridge (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics; Shaw, Douglas J. [London Univ. (United Kingdom). Astronomy Unit, School of Mathematical Sciences

    2009-02-15

    We demonstrate that the scatter in the luminosity relations of astrophysical objects can be used to search for axion-like-particles (ALPs). This analysis is applied to observations of active galactic nuclei, where we find evidence highly suggestive of the existence of a very light ALP. (orig.)

  5. Active Galactic Nuclei as High-Energy Neutrino Sources

    Murase, Kohta

    2015-01-01

    Active galactic nuclei (AGN) are believed to be promising candidates of extragalactic cosmic-ray accelerators and sources, and associated high-energy neutrino and hadronic gamma-ray emission has been studied for many years. We review models of high-energy neutrino production in AGN, and discuss their implications for the latest IceCube observation of the diffuse neutrino intensity.

  6. Conference Summary: The Central Engine of Active Galactic Nuclei

    Netzer, Hagai; Shields, Joseph C.

    2007-01-01

    The 2006 meeting in Xi'an on the Central Engine of Active Galactic Nuclei covered the enormous and continuously expanding area of AGN research, from theory to the most sophisticated observations and from gamma-ray energies to long radio wavelengths. This short summary gives some, but definitely not all, highlights and new results presented by the participants.

  7. The Radius-Luminosity Relationship for Active Galactic Nuclei

    Bentz, Misty C.; Peterson, Bradley M.; Pogge, Richard W.; Vestergaard, Marianne; Onken, Christopher A.

    2006-01-01

    We have obtained high resolution images of the central regions of 14 reverberation-mapped active galactic nuclei (AGN) using the Hubble Space Telescope Advanced Camera for Surveys High Resolution Camera to account for host-galaxy starlight contamination of measured AGN luminosities. We measure the...

  8. Black Hole Demography from Nearby Active Galactic Nuclei

    Ho, Luis C.

    2004-01-01

    A significant fraction of local galaxies show evidence of nuclear activity. I argue that the bulk of this activity, while energetically not remarkable, derives from accretion onto a central massive black hole. The statistics of nearby active galactic nuclei thus provide an effective probe of black hole demography. Consistent with the picture emerging from direct dynamical studies, the local census of nuclear activity strongly suggests that most, perhaps all, galaxies with a significant bulge ...

  9. The X-ray spectroscopy of active galactic nuclei

    Mushotzky, R.

    1985-01-01

    The scientific goals of X-ray spectroscopy of active galactic nuclei are discussed. The underlying energy source, the regions responsible for the optical emission lines, the different types of active galaxies, and cosmology are considered. The requirements for an X-ray mission of broad band width, large collecting area, modest spatial resolution and good spectral resolution are outlined. It is concluded that the ESA XMM mission meets these requirements.

  10. Thermal-nonthermal relationships in active galactic nuclei

    This dissertation reports on optical and radio observations of active galactic nuclei, selected on the basis of the presence of dominant narrow (narrow line radio galaxies, Seyfert II galaxies, QSOs) and/or broad (broad line radio galaxies, Seyfert I galaxies, QSOs) optical emission lines in their spectra. Special attention is drawn to possible relationships and physical links between the two regimes responsible for the optical (thermal) and radio (non-thermal) emission. Several projects, each studying such relationships on different angular (and thus linear) scales and at different observational frequencies were conceived with a variety of detection devices. (Auth.)

  11. Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei

    Mushotzky, R. F.; Edelson, R.; Baumgartner, W. H.; Gandhi, P.

    2012-01-01

    Over three quarters in 2010 - 2011, Kepler monitored optical emission from four active galactic nuclei (AGN) with approx 30 min sampling, > 90% duty cycle and approx AGN optical fluctuation power spectral density functions (PSDs) over a wide range in temporal frequency. Fits to these PSDs yielded power law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGN exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first order MRI theoretical calculations of accretion disk fluctuations.

  12. The role of active galactic nuclei in galaxy formation

    Thomas, P A

    2009-01-01

    We use Monte-Carlo Markov chain techniques to constrain acceptable parameter regions for the Munich L-Galaxies semi-analytic galaxy formation model. Feedback from active galactic nuclei (AGN) is required to limit star-formation in the most massive galaxies. However, we show that the introduction of tidal stripping of dwarf galaxies as they fall into and merge with their host systems can lead to a reduction in the required degree of AGN feedback. In addition, the new model correctly reproduces both the metallicity of large galaxies and the fraction of intracluster light.

  13. The interaction between feedback from active galactic nuclei and supernovae

    Booth, C. M.; Joop Schaye

    2012-01-01

    Energetic feedback from supernovae (SNe) and from active galactic nuclei (AGN) are both important processes that are thought to control how much gas is able to condense into galaxies and form stars. We show that although both AGN and SNe suppress star formation, they mutually weaken one another's effect by up to an order of magnitude in haloes in the mass range for which both feedback processes are efficient (10^11.25 M_sun < m_200 < 10^12.5 M_sun). These results demonstrate the importance of...

  14. Emission line regions of active galactic nuclei and quasars

    The observational constraints on the conditions in the gas which give rise to the emission lines seen in the spectra of quasars and active galactic nuclei are summarized, with particular attention being paid to the region responsible for the broad lines. Some general requirements on the physical conditions and geometry are described, and the emission line region of the quasar 3C273 is used to illustrate the successes, and shortcomings, of photoionization models. Comparisons of the emission line profiles of different ions show that there must be some radial flow, and obscuration, in the region of the emission line material

  15. Statistics of Superluminal Motion in Active Galactic Nuclei

    Yong-Wei Zhang; Jun-Hui Fan

    2008-01-01

    We have collected an up-to-date sample of 123 superluminal sources (84 quasars, 27 BL Lac objects and 12 galaxies) and calculated the apparent velocities (βapp) for 224 components in the sources with the A-CDM model. We checked the relationships between their proper motions, redshifts,βapp and 5 GHz flux densities. Our analysis shows that the radio emission is strongly boosted by the Doppler effect. The superluminal motion and the relativistic beaming boosting effect are, to some extent, the same in active galactic nuclei.

  16. Photon-axion conversion in Active Galactic Nuclei?

    Bassan, Nicola

    2009-01-01

    Axion-Like Particles (ALPs) are the focus of intense current research. We analyze photon-ALP conversion in the context of relativistic jet models of Active Galactic Nuclei (AGN) for more than 100 sources. Contrary to previous claims, we find that this process cannot occur above 100 GeV regardless of the actual AGN model and the values of ALP parameters. This result rules out a proposed strategy to bypass the cosmic opacity above 100 GeV, as apparently required by observations. We also show that for some AGN an observable effect can show up in the X and soft gamma-ray bands.

  17. Magnetic flare model of quasars and active galactic nuclei

    As a model of quasars and active galactic nuclei, we present the magnetic flare model which clarifies the connection between the primary energy source and the non-thermal phenomena. The behavior of the magnetic field generated in the accretion disk around a massive black hole is investigated in terms of the αω-dynamo and the magnetic buoyancy. The magnetic field is responsible not only for the angular momentum transfer but also for the vertical energy transfer owing to the magnetic buoyancy. Magnetic energy thus transferred should be released in the coronal region above the disk surface through its flare-like reconnection as in the solar flare. We expect that it will produce a variety of non-thermal activities characteristic to quasars and active galactic nuclei. We argue that the following scenario is compatible with various observations: A flare generates the relativistic shock behind which electrons are heated up to the relativistic energy. Subsequently, they produce X and γ rays by the inverse Compton scattering of low energy photons as well as emit from radio up to soft X photons by the synchrotron radiation. (author)

  18. The Angular Clustering of WISE-selected Active Galactic Nuclei: Different Halos for Obscured and Unobscured Active Galactic Nuclei

    Donoso, E.; Yan, Lin; Stern, D; Assef, R. J.

    2014-01-01

    We calculate the angular correlation function for a sample of ~170,000 active galactic nuclei (AGNs) extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1 − W2 > 0.8) and 4.6 μm flux densities brighter than 0.14 mJy). The sample is expected to be >90% reliable at identifying AGNs and to have a mean redshift of 〈z〉 = 1.1. In total, the angular clustering of WISE AGNs is roughly similar to that of optical AGNs. We cross-match these objects...

  19. TANAMI - Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry

    Mueller, Cornelia; Ojha, Roopesh; Boeck, M; Booth, R; Dutka, M S; Edwardsk, P; Fey, A L; Fuhrmann, L; Hase, H; Horiuchi, S; Jauncey, D L; Johnston, K J; Katz, U; Lister, M; Lovell, J E J; Ploetz, C; Quick, J F H; Ros, E; Taylor, G B; Thompson, D J; Tingay, S J; Tosti, G; Tzioumisk, A K; Wilms, J; Zensus, J A

    2009-01-01

    We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Australian Long Baseline Array (LBA) and the trans-oceanic antennas Hartebeesthoek, TIGO, and O'Higgins. TANAMI is focusing on extragalactic sources south of -30 degrees declination with observations at 8.4 GHz and 22 GHz every ~2 months at milliarcsecond resolution. The initial TANAMI sample of 43 sources has been defined before the launch of the Fermi Gamma Ray Space Telescope to include the most promising candidates for bright gamma-ray emission to be detected with its Large Area Telescope (LAT). Since November 2008, we have been adding new sources to the sample, which now includes all known radio- and gamma-ray bright AGN of the Southern Hemisphere. The combination of VLBI and gamma-ray observations is crucial to u...

  20. Active galactic nuclei at gamma-ray energies

    Dermer, Charles Dennison

    2016-01-01

    Active Galactic Nuclei can be copious extragalactic emitters of MeV-GeV-TeV gamma rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. Most of gamma-ray emitting active galactic nuclei, with more than 1500 known at GeV energies, and more than 60 at TeV energies, are called "blazars". The standard blazar paradigm features a jet of relativistic magnetized plasma ejected from the neighborhood of a spinning and accreting super-massive black hole, close to the observer direction. Two classes of blazars are distinguished from observations: the flat-spectrum radio-quasar class (FSRQ) is characterized by strong external radiation fields, emission of broad optical lines, and dust tori. The BL Lac class (from the name of one of its members, BL Lacertae) corresponds to weaker advection-dominated flows with gamma-ray spectra dominated by the inverse Compton effect on synchrotron photons. This paradigm has been very successful for modeling t...

  1. The effects of the local environment on active galactic nuclei

    Manzer, L. H.; De Robertis, M. M., E-mail: liannemanzer@gmail.com, E-mail: mmdr@yorku.ca [Department of Physics and Astronomy, York University, Toronto, ON M3J 1P3 (Canada)

    2014-06-20

    There continues to be significant controversy regarding the mechanism(s) responsible for the initiation and maintenance of activity in galactic nuclei. In this paper we will investigate possible environmental triggers of nuclear activity through a statistical analysis of a large sample of galaxy groups. The focus of this paper is to identify active galactic nuclei (AGNs) and other emission-line galaxies in these groups and to compare their frequency with a sample of over 260,000 isolated galaxies from the same catalog. The galaxy groups are taken from the catalog of Yang et al., in which over 20,000 virialized groups of galaxies (2 ≤ N ≤ 20) with redshifts between 0.01 and 0.20 are from the Sloan Digital Sky Survey. We first investigate the completeness of our data set and find, though biases are a concern particularly at higher redshift, that our data provide a fair representation of the local universe. After correcting emission-line equivalent widths for extinction and underlying Balmer stellar absorption, we classify galaxies in the sample using traditional emission-line ratios, while incorporating measurement uncertainties. We find a significantly higher fraction of AGNs in groups compared with the isolated sample. Likewise, a significantly higher fraction of absorption-line galaxies are found in groups, while a higher fraction of star-forming galaxies prefer isolated environments. Within grouped environments, AGNs and star-forming galaxies are found more frequently in small- to medium-richness groups, while absorption-line galaxies prefer groups with larger richnesses. Groups containing only emission-line galaxies have smaller virial radii, velocity dispersions, and masses compared with those containing only absorption-line galaxies. Furthermore, the AGN fraction increases with decreasing distance to the group centroid, independent of galaxy morphology. Using properties obtained from Galaxy Zoo, there is an increased fraction of AGNs within merging systems

  2. The effects of the local environment on active galactic nuclei

    There continues to be significant controversy regarding the mechanism(s) responsible for the initiation and maintenance of activity in galactic nuclei. In this paper we will investigate possible environmental triggers of nuclear activity through a statistical analysis of a large sample of galaxy groups. The focus of this paper is to identify active galactic nuclei (AGNs) and other emission-line galaxies in these groups and to compare their frequency with a sample of over 260,000 isolated galaxies from the same catalog. The galaxy groups are taken from the catalog of Yang et al., in which over 20,000 virialized groups of galaxies (2 ≤ N ≤ 20) with redshifts between 0.01 and 0.20 are from the Sloan Digital Sky Survey. We first investigate the completeness of our data set and find, though biases are a concern particularly at higher redshift, that our data provide a fair representation of the local universe. After correcting emission-line equivalent widths for extinction and underlying Balmer stellar absorption, we classify galaxies in the sample using traditional emission-line ratios, while incorporating measurement uncertainties. We find a significantly higher fraction of AGNs in groups compared with the isolated sample. Likewise, a significantly higher fraction of absorption-line galaxies are found in groups, while a higher fraction of star-forming galaxies prefer isolated environments. Within grouped environments, AGNs and star-forming galaxies are found more frequently in small- to medium-richness groups, while absorption-line galaxies prefer groups with larger richnesses. Groups containing only emission-line galaxies have smaller virial radii, velocity dispersions, and masses compared with those containing only absorption-line galaxies. Furthermore, the AGN fraction increases with decreasing distance to the group centroid, independent of galaxy morphology. Using properties obtained from Galaxy Zoo, there is an increased fraction of AGNs within merging systems

  3. Powerful Outflows and Feedback from Active Galactic Nuclei

    King, Andrew

    2015-01-01

    Active Galactic Nuclei (AGN) represent the growth phases of the supermassive black holes in the center of almost every galaxy. Powerful, highly ionized winds, with velocities $\\sim 0.1- 0.2c$ are a common feature in X--ray spectra of luminous AGN, offering a plausible physical origin for the well known connections between the hole and properties of its host. Observability constraints suggest that the winds must be episodic, and detectable only for a few percent of their lifetimes. The most powerful wind feedback, establishing the $M -\\sigma$ relation, is probably not directly observable at all. The $M - \\sigma$ relation signals a global change in the nature of AGN feedback. At black hole masses below $M-\\sigma$ feedback is confined to the immediate vicinity of the hole. At the $M-\\sigma$ mass it becomes much more energetic and widespread, and can drive away much of the bulge gas as a fast molecular outflow.

  4. KEPLER OBSERVATIONS OF RAPID OPTICAL VARIABILITY IN ACTIVE GALACTIC NUCLEI

    Over three quarters in 2010-2011, Kepler monitored optical emission from four active galactic nuclei (AGNs) with ∼30 minute sampling, >90% duty cycle, and ∼<0.1% repeatability. These data determined the AGN optical fluctuation power spectral density (PSD) functions over a wide range in temporal frequency. Fits to these PSDs yielded power-law slopes of –2.6 to –3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGNs exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first-order magnetorotational instability theoretical calculations of accretion disk fluctuations.

  5. Variability in the continuum of active galactic nuclei

    Variability in the continuum of Active Galactic Nuclei (AGN) is briefly reviewed. Emphasis is put on the importance of systematic, broad band, coordinated monitoring observations to the investigation of the basic structural properties and radiation mechanisms of the continuum source as well as the origins of the observed variations. Two particular problems are discussed in some detail. The first concerns the case for relativistic beaming in BL Lac type objects and the critical observations in the radio and X-ray bands needed to establish the case are pointed out. The second concerns the constraints which follow from variability studies on non-thermal models of the optical-ultraviolet and of the X-ray emission in Seyfert galaxies. (Auth.)

  6. Active Galactic Nuclei: The TeV Challenge

    Blandford, R; Nalewajko, K; Yuan, Y; Zrake, J

    2015-01-01

    Jets associated with Active Galactic Nuclei (AGN) have been observed for almost a century, initially at optical and radio wavelengths. They are now widely accepted as "exhausts" produced electromagnetically by the central, spinning, massive black hole and its orbiting, accreting gas. Observations at X-ray and, especially, gamma-ray energies have transformed our understanding of how these jets evolve dynamically, accelerate electrons (and positrons) and radiate throughout the entire electromagnetic spectrum. Some new approaches to modeling the powerful and rapidly variable TeV emission observed from many blazars are sketched. Observations at the highest TeV energies, to which the High Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) will contribute, promise crucial discrimination between rival models of AGN jets.

  7. The interaction between feedback from active galactic nuclei and supernovae

    Booth, C M

    2012-01-01

    Energetic feedback from supernovae (SNe) and from active galactic nuclei (AGN) are both important processes that are thought to control how much gas is able to condense into galaxies and form stars. We show that although both AGN and SNe suppress star formation, they mutually weaken one another's effect by up to an order of magnitude in haloes in the mass range for which both feedback processes are efficient (10^11.25 M_sun < m_200 < 10^12.5 M_sun). These results demonstrate the importance of the simultaneous, non-independent inclusion of these two processes in models of galaxy formation to estimate the total feedback strength. These results are of particular relevance to semi-analytic models, which implicitly assume the effects of the two feedback processes to be independent, and also to hydrodynamical simulations that model only one of the feedback processes.

  8. Time Delay Evolution of Five Active Galactic Nuclei

    A. Kovačević; L. Č. Popović; A. I. Shapovalova; D. Ilić; A. N. Burenkov; V. H. Chavushyan

    2015-12-01

    Here we investigate light curves of the continuum and emission lines of five type 1 active galactic nuclei (AGN) from our monitoring campaign, to test time-evolution of their time delays. Using both modeled and observed AGN light curves, we apply Gaussian kernel-based estimator to capture variation of local patterns of their time evolving delays. The largest variations of time delays of all objects occur in the period when continuum or emission lines luminosity is the highest. However, Gaussian kernel-based method shows instability in the case of NGC 5548, 3C 390.3, E1821+643 and NGC 4051 possibly due to numerical discrepancies between damped random walk (DRW) time scale of light curves and sliding time windows of the method. The temporal variations of time lags of Arp 102B can correspond to the real nature of the time lag evolution.

  9. Emission Line Galaxies and Active Galactic Nuclei in WINGS clusters

    Marziani, P; Bettoni, D; Poggianti, B M; Moretti, A; Fasano, G; Fritz, J; Cava, A; Varela, J; Omizzolo, A

    2016-01-01

    We present the analysis of the emission line galaxies members of 46 low redshift (0.04 < z < 0.07) clusters observed by WINGS (WIde-field Nearby Galaxy cluster Survey, Fasano et al. 2006). Emission line galaxies were identified following criteria that are meant to minimize biases against non-star forming galaxies and classified employing diagnostic diagrams. We have examined the emission line properties and frequencies of star forming galaxies, transition objects and active galactic nuclei (AGNs: LINERs and Seyferts), unclassified galaxies with emission lines, and quiescent galaxies with no detectable line emission. A deficit of emission line galaxies in the cluster environment is indicated by both a lower frequency with respect to control samples, and by a systematically lower Balmer emission line equivalent width and luminosity (up to one order of magnitude in equivalent width with respect to control samples for transition objects) that implies a lower amount of ionised gas per unit mass and a lower s...

  10. Photon losses in cosmic ray acceleration in active galactic nuclei

    Colgate, S.A.

    1984-01-01

    The usual assumption of the acceleration of ultrahigh energy cosmic rays, greater than or equal to 10/sup 18/ eV in quasars, Seyfert galaxies, and other active galactic nuclei is challenged on the basis of the photon interactions with the accelerated nucleons. This is similar to the effect of the black body radiation on particles > 10/sup 20/ eV for times of the age of the universe except that the photon spectrum is harder and the energy density greater by approx. = 10/sup 13/. Hence, a single traversal, radial or circumferential, of radiation whose energy density is no greater than the emitted flux will damp an ultrahigh energy cosmic ray 10/sup 20/ eV by greater than 10/sup 4/ times its energy. Hence, it is unlikely that any reasonable configuration of acceleration can avoid disastrous photon energy loss. A different site for ultrahigh energy cosmic ray acceleration must be found.

  11. Neutrinos in IceCube from active galactic nuclei

    Kalashev, O., E-mail: kalashev@inr.ac.ru [Russian Academy of Sciences, Institute for Nuclear Research (Russian Federation); Semikoz, D. [Laboratory of AstroParticle and Cosmology (APC) (France); Tkachev, I. [Russian Academy of Sciences, Institute for Nuclear Research (Russian Federation)

    2015-03-15

    Recently, the IceCube collaboration reported first evidence for the astrophysical neutrinos. Observation corresponds to the total astrophysical neutrino flux of the order of 3 × 10{sup −8} GeV cm{sup −2} s{sup −1} sr{sup −1} in a PeV energy range [1]. Active galactic nuclei (AGN) are natural candidate sources for such neutrinos. To model the neutrino creation in AGNs, we study photopion production processes on the radiation field of the Shakura-Sunyaev accretion discs in the black hole vicinity. We show that this model can explain the detected neutrino flux and at the same time avoids the existing constraints from the gamma-ray and cosmic-ray observations.

  12. DISCOVERY OF 5000 ACTIVE GALACTIC NUCLEI BEHIND THE MAGELLANIC CLOUDS

    We show that using mid-IR color selection to find active galactic nuclei (AGNs) is as effective in dense stellar fields such as the Magellanic Clouds as it is in extragalactic fields with low stellar densities using comparisons between the Spitzer Deep Wide Field Survey data for the NOAO Deep Wide Field Survey Boeotes region and the SAGE Survey of the Large Magellanic Cloud. We use this to build high-purity catalogs of ∼5000 AGN candidates behind the Magellanic Clouds. Once confirmed, these quasars will expand the available astrometric reference sources for the Clouds and the numbers of quasars with densely sampled, long-term (>decade) monitoring light curves by well over an order of magnitude and potentially identify sufficiently bright quasars for absorption line studies of the interstellar medium of the Clouds.

  13. Studies of Relativistic Jets in Active Galactic Nuclei with SKA

    Agudo, Ivan; Falcke, Heino; Georganopoulos, Markos; Ghisellini, Gabriele; Giovannini, Gabriele; Giroletti, Marcello; Gomez, Jose L; Gurvits, Leonid; Laing, Robert; Lister, Matthew; Marti, Jose-Maria; Meyer, Eileen T; Mizuno, Yosuke; O'Sullivan, Shane; Padovani, Paolo; Paragi, Zsolt; Perucho, Manel; Schleicher, Dominik; Stawarz, Lukasz; Vlahakis, Nektarios; Wardle, John

    2015-01-01

    Relativistic jets in active galactic nuclei (AGN) are among the most powerful astrophysical objects discovered to date. Indeed, jetted AGN studies have been considered a prominent science case for SKA, and were included in several different chapters of the previous SKA Science Book (Carilli & Rawlings 2004). Most of the fundamental questions about the physics of relativistic jets still remain unanswered, and await high-sensitivity radio instruments such as SKA to solve them. These questions will be addressed specially through analysis of the massive data sets arising from the deep, all-sky surveys (both total and polarimetric flux) from SKA1. Wide-field very-long-baseline-interferometric survey observations involving SKA1 will serve as a unique tool for distinguishing between extragalactic relativistic jets and star forming galaxies via brightness temperature measurements. Subsequent SKA1 studies of relativistic jets at different resolutions will allow for unprecedented cosmological studies of AGN jets up...

  14. Variability Analysis and the Structure of Active Galactic Nuclei

    Krolik, Julian H.

    1998-01-01

    This five-year Long-Term Space Astrophysics grant provided the support for several major steps in advancing our knowledge of the internal structure of active galactic nuclei. The single largest portion of this program had to do with the development and application of techniques for 'reverberation mapping, the use of spectral monitoring of several different bands related by radiation reprocessing to infer the internal geometry of sources. Major steps were taken in d-ds regard, particularly in establishing the distribution in radius of emission line material, and in relating the apparent reprocessing of continuum bands to the underlying structure of the accretion disk. Another major effort built directly upon these results. Once the case for continuum reprocessing was made by the monitoring, it next behooved us to understand the spectral output of AGN as a result of this reprocessing. As a result, our view of continuum production in AGN is now much better focussed on the key problems. A third focus of effort had to do with the nature of X-ray variability in AGN, and what it can tell us about the dynamics of extremely hot material in the immediate outskirts of the supermassive black holes that form the central engines of active galactic nuclei. In addition to these primary efforts, this grant also supported many other, smaller projects. Several of these were demonstrations of how the material spewed out of AGN in relativistic jets generate the radiation by which we observe them. Finally, the portion of this study that had to do with continuum production by accretion disks in AGN led naturally to several papers in which new developments were presented having to do with 'advection-dominated accretion disks', those disks in which accretion appears to proceed at a substantial rate, but in which radiation processes are weak.

  15. Spatially Offset Active Galactic Nuclei I: Selection and Spectroscopic Properties

    Barrows, R Scott; Greene, Jenny E; Pooley, David

    2016-01-01

    We present a sample of 18 optically-selected and X-ray detected spatially offset active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS). In 9 systems, the X-ray AGN is spatially offset from the galactic stellar core that is located within the 3'' diameter SDSS spectroscopic fiber. In 11 systems, the X-ray AGN is spatially offset from a stellar core that is located outside the fiber, with an overlap of 2. To build the sample, we cross-matched Type II AGN selected from the SDSS galaxy catalogue with archival Chandra imaging and employed our custom astrometric and registration procedure. The projected angular (physical) offsets span a range of 0."6 (0.8 kpc) to 17."4 (19.4 kpc), with a median value of 2."7 (4.6 kpc). The offset nature of an AGN is an unambiguous signature of a galaxy merger, and these systems can be used to study the properties of AGN in galaxy mergers without the biases introduced by morphological merger selection techniques. In this paper (Paper I), we use our sample to assess t...

  16. Accretion and jet power in active galactic nuclei

    Luigi Foschini

    2011-01-01

    The classical diagrams of radio loudness and jet power as a function of mass and accretion rate of the central spacetime singularity in active galactic nuclei are reanalyzed by including the data of the recently discovered powerful relativistic jets in Narrow-Line Seyfert 1 Galaxies.The results are studied in the light of the known theories of relativistic jets,indicating that,although the Blandford-Znajek mechanism is sufficient to explain the power radiated by BL Lac Objects,it fails to completely account for the power from quasars and Narrow-Line Seyfert 1 Galaxies.This favors the scenario outlined by Cavaliere & D' Elia of a composite jet,with a magnetospheric core plus a hydromagnetic component emerging when the accretion power increases and the disk becomes radiation-pressure dominated.A comparison with Galactic compact objects is also made,finding some striking similarities,indicating that since neutron stars are low-mass jet systems analogous to black holes,Narrow-Line Seyfert 1 Galaxies are low-mass counterparts of blazars.

  17. Unwrapping the X-ray spectra of active galactic nuclei

    Reynolds, C. S.

    2016-05-01

    Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales, the outer accretion disk and molecular torus act as the reservoirs of gas for the continuing AGN activity. And on all scales from the black hole outwards, powerful winds are seen that probably affect the evolution of the host galaxy as well as regulate the feeding of the AGN itself. In this review article, we discuss how X-ray spectroscopy can be used to study each of these components. We highlight how recent measurements of the high-energy cutoff in the X-ray continuum by NuSTAR are pushing us to conclude that X-ray coronae are radiatively-compact and have electron temperatures regulated by electron-positron pair production. We show that the predominance of rapidly-rotating objects in current surveys of SMBH spin is entirely unsurprising once one accounts for the observational selection bias resulting from the spin-dependence of the radiative efficiency. We review recent progress in our understanding of fast (v˜ (0.1-0.3)c, highly-ionized (mainly visible in Fe XXV and Fe XXVI lines), high-column density winds that may dominate quasar-mode galactic feedback. Finally, we end with a brief look forward to the promise of Astro-H and future X-ray spectropolarimeters.

  18. MAGNETIC FLUX PARADIGM FOR RADIO LOUDNESS OF ACTIVE GALACTIC NUCLEI

    We argue that the magnetic flux threading the black hole (BH), rather than BH spin or Eddington ratio, is the dominant factor in launching powerful jets and thus determining the radio loudness of active galactic nuclei (AGNs). Most AGNs are radio quiet because the thin accretion disks that feed them are inefficient in depositing magnetic flux close to the BH. Flux accumulation is more likely to occur during a hot accretion (or thick disk) phase, and we argue that radio-loud quasars and strong emission-line radio galaxies occur only when a massive, cold accretion event follows an episode of hot accretion. Such an event might be triggered by the merger of a giant elliptical galaxy with a disk galaxy. This picture supports the idea that flux accumulation can lead to the formation of a so-called magnetically choked accretion flow. The large observed range in radio loudness reflects not only the magnitude of the flux pressed against the BH, but also the decrease in UV flux from the disk, due to its disruption by the ''magnetosphere'' associated with the accumulated flux. While the strongest jets result from the secular accumulation of flux, moderate jet activity can also be triggered by fluctuations in the magnetic flux deposited by turbulent, hot inner regions of otherwise thin accretion disks, or by the dissipation of turbulent fields in accretion disk coronae. These processes could be responsible for jet production in Seyferts and low-luminosity AGNs, as well as jets associated with X-ray binaries.

  19. Unwrapping the X-ray Spectra of Active Galactic Nuclei

    Reynolds, Christopher S

    2015-01-01

    Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales, the outer accretion disk and molecular torus act as the reservoirs of gas for the continuing AGN activity. And on all scales from the black hole outwards, powerful winds are seen that probably affect the evolution of the host galaxy as well as regulate the feeding of the AGN itself. In this review article, we discuss how X-ray spectroscopy can be used to study each of these components. We highlight how recent measurements of the high-energy cutoff in the X-ray continuum by NuSTAR are pushing us to conclude that X-ray coronae are radiatively-compact and have electron temperatures regulated by electron-positron pair production. We show that the predominance of rapidly-rotating objects in current surveys of SMBH spin is entirely unsurprising once one accounts for the observat...

  20. The suppression of star formation by powerful active galactic nuclei.

    Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2012-05-10

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time. PMID:22575961

  1. Optical spectral properties of active galactic nuclei and quasars

    Four separate investigations dealing with the properties of optical continuum and emission-lines of active galactic nuclei (AGN) and quasars are presented. Multichannel scans of 3CR radio galaxies are decomposed by using a two-component model-an elliptical galaxy and a power-law nonthermal component. It is found that there is a strong correlation between the luminosity of the power-law component and the strength of the Balmer emission-lines. In most cases, by extrapolating to the Lyman continuum, the power-law models derived provide enough ionizing radiation to account for the Balmer line strengths. Extending the study of radio galaxies to include Seyfert galaxies and quasars, it is found that there is a strong continuity between broad-line AGN's and quasars in terms of similarities in the correlations between line luminosities and nonthermal continuum luminosity. Next, a study of the variability of absolute optical energy distribution and emission-lines of the N-galaxies 3C382 and 3C390.3 is made. Lastly, a preliminary study of surface photometry of Markarian Seyfert galaxies are presented. It is found that the properties of the underlying galaxies such as scale-length and surface brightness of the disk, color, and total brightness, do not depart systematically from those of luminous normal spiral galaxies

  2. The suppression of star formation by powerful active galactic nuclei

    Page, M J; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodr'iguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Perez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Portal, M Sanchez; Schulz, B; Scott, Douglas; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2013-01-01

    The old, red stars which constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly from accretion onto black holes. It is widely suspected, but unproven, that the tight correlation in mass of the black hole and stellar components results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, while powerful star-forming galaxies are usually dust-obscured and are brightest at infrared to submillimetre wavelengths. Here we report observations in the submillimetre and X-ray which show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 Gyrs old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10^44 erg/s. This suppression of star formation in the host galaxies of powerful AGN ...

  3. Active Galactic Nuclei under the scrutiny of CTA

    Sol, H; Boisson, C; de Almeida, U Barres; Biteau, J; Contreras, J -L; Giebels, B; Hassan, T; Inoue, Y; Katarzynski, K; Krawczynski, H; Mirabal, N; Poutanen, J; Rieger, F; Totani, T; Benbow, W; Cerruti, M; Errando, M; Fallon, L; Pino, E de Gouveia Dal; Hinton, J -A; Inoue, S; Lenain, J -P; Neronov, A; Takahashi, K; Takami, H; White, R

    2013-01-01

    Active Galactic Nuclei (hereafter AGN) produce powerful outflows which offer excellent conditions for efficient particle acceleration in internal and external shocks, turbulence, and magnetic reconnection events. The jets as well as particle accelerating regions close to the supermassive black holes (hereafter SMBH) at the intersection of plasma inflows and outflows, can produce readily detectable very high energy gamma-ray emission. As of now, more than 45 AGN including 41 blazars and 4 radiogalaxies have been detected by the present ground-based gamma-ray telescopes, which represents more than one third of the cosmic sources detected so far in the VHE gamma-ray regime. The future Cherenkov Telescope Array (CTA) should boost the sample of AGN detected in the VHE range by about one order of magnitude, shedding new light on AGN population studies, and AGN classification and unification schemes. CTA will be a unique tool to scrutinize the extreme high-energy tail of accelerated particles in SMBH environments, t...

  4. The star formation rates of active galactic nuclei host galaxies

    Ellison, Sara L.; Teimoorinia, Hossen; Rosario, David J.; Mendel, J. Trevor

    2016-05-01

    Using artificial neural network predictions of total infrared luminosities (LIR), we compare the host galaxy star formation rates (SFRs) of ˜21 000 optically selected active galactic nuclei (AGN), 466 low-excitation radio galaxies (LERGs) and 721 mid-IR-selected AGN. SFR offsets (ΔSFR) relative to a sample of star-forming `main-sequence' galaxies (matched in M⋆, z and local environment) are computed for the AGN hosts. Optically selected AGN exhibit a wide range of ΔSFR, with a distribution skewed to low SFRs and a median ΔSFR = -0.06 dex. The LERGs have SFRs that are shifted to even lower values with a median ΔSFR = -0.5 dex. In contrast, mid-IR-selected AGN have, on average, SFRs enhanced by a factor of ˜1.5. We interpret the different distributions of ΔSFR amongst the different AGN classes in the context of the relative contribution of triggering by galaxy mergers. Whereas the LERGs are predominantly fuelled through low accretion rate secular processes which are not accompanied by enhancements in SFR, mergers, which can simultaneously boost SFRs, most frequently lead to powerful, obscured AGN.

  5. The star formation rates of active galactic nuclei host galaxies

    Ellison, Sara L; Rosario, David J; Mendel, J Trevor

    2016-01-01

    Using artificial neural network (ANN) predictions of total infra-red luminosities (LIR), we compare the host galaxy star formation rates (SFRs) of ~21,000 optically selected active galactic nuclei (AGN), 466 low excitation radio galaxies (LERGs) and 721 mid-IR selected AGN. SFR offsets (Delta SFR) relative to a sample of star-forming `main sequence' galaxies (matched in M*, z and local environment) are computed for the AGN hosts. Optically selected AGN exhibit a wide range of Delta SFR, with a distribution skewed to low SFRs and a median Delta SFR = -0.06 dex. The LERGs have SFRs that are shifted to even lower values with a median Delta SFR = -0.5 dex. In contrast, mid-IR selected AGN have, on average, SFRs enhanced by a factor ~1.5. We interpret the different distributions of Delta SFR amongst the different AGN classes in the context of the relative contribution of triggering by galaxy mergers. Whereas the LERGs are predominantly fuelled through low accretion rate secular processes which are not accompanied ...

  6. Penetrating the Deep Cover of Compton Thick Active Galactic Nuclei

    Levenson, N A; Krolik, J H; Weaver, K A; Zycki, P T

    2006-01-01

    We analyze observations obtained with the Chandra X-ray Observatory of bright Compton thick active galactic nuclei (AGNs), those with column densities in excess of 1.5 x 10^{24} cm^{-2} along the lines of sight. We therefore view the powerful central engines only indirectly, even at X-ray energies. Using high spatial resolution and considering only galaxies that do not contain circumnuclear starbursts, we reveal the variety of emission AGNs alone may produce. Approximately 1% of the continuum's intrinsic flux is detected in reflection in each case. The only hard X-ray feature is the prominent Fe K alpha fluorescence line, with equivalent width greater than 1 keV in all sources. The Fe line luminosity provides the best X-ray indicator of the unseen intrinsic AGN luminosity. In detail, the morphologies of the extended soft X-ray emission and optical line emission are similar, and line emission dominates the soft X-ray spectra. Thus, we attribute the soft X-ray emission to material that the central engines photo...

  7. Feedback of Active Galactic Nuclei in Seyfert 2 Galaxies

    En-Peng Zhang; Wei-Hao Bian; Chen Hu; Wei-Ming Mao; ALi Luo; Yong-Heng Zhao

    2008-01-01

    It is well accepted that feedback from active galactic nuclei (AGNs) plays an important role in the coevolution of the supermassive black hole (SMBH) and its host galaxy,but the concrete mechanism of feedback remains unclear.A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy.We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties.Although there are some uncertainties,our data still imply the deviation from the star formation law (Kennicutt-Schmidt law).Further,they indicate that:(1) Feedback correlates with the Eddington ratio,rather than with the mass of SMBH,as a result of decreasing star formation efficiency.(2) The SMBH and the torus are probably undergoing coevolution.Conclusions presented here can be refined through future high resolution CO or HCN observations.

  8. Broad-line Balmer Decrements in Blue Active Galactic Nuclei

    Dong, Xiaobo; Wang, Jianguo; Yuan, Weimin; Zhou, Hongyan; Dai, Haifeng; Zhang, Kai

    2007-01-01

    We have investigated the broad-line Balmer decrements (Halpha/Hbeta) for a large, homogeneous sample of Seyfert 1 galaxies and QSOs using spectroscopic data obtained in the Sloan Digital Sky Survey. The sample, drawn from the Fourth Data Release, comprises 446 low redshift (z < 0.35) active galactic nuclei (AGN) that have blue optical continua as indicated by the spectral slopes in order to minimize the effect of dust extinction. We find that (i) the distribution of the intrinsic broad-line Halpha/Hbeta ratio can be well described by log-Gaussian, with a peak at Halpha/Hbeta=3.06 and a standard deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate with AGN properties such as luminosity, accretion rate, and continuum slope, etc.; (iii) on average, the Balmer decrements are found to be only slightly larger in radio-loud sources (3.37) and sources having double-peaked emission-line profiles (3.27) compared to the rest of the sample. We therefore suggest that the broad-line Halpha/Hbet...

  9. On the efficient acceleration of clouds in active galactic nuclei

    Waters, Tim; Proga, Daniel

    2016-07-01

    In the broad line region of active galactic nuclei (AGN), acceleration occurs naturally when a cloud condenses out of the hot confining medium due to the increase in line opacity as the cloud cools. However, acceleration by radiation pressure is not very efficient when the flux is time-independent, unless the flow is 1D. Here, we explore how acceleration is affected by a time-varying flux, as AGN are known to be highly variable. If the period of flux oscillations is longer than the thermal time-scale, we expect the gas to cool during the low flux state, and therefore line opacity should quickly increase. The cloud will receive a small kick due to the increased radiation force. We perform hydrodynamical simulations using ATHENA to confirm this effect and quantify its importance. We find that despite the flow becoming turbulent in 2D due to hydrodynamic instabilities, a 20 per cent modulation of the flux leads to a net increase in acceleration - by more than a factor of 2 - in both 1D and 2D. We show that this acceleration is sufficient to produce the observed line widths, although we only consider optically thin clouds. We discuss the implications of our results for photoionization modelling and reverberation mapping.

  10. Variability in Active Galactic Nuclei from Propagating Turbulent Relativistic Jets

    Pollack, Maxwell; Wiita, Paul J

    2016-01-01

    We use the Athena hydrodynamics code to model propagating two-dimensional relativistic jets as approximations to the growth of radio-loud active galactic nuclei for various input jet velocities and jet-to-ambient matter density ratios. Using results from these simulations we estimate the changing synchrotron emission by summing the fluxes from a vertical strip of zones behind the reconfinement shock, which is nearly stationary, and from which a substantial portion of the flux variability should arise. We explore a wide range of time scales by considering two light curves from each simulation; one uses a relativistic turbulence code with bulk velocities taken from our simulations as input, while the other uses the bulk velocity data to compute fluctuations caused by variations in the Doppler boosting due to changes in the direction and the speed of the flow through all zones in the strip. We then calculate power spectral densities (PSDs) from the light curves for both turbulent and bulk velocity origins for va...

  11. The dust covering factor in active galactic nuclei

    Stalevski, Marko; Ueda, Yoshihiro; Lira, Paulina; Fritz, Jacopo; Baes, Maarten

    2016-01-01

    The primary source of emission of active galactic nuclei (AGN), the accretion disk, is surrounded by an optically and geometrically thick dusty structure ("the so-called dusty torus"). The infrared radiation emitted by the dust is nothing but a reprocessed fraction of the accretion disk emission, so the ratio of the torus to the AGN luminosity ($L_{\\text{torus}}/L_{\\text{AGN}}$) should correspond to the fraction of the sky obscured by dust, i.e. the covering factor. We undertook a critical investigation of the $L_{\\text{torus}}/L_{\\text{AGN}}$ as the dust covering factor proxy. Using state-of-the-art 3D Monte Carlo radiative transfer code, we calculated a grid of SEDs emitted by the clumpy two-phase dusty structure. With this grid of SEDs, we studied the relation between $L_{\\text{torus}}/L_{\\text{AGN}}$ and the dust covering factor for different parameters of the torus. We found that in case of type 1 AGNs the torus anisotropy makes $L_{\\text{torus}}/L_{\\text{AGN}}$ underestimate low covering factors and ove...

  12. FERMI OBSERVATIONS OF TeV-SELECTED ACTIVE GALACTIC NUCLEI

    We report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects). The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV-TeV sources, and 29 were not in the third EGRET catalog. For each of the 38 Fermi-detected sources, spectra and light curves are presented. Most can be described with a power law of spectral index harder than 2.0, with a spectral break generally required to accommodate the TeV measurements. Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments. Evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light.

  13. MAGNETIC FLUX PARADIGM FOR RADIO LOUDNESS OF ACTIVE GALACTIC NUCLEI

    Sikora, Marek [Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw (Poland); Begelman, Mitchell C., E-mail: sikora@camk.edu.pl, E-mail: mitch@jila.colorado.edu [JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309 (United States)

    2013-02-20

    We argue that the magnetic flux threading the black hole (BH), rather than BH spin or Eddington ratio, is the dominant factor in launching powerful jets and thus determining the radio loudness of active galactic nuclei (AGNs). Most AGNs are radio quiet because the thin accretion disks that feed them are inefficient in depositing magnetic flux close to the BH. Flux accumulation is more likely to occur during a hot accretion (or thick disk) phase, and we argue that radio-loud quasars and strong emission-line radio galaxies occur only when a massive, cold accretion event follows an episode of hot accretion. Such an event might be triggered by the merger of a giant elliptical galaxy with a disk galaxy. This picture supports the idea that flux accumulation can lead to the formation of a so-called magnetically choked accretion flow. The large observed range in radio loudness reflects not only the magnitude of the flux pressed against the BH, but also the decrease in UV flux from the disk, due to its disruption by the ''magnetosphere'' associated with the accumulated flux. While the strongest jets result from the secular accumulation of flux, moderate jet activity can also be triggered by fluctuations in the magnetic flux deposited by turbulent, hot inner regions of otherwise thin accretion disks, or by the dissipation of turbulent fields in accretion disk coronae. These processes could be responsible for jet production in Seyferts and low-luminosity AGNs, as well as jets associated with X-ray binaries.

  14. Ultrafast outflows in radio-loud active galactic nuclei

    Tombesi, F.; Tazaki, F.; Mushotzky, R. F.; Ueda, Y.; Cappi, M.; Gofford, J.; Reeves, J. N.; Guainazzi, M.

    2014-09-01

    Recent X-ray observations show absorbing winds with velocities up to mildly relativistic values of the order of ˜0.1c in a limited sample of six broad-line radio galaxies. They are observed as blueshifted Fe XXV-XXVI K-shell absorption lines, similarly to the ultrafast outflows (UFOs) reported in Seyferts and quasars. In this work we extend the search for such Fe K absorption lines to a larger sample of 26 radio-loud active galactic nuclei (AGN) observed with XMM-Newton and Suzaku. The sample is drawn from the Swift Burst Alert Telescope 58-month catalogue and blazars are excluded. X-ray bright Fanaroff-Riley Class II radio galaxies constitute the majority of the sources. Combining the results of this analysis with those in the literature we find that UFOs are detected in >27 per cent of the sources. However, correcting for the number of spectra with insufficient signal-to-noise ratio, we can estimate that the incidence of UFOs is this sample of radio-loud AGN is likely in the range f ≃ (50 ± 20) per cent. A photoionization modelling of the absorption lines with XSTAR allows us to estimate the distribution of their main parameters. The observed outflow velocities are broadly distributed between vout ≲ 1000 km s-1 and vout ≃ 0.4c, with mean and median values of vout ≃ 0.133c and vout ≃ 0.117c, respectively. The material is highly ionized, with an average ionization parameter of logξ ≃ 4.5 erg s-1 cm, and the column densities are larger than NH > 1022 cm-2. Overall, these characteristics are consistent with the presence of complex accretion disc winds in a significant fraction of radio-loud AGN and demonstrate that the presence of relativistic jets does not preclude the existence of winds, in accordance with several theoretical models.

  15. Spectropolarimetry, variability, and the taxonomy of active galactic nuclei

    Two subclasses of active galactic nuclei (AGN) are studied using spectropolarimetry, with the intent of defining the relationships of the subclasses to other classes of AGNs, and to study the physics of the objects themselves. In the Seyfert 1.8/1.9 class there is good evidence for dust just outside of the broad-line regions in two objects, IRAS 1958-183 and NGC 2622. Spectropolarimetry of the latter object reveals the presence of dust moving at ∼ -800 s-1 along the our line-of-sight, and causing much of the polarization in the object. In addition, three of these objects have undergone extreme variability. Combining IDS data from Osterbrock and collaborators with the more recent CCD data it is shown that in all three cases the changes in both broad emission line fluxes and featureless continuum are consistent with changes in the line-of-sight reddening to the broad-line region. Together with the polarimetric evidence for dust and IRAS photometry this strongly suggests that the Seyfert 1.8/1.9 character is caused by dust and the consequent reddening and extinction. Variability occurs when dust clouds evaporate or move out of line-of-sight, and the extinction then changes. In the so-called narrow line Seyfert 1s spectropolarimetry reveals seven highly-polarized objects. In Mrk 1239 there is evidence for at least two components of polarization, one probably due to dust reflection. In two other objects, Mrk 766 and IRAS 1509-211, the polarization also appears to indicate dust reflection as the polarigenic mechanism. There is a weak circumstantial evidence for an association of the low-density region and the polarizing source, provided by comparison of the radio axes and polarization position angles in Mrk 766 and Mrk 1126

  16. The dust covering factor in active galactic nuclei

    Stalevski, Marko; Ricci, Claudio; Ueda, Yoshihiro; Lira, Paulina; Fritz, Jacopo; Baes, Maarten

    2016-05-01

    The primary source of emission of active galactic nuclei (AGNs), the accretion disc, is surrounded by an optically and geometrically thick dusty structure (`the so-called dusty torus'). The infrared radiation emitted by the dust is nothing but a reprocessed fraction of the accretion disc emission, so the ratio of the torus to the AGN luminosity (Ltorus/LAGN) should corresponds to the fraction of the sky obscured by dust, i.e. the covering factor. We undertook a critical investigation of the Ltorus/LAGN as the dust covering factor proxy. Using state-of-the-art 3D Monte Carlo radiative transfer code, we calculated a grid of spectral energy distributions (SEDs) emitted by the clumpy two-phase dusty structure. With this grid of SEDs, we studied the relation between Ltorus/LAGN and the dust covering factor for different parameters of the torus. We found that in the case of type 1 AGNs the torus anisotropy makes Ltorus/LAGN underestimate low covering factors and overestimate high covering factors. In type 2 AGNs Ltorus/LAGN always underestimates covering factors. Our results provide a novel easy-to-use method to account for anisotropy and obtain correct covering factors. Using two samples from the literature, we demonstrated the importance of our result for inferring the obscured AGN fraction. We found that after the anisotropy is properly accounted for, the dust covering factors show very weak dependence on LAGN, with values in the range of ≈0.6-0.7. Our results also suggest a higher fraction of obscured AGNs at high luminosities than those found by X-ray surveys, in part owing to the presence of a Compton-thick AGN population predicted by population synthesis models.

  17. The angular clustering of WISE-selected active galactic nuclei: Different halos for obscured and unobscured active galactic nuclei

    Donoso, E. [Instituto de Ciencias Astronómicas, de la Tierra, y del Espacio (ICATE), 5400 San Juan (Argentina); Yan, Lin [Infrared Processing and Analysis Center, Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Stern, D.; Assef, R. J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2014-07-01

    We calculate the angular correlation function for a sample of ∼170,000 active galactic nuclei (AGNs) extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1 – W2 > 0.8) and 4.6 μm flux densities brighter than 0.14 mJy). The sample is expected to be >90% reliable at identifying AGNs and to have a mean redshift of (z) = 1.1. In total, the angular clustering of WISE AGNs is roughly similar to that of optical AGNs. We cross-match these objects with the photometric Sloan Digital Sky Survey catalog and distinguish obscured sources with r – W2 > 6 from bluer, unobscured AGNs. Obscured sources present a higher clustering signal than unobscured sources. Since the host galaxy morphologies of obscured AGNs are not typical red sequence elliptical galaxies and show disks in many cases, it is unlikely that the increased clustering strength of the obscured population is driven by a host galaxy segregation bias. By using relatively complete redshift distributions from the COSMOS survey, we find that obscured sources at (z) ∼ 0.9 have a bias of b = 2.9 ± 0.6 and are hosted in dark matter halos with a typical mass of log (M/M {sub ☉} h {sup –1}) ∼ 13.5. In contrast, unobscured AGNs at (z) ∼ 1.1 have a bias of b = 1.6 ± 0.6 and inhabit halos of log (M/M {sub ☉} h {sup –1}) ∼ 12.4. These findings suggest that obscured AGNs inhabit denser environments than unobscured AGNs, and they are difficult to reconcile with the simplest AGN unification models, where obscuration is driven solely by orientation.

  18. On the metal abundance of low-activity galactic nuclei

    The characteristics of the nuclear spectrum of six Seyfert 2 and LINER nuclei with low activity and strong lines of ionized nitrogen are investigated. From the equivalent widths of the absorption lines, the age and metallicity of the stellar population are derived. A comparison of the observed emission-line intensities with photoionization and shock model calculations leads to the conclusion that these nuclei are photoionized by a power-law continuum, and that the only way to reproduce the large forbidden line N II/H-alpha ratio for at least four of them is with an overabundance of nitrogen relative to the other heavy elements. 30 refs

  19. X-Ray bright active galactic nuclei in massive galaxy clusters - II. The fraction of galaxies hosting active nuclei

    Ehlert, S.; von der Linden, A.; Allen, S. W.;

    2013-01-01

    We present a measurement of the fraction of cluster galaxies hosting X-ray bright active galactic nuclei (AGN) as a function of clustercentric distance scaled in units of r500. Our analysis employs high-quality Chandra X-ray and Subaru optical imaging for 42 massive X-ray-selected galaxy cluster...... fields spanning the redshift range 0.2 z ..., both of which are also suppressed near cluster centres to a comparable extent. These results strongly support the idea that X-ray AGN activity and strong star formation are linked through their common dependence on available reservoirs of cold gas. © 2013 The Authors. Published by Oxford University...

  20. Study and modeling of the most energetic Active Galactic Nuclei with the Fermi satellite

    The Fermi satellite was launched in June 2008. The onboard LAT detector is dedicated to the study of galactic and extra-galactic gamma sources with an energy comprised between 200 MeV and 300 GeV. 1451 sources have been detected in less than 11 months. This document is divided into 6 chapters: 1) gamma astronomy, 2) the Fermi satellite, 3) the active galactic nuclei (NAG), 4) the observation of several blazars (PKS-2155-304 and PG-1553+113) and its simulation, 5) the observation of PKS-2155-304 with both RXTE and Fermi, and 6) conclusion

  1. PeV Neutrinos Observed by IceCube from Cores of Active Galactic Nuclei

    Stecker, Floyd W.

    2013-01-01

    I show that the high energy neutrino flux predicted to arise from active galactic nuclei cores can explain the PeV neutrinos detected by IceCube without conflicting with the constraints from the observed extragalactic cosmic-ray and gamma-ray backgrounds.

  2. Present and future of high resolution radio observations of active galactic nuclei

    Using Cygnus A and 3C273 as examples, an introduction to radio interferometric observations of active galactic nuclei is made. Some aspects of present day research in extended and compact radio sources are presented. New instruments which are being presently built or planned and their possible scientific impact are discussed

  3. On the Evolution of High-Redshift Active Galactic Nuclei

    Mao, Jirong

    2016-01-01

    We build a simple physical model to study the high-redshift active galactic Nucleus (AGN) evolution within the co-evolution framework of central black holes (BHs) and their host galaxies. The correlation between the circular velocity of a dark halo $V_c$ and the velocity dispersion of a galaxy $\\sigma$ is used to link the dark matter halo mass and BH mass. The dark matter halo mass function is converted to the BH mass function for any given redshift. The high-redshift optical AGN luminosity functions (LFs) are constructed. At $z\\sim 4$, the flattening feature is not shown at the faint end of the optical AGN LF. This is consistent with observational results. If the optical AGN LF at $z\\sim 6$ can be reproduced in the case in which central BHs have the Eddington-limited accretion, it is possible for the AGN lifetime to have a small value of $2\\times 10^5$ yrs. The X-ray AGN LFs and X-ray AGN number counts are also calculated at $2.03$, respectively, using the same parameters adopted in the calculation for the o...

  4. Supermassive Black Holes in Active Galactic Nuclei. II. Calibration of the Black Hole Mass-Velocity Dispersion Relationship for Active Galactic Nuclei

    Onken, Christopher A.; Ferrarese, Laura; Merritt, David;

    2004-01-01

    We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the correlation between black hole mass, M, and bulge/spheroid stellar velocity dispersion, sigma. We use new measurements of sigma for 6 AGNs and published velocity dispersions for 10 others......, in conjunction with improved reverberation mapping results, to determine the scaling factor required to bring reverberation-based black hole masses into agreement with the quiescent galaxy M-sigma relationship. The scatter in the AGN black hole masses is found to be less than a factor of 3. The current...

  5. STEPS TOWARD UNVEILING THE TRUE POPULATION OF ACTIVE GALACTIC NUCLEI: PHOTOMETRIC CHARACTERIZATION OF ACTIVE GALACTIC NUCLEI IN COSMOS

    Using a physically motivated, model-based active galactic nucleus (AGN) characterization technique, we fit a large sample of X-ray-selected AGNs with known spectroscopic redshifts from the Cosmic Evolution Survey field. We identify accretion disks in the spectral energy distributions of broad- and narrow-line AGNs, and infer the presence or absence of host galaxy light in the SEDs. Based on infrared and UV excess AGN selection techniques, our method involves fitting a given SED with a model consisting of three components: infrared power-law emission, optical-UV accretion disk emission, and host galaxy emission. Each component can be varied in relative contribution, and a reduced chi-square minimization routine is used to determine the optimum parameters for each object. Using this technique, both broad- and narrow-line AGNs fall within well-defined and plausible bounds on the physical parameters of the model, allowing trends with luminosity and redshift to be determined. In particular, based on our sample of spectroscopically confirmed AGNs, we find that approximately 95% of the broad-line AGNs and 50% of the narrow-line AGNs in our sample show evidence of an accretion disk, with maximum disk temperatures ranging from 1 to 10 eV. Because this fitting technique relies only on photometry, we hope to apply it in future work to the characterization and eventually the selection of fainter AGNs than are accessible in wide-field spectroscopic surveys, and thus probe a population of less luminous and/or higher redshift objects without prior redshift or X-ray data. With the abundant availability of photometric data from large surveys, the ultimate goal is to use this technique to create large samples that will complement and complete AGN catalogs selected by X-ray emission alone.

  6. Modeling the Polarization of Dusty Scattering Cones in Active Galactic Nuclei

    Goosmann, René; Gaskell, C. M.; Shoji, M.

    San Francisco : Astronomical Society of the Pacific, 2007 - (Ho, L.; Wang, J.), s. 485-486 ISBN 978-1-58381-307-2. - (ASP Conference Series. 373). [The Central Engine of Active Galactic Nuclei. Xi'an (CN), 16.10.2006-21.10.2006] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxies: active * polarization * dust Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  7. The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

    Ackermann, Markus; Ajello, M.; Blandford, R. D.; Nuss, E.; Ohno, M.; Ohsugi, T.; Ojha, R.; Omodei, N.; Orienti, M.; Orlando, E.; Paggi, A.; Paneque, D.; Perkins, J. S.; Bloom, E. D.; Pesce-Rollins, M.

    2015-01-01

    The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic (TS) greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10{\\\\deg}), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude...

  8. Interferometric Monitoring of Gamma-ray Bright Active Galactic Nuclei II: Frequency Phase Transfer

    Algaba, Juan-Carlos; Lee, Sang-Sung; Byun, Do-Young; Kang, Sin-Cheol; Kim, Dae-Won; Kim, Jae-Young; Kim, Jeong-Sook; Kim, Soon-Wook; Kino, Motoki; Miyazaki, Atsushi; Park, Jong-Ho; Trippe, Sascha; Wajima, Kiyoaki

    2015-01-01

    The Interferometric Monitoring of Gamma-ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma-ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non-optimal weather conditions.

  9. Light element nucleosynthesis from jet-cloud interactions in active galactic nuclei

    The production of light nuclei via the interactions of jets from the central engines of active galactic nuclei (AGNs) and the surrounding medium are studied. Several environments ranging from hot, dense knots of gas near the central engine to the cold broad line region clouds are simulated by a nuclear reaction network that couples the thermonuclear processes in the cloud to the reactions between the jet particles and the cloud. Reaction products from the jet-cloud interactions are followed until they react or are thermalized, which may involve several subsequent reactions. Enhanced production of light nuclei well above their primordial abundances is possible even, under some conditions, of CNO nuclei. In these scenarios, the jets can enhance abundances of CNO nuclei by first producing excess amounts of nuclei with A<8, then by increasing the cloud density to the point at which the thermonuclear reaction rates become important. The comparison to observed abundances in quasars (QSOs) leads to the conclusion that the interactions of ejected matter from AGNs may be responsible for large observed abundances of light nuclei in addition to significant abundances of nuclei in the CNO region

  10. Optical spectra of radio-loud and radio-quiet active galactic nuclei

    Many radio galaxies have strong emission lines in their optical spectra. The fraction with such lines is much larger than in ''normal'' galaxies. Radio galaxies generally also have very bright nuclei; thus those with strong emission lines are similar in both respects to Seyfert galaxies. Hence radio and Seyfert galaxies are both generally considered to be similar physical objects: active galactic nuclei. Their observational properties show they are closely related to quasars (quasi-stellar radio sources) and (radio-quiet) QSOs. A short table of the space density of these objects is presented and their optical spectra are discussed. (Auth.)

  11. Variability-selected active galactic nuclei from supernova search in the Chandra deep field south

    Trevese, D.; Boutsia, K.; Vagnetti, F.; Cappellaro, E.; Puccetti, S.

    2008-01-01

    Variability is a property shared by virtually all active galactic nuclei (AGNs), and was adopted as a criterion for their selection using data from multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light of their host galaxies, and cannot therefore be detected by the usual colour techniques. For this reason, their evolution in cosmic time is poorly known. Consistency with the evolution derived from X-ray detected samples has not been clearly established so far, also be...

  12. Modeling the X-ray fractional variability spectrum of Active Galactic Nuclei using multiple flares

    Goosmann, R. W.; Dovciak, M.; Karas, V.; Czerny, B.; Mouchet, M.; Ponti, G.

    2007-01-01

    Using Monte-Carlo simulations of X-ray flare distributions across the accretion disk of active galactic nuclei (AGN), we obtain modeling results for the energy-dependent fractional variability amplitude. Referring to previous results of this model, we illustrate the relation between the shape of the point-to-point fractional variability spectrum, F_pp, and the time-integrated spectral energy distribution, F_E. The results confirm that the spectral shape and variability of the iron Kalpha line...

  13. Modeling the X-ray Fractional Variability Spectrum of Active Galactic Nuclei Using Multiple Flares

    Goosmann, René; Dovčiak, Michal; Karas, Vladimír; Czerny, B.; Mouchet, M.; Ponti, G.

    San Francisco : Astronomical Society of the Pacific, 2007 - (Ho, L.; Wang, J.), s. 167-168 ISBN 978-1-58381-307-2. - (ASP Conference Series. 373). [The Central Engine of Active Galactic Nuclei. Xi'an (CN), 16.10.2006-21.10.2006] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : X-rays: galaxies * variability * flares Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  14. On the deceleration of relativistic jets in active galactic nuclei I: Radiation drag

    Beskin, V S

    2016-01-01

    Deceleration of relativistic jets from active galactic nuclei (AGNs) detected recently by MOJAVE team is discussed in connection with the interaction of the jet material with the external photon field. Appropriate energy density of the isotropic photon field which is necessary to decelerate jets is determined. It is shown that the disturbances of the electric potential and magnetic surfaces play important role in general dynamics of particle deceleration.

  15. Monitoring of bright, nearby Active Galactic Nuclei with the MAGIC telescopes

    R. Wagner; Backes, M.; Satalecka, K.; Bonnoli, G.; M. Doert(); B. Steinke(Max-Planck-Institut für Physik, D-80805 München, Germany); Strah, N.; Terzic, T.; Tescaro, D.; Uellenbeck, M.; The MAGIC Collaboration

    2011-01-01

    Observations and detections of Active Galactic Nuclei (AGN) by Cherenkov telescopes are often triggered by information about high flux states in other wavelength bands. To overcome this bias, the VHE gamma-ray telescope MAGIC has conducted dedicated monitoring observations of nearby AGN since 2006. Three well established, TeV-bright blazars were selected to be observed regularly: Mrk 421, Mrk 501, and 1ES1959+650. The goals of these observations are to obtain an unbiased distribution of flux ...

  16. Active Galactic Nuclei and Quasars: Why Still a Puzzle after 50 years?

    Antonucci, Robert

    2015-01-01

    The first part of this article is a historical and physical introduction to quasars and their close cousins, called Active Galactic Nuclei (AGN). In the second part, I argue that our progress in understanding them has been unsatisfactory and in fact somewhat illusory since their discovery fifty years ago, and that much of the reason is a pervasive lack of critical thinking in the research community. It would be very surprising if other fields do not suffer similar failings.

  17. Warped accretion disks and the unification of Active Galactic Nuclei

    Nayakshin, S

    2004-01-01

    Orientation of parsec-scale accretion disks in AGN is likely to be nearly random for different black hole feeding episodes. Since AGN accretion disks are unstable to self-gravity on parsec scales, star formation in these disks will create young stellar disks, similar to those recently discovered in our Galactic Center. The disks blend into the quasi-spherical star cluster enveloping the AGN on time scales much longer than a likely AGN lifetime. Therefore, the gravitational potential within the radius of the black hole influence is at best axi-symmetric rather than spherically symmetric. Here we show that as a result, a newly formed accretion disk will be warped. For the simplest case of a potential resulting from a thin stellar ring, we calculate the disk precession rates, and the time dependent shape. We find that, for a realistic parameter range, the disk becomes strongly warped in few hundred orbital times. We suggest that this, and possibly other mechanisms of accretion disk warping, have a direct relevan...

  18. Accessing the innermost regions of Active Galactic Nuclei

    Ros, E

    2006-01-01

    Very-long-baseline interferometry can image the parsec-scale structure of radio jets, but the accretion disk close to the black hole remains invisible. One way to probe this accretion flow is provided by X-ray flux density monitoring and spectroscopy. Here we report on preliminary results of a multi-band campaign on NGC1052 with the goal of combining both approaches to access to the innermost regions of this active galaxy and to establish a connection between the relativistic jets and the accretion region.

  19. Unification of Active Galactic Nuclei at X-rays and soft gamma-rays

    This HDR (accreditation to supervise research) report contains presentations of teaching activities in stellar astrophysics and extragalactic astronomy and cosmology, of student supervision activities in different academic places, and of various publications and participations to conferences and meetings. After a brief text highlighting the relevance and originality of his research works, the author proposes a large overview of his research works which dealt with different aspects of active galactic nuclei and related issues. Future projects are evoked. The report also contains numerous publications (press articles, conference proceedings, and so on)

  20. Host galaxies and environment of active galactic nuclei : a study of the XMM large scale structure survey

    Tasse, Cyril

    2008-01-01

    Active galactic nuclei (AGN) result from the infall of matter onto the super-massive black holes that are situated at the centres of galaxies. This process releases an enormous amount of energy into the inter-stellar and inter-galactic medium. Hence, the study of AGN becomes essential in the context

  1. Atomic hydrogen properties of active galactic nuclei host galaxies: H I in 16 nuclei of galaxies (NUGA) sources

    We present a comprehensive spectroscopic imaging survey of the distribution and kinematics of atomic hydrogen (H I) in 16 nearby spiral galaxies hosting low luminosity active galactic nuclei (AGN), observed with high spectral and spatial resolution (resolution: ∼20'', ∼5 km s–1) using the NRAO Very Large Array (VLA). The sample contains a range of nuclear types ranging from Seyfert to star-forming nuclei, and was originally selected for the NUclei of GAlaxies project (NUGA)—a spectrally and spatially resolved interferometric survey of gas dynamics in nearby galaxies designed to identify the fueling mechanisms of AGN and the relation to host galaxy evolution. Here we investigate the relationship between the H I properties of these galaxies, their environment, their stellar distribution, and their AGN type. The large-scale H I morphology of each galaxy is classified as ringed, spiral, or centrally concentrated; comparison of the resulting morphological classification with the AGN type reveals that ring structures are significantly more common in low-ionization narrow emission-line regions (LINER) than in Seyfert host galaxies, suggesting a time evolution of the AGN activity together with the redistribution of the neutral gas. Dynamically disturbed H I disks are also more prevalent in LINER host galaxies than in Seyfert host galaxies. While several galaxies are surrounded by companions (some with associated H I emission), there is no correlation between the presence of companions and the AGN type (Seyfert/LINER).

  2. Discovery of Millimeter-Wave Excess Emission in Radio-Quiet Active Galactic Nuclei

    Behar, Ehud; Baldi, Ranieri D.; Laor, Ari; Horesh, Assaf; Stevens, Jamie; Tzioumis, Tasso

    2015-01-01

    The physical origin of radio emission in Radio Quiet Active Galactic Nuclei (RQ AGN) remains unclear, whether it is a downscaled version of the relativistic jets typical of Radio Loud (RL) AGN, or whether it originates from the accretion disk. The correlation between 5 GHz and X-ray luminosities of RQ AGN, which follows $L_R = 10^{-5}L_X$ observed also in stellar coronae, suggests an association of both X-ray and radio sources with the accretion disk corona. Observing RQ AGN at higher (mm-wav...

  3. The Size of the Radio-Emitting Region in Low-luminosity Active Galactic Nuclei

    Anderson, James M.; Ulvestad, James S.

    2005-01-01

    We have used the VLA to study radio variability among a sample of 18 low luminosity active galactic nuclei (LLAGNs), on time scales of a few hours to 10 days. The goal was to measure or limit the sizes of the LLAGN radio-emitting regions, in order to use the size measurements as input to models of the radio emission mechanisms in LLAGNs. We detect variability on typical time scales of a few days, at a confidence level of 99%, in half of the target galaxies. Either variability that is intrinsi...

  4. Hard X-ray photon index as an indicator of bolometric correction in active galactic nuclei

    Zhou, Xin-Lin; Zhao, Yong-Heng

    2010-01-01

    We propose the rest-frame 2-10 keV photon index, \\ga, acting as an indicator of the bolometric correction, \\lb/$L_{\\rm 2-10keV}$ (where \\lb~ is the bolometric luminosity and $L_{\\rm 2-10keV}$ is the rest-frame 2-10 keV luminosity), in radio-quiet active galactic nuclei (AGNs). Correlations between \\ga~ and both bolometric correction and Eddington ratio are presented, based on simultaneous X-ray, UV, and optical observations of reverberation -mapped AGNs. These correlations can be compared wit...

  5. Theoretical hydrogen-line ratios for the narrow-line regions of active galactic nuclei

    H-alpha/H-beta (Ha/Hb) and other hydrogen line ratios for narrow line regions (NLR) of active galactic nuclei (AGN) were calculated, and their sensitivity to model parameters was investigated. The computations were performed with the photoionization code CLOUDY, with hydrogen treated as a seven-level plus continuum atom. Ha/Hb was sensitive to the ionization parameter and only weakly dependent on the electron density. Metallicity and the shape of the UV to X-ray continuum had the greatest impacts. It is recommended that Ha/Hb with a value of 3.0 be used as a reddening indicator for NLR of AGN. 21 references

  6. Search for emission of ultra high energy radiation from active galactic nuclei

    A search for emission of ultra-high energy gamma radiation from 13 active galactic nuclei that were detected by EGRET, using the CYGNUS extensive air-shower array, is described. The data set has been searched for continuous emission, emission on the time scale of one week, and for on the time scale of out day. No evidence for emission from any of the AGN on any of the time scales examined was found. The 90% C.L. upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5 x 10-14 cm-2s-1

  7. Does dichotomy of active galactic nuclei only depend on black hole spins?

    Ye, Yong-Chun; Wang, Ding-Xiong

    2004-01-01

    A toy model for jet powers and radio loudness of active galactic nuclei (AGNs) is proposed based on the coexistence of the Blandford-Znajek (BZ) and magnetic coupling (MC) processes (CEBZMC) in black hole (BH) accretion disc. It turns out that both the jet powers and radio-loudness of AGNs are controlled by more than one physical parameter besides the BH spin. The observed dichotomy between radio-loud and radio-quiet AGNs is well interpreted by the two parameters, the BH spin and the power-la...

  8. Search for emission of ultra high energy radiation from active galactic nuclei

    1993-01-01

    A search for emission of ultra-high energy gamma radiation from 13 active galactic nuclei that were detected by EGRET, using the CYGNUS extensive air-shower array, is described. The data set has been searched for continuous emission, emission on the time scale of one week, and for on the time scale of out day. No evidence for emission from any of the AGN on any of the time scales examined was found. The 90% C.L. upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5 [times] 10[sup [minus]14] cm[sup [minus]2]s[sup [minus]1].

  9. Search for emission of ultra high energy radiation from active galactic nuclei

    The CYGNUS Collaboration

    1993-05-01

    A search for emission of ultra-high energy gamma radiation from 13 active galactic nuclei that were detected by EGRET, using the CYGNUS extensive air-shower array, is described. The data set has been searched for continuous emission, emission on the time scale of one week, and for on the time scale of out day. No evidence for emission from any of the AGN on any of the time scales examined was found. The 90% C.L. upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5 {times} 10{sup {minus}14} cm{sup {minus}2}s{sup {minus}1}.

  10. Invisible Active Galactic Nuclei. II Radio Morphologies & Five New HI 21 cm Absorption Line Detections

    Yan, Ting; Stocke, John T.; Darling, Jeremy; Momjian, Emmanuel; Sharma, Soniya; Kanekar, Nissim

    2015-01-01

    We have selected a sample of 80 candidates for obscured radio-loud active galactic nuclei and presented their basic optical/near-infrared (NIR) properties in Paper 1. In this paper, we present both high-resolution radio continuum images for all of these sources and HI 21cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA continuum observations find that 52 sources are compact or have substantial compact components with size

  11. Scientific Highlights from Observations of Active Galactic Nuclei with the MAGIC Telescope

    Wagner, Robert

    2008-01-01

    Since 2004, the MAGIC gamma-ray telescope has newly discovered 6 TeV blazars. The total set of 13 MAGIC-detected active galactic nuclei includes well-studied objects at other wavelengths like Markarian 501 and the giant radio galaxy M 87, but also the distant the flat-spectrum radio quasar 3C 279, and the newly discovered TeV gamma-ray emitter S5 0716+71. In addition, also long-term and multi-wavelength studies on well-known TeV blazars and systematic searches for new TeV blazars have been...

  12. Scientific Highlights from Observations of Active Galactic Nuclei with the MAGIC Telescope

    Wagner, Robert; Collaboration, for the MAGIC

    2008-01-01

    Since 2004, the MAGIC gamma-ray telescope has newly discovered 6 TeV blazars. The total set of 13 MAGIC-detected active galactic nuclei includes well-studied objects at other wavelengths like Markarian 501 and the giant radio galaxy M87, but also the distant the flat-spectrum radio quasar 3C 279, and the newly discovered TeV gamma-ray emitter S5 0716+71. In addition, also long-term and multi-wavelength studies on well-known TeV blazars and systematic searches for new TeV blazars have been car...

  13. Evidence for Infrared-faint Radio Sources as z > 1 Radio-loud Active Galactic Nuclei

    Huynh, Minh T.; Norris, Ray P.; Siana, Brian; Middelberg, Enno

    2010-02-01

    Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6-70 μm) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the spectral energy distribution of these objects shows that they are consistent with high-redshift (z >~ 1) active galactic nuclei.

  14. Spectrophotometric monitoring of high luminosity active galactic nuclei. Pt. 1. The methods and data

    Perez, E. (Inst. de Astrofisica de Canarias, Tenerife (Spain)); Penston, M.V. (Royal Greenwich Observatory, Cambridge (UK)); Moles, M. (Inst. de Astrofisica de Andulucia, Granada (Spain))

    1989-07-01

    We report on a spectrophotometric monitoring programme of high luminosity active galactic nuclei (AGN) using the 2.5-m Issac Newton telescope. Data acquisition and analysis are explained, with emphasis on the care to be taken when comparing data from different epochs. The data are presented for individual objects. A comparison of the L{alpha}, CIV and CIII profiles shows that, contrary to what has previously been supposed, the profiles of different lines in a single object are not always the same as each other. (author).

  15. Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

    Serafinelli, Roberto; Middei, Riccardo

    2016-01-01

    The variability of the X-ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis, who found that slope variations are well correlated with flux variations, and that spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X-ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter $\\beta$, defined as the ratio between the change in spectral slope and the corresponding logarit...

  16. Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

    Serafinelli, R.; Vagnetti, F.; Middei, R.

    2016-02-01

    The variability of the X-Ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis [1], who found that slope variations are well correlated with flux variations, and that the spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X- Ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter β, defined by Trevese and Vagnetti [2] as the ratio between the change in spectral slope and the corresponding logarithmic flux variation. We find that the spectral variability of quasars has a softer when brighter behaviour, similarly to local AGNs.

  17. Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei

    Bartos, Imre; Haiman, Zoltán; Márka, Szabolcs

    2016-01-01

    Laser Interferometer Gravitational-Wave Observatory, LIGO, found direct evidence of double black hole binaries emitting gravitational waves. Galactic nuclei are expected to harbor the densest population of stellar-mass black holes, accounting for as much as ~2% of the mass of the nuclear stellar cluster. A significant fraction (~30%) of these black holes can reside in binaries. We examine the fate of the black hole binaries in active galactic nuclei, which get trapped in the inner region of the accretion disk around the central supermassive black hole. We show that binary black holes can migrate into and then rapidly merge within the disk well within a Salpeter time. The binaries may also accrete a significant amount of gas from the disk, well above the Eddington rate. This could lead to detectable X-ray or gamma-ray emission, but would require hyper-Eddington accretion with a few % radiative efficiency, comparable to thin disks. We discuss implications for gravitational wave observations and black hole popul...

  18. A High Fraction of Double-peaked Narrow Emission Lines in Powerful Active Galactic Nuclei

    Lyu, Yang

    2016-01-01

    One percent of redshift z~0.1 Active Galactic Nuclei (AGNs) show velocity splitting of a few hundred km/s in the narrow emission lines in spatially integrated spectra. Such line profiles have been found to arise from the bulk motion of ionized gas clouds associated with galactic-scale outflows, merging pairs of galaxies each harboring a supermassive black hole (SMBH), and/or galactic-scale disk rotation. It remains unclear, however, how the frequency of narrow-line velocity splitting may depend on AGN luminosity. Here we study the correlation between the fraction of Type 2 AGNs with double-peaked narrow emission lines and AGN luminosity as indicated by [O III]5007 emission-line luminosity L_[O III]. We combine the sample of Liu et al. (2010) at z~0.1 with a new sample of 178 Type 2 AGNs with double-peaked [O III] emission lines at z~0.5. We select the new sample from a parent sample of 2089 Type 2 AGNs from the SDSS-III/Baryon Oscillation Spectroscopic Survey. We find a statistically significant (~4.2\\sigma) ...

  19. A statistical method to search for recoiling supermassive black holes in active galactic nuclei

    Raffai, P.; Haiman, Z.; Frei, Z.

    2016-01-01

    We propose an observational test for gravitationally recoiling supermassive black holes (BHs) in active galactic nuclei, based on a correlation between the velocities of BHs relative to their host galaxies, |Δv|, and their obscuring dust column densities, Σdust (both measured along the line of sight). We use toy models for the distribution of recoil velocities, BH trajectories, and the geometry of obscuring dust tori in galactic centres, to simulate 2.5 × 105 random observations of recoiling quasars. BHs with recoil velocities comparable to the escape velocity from the galactic centre remain bound to the nucleus, and do not fully settle back to the centre of the torus due to dynamical friction in a typical quasar lifetime. We find that |Δv| and Σdust for these BHs are positively correlated. For obscured (Σdust > 0) and for partially obscured (0 103 km s-1) ≲ 0.4. This predicted trend can be compared to the observed fraction of type II quasars, and can further test combinations of recoil, trajectory, and dust torus models.

  20. A Statistical Method to Search for Recoiling Supermassive Black Holes in Active Galactic Nuclei

    Raffai, Peter; Frei, Zsolt

    2015-01-01

    We propose an observational test for gravitationally recoiling supermassive black holes (BHs) in active galactic nuclei, based on a correlation between the velocities of BHs relative to their host galaxies, |\\Delta v|, and their obscuring dust column densities, \\Sigma_{dust} (both measured along the line of sight). Proxies for both quantities can be derived from spectral features of individual quasars. We use toy models for the distribution of recoil velocities, BH trajectories, and the geometry of obscuring dust tori in galactic centres, to simulate 2.5x10^5 random observations of recoiling quasars. BHs with recoil velocities comparable to the escape velocity from the galactic centre remain bound to the nucleus, and do not fully settle back to the centre of the torus due to dynamical friction in a typical quasar lifetime. We find that |\\Delta v| and \\Sigma_ {dust} for these BHs are positively correlated. For obscured (\\Sigma_{dust}>0) and for partially obscured (0=45 km/s, the sample correlation coefficient ...

  1. Analysis of nearly simultaneous x-ray and optical observations of active galactic nuclei

    Rosemary Hill optical and EINSTEIN X-ray observations of a sample of 36 galactic nuclei (AGN) were reduced and analyzed. Seventy-two x-ray observations of these sources were reduced, nineteen of which yielded spectral information. Of these spectra observations, significant hydrogen column densities above the galactic value were required for nine of the active galactic nuclei. X-ray variability was detected in eight of the eleven sources which were observed more than once by EINSTEIN. Correlations between the x-ray and optical luminosities were investigated using the Jefferys method of least squares. This method allows for errors in both variables. The results indicate a strong correlation between the x-ray and optical luminosities for the entire sample. Division of the sample into groups with similar optical variability characteristics show that the less violently violent variable AGN are more highly correlated than the violently variable blazars. Infrared and radio observations were combined with the x-ray and optical observations of six AGN. These sources were modelled in terms of the synchrotron-self-Compton model. The turnover frequency falls between the infrared and radio data and reliable estimates of this parameter are difficult to estimate. Therefore the results were found as a function of the turnover frequency. Four sources required relativistic bulk motion or beaming. Multifrequency spectra made at different times for one individual source, 0235+164, required different amounts of beaming to satisfy the x-ray observations. Sizes of the emitting regions for the sources modelled ranged from 0.5 parsec to 1.0 parsec

  2. Stability of Cloud Orbits in the Broad Line Region of Active Galactic Nuclei

    schartmann, Martin Krause Andreas Burkert Marc

    2010-01-01

    We investigate the global dynamic stability of spherical clouds in the Broad Line Region (BLR) of Active Galactic Nuclei (AGN), exposed to radial radiation pressure, gravity of the central black hole (BH), and centrifugal forces assuming the clouds adapt their size according to the local pressure. We consider both, isotropic and anisotropic light sources. In both cases, stable orbits exist also for very sub-Keplerian rotation for which the radiation pressure contributes substantially to the force budget. We demonstrate that highly excentric, very sub-Keplerian stable orbits may be found that also agree with the recent finding by spectropolarimetry that the BLR is disk-like. This gives further support for the model of Marconi et al. 2008, which is designed to improve the agreement between black hole masses derived in certain active galaxies based on BLR dynamics, and black hole masses derived by other means in other galaxies by inclusion of a luminosity dependent term. For anisotropic illumination, the foresho...

  3. Gravitational Wave Recoil Oscillations of Black Holes: Implications for Unified Models of Active Galactic Nuclei

    Komossa, S

    2008-01-01

    We consider the consequences of gravitational wave recoil for unified models of active galactic nuclei (AGNs). Spatial oscillations of supermassive black holes (SMBHs) around the cores of galaxies following gravitational wave (GW) recoil imply that the SMBHs spend a significant fraction of time off-nucleus, at scales beyond that of the molecular obscuring torus. Assuming reasonable distributions of recoil velocities, we compute the off-core timescale of (intrinsically type-2) quasars. We find that roughly one-half of major mergers result in a SMBH being displaced beyond the torus for a time of 30 Myr or more, comparable to quasar activity timescales. Since major mergers are most strongly affected by GW recoil, our results imply a deficiency of type 2 quasars in comparison to Seyfert 2 galaxies. Other consequences of the recoil oscillations for the observable properties of AGNs are also discussed.

  4. A High Fraction of Double-peaked Narrow Emission Lines in Powerful Active Galactic Nuclei

    Lyu, Yang; Liu, Xin

    2016-08-01

    One percent of redshift z ˜ 0.1 Active Galactic Nuclei (AGNs) show velocity splitting of a few hundred km s-1 in the narrow emission lines in spatially integrated spectra. Such line profiles have been found to arise from the bulk motion of ionized gas clouds associated with galactic-scale outflows, merging pairs of galaxies each harboring a supermassive black hole (SMBH), and/or galactic-scale disk rotation. It remains unclear, however, how the frequency of narrow-line velocity splitting may depend on AGN luminosity. Here we study the correlation between the fraction of Type 2 AGNs with double-peaked narrow emission lines and AGN luminosity as indicated by [O III]λ5007 emission-line luminosity L[O III]. We combine the sample of Liu et al. (2010a) at z ˜ 0.1 with a new sample of 178 Type 2 AGNs with double-peaked [O III] emission lines at z ˜ 0.5. We select the new sample from a parent sample of 2089 Type 2 AGNs from the SDSS-III/Baryon Oscillation Spectroscopic Survey. We find a statistically significant (˜4.2σ) correlation between L[O III] and the fraction of objects that exhibit double-peaked narrow emission lines among all Type 2 AGNs, corrected for selection bias and incompleteness due to [O III] line width, equivalent width, splitting velocity, and/or equivalent width ratio between the two velocity components. Our result suggests that galactic-scale outflows and/or merging pairs of SMBHs are more prevalent in more powerful AGNs, although spatially resolved follow up observations are needed to resolve the origin(s) for the narrow-line velocity splitting for individual AGNs.

  5. X-ray spectra and time variability of active galactic nuclei

    X ray measurements taken with the HEAO-1 and -2 satellites are examined for clues to the source of emissions from active galactic nuclei (AGN). The data covered the energy range 2-100 keV and 0.5-4.5 keV and encompassed quasars, BL Lac objects, Seyfert I galaxies and broadline radio galaxies. The broadline spectra were best fit with a power law with a slope of about 0.68. The continua displayed roughly equivalent energy at all wavelengths except for radio bands. Spectral variability was detected in the BL Lac objects, which may emit optical, UV and soft X ray radiation from optically thin synchrotron emission with a hard X ray tail from inverse Compton scattering. No strong variability was evidenced with other AGN, suggesting that the emitting regions are below the Eddington luminosity and thus exhibit stable flow characteristics. 42 references

  6. Search of high energy neutrino flares from active galactic nuclei with the IceCube detector

    Cruz Silva, Angel Humberto; Bernardini, Elisa [DESY, Platanenallee 6, D 15738 Zeuthen (Germany); Gora, Dariusz [DESY, Platanenallee 6, D 15738 Zeuthen (Germany); Institute of Nuclear Physics PAN, ul. Radzikowskiego 152,31-342 Cracow, Krakow (Poland); Collaboration: IceCube-Collaboration

    2013-07-01

    Active Galactic Nuclei (AGN) are among the best candidates for sources of high energy cosmic rays. One of their properties is the extreme variability in their electromagnetic emission at different wavelengths with flare durations ranging from minutes, in some cases, to several weeks. This photon flares may be correlated with neutrinos emitted from the same source if protons are also accelerated in the AGN relativistic jet. Here we present a new statistical test method to look for neutrino flares from selected AGNs. The method takes into account a list of possible neutrino sources from different categories (FSRQs and BL-Lacs) in a so called stacking approach. The performance and results of the method using IceCube data in its 79 string configuration are presented.

  7. A new approach to the variability characterization of active galactic nuclei

    Middei, R.; Vagnetti, F.; Antonucci, M.; Serafinelli, R.

    2016-02-01

    The normalized excess variance is a popular method used by many authors to estimate the variability of active galactic nuclei (AGNs), especially in the X-ray band. We show that this estimator is affected by the cosmological time dilation, so that it should be appropriately corrected when applied to AGN samples distributed in wide redshift intervals. We propose a formula to modify this estimator, based on the use of the structure function. To verify the presence of the cosmological effect and the reliability of the proposed correction, we use data extracted from the XMM-Newton Serendipitous Source Catalogue, data release 5 (XMMSSC-DR5), and cross-matched with the Sloan Digital Sky Survey quasar catalogue, of data release 7 and 12.

  8. A mid-to far-infrared variability study of eight active galactic nuclei

    In this paper a mid-to far-infrared (MFIR) variability study of a heterogeneous sample of active galactic nuclei (AGN) is presented using data from the Infrared Astronomical Satellite (IRAS). The data have been taken from the IRAS Additional Observation (AO) archives. The source list comprises eight AGN; one Seyfert type 2 galaxy (NGC 1275), three Seyfert type 1 galaxies (NGC 4151, IIIZw2 and AKN 374), two quasars (PG 1351+64 and 1156+295) and two BL Lacertae objects (OJ287 and MKN 501). The observations cover a variety of time-scales from days to months. In only one case, that of the BL Lac object OJ 287, was significant evidence found for variability within the IRAS waveband, although the OVV quasar 1156+295 shows evidence for variability by comparison with archival ground-based data. (author)

  9. Linking the fate of massive black hole binaries to the active galactic nuclei luminosity function

    Dotti, Massimo; Montuori, Carmen

    2015-01-01

    Massive black hole binaries are naturally predicted in the context of the hierarchical model of structure formation. The binaries that manage to lose most of their angular momentum can coalesce to form a single remnant. In the last stages of this process, the holes undergo an extremely loud phase of gravitational wave emission, possibly detectable by current and future probes. The theoretical effort towards obtaining a coherent physical picture of the binary path down to coalescence is still underway. In this paper, for the first time, we take advantage of observational studies of active galactic nuclei evolution to constrain the efficiency of gas-driven binary decay. Under conservative assumptions we find that gas accretion toward the nuclear black holes can efficiently lead binaries of any mass forming at high redshift (> 2) to coalescence within the current time. The observed "downsizing" trend of the accreting black hole luminosity function further implies that the gas inflow is sufficient to drive light ...

  10. Optimal strategies for observation of active galactic nuclei variability with Imaging Atmospheric Cherenkov Telescopes

    Giomi, Matteo; Maier, Gernot

    2016-01-01

    Variable emission is one of the defining characteristic of active galactic nuclei (AGN). While providing precious information on the nature and physics of the sources, variability is often challenging to observe with time- and field-of-view-limited astronomical observatories such as Imaging Atmospheric Cherenkov Telescopes (IACTs). In this work, we address two questions relevant for the observation of sources characterized by AGN-like variability: what is the most time-efficient way to detect such sources, and what is the observational bias that can be introduced by the choice of the observing strategy when conducting blind surveys of the sky. Different observing strategies are evaluated using simulated light curves and realistic instrument response functions of the Cherenkov Telescope Array (CTA), a future gamma-ray observatory. We show that strategies that makes use of very small observing windows, spread over large periods of time, allows for a faster detection of the source, and are less influenced by the...

  11. Radius-luminosity and mass-luminosity relationships for active galactic nuclei

    Broad-line region (BLR) sizes derived from spectral variability and BLR line widths are used to directly derive the mass (M) of the central objects of ten active galactic nuclei (AGNs) in a uniform manner. It is shown that the luminosity-weighted C IV 1549-emitting BLR radius (R) correlates with the bolometric luminosity L(Bol) and is consistent with R about sq rt L(Bol). The measurements also permit a verification of the Dibai mass-luminosity (M-L) relationship (previously derived indirectly). It is found that L(Bol) is proportional to M exp (1.1 + or - 0.3). It is found that the efficiency factor epsilon, defined as the ratio of L(Bol) to the Eddington luminosity increases from 0.03 in the low-luminosity Seyferts up to 0.06 in the most luminous objects in the sample. 19 refs

  12. Time domain studies of Active Galactic Nuclei with the Square Kilometre Array

    Bignall, Hayley; Hovatta, Talvikki; Koay, Jun Yi; Lazio, Joseph; Macquart, Jean-Pierre; Reynolds, Cormac

    2015-01-01

    Variability of radio-emitting active galactic nuclei can be used to probe both intrinsic variations arising from shocks, flares, and other changes in emission from regions surrounding the central supermassive black hole, as well as extrinsic variations due to scattering by structures in our own Galaxy. Such interstellar scattering also probes the structure of the emitting regions, with microarcsecond resolution. Current studies have necessarily been limited to either small numbers of objects monitored over long periods of time, or large numbers of objects but with poor time sampling. The dramatic increase in survey speed engendered by the Square Kilometre Array will enable precision synoptic monitoring studies of hundreds of thousands of sources with a cadence of days or less. Statistics of variability, in particular concurrent observations at multiple radio frequencies and in other bands of the electromagnetic spectrum, will probe accretion physics over a wide range of AGN classes, luminosities, and orientat...

  13. EVIDENCE FOR INFRARED-FAINT RADIO SOURCES AS z > 1 RADIO-LOUD ACTIVE GALACTIC NUCLEI

    Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6-70 μm) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the spectral energy distribution of these objects shows that they are consistent with high-redshift (z ∼> 1) active galactic nuclei.

  14. A note on periodicity of long-term variations of optical continuum in active galactic nuclei

    Lu, Kai-Xing; Bi, Shao-Lan; Wang, Jian-Min

    2016-01-01

    Graham et al. found a sample of active galactic nuclei (AGNs) and quasars from the Catalina Real-time Transient Survey (CRTS) that have long-term periodic variations in optical continuum, the nature of the periodicity remains uncertain. We investigate the periodic variability characteristics of the sample by testing the relations of the observed variability periods with AGN optical luminosity, black hole mass and accretion rates, and find no significant correlations. We also test the observed periods in several different aspects related to accretion disks surrounding single black holes, such as the Keplerian rotational periods of 5100~\\AA\\ photon-emission regions and self-gravity dominated regions and the precessing period of warped disks. These tests shed new lights on understanding AGN variability in general. Under the assumption that the periodic behavior is associated with SMBHB systems in particular, we compare the separations ($\\mathscr{D}_{\\bullet}$) against characteristic radii of broad-line regions (...

  15. The optical polarization signatures of fragmented equatorial dusty structures in Active Galactic Nuclei

    Marin, F

    2015-01-01

    If the existence of an obscuring circumnuclear region around the innermost regions of active galactic nuclei (AGN) has been observationally proven, its geometry remains highly uncertain. The morphology usually adopted for this region is a toroidal structure, but other alternatives, such as flared disks, can be a good representative of equatorial outflows. Those two geometries usually provide very similar spectroscopic signatures, even when they are modeled under the assumption of fragmentation. In this lecture note, we show that the resulting polarization signatures of the two models, either a torus or a flared disk, are quite different from each other. We use a radiative transfer code that computes the 2000 - 8000 angstrom polarization of the two morphologies in a clumpy environment, and show that varying the sizes of a toroidal region has deep impacts onto the resulting polarization, while the polarization of flared disks is independent of the outer radius. Clumpy flared disks also produce higher polarizati...

  16. Photon damping in cosmic-ray acceleration in active galactic nuclei

    Colgate, S.A.

    1983-04-07

    The usual assumption of the acceleration of ultra high energy cosmic rays, greater than or equal to 10/sup 18/ eV in quasars, Seyfert galaxies and other active galactic nuclei is challenged on the basis of the photon interactions with the accelerated nucleons. This is similar to the effect of the black body radiation on particles > 10/sup 20/ eV for times of the age of the universe except that the photon spectrum is harder and the energy density greater by approx. = 10/sup 15/. Hence, a single traversal, radial or circumferential, of radiation whose energy density is no greater than the emitted flux will damp an ultra high energy. Hence, it is unlikely that any reasonable configuration of acceleration can void disastrous photon energy loss. A different site for ultra high energy cosmic ray acceleration must be found.

  17. EDDINGTON RATIO GOVERNS THE EQUIVALENT WIDTH OF Mg II EMISSION LINE IN ACTIVE GALACTIC NUCLEI

    We have investigated the ensemble regularities of the equivalent widths (EWs) of Mg II λ2800 emission line of active galactic nuclei (AGNs), using a uniformly selected sample of 2092 Seyfert 1 galaxies and quasars at 0.45 ≤ z ≤ 0.8 in the spectroscopic data set of the Sloan Digital Sky Survey Fourth Data Release. We find a strong correlation between the EW of Mg II and the AGN Eddington ratio (L/LEdd): EW(Mg II) ∝ (L/L Edd)-0.4. Furthermore, for AGNs with the same L/LEdd, their EWs of Mg II show no correlation with luminosity, black hole mass, or line width, and the Mg II line luminosity is proportional to continuum luminosity, as expected by photoionization theory. Our result shows that Mg II EW is not dependent on luminosity, but is solely governed by L/LEdd.

  18. Relativistic particles and gamma-rays in quasars and active galactic nuclei

    Protheroe, R. J.; Kazanas, D.

    1983-01-01

    A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via Pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

  19. Relativistic particles and gamma-rays in quasars and active galactic nuclei

    A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a non-thermal spectrum of high energy protons. These protons may be responsible for the secondary production (via πsup(+-) decay) of the radio emitting high energy electrons and also of high energy γ-rays (via π0 decay and inverse Compton interactions of the electrons). The correlation between radio and γ-ray emission implied by the model is in good agreement with observations of 3C273. Observations of the flux of high energy neutrinos from quasars may provide a test for the model. (orig.)

  20. Relativistic particles and gamma-ray in quasars and active galactic nuclei

    A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model

  1. Relativistic particles and gamma-ray in quasars and active galactic nuclei

    Protheroe, R. J.; Kazanas, D.

    1982-01-01

    A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

  2. Relativistic particles and gamma-ray in quasars and active galactic nuclei

    Protheroe, R.J.; Kazanas, D.

    1982-07-01

    A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

  3. X-ray spectroscopy of AGN with the AXAF 'Microcalorimeter'. [Active Galactic Nuclei

    Holt, Stephen S.

    1987-01-01

    A novel technique for X-ray spectroscopy has been configured as part of the definition payload of the AXAF Observatory. It is basically a calorimeter which, operating at 0.1 K, senses the total conversion of single photoelectrically absorbed X-rays via the differential temperature rise of the absorber. The technique promises to achieve less than 10 eV FWHM with near-unit efficiency simultaneously over the entire AXAF bandpass. This combination of high resolution and high efficiency allows for the possibility of investigating thermal, fluorescent and absorption X-ray line features in many types of X-ray source, including a large sample of active galactic nuclei.

  4. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    Tombesi, Francesco

    2016-01-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been dir...

  5. A Polarimetric Method for Measuring Black Hole Masses in Active Galactic Nuclei

    Piotrovich, M Yu; Silant'ev, N A; Natsvlishvili, T M; Buliga, S D

    2015-01-01

    The structure of the broad emission line region (BLR) in active galactic nuclei (AGN) remains unclear. We test in this paper a flattened configuration model for BLR. The virial theorem, by taking into account the disc shape of BLR, allows us to get a direct connection between the mass of a supermassive black hole (SMBH) and the inclination angle of the accretion flow. The inclination angle itself is derived from the spectropolarimetric data on broad emission lines using the theory for the generation of polarized radiation developed by Sobolev and Chandrasekhar. As the result, the new estimates of SMBH masses in AGN with measured polarization of BLR are presented. It is crucial that the polarimetric data allow also to determine the value of the virial coefficient that is essential for determining SMBH masses.

  6. A polarimetric method for measuring black hole masses in Active Galactic Nuclei

    Piotrovich, M. Yu.; Gnedin, Yu. N.; Silant'ev, N. A.; Natsvlishvili, T. M.; Buliga, S. D.

    2015-11-01

    The structure of the broad emission line region (BLR) in active galactic nuclei (AGN) remains unclear. We test in this paper a flattened configuration model for BLR. The virial theorem, by taking into account the disc shape of BLR, allows us to get a direct connection between the mass of a supermassive black hole (SMBH) and the inclination angle of the accretion flow. The inclination angle itself is derived from the spectropolarimetric data on broad emission lines using the theory for the generation of polarized radiation developed by Sobolev and Chandrasekhar. As the result, the new estimates of SMBH masses in AGN with measured polarization of BLR are presented. It is crucial that the polarimetric data allow also to determine the value of the virial coefficient that is essential for determining SMBH masses.

  7. Search for Correlations between HiRes Stereo Events and Active Galactic Nuclei

    Abbasi, R U; Allen, M; Amman, J F; Archbold, G; Belov, K; Belz, J W; BenZvi, S Y; Bergman, D R; Blake, S A; Boyer, J H; Brusova, O A; Burt, G W; Cannon, C; Cao, Z; Deng, W; Fedorova, Y; Findlay, J; Finley, C B; Gray, R C; Hanlon, W F; Hoffman, C M; Holzscheiter, M H; Hughes, G; Hüntemeyer, P; Ivanov, D; Jones, B F; Jui, C C H; Kim, K; Kirn, M A; Knapp, B C; Loh, E C; Maestas, M M; Manago, N; Mannel, E J; Marek, L J; Martens, K; Matthews, J N; Moore, S A; O'Neill, A; Painter, C A; Perera, L; Reil, K; Riehle, R; Roberts, M D; Sasaki, D Rodriguez N; Schnetzer, S R; Scott, L M; Seman, M; Sinnis, G; Smith, J D; Snow, R; Sokolsky, P; Song, C; Springer, R W; Stokes, B T; Stratton, S R; Thomas, J R; Thomas, S B; Thomson, G B; Tupa, D; Wiencke, L R; Zech, A; Zhang, X

    2008-01-01

    We have searched for correlations between the pointing directions of ultrahigh energy cosmic rays observed by the High Resolution Fly's Eye experiment and Active Galactic Nuclei visible from its northern hemisphere location. No correlations, other than random correlations, have been found. We report our results using search parameters prescribed by the Pierre Auger collaboration. Using these parameters, the Auger collaboration concludes that a positive correlation exists for sources visible to their southern hemisphere location. We also describe results using two methods for determining the chance probability of correlations: one in which a hypothesis is formed from scanning one half of the data and tested on the second half, and another which involves a scan over the entire data set. The most significant correlation found occurred with a chance probability of 24%.

  8. A new approach to the variability characterization of active galactic nuclei

    Middei, Riccardo; Antonucci, Marco; Serafinelli, Roberto

    2016-01-01

    The normalized excess variance is a popular method used by many authors to estimate the variability of active galactic nuclei (AGNs), especially in the X-ray band. We show that this estimator is affected by the cosmological time dilation, so that it should be appropriately corrected when applied to AGN samples distributed in wide redshift intervals. We propose a formula to modify this estimator, based on the use of the structure function. To verify the presence of the cosmological effect and the reliability of the proposed correction, we use data extracted from the XMM-Newton Serendipitous Source Catalogue, data release 5 (XMMSSC-DR5), and cross-matched with the Sloan Digital Sky Survey quasar catalogue, of data release 7 and 12.

  9. X-ray and infrared diagnostics of nearby active galactic nuclei with MAXI and AKARI

    Isobe, Naoki; Oyabu, Shinki; Nakagawa, Takao; Baba, Shunsuke; Yano, Kenichi; Ueda, Yoshihiro; Toba, Yoshiki

    2016-01-01

    Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far infrared wavelengths, with Monitor of All-sky X-ray Image (MAXI) and the Japanese infrared observatory AKARI, respectively. Among the X-ray sources listed in the second release of the MAXI all-sky X-ray source catalog, 100 ones are currently identified as a non-blazar-type active galactic nucleus. These include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1 and 27 type-2 objects. The AKARI all-sky survey point source catalog was searched for their mid- and far-infrared counterparts at 9, 18, and 90 $\\mu$m. As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2 ones) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV) and infrared luminosities of these objects were investigated, together with their color information. Adopting the canonical photon index, $\\Gamma = 1.9$, of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness ratio between the 3-4 and 4-10 ...

  10. MOJAVE: MONITORING OF JETS IN ACTIVE GALACTIC NUCLEI WITH VLBA EXPERIMENTS. VII. BLAZAR JET ACCELERATION

    We discuss acceleration measurements for a large sample of extragalactic radio jets from the Monitoring Of Jets in Active Galactic Nuclei with VLBA Experiments (MOJAVE) program, which studies the parsec-scale jet structure and kinematics of a complete, flux-density-limited sample of active galactic nuclei (AGNs). Accelerations are measured from the apparent motion of individual jet features or 'components' which may represent patterns in the jet flow. We find that significant accelerations are common both parallel and perpendicular to the observed component velocities. Parallel accelerations, representing changes in apparent speed, are generally larger than perpendicular acceleration that represent changes in apparent direction. The trend for larger parallel accelerations indicates that a significant fraction of these changes in apparent speed are due to changes in intrinsic speed of the component rather than changes in direction to the line of sight. We find an overall tendency for components with increasing apparent speed to be closer to the base of their jets than components with decreasing apparent speed. This suggests a link between the observed pattern motions and the underlying flow which, in some cases, may increase in speed close to the base and decrease in speed further out; however, common hydrodynamical processes for propagating shocks may also play a role. About half of the components show 'non-radial' motion, or a misalignment between the component's structural position angle and its velocity direction, and these misalignments generally better align the component motion with the downstream emission. Perpendicular accelerations are closely linked with non-radial motion. When observed together, perpendicular accelerations are usually in the correct direction to have caused the observed misalignment.

  11. Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei

    Collaboration, The Pierre auger

    2007-12-01

    Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with the highest energies, which are correlated with the positions of relatively nearby active galactic nuclei (AGN) [1]. The correlation has maximum significance for cosmic rays with energy greater than {approx} 6 x 10{sup 19} eV and AGN at a distance less than {approx} 75 Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parameters specified a priori, using an independent data set. The observed correlation is compatible with the hypothesis that cosmic rays with the highest energies originate from extra-galactic sources close enough so that their flux is not significantly attenuated by interaction with the cosmic background radiation (the Greisen-Zatsepin-Kuzmin effect). The angular scale of the correlation observed is a few degrees, which suggests a predominantly light composition unless the magnetic fields are very weak outside the thin disk of our galaxy. Our present data do not identify AGN as the sources of cosmic rays unambiguously, and other candidate sources which are distributed as nearby AGN are not ruled out. We discuss the prospect of unequivocal identification of individual sources of the highest-energy cosmic rays within a few years of continued operation of the Pierre Auger Observatory.

  12. Ion-heated thermal Comptonization models and x-ray spectral correlations in active galactic nuclei

    Recent Ginga observations of the Seyfert 1 galaxies NGC 4051 and MCG 6-30-15 show a positive correlation between the 2-10 keV luminosity and photon spectral index α. Similar behavior has also been reported in Exosat and Einstein observations of other active galactic nuclei, and is suggested in hard x-ray low-state data of the galactic black-hole candidate Cygnus X-1. A two-temperature thermal Comptonization model with internal soft-photon production provides a simple explanation for this correlation. The electron temperature, determined by a balance between ion heating and radiative cooling, decreases in response to an enhancement of the soft photon flux, resulting in a softening of the spectrum and an increase in the soft x-ray luminosity. The bulk of the soft photons are produced through pion production in collisions between the hot ions. Pivoting of the spectrum at photon energies var-epsilon > 50 keV is a consequence of variations in the ion temperature. An important test of the model would be time correlations between soft and hard x-ray bands. 17 refs., 9 figs., 1 tab

  13. Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei

    Abraham, J; Aglietta, M; Aguirre, C; Allard, D; Allekotte, I; Allen, J; Allison, P; Alvarez, C; Alvarez-Muñiz, J; Ambrosio, M; Anchordoqui, L; Andringa, S; Anzalone, A; Aramo, C; Argiro, S; Arisaka, K; Armengaud, E; Arneodo, F; Arqueros, F; Asch, T; Asorey, H; Assis, P; Atulugama, B S; Aublin, J; Ave, M; Avila, G; Backer, T; Badagnani, D; Barbosa-Ademarlaudo, F; Barnhill, D; Barroso, S L C; Bauleo, P; Beatty, J J; Beau, T; Becker, B R; Becker, K H; Bellido, J A; Ben Zvi, S; Bérat, C; Bergmann, T; Bernardini, P; Bertou, X; Biermann, P L; Billoir, P; Blanch-Bigas, O; Blanco, F; Blasi, P; Bleve, C; Blümer, H; Bohaov, M; Bonifazi, C; Bonino, R; Boratav, M; Brack, J; Brogueira, P; Brown, W C; Buchholz, P; Bueno, A; Burton, R E; Busca, N G; Caballero-Mora, K S; Cai, B; Camin, D V; Caramete, L; Caruso, R; Carvalho, W; Castellina, A; Catalano, O; Cataldi, G; Cazon, L; Cester, R; Chauvin, J; Chiavassa, A; Chinellato, J A; Chou, A; Chye, J; Clark, P D J; Clay, R W; Colombo, E; Conceico, R; Connolly, B; Contreras, F; Coppens, J; Cordier, A; Cotti, U; Coutu, S; Covault, C E; Creusot, A; Criss, A; Cronin, J; Curutiu, A; Dagoret-Campagne, S; Daumiller, K; Dawson, B R; de Almeida, R M; De Donato, C; De Jong, S J; De La Vega, G; de Mello Junior, W J M; De Mello-Neto, J R T; De Mitri, I; De Souza, V; Del Peral, L; Deligny, O; Della Selva, A; Delle Fratte, C; Dembinski, H; Di Giulio, C; Diaz, J C; Dobrigkeit, C; D'Olivo, J C; Dornic, D; Dorofeev, A; dos Anjos, J C; Dova, M T; D'Urso, D; Dutan, I; Duvernois, M A; Engel, R; Epele, L; Erdmann, M; Escobar, C O; Etchegoyen, A; Facal San Luis, P; Falcke, H; Farrar, G; Fauth, A C; Fazzini, N; Fernández, A; Ferrer, F; Ferry, S; Fick, B; Filevich, A; Filipi, A; Fleck, ccI; Fonte, R; Fracchiolla, C E; Fulgione, W; Garca, B; Garca Gamez, D; Garcia-Pinto, D; Garrido, X; Geenen, H; Gelmini, i G; Gemmeke, H; Ghia, P L; Giller, M; Glass, H; Gold, M S; Golup, G; Gomez Albarracin, F; Gomez Berisso, M; Gmez Herrero, R; Gonalves, P; Goncalvesdo Amaral, M; González, D; Gonzalez, J G; González, M; Gora, D; Gorgi, A; Gouffon, P; Grassi, V; Grillo, A F; Grunfeld, C; Guardincerri, Y; Guarino, F; Guedes, G P; Gutirrez, J; Hague, J D; Hamilton, J C; Hansen, P; Harari, D; Harmsma, S; Harton, J L; Haungs, A; Hauschildt, T; Healy, M D; Hebbeker, T; Hebrero, G; Heck, D; Hojvat, C; Holmes, V C; Homola, P; Horandel, J; Horneffer, A; Horvat, M; Hrabovsky, M; Huege, T; Hussain, M; Iarlori, M; Insolia, A; Ionita, F; Italiano, A; Kaducak, M; Kampert, K H; Karova, T; Kgl, B; Keilhauer, B; Kemp, E; Kieckhafer, R M; Klages, H O; Kleifges, M; Kleinfeller, J; Knapik, R; Knapp, J; Koang, D H; Krieger, A; Krömer, O; Kuempel, D; Kunka, N; Kusenko, A; La Rosa, G; Lachaud, C; Lago, B L; Lebrun, D; Le Brun, P; Lee, J; Leiguide Oliveira, M A; Letessier-Selvon, A A; Leuthold, M; Lhenry-Yvon, I; López, R; López-Aguera, A; LozanoBahilo, J; Luna Garca, R; Maccarone, M C; Macolino, C; Maldera, S; Mancarella, G; Mancenido, M E; Mandat, D; Mantsch, P; Mariazzi, A G; Maris, I C; Marquez Falcon, H R; Martello, D; Martínez, J; Martinez Bravo, O; Mathes, H J; Matthews, J; Matthews, ii J A J; Matthiae, Giorgio; Maurizio, D; Mazur, P O; McCauley, T; McEwen, M; McNeil, R R; Medina, M C; Medina-Tanco, G; Meli, A; Melo, D; Menichetti, E; Menschikov, A; Meurer, Chr; Meyhandan, R; Micheletti, M I; Miele, G; Miller, W; Mollerach, S; Monasor, M; Monnier Ragaigne, D; Montanet, F; Morales, B; Morello, C; Moreno, E; Moreno, J C; Morris, C; Mostaf, M; Muller, M A; Mussa, R; Navarra, G; Navarro, J L; Navas, a S; Necesal, P; Nellen, L; Newman-Holmes, C; Newton, D; Nguyen Thi, T; Nierstenhoefer, N; Nitz, D; Nosek, D; Noka, L; Oehlschläger, J; Ohnuki, T; Olinto, A; Olmos-Gilbaja, V M; Ortiz, M; Ortolani, F; Ostapchenko, S; Otero, L; Pacheco, N; Pakk Selmi-Dei, D; Palatka, M; Pallotta, J; Parente, G; Parizot, E; Parlati, S; Pastor, S; Patel, M; Paul, T; Pavlidou, V; Payet, K; Pech, M; Pkala, J; Pelayo, R; Pepe, I M; Perrone, L; Petrera, S; Petrinca, P; Petrov, Y; Diep Pham Ngoc Dong Pham Ngoc; Pham Thi, T N; Pichel, A; Piegaia, R; Pierog, T; Pimenta, M; Pinto, T; Pirronello, V; Pisanti, O; Platino, M; Pochon, J; Porter, T A; Privitera, P; Prouza, M; Quel, E J; Rautenberg, J; Redondo, A; Reucroft, S; Revenu, B; Rezende, F A S; Rídky, J; Riggi, S; Risse, M; Rivi`re, C; Rizi, V; Roberts, M; Robledo, C; Rodríguez, G; Rodrguez Fras, D; Rodríguez-Martino, J; RodrigueziiRojo, J; Rodriguez-Cabo, I; Ros, G; Rosado, J; Roth, M; Rouill-d'Orfeuil, B; Roulet, E; Rovero, A C; Salamida, F; Salazar, H; Salina, G; Sánchez, F; Santander, M; Santo, C E; Santos, E M; Sarazin, F; Sarkar, S; Sato, R; Scherini, V; Schieler, H; Schmidt, A; Schmidt, F; Schmidt, T; Scholten, O; Schovnek, P; Schussler, F; Sciutto, S J; Scuderi, M; Segreto, A; Semikoz, D; Settimo, M; Shellard, R C; Sidelnik, I; Siffert, B B; Sigl, i G; Smetniansky De Grande, N; Smialkowski, A; Smda, R; Smith, A G K; Smith, B E; Snow, G R; Sokolsky, P; Sommers, P; Sorokin, J; Spinka, H; Squartini, R; Strazzeri, E; Stutz, A; Suárez, F; Suomijärvi, T; Supanitsky, A D; Sutherland, M S; Swain, J; Szadkowski, Z; Takahashi, J; Tamashiro, A; Tamburro, A; Tacu, O; Tcaciuc, R; Thomas, D; Ticona, R; Tiffenberg, J; Timmermans, C; Tkaczyk, W; Todero Peixoto, C J; Tom, B; Tonachini, A; Torres, I; Torresi, D; Travnicek, P; Tripathi, A; Tristram, G; Tscherniakhovski, D; Tueros, M; Tunnicliffe, V; Ulrich, R; Unger, M; Urban, M; Valds Galicia, J F; Valino, I; Valore, e L; vanden Berg, A M; van Elewyck, V; Vázquez, R A; Veberi, D; Veiga, A; Velarde, A; Venters, T; Verzi, V; Videla, cM; Villaseñor, L; Vorobiov, S; Voyvodic, L; Wahlberg, H; Wainberg, O; Walker, P; Warner, D; Watson, A A; Westerhoff, S; Wieczorek, G; Wiencke, L; Wilczynska, B; Wilczynski, H; Wileman, C; Winnick, M G; Wu, H; Wundheiler, B; Yamamoto, T; Younk, P; Zas, E; Zavrtanik, D; Zavrtanik, M; Zech, A; Zepeda, A; Ziolkowski, M

    2007-01-01

    Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with the highest energies, which are correlated with the positions of relatively nearby active galactic nuclei (AGN) \\cite{science}. The correlation has maximum significance for cosmic rays with energy greater than ~ 6x10^{19}$ eV and AGN at a distance less than ~ 75 Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parameters specified {\\em a priori}, using an independent data set. The observed correlation is compatible with the hypothesis that cosmic rays with the highest energies originate from extra-galactic sources close enough so that their flux is not significantly attenuated by interaction with the cosmic background radiation (the Greisen-Zatsepin-Kuz'min effect). The angular scale of the correlation observed is a few degrees, which suggests a predominantly light composition unless the magnetic fields are very weak outside the thin d...

  14. A SCALING RELATION BETWEEN MEGAMASER DISK RADIUS AND BLACK HOLE MASS IN ACTIVE GALACTIC NUCLEI

    Wardle, Mark [Astronomy, Astrophysics and Astrophotonics Research Centre and Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Yusef-Zadeh, Farhad, E-mail: mark.wardle@mq.edu.au, E-mail: zadeh@northwestern.edu [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)

    2012-05-10

    Several thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and the black hole mass. We demonstrate that such disks are naturally formed by the partial capture of molecular clouds passing through the galactic nucleus and temporarily engulfing the central supermassive black hole. Imperfect cancellation of the angular momenta of the cloud material colliding after passing on opposite sides of the hole leads to the formation of a compact disk. The radial extent of the disk is determined by the efficiency of this process and the Bondi-Hoyle capture radius of the black hole, and naturally produces the empirical linear correlation of the radial extent of the maser distribution with black hole mass. The disk has sufficient column density to allow X-ray irradiation from the central source to generate physical and chemical conditions conducive to the formation of 22 GHz H{sub 2}O masers. For initial cloud column densities {approx}< 10{sup 23.5} cm{sup -2} the disk is non-self-gravitating, consistent with the ordered kinematics of the edge-on megamaser disks; for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic center.

  15. A SCALING RELATION BETWEEN MEGAMASER DISK RADIUS AND BLACK HOLE MASS IN ACTIVE GALACTIC NUCLEI

    Several thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and the black hole mass. We demonstrate that such disks are naturally formed by the partial capture of molecular clouds passing through the galactic nucleus and temporarily engulfing the central supermassive black hole. Imperfect cancellation of the angular momenta of the cloud material colliding after passing on opposite sides of the hole leads to the formation of a compact disk. The radial extent of the disk is determined by the efficiency of this process and the Bondi-Hoyle capture radius of the black hole, and naturally produces the empirical linear correlation of the radial extent of the maser distribution with black hole mass. The disk has sufficient column density to allow X-ray irradiation from the central source to generate physical and chemical conditions conducive to the formation of 22 GHz H2O masers. For initial cloud column densities ∼23.5 cm–2 the disk is non-self-gravitating, consistent with the ordered kinematics of the edge-on megamaser disks; for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic center.

  16. The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

    Ackermann, M; Atwood, W; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Gonzalez, J; Bellazzini, R; Bissaldi, E; Blandford, R; Bloom, E; Bonino, R; Bottacini, E; Brandt, T; Bregeon, J; Britto, R; Bruel, P; Buehler, R; Buson, S; Caliandro, G; Cameron, R; Caragiulo, M; Caraveo, P; Casandjian, J; Cavazzuti, E; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cohen-Tanugi, J; Cominsky, L; Conrad, J; Cutini, S; D'Abrusco, R; D'Ammando, F; Angelis, A; Desiante, R; Digel, S; Venere, L; Drell, P; Favuzzi, C; Fegan, S; Ferrara, E; Finke, J; Focke, W; Franckowiak, A; Fuhrmann, L; Furniss, A; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I; Grove, J; Guiriec, S; Hewitt, J W; Hill, A; Horan, D; J'ohannesson, G; Johnson, A; Johnson, W; Kataoka, J; Kuss, M; Mura, G; Larsson, S; Latronico, L; Leto, C; Li, J; Li, L; Longo, F; Loparco, F; Lott, B; Lovellette, M; Lubrano, P; Madejski, G; Mayer, M; Mazziotta, M; McEnery, J; Michelson, P; Mizuno, T; Moiseev, A; Monzani, M; Morselli, A; Moskalenko, I; Murgia, S; Nuss, E; Ohno, M; Ohsugi, T; Ojha, R; Omodei, N; Orienti, M; Orlando, E; Paggi, A; Paneque, D; Perkins, J; Pesce-Rollins, M; Piron, F; Pivato, G; Porter, T; Rain`o, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Romani, R; Salvetti, D; Schaal, M; Schinzel, F; Schulz, A; Sgr`o, C; Siskind, E; Sokolovsky, K; Spada, F; Spandre, G; Spinelli, P; Stawarz, L; Suson, D; Takahashi, H; Takahashi, T; Tanaka, Y; Thayer, J; Tibaldo, L; Torres, D; Torresi, E; Tosti, G; Troja, E; Uchiyama, Y; Vianello, G; Winer, B; Wood, K; Zimmer, S

    2015-01-01

    The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected with a test statistic (TS) greater than 25, using the first 4 years of data. The 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10{\\deg}), which is a 71% increase over the second catalog that was based on 2 years of data. There are 28 duplicate associations (two counterparts to the same gamma-ray source), thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. A very large majority of these AGNs (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their spectral properties, these sources are evenly split between FSRQs and BL~Lacs. The general properties of the 3LAC sample confirm previous findings from earlier catalogs, but some new subclasses (e.g., ...

  17. THE FIRST CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE

    We present the first catalog of active galactic nuclei (AGNs) detected by the Large Area Telescope (LAT), corresponding to 11 months of data collected in scientific operation mode. The First LAT AGN Catalog (1LAC) includes 671 γ-ray sources located at high Galactic latitudes (|b|>100) that are detected with a test statistic greater than 25 and associated statistically with AGNs. Some LAT sources are associated with multiple AGNs, and consequently, the catalog includes 709 AGNs, comprising 300 BL Lacertae objects, 296 flat-spectrum radio quasars, 41 AGNs of other types, and 72 AGNs of unknown type. We also classify the blazars based on their spectral energy distributions as archival radio, optical, and X-ray data permit. In addition to the formal 1LAC sample, we provide AGN associations for 51 low-latitude LAT sources and AGN 'affiliations' (unquantified counterpart candidates) for 104 high-latitude LAT sources without AGN associations. The overlap of the 1LAC with existing γ-ray AGN catalogs (LBAS, EGRET, AGILE, Swift, INTEGRAL, TeVCat) is briefly discussed. Various properties-such as γ-ray fluxes and photon power-law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities-and their correlations are presented and discussed for the different blazar classes. We compare the 1LAC results with predictions regarding the γ-ray AGN populations, and we comment on the power of the sample to address the question of the blazar sequence.

  18. Supermassive Black Holes in Galactic Nuclei

    Ho, L C

    1998-01-01

    I review the status of observational determinations of central masses in nearby galactic nuclei. Results from a variety of techniques are summarized, including ground-based and space-based optical spectroscopy, radio VLBI measurements of luminous water vapor masers, and variability monitoring studies of active galactic nuclei. I will also discuss recent X-ray observations that indicate relativistic motions arising from the accretion disks of active nuclei. The existing evidence suggests that supermassive black holes are an integral component of galactic structure, at least in elliptical and bulge-dominated galaxies. The black hole mass appears to be correlated with the mass of the spheroidal component of the host galaxy. This finding may have important implications for many astrophysical issues.

  19. Active galactic nuclei synapses: X-ray versus optical classifications using artificial neural networks

    Gonzalez-Martin, O; Acosta-Pulido, J A; Masegosa, J; Papadakis, I E; Rodriguez-Espinosa, J M; Marquez, I; Hernandez-Garcia, L

    2014-01-01

    (Abridged) Many classes of active galactic nuclei (AGN) have been defined entirely throughout optical wavelengths while the X-ray spectra have been very useful to investigate their inner regions. However, optical and X-ray results show many discrepancies that have not been fully understood yet. The aim of this paper is to study the "synapses" between the X-ray and optical classifications. For the first time, the new EFLUXER task allowed us to analyse broad band X-ray spectra of emission line nuclei (ELN) without any prior spectral fitting using artificial neural networks (ANNs). Our sample comprises 162 XMM-Newton/pn spectra of 90 local ELN in the Palomar sample. It includes starbursts (SB), transition objects (T2), LINERs (L1.8 and L2), and Seyferts (S1, S1.8, and S2). The ANNs are 90% efficient at classifying the trained classes S1, S1.8, and SB. The S1 and S1.8 classes show a wide range of S1- and S1.8-like components. We suggest that this is related to a large degree of obscuration at X-rays. The S1, S1.8...

  20. UNDERSTANDING AGN-HOST CONNECTION IN PARTIALLY OBSCURED ACTIVE GALACTIC NUCLEI. III. PROPERTIES OF ROSAT-SELECTED SDSS ACTIVE GALACTIC NUCLEI

    As the third paper of our series of studies that aim at examining the AGN-host co-evolution by using partially obscured active galactic nuclei (AGNs), we extend the broad-line composite galaxies (composite AGNs) into ROSAT-selected Seyfert 1.8/1.9 galaxies based upon the ROSAT All Sky Survey/Sloan Digital Sky Survey Data Release 5 (SDSS-DR5) catalog given by Anderson et al. The SDSS spectra of a total of 92 objects are analyzed by the same method used in our previous studies, after requiring the signal-to-noise ratio in the SDSS r' band to be larger than 20. Combining the ROSAT-selected Seyfert galaxies with the composite AGNs reinforces the tight correlation between the line ratio [O I]/Hα versus Dn (4000), and establishes a new tight correlation between [S II]/Hα versus Dn (4000). Both correlations suggest that the two line ratios are plausible age indicators of the circumnuclear stellar population for typical Type I AGNs in which the stellar populations are difficult to derive from their optical spectra. The ROSAT-selected Seyfert galaxies show that the two correlations depend on the soft X-ray spectral slope α X, which is roughly estimated from the hardness ratios by requiring that the X-ray count rates within 0.1-2.4 keV be larger than 0.02 counts s-1. However, we fail to establish a relationship between α X and Dn (4000), which is likely caused by the relatively large uncertainties of both the parameters (especially for α X because of the AGN intrinsic obscuration). The previously established L/L Edd-Dn (4000) evolutionary sequence is reinforced again by the extension to the ROSAT-selected Seyfert galaxies. These X-ray-selected Seyfert galaxies are, however, biased against the two ends of the sequence, which implies that the X-ray Seyfert galaxies present a population at a middle evolutionary stage.

  1. Fueling active galactic nuclei. II. Spatially resolved molecular inflows and outflows

    Davies, R. I.; Erwin, P.; Burtscher, L.; Lin, M.; Orban de Xivry, G.; Rosario, D. J.; Schnorr-Müller, A. [Max-Planck-Institute für Extraterrestrische Physik, Postfach 1312, D-85741 Garching (Germany); Maciejewski, W. [Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, L3 5RF (United Kingdom); Hicks, E. K. S. [Astronomy Department, University of Alaska, Anchorage, Alaska 99508 (United States); Emsellem, E. [European Southern Observatory, Karl-Schwarzschild Str. 1, D-85748 Garching (Germany); Dumas, G. [Institut de Radio Astronomie Millimétrique (IRAM), 300 Rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d' Heres (France); Malkan, M. A. [Astronomy Division, University of California, Los Angeles, CA 90095-1562 (United States); Müller-Sánchez, F. [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389 (United States); Tran, A. [Department of Astronomy, University of Washington Seattle, WA 98195 (United States)

    2014-09-10

    We analyze the two-dimensional distribution and kinematics of the stars as well as molecular and ionized gas in the central few hundred parsecs of five active and five matched inactive galaxies. The equivalent widths of the Brγ line indicate that there is no ongoing star formation in their nuclei, although recent (terminated) starbursts are possible in the active galaxies. The stellar velocity fields show no signs of non-circular motions, while the 1-0 S(1) H{sub 2} kinematics exhibit significant deviations from simple circular rotation. In the active galaxies the H{sub 2} kinematics reveal inflow and outflow superimposed on disk rotation. Steady-state circumnuclear inflow is seen in three active galactic nuclei (AGNs), and hydrodynamical models indicate it can be driven by a large-scale bar. In three of the five AGNs, molecular outflows are spatially resolved. The outflows are oriented such that they intersect, or have an edge close to, the disk, which may be the source of molecular gas in the outflow. The relatively low speeds imply the gas will fall back onto the disk, and with moderate outflow rates, they will have only a local impact on the host galaxy. H{sub 2} was detected in two inactive galaxies. These exhibit chaotic circumnuclear dust morphologies and have molecular structures that are counter-rotating with respect to the main gas component, which could lead to gas inflow in the near future. In our sample, all four galaxies with chaotic dust morphology in the circumnuclear region exist in moderately dense groups with 10-15 members where accretion of stripped gas can easily occur.

  2. Deep Chandra observations of HCG 16. I. Active nuclei, star formation, and galactic winds

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ∼400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ∼0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.

  3. Deep Chandra observations of HCG 16. I. Active nuclei, star formation, and galactic winds

    O' Sullivan, E.; Zezas, A.; Vrtilek, J. M.; David, L. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Giacintucci, S. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Trevisan, M. [Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758, 12227-010, São José dos Campos (Brazil); Ponman, T. J.; Raychaudhury, S. [School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT (United Kingdom); Mamon, G. A., E-mail: eosullivan@cfa.harvard.edu [Institut d' Astrophysique de Paris (UMR 7095 CNRS and UMPC), 98 bis Bd Arago, F-75014 Paris (France)

    2014-10-01

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ∼400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ∼0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.

  4. Ionized Absorbers in Active Galactic Nuclei and Very Steap Soft X-Ray Quasars

    Fiore, Fabrizio; White, Nicholas (Technical Monitor)

    2000-01-01

    Steep soft X-ray (0.1-2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2-10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of approximately 2 in 10 ks), despite a factor of approximately 10 difference in the 0.5-10 keV luminosity (7.3 x 10(exp 43) erg/s for PG 1244 + 026 and 6.4 x 10(exp 44) erg/s for NAB 0205 + 024, assuming isotropic emission, H(sub 0) = 50.0 and q(sub 0) = 0.0). The X-ray continuum of the two quasars flattens by 0.5-1 going from the 0.1-2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centered at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3-0.6 c).

  5. Optical Counterparts of Undetermined Type -Ray Active Galactic Nuclei with Blazar-Like Spectral Energy Distributions

    Giovanni La Mura; Graziano Chiaro; Stefano Ciroi; Piero Rafanelli; David Salvetti; Marco Berton; Valentina Cracco; Fermi-LAT collaboration

    2015-12-01

    During its first four years of scientific observations, the Fermi Large Area Telescope (Fermi-LAT) detected 3033 -ray sources above a 4 significance level. Although most of the extra-galactic sources are active galactic nuclei (AGN) of the blazar class, other families of AGNs are observed too, while a still high fraction of detections (∼30%) remains with uncertain association or classification. According to the currently accepted interpretation, the AGN -ray emission arises from inverse Compton (IC) scattering of low energy photons by relativistic particles confined in a jet, which, in the case of blazars, is oriented very close to our line-of-sight. Taking advantage of data from radio and X-ray wavelengths, which we expect to be produced together with -rays, providing a much better source localization potential, we focused our attention on a sample of -ray Blazar Candidates of Undetermined type (BCUs), starting a campaign of optical spectroscopic observations. The main aims of our investigation include a census of the AGN families that contribute to -ray emission and a study of their redshift distribution, with the subsequent implications on the intrinsic source power. We furthermore analyze which -ray properties can better constrain the nature of the source, thus helping in the study of objects not yet associated with a reliable low frequency counterpart. Here we report on the instruments and techniques used to identify the optical counterparts of -ray sources, we give an overview on the status of our work, and we discuss the implications of a large scale study of -ray emitting AGNs.

  6. DO MOST ACTIVE GALACTIC NUCLEI LIVE IN HIGH STAR FORMATION NUCLEAR CUSPS?

    We present early results of the Herschel PACS (70 and 160 μm) and SPIRE (250, 350, and 500 μm) survey of 313 low redshift (z < 0.05), ultra-hard X-ray (14-195 keV) selected active galactic nuclei (AGNs) from the 58 month Swift/Burst Alert Telescope catalog. Selection of AGNs from ultra-hard X-rays avoids bias from obscuration, providing a complete sample of AGNs to study the connection between nuclear activity and star formation in host galaxies. With the high angular resolution of PACS, we find that >35% and >20% of the sources are ''point-like'' at 70 and 160 μm respectively and many more have their flux dominated by a point source located at the nucleus. The inferred star formation rates (SFRs) of 0.1-100 M ☉ yr–1 using the 70 and 160 μm flux densities as SFR indicators are consistent with those inferred from Spitzer Ne II fluxes, but we find that 11.25 μm polycyclic aromatic hydrocarbon data give ∼3× lower SFR. Using GALFIT to measure the size of the far-infrared emitting regions, we determined the SFR surface density (M ☉ yr–1 kpc–2) for our sample, finding that a significant fraction of these sources exceed the threshold for star formation driven winds (0.1 M ☉ yr–1 kpc–2)

  7. The Relationship of Active Galactic Nuclei & Quasars With Their Local Galaxy Environment

    Strand, Natalie Erin

    2009-01-01

    We explore how the local environment is related to properties of active galactic nuclei (AGNs) of various luminosities. Recent simulations and observations are converging on the view that the extreme luminosity of quasars, the brightest of AGNs, is fueled in major mergers of gas-rich galaxies. In such a picture, quasars, the highest luminosity AGNs, are expected to be located in regions with a higher density of galaxies on small scales where mergers are more likely to take place. However, in this picture, the activity observed in low-luminosity AGNs is due to secular processes that are less dependent on the local galaxy density. To test this hypothesis, we compare the local photometric galaxy density on kiloparsec scales around spectroscopic type I and type II quasars to the local density around lower-luminosity spectroscopic type I and type II AGNs. To minimize projection effects and evolution in the photometric galaxy sample we use to characterize AGN environments, we place our random control sample at the ...

  8. The Evolution of Active Galactic Nuclei in Clusters of Galaxies from the Dark Energy Survey

    Bufanda, E; Jeltema, T E; Rykoff, E S; Rozo, E; Martini, P; Abbott, T M C; Abdalla, F B; Allam, S; Banerji, M; Benoit-Levy, A; Bertin, E; Brooks, D; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Cunha, C E; da Costa, L N; Desai, S; Diehl, H T; Dietrich, J P; Evrard, A E; Neto, A Fausti; Flaugher, B; Frieman, J; Gerdes, D W; Goldstein, D A; Gruen, D; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D J; Kuehn, K; Kuropatkin, N; Lima, M; Maia, M A G; Marshall, J L; Melchior, P; Miquel, R; Mohr, J J; Ogando, R; Plazas, A A; Romer, A K; Rooney, P; Sanchez, E; Santiago, B; Scarpine, V; Sevilla-Noarbe, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Tarle, G; Thomas, D; Tucker, D L; Walker, A R

    2016-01-01

    The correlation between active galactic nuclei (AGN) and environment provides important clues to AGN fueling and the relationship of black hole growth to galaxy evolution. In this paper, we analyze the fraction of galaxies in clusters hosting AGN as a function of redshift and cluster richness for X-ray detected AGN associated with clusters of galaxies in Dark Energy Survey (DES) Science Verification data. The present sample includes 33 AGN with L_X > 10^43 ergs s^-1 in non-central, host galaxies with luminosity greater than 0.5 L* from a total sample of 432 clusters in the redshift range of 0.10.7. This result is in good agreement with previous work and parallels the increase in star formation in cluster galaxies over the same redshift range. However, the AGN fraction in clusters is observed to have no significant correlation with cluster mass. Future analyses with DES Year 1 and 2 data will be able to clarify whether AGN activity is correlated to cluster mass and will tightly constrain the relationship betwe...

  9. Active galactic nuclei at z ~ 1.5: I. Spectral energy distribution and accretion discs

    Capellupo, Daniel M; Lira, Paulina; Trakhtenbrot, Benny; Mejía-Restrepo, Julían

    2014-01-01

    The physics of active super massive black holes (BHs) is governed by their mass (M_BH), spin (a*) and accretion rate ($\\dot{M}$). This work is the first in a series of papers with the aim of testing how these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centered on z~1.55, that covers a wide range in M_BH and $\\dot{M}$, and are observing them with X-shooter, covering rest wavelengths ~1200-9800 \\AA. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating M_BH and $\\dot{M}$ based on each observed SED, we use thin AD models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining 8 SEDs, 3 can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and 4 can be fit by adding a disc wind to the model. In four of these 8 sources, Milky Way-type exti...

  10. Alignments Of Black Holes with Their Warped Accretion Disks and Episodic Lifetimes of Active Galactic Nuclei

    Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

    2015-05-01

    Warped accretion disks have attracted intense attention because of their critical role in shaping the spin of supermassive massive black holes (SMBHs) through the Bardeen-Petterson effect, a general relativistic effect that leads to final alignments or anti-alignments between black holes and warped accretion disks. We study such alignment processes by explicitly taking into account the finite sizes of accretion disks and the episodic lifetimes of active galactic nuclei (AGNs) that delineate the duration of gas fueling onto accretion disks. We employ an approximate global model to simulate the evolution of accretion disks, allowing us to determine the gravitomagnetic torque that drives the alignments in a simple way. We then track down the evolutionary paths for mass and spin of black holes both in a single activity episode and over a series of episodes. Given with randomly and isotropically oriented gas fueling over episodes, we calculate the spin evolution with different episodic lifetimes and find that it is quite sensitive to the lifetimes. We therefore propose that the spin distribution of SMBHs can place constraints on the episodic lifetimes of AGNs and vice versa. The applications of our results on the observed spin distributions of SMBHs and the observed episodic lifetimes of AGNs are discussed, although both measurements at present are too ambiguous for us to draw a firm conclusion. Our prescription can be easily incorporated into semi-analytic models for black hole growth and spin evolution.

  11. Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual AGNs?

    Wang, J -M; Hu, C; Mao, W -M; Zhang, S; Bian, W -H

    2009-01-01

    Double-peaked [O III]5007, profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from $\\sim$ 7000 active galaxies in SDSS DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III]5007, profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O III] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at $\\sim 1$ kpc scale, showing an intermediate phase of...

  12. MID- AND FAR-INFRARED PROPERTIES OF A COMPLETE SAMPLE OF LOCAL ACTIVE GALACTIC NUCLEI

    Ichikawa, Kohei; Ueda, Yoshihiro [Department of Astronomy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake cho, Kyoto 606-8502 (Japan); Terashima, Yuichi [Department of Physics, Faculty of Science, Ehime University, Matsuyama 790-8577 (Japan); Oyabu, Shinki [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Gandhi, Poshak; Nakagawa, Takao [Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Matsuta, Keiko, E-mail: ichikawa@kusastro.kyoto-u.ac.jp [Department of Space and Astronautical Science, Graduate University for Advanced Studies, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)

    2012-07-20

    We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky hard X-ray (14-195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with Infrared Astronomical Satellite and Wide-field Infrared Survey Explorer. Out of 135 non-blazer AGNs in the Swift/BAT nine-month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 {mu}m band. We find good correlation between their hard X-ray and MIR luminosities over three orders of magnitude (42 < log {lambda}L{sub {lambda}}(9, 18 {mu}m) < 45), which is tighter than that with the FIR luminosities at 90 {mu}m. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 {mu}m in the averaged infrared spectral energy distribution from heavy obscured 'new type' AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the polycyclic aromatic hydrocarbon emission feature, suggesting that their host galaxies have strong starburst activities.

  13. The Near-Infrared Coronal Line Spectrum of 54 Nearby Active Galactic Nuclei

    Rodríguez-Ardila, A; Portilla, J G; Tejeiro, J M

    2011-01-01

    (Abridge) The relationship between coronal line (CL) emission and nuclear activity in active galactic nuclei (AGNs) is analyzed, for the first time, based on NIR spectra. The 8 CLs studied, of Si, S, Fe, Al and Ca elements and corresponding to ionization potentials (IP) in the range 125-450 eV, are detected in 67% (36 AGNs) of the sample. The four most frequent CLs - [SiVI] 19630\\AA, [SVIII] 9913\\AA, [SIX] 12520\\AA\\ and [SiX] 14320\\AA, - display a narrow range in luminosity, with most lines located in the interval logL 39-40 erg/s. We found that the non-detection is largely associated with either a lost of spatial resolution or increasing object distance. Yet, there are AGNs where the lack of CLs may be genuine and reflect an AGN ionising continuum lacking photons below a few keV. The FWHM of the lines profiles increases with increasing IP up to energies around 300 eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IP. We ascribe this...

  14. Far-infrared and accretion luminosities of the present-day active galactic nuclei

    Matsuoka, Kenta

    2015-01-01

    We investigate the relation between star formation (SF) and black hole accretion luminosities, using a sample of 492 type-2 active galactic nuclei (AGNs) at z < 0.22, which are detected in the far-infrared (FIR) surveys with AKARI and Herschel. We adopt FIR luminosities at 90 and 100 um as SF luminosities, assuming the proposed linear proportionality of star formation rate with FIR luminosities. By estimating AGN luminosities from [OIII]5007 and [OI]6300 emission lines, we find a positive linear trend between FIR and AGN luminosities over a wide dynamical range. This result appears to be inconsistent with the recent reports that low-luminosity AGNs show essentially no correlation between FIR and X-ray luminosities, while the discrepancy is likely due to the Malmquist and sample selection biases. By analyzing the spectral energy distribution, we find that pure-AGN candidates, of which FIR radiation is thought to be AGN-dominated, show significantly low-SF activities. These AGNs hosted by low-SF galaxies are...

  15. THE NUCLEAR INFRARED EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

    Mason, R. E. [Gemini Observatory, Northern Operations Center, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); Lopez-Rodriguez, E.; Packham, C. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Alonso-Herrero, A. [Instituto de Fisica de Cantabria, CSIC-UC, Avenida de los Castros s/n, 39005 Santander (Spain); Levenson, N. A.; Radomski, J. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Ramos Almeida, C. [Instituto de Astrofisica de Canarias, C/Via Lactea, s/n, E-38205, La Laguna, Tenerife (Spain); Colina, L. [Departamento de Astrofisica, Centro de Astrobiologia (CSIC/INTA), Instituto Nacional de Tecnica Aeroespacial, Crta de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid (Spain); Elitzur, M. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); Aretxaga, I. [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Aptdo. Postal 51 y 216, 72000 Puebla (Mexico); Roche, P. F. [Astrophysics, Department of Physics, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom); Oi, N. [Department of Astronomy, School of Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588 (Japan)

    2012-07-15

    We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs), and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGNs; L{sub bol} {approx}< 10{sup 42} erg s{sup -1}). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGNs, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGNs have not yet been well determined. We separate the present LLAGN sample into three categories depending on their Eddington ratio and radio emission, finding different IR characteristics for each class. (1) At the low-luminosity, low-Eddington-ratio (log L{sub bol}/L{sub Edd} < -4.6) end of the sample, we identify 'host-dominated' galaxies with strong polycyclic aromatic hydrocarbon bands that may indicate active (circum-)nuclear star formation. (2) Some very radio-loud objects are also present at these low Eddington ratios. The IR emission in these nuclei is dominated by synchrotron radiation, and some are likely to be unobscured type 2 AGNs that genuinely lack a broad-line region. (3) At higher Eddington ratios, strong, compact nuclear sources are visible in the MIR images. The nuclear SEDs of these galaxies are diverse; some resemble typical Seyfert nuclei, while others lack a well-defined MIR 'dust bump'. Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGNs do not host a Seyfert-like obscuring torus. We anticipate that detailed modeling of the new data and SEDs in terms of accretion disk, jet, radiatively inefficient accretion flow, and torus components will provide further

  16. X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei

    Marin, F

    2014-01-01

    Context: A fraction of active galactic nuclei (AGN) show dramatic X-ray spectral changes on the day-to-week time scales associated with variation in the line of sight of the cold absorber. Aims: We intend to model the polarization fluctuations arising from an obscuration event, thereby offering a method of determining whether flux variations are due to occultation or extreme intrinsic emission variability. Methods: Undertaking 1 - 100 keV polarimetric simulations with the Monte Carlo code STOKES, we simulated the journey of a variety of cold gas clouds in front of an extended primary source. We varied the hydrogen column density nH and size of the absorber, as well as the initial polarization state of the emitting source, to cover a wide range of scenarios. Results: For unpolarized primary fluxes, large (about 50deg) variations of the polarization position angle psi are expected before and after an occultation event, which is associated with very low residual polarization degrees (P lower than 1 per cent). In...

  17. The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei

    Allen, J T; Scott, N; Fogarty, L M R; Ho, I -T; Medling, A M; Leslie, S K; Bland-Hawthorn, J; Bryant, J J; Croom, S M; Goodwin, M; Green, A W; Konstantopoulos, I S; Lawrence, J S; Owers, M S; Richards, S N; Sharp, R

    2015-01-01

    We have observed two kinematically offset active galactic nuclei (AGN), whose ionised gas is at a different line-of-sight velocity to their host galaxies, with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas kinematics very different to the stellar kinematics, indicating a recent merger or accretion event. We demonstrate that the star formation associated with this event was triggered within the last 100 Myr. The other galaxy shows simple disc rotation in both gas and stellar kinematics, aligned with each other, but in the central region has signatures of an outflow driven by the AGN. Other than the outflow, neither galaxy shows any discontinuity in the ionised gas kinematics at the galaxy's centre. We conclude that in these two cases there is no direct evidence of the AGN being in a supermassive black hole binary system. Our study demonstrates that selecting kinematically offset AGN from single-fibre spectroscopy provides, by definition, samples of kinematically peculiar objects, bu...

  18. Simulating the formation of disk galaxies: The impact of Jets from Active Galactic Nuclei

    Okamoto, Takashi; Bower, Richard G

    2007-01-01

    Recent semi-analytic models have highlighted the role of AGN jets in regulating the formation of galaxies. In this paper, we present a new implementation of feedback due to active galactic nuclei (AGN) in cosmological hydrodynamic simulations of galaxy formation in which AGN feedback is assumed to heat the halo gas through the production of jets. Combining a theoretical model of mass accretion onto black holes with a multiphase description of star-forming gas, we self-consistently follow evolution of both galaxies and their central black holes. The novelty in our model is that we consider the two distinct accretion modes: standard radiatively efficient thin accretion disks and radiatively inefficient accretion flows which we will generically refer to as RIAFs; motivated by the theoretical modelsfor jet production in accretion disks, we assume that only the RIAF is responsible for the production of powerful jets. The focus of this paper is to investigate the interplay between galaxies and their central black h...

  19. X-ray spectra and time variability of active galactic nuclei

    The X-ray spectra of broad line active galactic nuclei (AGN) of all types (Seyfert I's, NELG's, broadline radio galaxies) are well fit by a power law in the .5 to 100 keV band of man energy slope alpha .68 + or - .15. There is, as yet, no strong evidence for time variability of this slope in a given object. The constraints that this places on simple models of the central energy source are discussed. BL Lac objects have quite different X-ray spectral properties and show pronounced X-ray spectral variability. On time scales longer than 12 hours most radio quiet AGN do not show strong, delta I/I .5, variability. The probability of variability of these AGN seems to be inversely related to their luminosity. However characteristics timescales for variability have not been measured for many objects. This general lack of variability may imply that most AGN are well below the Eddington limit. Radio bright AGN tend to be more variable than radio quiet AGN on long, tau approx 6 month, timescales

  20. Changing-Look Active Galactic Nuclei With The Time Domain Spectroscopic Survey (TDSS)

    Runnoe, J.

    2015-09-01

    Changing-look active galactic nuclei (CL-AGNs) present a unique opportunity to study AGN unification and physics. They are observed to transformation between the Type 1 and 2 classifications, supporting a picture in which both orientation to the observer and intrinsic spectral and luminosity evolution can play important roles in unification. In the same spirit, CL-AGNs also offer a way to study behavior brought about by abrupt changes in the accretion rate and may represent a previously unappreciated mode of quasar variability: prolonged "on-" and "off-states". CL-AGNs are uncommon, with only a handful identified to date, but several have been discovered in the Time Domain Spectroscopic Survey (TDSS), and these are likely just the tip of the iceberg. The TDSS offers a promising way of discovering substantial numbers of CL-AGN because it will revisit several thousand objects with previous spectra from the SDSS, many of which are selected based on substantial photometric variability. A statistical sample of these objects will allow us to move beyond the detailed case studies and start to understand the underlying physical mechanisms responsible for these dramatic spectral changes. I will describe our systematic search for CL-AGN in the TDSS and discuss what we have learned from a growing sample of these objects.

  1. The optical polarization signatures of fragmented equatorial dusty structures in Active Galactic Nuclei

    Marin, F.; Stalevski, M.

    2015-12-01

    If the existence of an obscuring circumnuclear region around the innermost regions of active galactic nuclei (AGN) has been observationally proven, its geometry remains highly uncertain. The morphology usually adopted for this region is a toroidal structure, but other alternatives, such as flared disks, can be a good representative of equatorial outflows. Those two geometries usually provide very similar spectroscopic signatures, even when they are modeled under the assumption of fragmentation. In this lecture note, we show that the resulting polarization signatures of the two models, either a torus or a flared disk, are quite different from each other. We use a radiative transfer code that computes the 2000 -- 8000 Å polarization of the two morphologies in a clumpy environment, and show that varying the sizes of a toroidal region has deep impacts onto the resulting polarization, while the polarization of flared disks is independent of the outer radius. Clumpy flared disks also produce higher polarization degrees (˜ 10 % at best) together with highly variable polarization position angles.

  2. Current issues in the X-ray properties of active galactic nuclei

    Some issues raised by soft X-ray spectra and hours variability observations of active galactic nuclei (AGN), made possible by improved energy calibration of the Einstein IPC and the launch of Exosat into a unique 72-hour highly elliptical orbit, are presented. Explanations for steep soft excesses in quasars include the emission from the hot tail of an accretion disk spectrum, and from optically thin bremsstrahlung at 1-2 x 10 to the 6th K from a large volume. Mechanisms for the approximately 1.0 slope in the 0.2-4 keV soft IPC X-ray band quasars include direct synchrotron emission, unsaturated Comptonization of an arbitrary seed spectrum, and synchro-Compton scattering from the infrared. The Exosat observation of NGC 4051 revealed six 1-hour cycles with spectral changes during the variations. AGN time variations may now be able to limit emission models through studying, for example, the lag times between soft and hard variations. 47 references

  3. On the Contribution of Active Galactic Nuclei to the High-Redshift Metagalactic Ionizing Background

    D'Aloisio, Anson; McQuinn, Matthew; Trac, Hy; Shapiro, Paul R

    2016-01-01

    Motivated by the claimed detection of a large population of faint active galactic nuclei (AGN) at high redshift, recent studies have proposed models in which AGN contribute significantly to the z > 4 H I ionizing background. In some models, AGN are even the chief sources of reionization. If correct, these models would make necessary a complete revision to the standard view that galaxies dominated the high-redshift ionizing background. It has been suggested that AGN-dominated models can better account for two recent observations that appear to be in conflict with the standard view: (1) large opacity variations in the z ~ 5.5 H I Lyman-alpha forest, and (2) slow evolution in the mean opacity of the He II Lyman-alpha forest. Large spatial fluctuations in the ionizing background from the brightness and rarity of AGN may account for the former, while the earlier onset of He II reionization in these models may account for the latter. Here we show that models in which AGN emissions source >~ 50 % of the ionizing bac...

  4. THREE-YEAR SWIFT-BAT SURVEY OF ACTIVE GALACTIC NUCLEI: RECONCILING THEORY AND OBSERVATIONS?

    It is well accepted that unabsorbed as well as absorbed active galactic nuclei (AGNs) are needed to explain the nature and shape of the Cosmic X-ray background (CXB), even if the fraction of highly absorbed objects (dubbed Compton-thick sources) still substantially escapes detection. We derive and analyze the absorption distribution using a complete sample of AGNs detected by Swift-BAT in the first three years of the survey. The fraction of Compton-thick AGNs represents only 4.6% of the total AGN population detected by Swift-BAT. However, we show that once corrected for the bias against the detection of very absorbed sources the real intrinsic fraction of Compton-thick AGNs is 20-6+9%. We proved for the first time (also in the Burst Alert Telescope (BAT) band) that the anti-correlation of the fraction of absorbed AGNs and luminosity is tightly connected to the different behavior of the X-ray luminosity functions (XLFs) of absorbed and unabsorbed AGNs. This points toward a difference between the two subsamples of objects with absorbed AGNs being, on average, intrinsically less luminous than unobscured ones. Moreover, the XLFs show that the fraction of obscured AGNs might also decrease at very low luminosity. This can be successfully interpreted in the framework of a disk cloud outflow scenario as the disappearance of the obscuring region below a critical luminosity. Our results are discussed in the framework of population synthesis models and the origin of the CXB.

  5. Radio/gamma-ray time delay in the parsec-scale cores of active galactic nuclei

    Pushkarev, A B; Lister, M L

    2010-01-01

    We report the detection of a non-zero time delay between radio emission measured by the VLBA at 15.4 GHz and gamma-ray radiation (gamma-ray leads radio) registered by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope for a sample of 183 radio and gamma-ray bright active galactic nuclei (AGNs). For the correlation analysis we used 100 MeV - 100 GeV gamma-ray photon fluxes, taken from monthly binned measurements from the first Fermi LAT catalog, and 15.4 GHz radio flux densities from the MOJAVE VLBA program. The correlation is most pronounced if the core flux density is used, strongly indicating that the gamma-ray emission is generated within the compact region of the 15 GHz VLBA core. Determining the Pearson's r and Kendall's tau correlation coefficients for different time lags, we find that for the majority of sources the radio/gamma-ray delay ranges from 1 to 8 months in the observer's frame and peaks at about 1.2 months in the source's frame. We interpret the primary source of the ...

  6. Coexistence of Gravitationally Bound and Radiation Driven CIV Emission Line Regions in Active Galactic Nuclei

    Wang, Huiyuan; Zhou, Hongyan; Liu, Bo; Wang, Jianguo; Yuan, Weimin; Dong, Xiaobo

    2011-01-01

    There are mutually contradictory views in the literature of the kinematics and structure of high-ionization line (e.g. CIV) emitting regions in active galactic nuclei (AGNs). Two kinds of broad emission line region (BELR) models have been proposed, outflow and gravitationally bound BELR, which are supported respectively by blueshift of the CIV line and reverberation mapping observations. To reconcile these two apparently different models, we present a detailed comparison study between the CIV and MgII lines using a sample of AGNs selected from the Sloan Digital Sky Survey. We find that the kinematics of the CIV region is different from that of MgII, which is thought to be controlled by gravity. A strong correlation is found between the blueshift and asymmetry of the CIV profile and the Eddington ratio. This provides strong observational support for the postulation that the outflow is driven by radiation pressure. In particular, we find robust evidence that the CIV line region is largely dominated by outflow a...

  7. THE BALDWIN EFFECT IN THE NARROW EMISSION LINES OF ACTIVE GALACTIC NUCLEI

    The anti-correlations between the equivalent widths of emission lines and the continuum luminosity in active galactic nuclei (AGNs), known as the Baldwin effect, are well established for broad lines, but are less well studied for narrow lines. In this paper we explore the Baldwin effect of narrow emission lines over a wide range of ionization levels and critical densities using a large sample of broad-line, radio-quiet AGNs taken from Sloan Digital Sky Survey Data Release 4. These type 1 AGNs span three orders of magnitude in continuum luminosity. We show that most narrow lines show a similar Baldwin effect slope of about –0.2, while the significant deviations of the slopes for [N II] λ6583, [O II] λ3727, [Ne V] λ3425, and the narrow component of Hα can be explained by the influence of metallicity, star formation contamination, and possibly by the difference in the shape of the UV-optical continuum. The slopes do not show any correlation with either the ionization potential or the critical density. We show that a combination of 50% variations in continuum near 5100 Å and a lognormal distribution of observed luminosity can naturally reproduce a constant Baldwin effect slope of –0.2 for all narrow lines. The variations of the continuum could be due to variability, intrinsic anisotropic emission, or an inclination effect.

  8. On the central abundances of Active Galactic Nuclei and Star-forming Galaxies

    Dors, O L; Hagele, G F; Rodrigues, I; Grebel, E K; Pilyugin, L S; Freitas-Lemes, P; Krabbe, A C

    2015-01-01

    We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method (the theoretical calibration of Storchi-Bergmann et al.(1998)), via the direct Te-method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the Te-method underestimates the oxygen abundances by up to ~2 dex (with average value of ~0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called "temperature problem" in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and Star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (~2 times...

  9. Prospect for Future MeV Gamma-ray Active Galactic Nuclei Population Studies

    Inoue, Yoshiyuki; Odaka, Hirokazu; Takada, Atsushi; Ichinohe, Yuto; Saito, Shinya; Takeda, Shin'ichiro; Takahashi, Tadayuki

    2015-01-01

    While the X-ray, GeV gamma-ray, and TeV gamma-ray skies have been extensively studied, the MeV gamma-ray sky is not well investigated after the Imaging Compton Telescope (COMPTEL) scanned the sky about two decades ago. In this paper, we investigate prospects for active galactic nuclei population studies with future MeV gamma-ray missions using recent spectral models and luminosity functions of Seyfert and flat spectrum radio quasars (FSRQs). Both of them are plausible candidates as the origins of the cosmic MeV gamma-ray background. If the cosmic MeV gamma-ray background radiation is dominated by non-thermal emission from Seyferts, the sensitivity of 10^-12 erg cm^-2 s^-1 is required to detect several hundred Seyferts in the entire sky. If FSRQs make up the cosmic MeV gamma-ray background, the sensitivity of ~4 x 10^-12 erg cm^-2 s^-1 is required to detect several hundred FSRQs following the recent FSRQ X-ray luminosity function. However, based on the latest FSRQ gamma-ray luminosity function, with which FSRQ...

  10. HerMES: Disentangling active galactic nuclei and star formation in the radio source population

    Rawlings, J I; Symeonidis, M; Bock, J; Cooray, A; Farrah, D; Guo, K; Hatziminaoglou, E; Ibar, E; Oliver, S J; Roseboom, I G; Scott, Douglas; Seymour, N; Vaccari, M; Wardlow, J L

    2015-01-01

    We separate the extragalactic radio source population above ~50 uJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC and MIPS and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that r...

  11. The resolved star-formation relation in nearby active galactic nuclei

    Casasola, Viviana; Combes, Francoise; Garcia-Burillo, Santiago

    2015-01-01

    We present an analysis of the relation between star formation rate (SFR) surface density (sigmasfr) and mass surface density of molecular gas (sigmahtwo), commonly referred to as the Kennicutt-Schmidt (K-S) relation, at its intrinsic spatial scale, i.e. the size of giant molecular clouds (10-150 pc), in the central, high-density regions of four nearby low-luminosity active galactic nuclei (AGN). We used interferometric IRAM CO(1-0) and CO(2-1), and SMA CO(3-2) emission line maps to derive sigmahtwo and HST-Halpha images to estimate sigmasfr. Each galaxy is characterized by a distinct molecular SF relation at spatial scales between 20 to 200 pc. The K-S relations can be sub-linear, but also super-linear, with slopes ranging from 0.5 to 1.3. Depletion times range from 1 and 2Gyr, compatible with results for nearby normal galaxies. These findings are valid independently of which transition, CO(1-0), CO(2-1), or CO(3-2), is used to derive sigmahtwo. Because of star-formation feedback, life-time of clouds, turbule...

  12. Modeling the Emission from Turbulent Relativistic Jets in Active Galactic Nuclei

    Victoria Calafut; Paul J. Wiita

    2015-06-01

    We present a numerical model developed to calculate observed fluxes of relativistic jets in active galactic nuclei. The observed flux of each turbulent eddy is dependent upon its variable Doppler boosting factor, computed as a function of the relativistic sum of the individual eddy and bulk jet velocities, and our viewing angle to the jet. The total observed flux is found by integrating the radiation from the eddies over the turbulent spectrum. We consider jets that contain turbulent eddies that have either standard Kolmogorov or recently derived relativistic turbulence spectra. We also account for the time delays in receiving the emission of the eddies due to their different simulated positions in the jet, as well as due to the varying beaming directions as they turn over. We examine these theoretical light curves and compute power spectral densities (PSDs) for a range of viewing angles, bulk velocities of the jet, and turbulent velocities. These PSD slopes depend significantly on the turbulent velocity, and are essentially independent of viewing angle and bulk velocity. The flux variations produced in the simulations for realistic values of the parameters tested are consistent with the types of variations observed in radio-loud AGN as, for example, recently measured with the Kepler satellite, as long as the turbulent velocities are not too high.

  13. Study of Swift/BAT Selected Low-luminosity Active Galactic Nuclei Observed with Suzaku

    Kawamuro, Taiki; Tazaki, Fumie; Terashima, Yuichi; Mushotzky, Richard

    2016-01-01

    We systematically analyze the broadband (0.5--200 keV) X-ray spectra of hard X-ray ($>10$ keV) selected local low-luminosity active galactic nuclei (LLAGNs) observed with {\\it Suzaku} and {\\it Swift}/BAT. The sample consists of ten LLAGNs detected with {\\it Swift}/BAT with intrinsic 14--195 keV luminosities smaller than $10^{42}$ erg s$^{-1}$ available in the {\\it Suzaku} archive, covering a wide range of the Eddington ratio from $10^{-5}$ to $10^{-2}$. The overall spectra can be reproduced with an absorbed cut-off power law, often accompanied by reflection components from distant cold matter, and/or optically-thin thermal emission from the host galaxy. In all objects, relativistic reflection components from the innermost disk are not required. Eight objects show a significant narrow iron-K$\\alpha$ emission line. Comparing their observed equivalent widths with the predictions from the Monte-Carlo based torus model by \\cite{Ike09}, we constrain the column density in the equatorial plane to be $\\log N^{\\rm eq}_...

  14. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    Tombesi, F.

    2016-05-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).

  15. Ultra-High-Energy Cosmic Rays from Low-Luminosity Active Galactic Nuclei

    Dutan, Ioana

    2014-01-01

    We investigate the production of ultra-high-energy cosmic ray (UHECR) in relativistic jets from low-luminosity active galactic nuclei (LLAGN). We start by proposing a model for the UHECR contribution from the black holes (BHs) in LLAGN, which present a jet power $P_{\\mathrm{j}} \\leqslant 10^{46}$ erg s$^{-1}$. This is in contrast to the opinion that only high-luminosity AGN can accelerate particles to energies $ \\geqslant 50$ EeV. We rewrite the equations which describe the synchrotron self-absorbed emission of a non-thermal particle distribution to obtain the observed radio flux density from sources with a flat-spectrum core and its relationship to the jet power. We find that the UHECR flux is dependent on the {\\it observed radio flux density, the distance to the AGN, and the BH mass}, where the particle acceleration regions can be sustained by the magnetic energy extraction from the BH at the center of the AGN. We use a complete sample of 29 radio sources with a total flux density at 5 GHz greater than 0.5 ...

  16. A Scaling Relation Between Megamaser Disk Radius and Black Hole Mass in Active Galactic Nuclei

    Wardle, Mark

    2011-01-01

    Several thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and the black hole mass. We demonstrate that such disks are naturally formed by the partial capture of molecular clouds passing through the galactic nucleus and temporarily engulfing the central supermassive black hole. Imperfect cancellation of the angular momenta of the cloud material colliding after passing on opposite sides of the hole leads to the formation of a compact disk. The radial extent of the disk is determined by the efficiency of this process and the Bondi-Hoyle capture radius of the black hole, and naturally produces the empirical linear correlation of the radial extent of the maser distribution with black hole mass. The disk has sufficient column density to allow X-ray irradiation from the central source to generate physical and chemical conditi...

  17. Optimal strategies for observation of active galactic nuclei variability with Imaging Atmospheric Cherenkov Telescopes

    Giomi, Matteo; Gerard, Lucie; Maier, Gernot

    2016-07-01

    Variable emission is one of the defining characteristic of active galactic nuclei (AGN). While providing precious information on the nature and physics of the sources, variability is often challenging to observe with time- and field-of-view-limited astronomical observatories such as Imaging Atmospheric Cherenkov Telescopes (IACTs). In this work, we address two questions relevant for the observation of sources characterized by AGN-like variability: what is the most time-efficient way to detect such sources, and what is the observational bias that can be introduced by the choice of the observing strategy when conducting blind surveys of the sky. Different observing strategies are evaluated using simulated light curves and realistic instrument response functions of the Cherenkov Telescope Array (CTA), a future gamma-ray observatory. We show that strategies that makes use of very small observing windows, spread over large periods of time, allows for a faster detection of the source, and are less influenced by the variability properties of the sources, as compared to strategies that concentrate the observing time in a small number of large observing windows. Although derived using CTA as an example, our conclusions are conceptually valid for any IACTs facility, and in general, to all observatories with small field of view and limited duty cycle.

  18. THE CLUSTERING OF GALAXIES AROUND RADIO-LOUD ACTIVE GALACTIC NUCLEI

    We examine the hypothesis that mergers and close encounters between galaxies can fuel active galactic nuclei (AGNs) by increasing the rate at which gas accretes toward the central black hole. We compare the clustering of galaxies around radio-loud AGNs with the clustering around a population of radio-quiet galaxies with similar masses, colors, and luminosities. Our catalog contains 2178 elliptical radio galaxies with flux densities greater than 2.8 mJy at 1.4 GHz from the Six Degree Field Galaxy Survey. We find tentative evidence that radio AGNs with more than 200 times the median radio power have, on average, more close (r < 160 kpc) companions than their radio-quiet counterparts, suggesting that mergers play a role in forming the most powerful radio galaxies. For ellipticals of fixed stellar mass, the radio power is neither a function of large-scale environment nor halo mass, consistent with the radio powers of ellipticals varying by orders of magnitude over billions of years

  19. A growth-rate indicator for Compton-thick active galactic nuclei

    Brightman, M; Ballantyne, D R; Baloković, M; Brandt, W N; Chen, C -T; Comastri, A; Farrah, D; Gandhi, P; Harrison, F A; Ricci, C; Stern, D; Walton, D J

    2016-01-01

    Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGN) is difficult to measure. A statistically significant correlation between the Eddington ratio, {\\lambda}$_{Edd}$, and the X-ray power-law index, {\\Gamma}, observed in unobscured AGN offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line-of-sight to the central engine is heavily obscured, the recovery of the intrinsic {\\Gamma} is challenging. Here we study a sample of local, predominantly Compton-thick megamaser AGN, where the black hole mass, and thus Eddington luminosity, are well known. We compile results on X-ray spectral fitting of these sources with sensitive high-energy (E> 10 keV) NuSTAR data, where X-ray torus models which take into account the reprocessing effects have been used to recover the intrinsic {\\Gamma} values and X-ray luminosities, L$_...

  20. A note on periodicity of long-term variations of optical continuum in active galactic nuclei

    Lu, Kai-Xing; Li, Yan-Rong; Bi, Shao-Lan; Wang, Jian-Min

    2016-06-01

    Graham et al. found a sample of active galactic nuclei (AGNs) and quasars from the Catalina Real-time Transient Survey (CRTS) that have long-term periodic variations in optical continuum. The nature of the periodicity remains uncertain. We investigate the periodic variability characteristics of the sample by testing the relations of the observed variability periods with AGN optical luminosity, black hole mass and accretion rates, and find no significant correlations. We also test the observed periods in several different aspects related to accretion discs surrounding single black holes, such as the Keplerian rotational periods of 5100 Å photon-emission regions and self-gravity dominated regions and the precessing period of warped discs. These tests shed new lights on understanding AGN variability in general. Under the assumption that the periodic behaviour is associated with supermassive black hole binary systems in particular, we compare the separations (r {D}_{bullet }) against characteristic radii of broad-line regions (R_riptscriptstyle BLR) of the binaries and find r {D}_{bullet }≈ 0.05R_riptscriptstyle BLR. This interestingly implies that these binaries have only circumbinary BLRs.

  1. A note on periodicity of long-term variations of optical continuum in active galactic nuclei

    Lu, Kai-Xing; Li, Yan-Rong; Bi, Shao-Lan; Wang, Jian-Min

    2016-04-01

    Graham et al. found a sample of active galactic nuclei (AGNs) and quasars from the Catalina Real-time Transient Survey (CRTS) that have long-term periodic variations in optical continuum, the nature of the periodicity remains uncertain. We investigate the periodic variability characteristics of the sample by testing the relations of the observed variability periods with AGN optical luminosity, black hole mass and accretion rates, and find no significant correlations. We also test the observed periods in several different aspects related to accretion disks surrounding single black holes, such as the Keplerian rotational periods of 5100 Å photon-emission regions and self-gravity dominated regions and the precessing period of warped disks. These tests shed new lights on understanding AGN variability in general. Under the assumption that the periodic behavior is associated with SMBHB systems in particular, we compare the separations (D_{bullet }) against characteristic radii of broad-line regions (RBLR) of the binaries and find D_{bullet }≈ 0.05R_{BLR}. This interestingly implies that these binaries have only circumbinary BLRs.

  2. Optical Spectral Properties of Swift BAT Hard X-ray Selected Active Galactic Nuclei Sources

    Winter, Lisa M; Koss, Michael; Veilleux, Sylvain; Keeney, Brian; Mushotzky, Richard F

    2010-01-01

    The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unprecedented view of local AGNs ( = 0.03) and their host galaxy properties. In this paper, we present an analysis of the optical spectra of a sample of 64 AGNs from the 9-month survey, detected solely based on their 14-195 keV flux. Our analysis includes both archived spectra from the Sloan Digital Sky Survey and our own observations from the 2.1-m Kitt Peak National Observatory telescope. Among our results, we include line ratio classifications utilizing standard emission line diagnostic plots, [O III] 5007 A luminosities, and H-beta derived black hole masses. As in our X-ray study, we find the type 2 sources to be less luminous (in [O III] 5007 A and 14-195 keV luminosities) with lower accretion rates than the type 1 sources. We find that the optically classified LINERs, H II/composite galaxies, and ambiguous sources have the lowest luminosities, while both broad line and narrow line Seyferts have similar luminosit...

  3. X-Ray Spectral Parameters for a Sample of 95 Active Galactic Nuclei

    Vasylenko, A; Fedorova, E

    2015-01-01

    We present a broadband X-ray analysis of a new homogeneous sample of 95 active galactic nuclei (AGN) from the 22-month Swift/BAT all-sky survey. For this sample we treated jointly the X-ray spectra observed by XMM-Newton and INTEGRAL missions for the total spectral range of 0.5-250 keV. Photon index \\Gamma, relative reflection R, equivalent width of Fe $K_{\\alpha}$ line (EW Fe $K_{\\alpha}$), hydrogen column density $N_{H}$, exponential cut-off energy $E_{c}$ and intrinsic luminosity $L_{corr}$ are determined for all objects of the sample. We investigated correlations \\Gamma - R, EW Fe $K_{\\alpha}$ - $L_{corr}$, \\Gamma - $E_{c}$, EW Fe $K_{\\alpha}$ - $N_{H}$. Dependence \\Gamma - R for Seyfert 1 and 2 type of galaxies has been investigated separately. We found that the relative reflection parameter at low power-law indexes for Seyfert 2 galaxies is systematically higher than for Seyfert 1 ones. This can be related to an increasing contribution of the reflected radiation from the gas-dust torus. Our data show th...

  4. THE CLUSTERING OF GALAXIES AROUND RADIO-LOUD ACTIVE GALACTIC NUCLEI

    Worpel, Hauke [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Clayton, Victoria 3800 (Australia); Brown, Michael J. I.; Jones, D. Heath; Floyd, David J. E. [Monash Centre for Astrophysics, School of Physics, Monash University, Clayton, Victoria 3800 (Australia); Beutler, Florian [ICRAR, University of Western Australia, 35 Stirling Highway, Perth, WA 6009 (Australia)

    2013-07-20

    We examine the hypothesis that mergers and close encounters between galaxies can fuel active galactic nuclei (AGNs) by increasing the rate at which gas accretes toward the central black hole. We compare the clustering of galaxies around radio-loud AGNs with the clustering around a population of radio-quiet galaxies with similar masses, colors, and luminosities. Our catalog contains 2178 elliptical radio galaxies with flux densities greater than 2.8 mJy at 1.4 GHz from the Six Degree Field Galaxy Survey. We find tentative evidence that radio AGNs with more than 200 times the median radio power have, on average, more close (r < 160 kpc) companions than their radio-quiet counterparts, suggesting that mergers play a role in forming the most powerful radio galaxies. For ellipticals of fixed stellar mass, the radio power is neither a function of large-scale environment nor halo mass, consistent with the radio powers of ellipticals varying by orders of magnitude over billions of years.

  5. Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei

    Miyaji, T; Salvato, M; Brusa, M; Cappelluti, N; Civano, F; Puccetti, S; Elvis, M; Brunner, H; Fotopoulou, S; Ueda, Y; Griffiths, R E; Koekemoer, A M; Akiyama, M; Comastri, A; Gilli, R; Lanzuisi, G; Merloni, A; Vignali, C

    2015-01-01

    We construct the rest-frame 2--10 keV intrinsic X-ray luminosity function of Active Galactic Nuclei (AGNs) from a combination of X-ray surveys from the all-sky Swift BAT survey to the Chandra Deep Field-South. We use ~3200 AGNs in our analysis, which covers six orders of magnitude in flux. The inclusion of the XMM and Chandra COSMOS data has allowed us to investigate the detailed behavior of the XLF and evolution. In deriving our XLF, we take into account realistic AGN spectrum templates, absorption corrections, and probability density distributions in photometric redshift. We present an analytical expression for the overall behavior of the XLF in terms of the luminosity-dependent density evolution, smoothed two power-law expressions in 11 redshift shells, three-segment power-law expression of the number density evolution in four luminosity classes, and binned XLF. We observe a sudden flattening of the low luminosity end slope of the XLF slope at z>~0.6. Detailed structures of the AGN downsizing have been als...

  6. Long-term variability of active galactic nuclei from the "Planck" catalog

    Volvach, A. E.; Kardashev, N. S.; Larionov, M. G.; Volvach, L. N.

    2016-07-01

    A complete sample of 104 bright active galactic nuclei (AGNs) from the "Planck" catalog (early results) were observed at 36.8 GHz with the 22-m radio telescope of the Crimean Astrophysical Observatory (CrAO).Variability indices of the sources at this frequency were determined based on data from theWMAP space observatory, theMetsa¨ hovi RadioObservatory (Finland), and the CrimeanAstrophysical Observatory. New observational results confirm that the variability of these AGNs is stronger in the millimeter than at other radio wavelengths. The variability indices probably change as a result of the systematic decrease in the AGN flux densities in the transition to the infrared. Some radio sources demonstrate significant flux-density variations, including decreases, which sometimes cause them to fall out of the analysed sample. The change of the variability index in the millimeter is consistent with the suggestion that this variability is due to intrinsic processes in binary supermassive black holes at an evolutionary stage close to coalescence. All 104 of the sources studied are well known objects that are included in various radio catalogs and have flux densities exceeding 1 Jy at 36.8 GHz.

  7. The different neighbours around Type-1 and Type-2 active galactic nuclei

    Villarroel, Beatriz

    2014-01-01

    One of the most intriguing open issues in galaxy evolution is the structure and evolution of active galactic nuclei (AGN) that emit intense light believed to come from an accretion disk near a super-massive black hole (Rees 1984, Lynden-Bell 1969). To understand the zoo of different AGN classes, it has been suggested that all AGN are the same type of object viewed from different angles (Antonucci 1993). This model -- called AGN unification -- has been successful in predicting e.g. the existence of hidden broad optical lines in the spectrum of many narrow-line AGN. But this model is not unchallenged (Tran 2001) and it is an open problem whether more than viewing angle separates the so-called Type-1 and Type-2 AGN. Here we report the first large-scale study that finds strong differences in the galaxy neighbours to Type-1 and Type-2 AGN with data from the Sloan Digital Sky Survey (SDSS) (York et al. 2000) Data Release 7 (DR7) (Abazajian et al. 2008) and Galaxy Zoo (Lintott et al, 2008, Lintott et al 2011). We fi...

  8. The subarcsecond mid-infrared view of local active galactic nuclei: III. Polar dust emission

    Asmus, D; Gandhi, P

    2016-01-01

    Recent mid-infrared (MIR) interferometric observations showed in few active galactic nuclei (AGN) that the bulk of the infrared emission originates from the polar region above the putative torus, where only little dust should be present. Here, we investigate whether such strong polar dust emission is common in AGN. Out of 149 Seyferts in the MIR atlas of local AGN (Asmus et al.), 21 show extended MIR emission on single dish images. In 18 objects, the extended MIR emission aligns with the system axis position angle, established by [OIII], radio, polarisation and maser based position angle measurements. The relative amount of resolved MIR emission is at least 40 per cent and scales with the [OIV] fluxes implying a strong connection between the extended continuum and [OIV] emitters. These results together with the radio-quiet nature of the Seyferts support the scenario that the bulk of MIR emission is emitted by dust in the polar region and not by the torus, which would demand a new paradigm for the infrared emi...

  9. ESTIMATING BLACK HOLE MASSES IN ACTIVE GALACTIC NUCLEI USING THE Mg II λ2800 EMISSION LINE

    We investigate the relationship between the linewidths of broad Mg II λ2800 and Hβ in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe II contamination. We show that, contrary to popular belief, the velocity width of Mg II tends to be smaller than that of Hβ, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg II and Hβ lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.

  10. Invisible Active Galactic Nuclei. II Radio Morphologies & Five New HI 21 cm Absorption Line Detections

    Yan, Ting; Darling, Jeremy; Momjian, Emmanuel; Sharma, Soniya; Kanekar, Nissim

    2015-01-01

    We have selected a sample of 80 candidates for obscured radio-loud active galactic nuclei and presented their basic optical/near-infrared (NIR) properties in Paper 1. In this paper, we present both high-resolution radio continuum images for all of these sources and HI 21cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA continuum observations find that 52 sources are compact or have substantial compact components with size 0.1 Jy at 4.9 GHz. The most compact 36 sources were then observed with the VLBA at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, a detection rate of CSOs ~3 times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty seven sources were observed for HI 21cm absorption at their photometric or spectroscopic redshifts with only ...

  11. Constraining the Contribution of Galaxies and Active Galactic Nuclei to Cosmic Reionization

    Yoshiura, Shintaro; Ichiki, Kiyotomo; Tashiro, Hiroyuki; Shimabukuro, Hayato; Takahashi, Keitaro

    2016-01-01

    We constrain the contribution of high-$z$ galaxies and active galactic nuclei (AGNs) to reionization, by comparing numerically computed H/He reionization with the observed HI/HeII fractions at various redshifts and optical depth to Thomson scattering. In the model, the contribution of galaxies is controlled by a parameter $f_{\\rm esc}$ which indicates the escape fraction of ionizing photons from the galaxies, adopting an observed cosmic star formation history. On the other hand, in order to take ionizing photons from ANGs into account, observed X-ray luminosity functions and a composite spectral energy density with the energies in the range of $13.6\\rm eV$ to $100\\rm keV$ are assumed at $z\\leq3$, while the redshift evolution of AGN abundance at $z>3$ is assumed to be proportional to $(1+z)^\\beta$, where $\\beta$ is a parameter in the model. We find that there are observationally allowed sets of the parameters $f_{\\rm esc}$ and $\\beta$. According to the comparisons, $\\beta$ should satisfy $-4.20.18$ are also un...

  12. The Fundamental Plane of the Broad-line Region in Active Galactic Nuclei

    Du, Pu; Hu, Chen; Ho, Luis C; Li, Yan-Rong; Bai, Jin-Ming

    2016-01-01

    Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by ${\\cal D}_{_{\\rm H\\beta}}={\\rm FWHM}/\\sigma_{_{\\rm H\\beta}}$, the ratio of full width at half maximum to the dispersion of broad H$\\beta$, reflects the dynamics of the broad-line region (BLR) and correlates with the dimensionless accretion rate ($\\dot{\\mathscr{M}}$) or Eddington ratio ($L_{\\rm bol}/L_{\\rm Edd}$). At the same time, $\\dot{\\mathscr{M}}$ and $L_{\\rm bol}/L_{\\rm Edd}$ correlate with ${\\cal R}_{\\rm Fe}$, the ratio of optical Fe II to H$\\beta$ line flux emission. Assembling all AGNs with reverberation mapping measurements of broad H$\\beta$, both from the literature and from new observations reported here, we find a strong bivariate correlation of the form $\\log(\\dot{\\mathscr{M}},L_{\\rm bol}/L_{\\rm Edd})=\\alpha+\\beta{\\cal D}_{_{\\rm H\\beta}}+\\gamma{\\cal R}_{\\rm Fe},$ where $\\alpha=(2.47,0.31...

  13. The Nature of Active Galactic Nuclei with Velocity Offset Emission Lines

    Müller-Sánchez, Francisco; Stern, Daniel; Harrison, Fiona A

    2016-01-01

    We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field spectroscopy to probe the morphology and kinematics of the ionized gas in four velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. These objects possess optical emission lines that are offset in velocity from systemic as measured from stellar absorption features. At a resolution of ~0.18", OSIRIS allows us to distinguish which velocity offset emission lines are produced by the motion of an AGN in a dual supermassive black hole system, and which are produced by outflows or other kinematic structures. In three galaxies, J1018+2941, J1055+1520 and J1346+5228, the spectral offset of the emission lines is caused by AGN-driven outflows. In the remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that contains the peak of Pa$\\alpha$ emission 0.2" from the center of the galaxy. The most plausible explanation for the origin of this spatially and kinematically offset peak is that it is a region of en...

  14. NO EVIDENCE FOR A SYSTEMATIC Fe II EMISSION LINE REDSHIFT IN TYPE 1 ACTIVE GALACTIC NUCLEI

    Sulentic, Jack W. [Instituto de Astrofisica de Andalucia, CSIC (Spain); Marziani, Paola [INAF, Astronomical Observatory of Padova (Italy); Zamfir, Sebastian; Meadows, Zachary A., E-mail: sulentic@iaa.es, E-mail: paola.marziani@oapd.inaf.it, E-mail: szamfir@uwsp.edu, E-mail: Zachary.A.Meadows@uwsp.edu [Department of Physics and Astronomy, University of Wisconsin, Stevens Point (United States)

    2012-06-10

    We test the recent claim by Hu et al. that Fe II emission in type 1 active galactic nuclei shows a systematic redshift relative to the local source rest frame and broad-line H{beta}. We compile high signal-to-noise median composites using Sloan Digital Sky Survey spectra from both the Hu et al. sample and our own sample of the 469 brightest DR5 spectra. Our composites are generated in bins of FWHM H{beta} and Fe II strength as defined in our 4D Eigenvector 1 formalism. We find no evidence for a systematic Fe II redshift and consistency with previous assumptions that Fe II shift and width (FWHM) follow H{beta} shift and FWHM in virtually all sources. This result is consistent with the hypothesis that Fe II emission (quasi-ubiquitous in type 1 sources) arises from a broad-line region with geometry and kinematics the same as that producing the Balmer lines.

  15. BeppoSAX view of radio-loud Active Galactic Nuclei

    Grandi, P; Fiocchi, M; Grandi, Paola; Malaguti, Giuseppe; Fiocchi, Mariateresa

    2006-01-01

    A systematic analysis of a large sample of radio-loud Active Galactic Nuclei available in the BeppoSAX public archive has been performed. The sample includes 3 Narrow Line Radio Galaxies (NLRG), 10 Broad Line Radio Galaxies (BLRG), 6 Steep Spectrum Radio Quasars (SSRQ), and 16 Flat Spectrum Radio Quasars (FSRQ). According to the unified models, these classes correspond to objects with increasing viewing angles. As expected, the presence of a non-thermal beamed component emerges clearly in FSRQ. This class shows in fact a featureless continuum (with the exception of 3C273), and a significantly flatter average spectral slope. On the contrary, traces of a non-thermal Doppler enhanced radiation are elusive in the other classes. We find that the iron line equivalent widths (EW) are generally weaker in radio- loud AGN than in Seyfert 1 galaxies, and confirm the presence of an X-ray Baldwin effect, i.e. a decrease of EW with the 2--10 keV luminosity (L) from Seyferts to BLRG and quasars. Since the EW--L anti-correla...

  16. Evidence of the Link between Broad Emission Line Regions and Accretion Disks in Active Galactic Nuclei

    Yun Xu; Xin-Wu Cao

    2007-01-01

    There is observational evidence that broad-line regions (BLRs) exist in most active galactic nuclei (AGNs), but their origin is still unclear. One scenario is that the BLRs originate from winds accelerated from the hot coronae of the disks, and the winds are suppressed when the black hole is accreting at low rates. This model predicts a relation between (m) ((m) = (M)/(M)Edd) and the FWHM of broad emission lines. We estimate the central black hole masses for a sample of bright AGNs by using their broad Hβ line-widths and optical luminosities. The dimensionless accretion rates (m) = (M)/(M)Edd are derived from the optical continuum luminosities by using two different models: using an empirical relation between the bolometric luminosity Lbol and the optical luminosity ((m) = Lbol/LEdd, a fixed radiative efficiency is adopted); and calculating the optical spectra of accretion disks as a function of (m). We find a significant correlation between the derived (m) and the observed line width of Hβ,FWHM∝ (m)-0.37, which almost overlaps the disk-corona model calculations, if the viscosity α≈ 0.1 - 0.2 is adopted. Our results provide strong evidence for the physical link between the BLRs and accretion disks in AGNs.

  17. Off-axis irradiation and the polarization of broad emission lines in active galactic nuclei

    Goosmann, Rene W; Marin, Frederic

    2013-01-01

    The STOKES Monte Carlo radiative transfer code has been extended to model the velocity dependence of the polarization of emission lines. We use STOKES to present improved modelling of the velocity-dependent polarization of broad emission lines in active galactic nuclei. We confirm that off-axis continuum emission can produce observed velocity dependencies of both the degree and position angle of polarization. The characteristic features are a dip in the percentage polarization and an S-shaped swing in the position angle of the polarization across the line profile. Some differences between our STOKES results and previous modelling of polarization due to off-axis emission are noted. In particular we find that the presence of an offset between the maximum in line flux and the dip in the percentage of polarization or the central velocity of the swing in position angle does not necessarily imply that the scattering material is moving radially. Our model is an alternative scenario to the equatorial scattering disk ...

  18. Low-Mass Active Galactic Nuclei with Rapid X-Ray Variability

    Ho, Luis

    2016-01-01

    We present a detailed study of the optical spectroscopic properties of 12 active galactic nuclei (AGNs) with candidate low-mass black holes (BHs) selected by Kamizasa et al. through rapid X-ray variability. The high-quality, echellette Magellan spectra reveal broad H$\\alpha$ emission in all the sources, allowing us to estimate robust viral BH masses and Eddington ratios for this unique sample. We confirm that the sample contains low-mass BHs accreting at high rates: the median $M_{\\rm BH} = 1.2\\times 10^6M_\\odot$ and median $L_{\\rm bol}/L_{\\rm Edd}=0.44$. The sample follows the $M_{\\rm BH}-\\sigma_*$ relation, within the considerable scatter typical of pseudobulges, the probable hosts of these low-mass AGNs. Various lines of evidence suggest that ongoing star formation is prevalent in these systems. We propose a new strategy to estimate star formation rates in AGNs hosted by low-mass, low-metallicity galaxies, based on modification of an existing method using the strength of [O II] $\\lambda 3727$, [O III] $\\la...

  19. Long-Term X-ray Variability of Typical Active Galactic Nuclei in the Distant Universe

    Yang, G; Luo, B; Xue, Y; Bauer, F; Sun, M; Kim, S; Schulze, S; Zheng, X; Paolillo, M; Shemmer, O; Liu, T; Schneider, D; Vignali, C; Vito, F; Wang, J -X

    2016-01-01

    We perform long-term ($\\approx 15$ yr, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6 Ms $Chandra$ Deep Field-South (CDF-S) survey; the majority are in the redshift range of $0.6-3.1$, providing access to penetrating rest-frame X-rays up to $\\approx 10-30$ keV. Twenty-four of the 68 sources are optical spectral type I AGNs, and the rest (44) are type II AGNs. The time scales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon-flux variability: $90\\%$ of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity ($L_{\\rm{X}}$) and absorption ($N_{\\rm{H}}$) variability via spectral fitting. Most (74%) sources show $L_{\\rm{X}}$ variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variabili...

  20. Offset Active Galactic Nuclei as Tracers of Galaxy Mergers and Supermassive Black Hole Growth

    Comerford, Julia M

    2014-01-01

    Offset active galactic nuclei (AGNs) are AGNs that are in ongoing galaxy mergers, which produce kinematic offsets in the AGNs relative to their host galaxies. Offset AGNs are also close relatives of dual AGNs. We conduct a systematic search for offset AGNs in the Sloan Digital Sky Survey, by selecting AGN emission lines that exhibit statistically significant line-of-sight velocity offsets relative to systemic. From a parent sample of 18314 Type 2 AGNs at z<0.21, we identify 351 offset AGN candidates with velocity offsets of 50 km/s < |v| < 410 km/s. When we account for projection effects in the observed velocities, we estimate that 4% - 8% of AGNs are offset AGNs. We designed our selection criteria to bypass velocity offsets produced by rotating gas disks, AGN outflows, and gravitational recoil of supermassive black holes, but follow-up observations are still required to confirm our candidates as offset AGNs. We find that the fraction of AGNs that are offset candidates increases with AGN bolometric l...

  1. DETECTING ACTIVE GALACTIC NUCLEI USING MULTI-FILTER IMAGING DATA. II. INCORPORATING ARTIFICIAL NEURAL NETWORKS

    Dong, X. Y.; De Robertis, M. M., E-mail: xydong@yorku.ca [Physics and Astronomy Department, York University, Toronto, ON M3J 1P3 (Canada)

    2013-10-01

    This is the second paper of the series Detecting Active Galactic Nuclei Using Multi-filter Imaging Data. In this paper we review shapelets, an image manipulation algorithm, which we employ to adjust the point-spread function (PSF) of galaxy images. This technique is used to ensure the image in each filter has the same and sharpest PSF, which is the preferred condition for detecting AGNs using multi-filter imaging data as we demonstrated in Paper I of this series. We apply shapelets on Canada-France-Hawaii Telescope Legacy Survey Wide Survey ugriz images. Photometric parameters such as effective radii, integrated fluxes within certain radii, and color gradients are measured on the shapelets-reconstructed images. These parameters are used by artificial neural networks (ANNs) which yield: photometric redshift with an rms of 0.026 and a regression R-value of 0.92; galaxy morphological types with an uncertainty less than 2 T types for z ≤ 0.1; and identification of galaxies as AGNs with 70% confidence, star-forming/starburst (SF/SB) galaxies with 90% confidence, and passive galaxies with 70% confidence for z ≤ 0.1. The incorporation of ANNs provides a more reliable technique for identifying AGN or SF/SB candidates, which could be very useful for large-scale multi-filter optical surveys that also include a modest set of spectroscopic data sufficient to train neural networks.

  2. DETECTING ACTIVE GALACTIC NUCLEI USING MULTI-FILTER IMAGING DATA. II. INCORPORATING ARTIFICIAL NEURAL NETWORKS

    This is the second paper of the series Detecting Active Galactic Nuclei Using Multi-filter Imaging Data. In this paper we review shapelets, an image manipulation algorithm, which we employ to adjust the point-spread function (PSF) of galaxy images. This technique is used to ensure the image in each filter has the same and sharpest PSF, which is the preferred condition for detecting AGNs using multi-filter imaging data as we demonstrated in Paper I of this series. We apply shapelets on Canada-France-Hawaii Telescope Legacy Survey Wide Survey ugriz images. Photometric parameters such as effective radii, integrated fluxes within certain radii, and color gradients are measured on the shapelets-reconstructed images. These parameters are used by artificial neural networks (ANNs) which yield: photometric redshift with an rms of 0.026 and a regression R-value of 0.92; galaxy morphological types with an uncertainty less than 2 T types for z ≤ 0.1; and identification of galaxies as AGNs with 70% confidence, star-forming/starburst (SF/SB) galaxies with 90% confidence, and passive galaxies with 70% confidence for z ≤ 0.1. The incorporation of ANNs provides a more reliable technique for identifying AGN or SF/SB candidates, which could be very useful for large-scale multi-filter optical surveys that also include a modest set of spectroscopic data sufficient to train neural networks

  3. Ensemble X-ray variability of Active Galactic Nuclei. II. Excess Variance and updated Structure Function

    Vagnetti, F; Antonucci, M; Paolillo, M; Serafinelli, R

    2016-01-01

    Most investigations of the X-ray variability of active galactic nuclei (AGN) have been concentrated on the detailed analyses of individual, nearby sources. A relatively small number of studies have treated the ensemble behaviour of the more general AGN population in wider regions of the luminosity-redshift plane. We want to determine the ensemble variability properties of a rich AGN sample, called Multi-Epoch XMM Serendipitous AGN Sample (MEXSAS), extracted from the latest release of the XMM-Newton Serendipitous Source Catalogue, with redshift between 0.1 and 5, and X-ray luminosities, in the 0.5-4.5 keV band, between 10^{42} and 10^{47} erg/s. We caution on the use of the normalised excess variance (NXS), noting that it may lead to underestimate variability if used improperly. We use the structure function (SF), updating our previous analysis for a smaller sample. We propose a correction to the NXS variability estimator, taking account of the light-curve duration in the rest-frame, on the basis of the knowle...

  4. A hybrid model for the evolution of galaxies and Active Galactic Nuclei in the infrared

    Cai, Zhen-Yi; Xia, Jun-Qing; De Zotti, Gianfranco; Negrello, Mattia; Gruppioni, Carlotta; Rigby, Emma; Castex, Guillaume; Delabrouille, Jacques; Danese, Luigi

    2013-01-01

    [Abridged] We present a comprehensive investigation of the cosmological evolution of the luminosity function (LF) of galaxies and active galactic nuclei (AGN) in the infrared (IR). Based on the observed dichotomy in the ages of stellar populations of early-type galaxies on one side and late-type galaxies on the other, the model interprets the epoch-dependent LFs at z \\geq 1.5 using a physical model for the evolution of proto-spheroidal galaxies and of the associated AGNs, while IR galaxies at z<1.5 are interpreted as being mostly late-type 'cold' (normal) and 'warm' (starburst) galaxies. As for proto-spheroids, in addition to the epoch-dependent LFs of stellar and AGN components separately, we have worked out the evolving LFs of these objects as a whole (stellar plus AGN component). The model provides a physical explanation for the observed positive evolution of both galaxies and AGNs up to z \\simeq 2.5 and for the negative evolution at higher redshifts, for the sharp transition from Euclidean to extremely...

  5. A Simple test for the existence of two accretion modes in active galactic nuclei

    Jester, Sebastian; /Fermilab

    2005-02-01

    By analogy to the different accretion states observed in black-hole X-ray binaries (BHXBs), it appears plausible that accretion disks in active galactic nuclei (AGN) undergo a state transition between a radiatively efficient and inefficient accretion flow. If the radiative efficiency changes at some critical accretion rate, there will be a change in the distribution of black hole masses and bolometric luminosities at the corresponding transition luminosity. To test this prediction, the author considers the joint distribution of AGN black hole masses and bolometric luminosities for a sample taken from the literature. The small number of objects with low Eddington-scaled accretion rates m < 0.01 and black hole masses M{sub BH} < 10{sup 9} M{sub {circle_dot}} constitutes tentative evidence for the existence of such a transition in AGN. Selection effects, in particular those associated with flux-limited samples, systematically exclude objects in particular regions of the (M{sub BH}, L{sub bol}) plane. Therefore, they require particular attention in the analysis of distributions of black hole mass, bolometric luminosity, and derived quantities like the accretion rate. The author suggests further observational tests of the BHXB-AGN unification scheme which are based on the jet domination of the energy output of BHXBs in the hard state, and on the possible equivalence of BHXB in the very high (or steep power-law) state showing ejections and efficiently accreting quasars and radio galaxies with powerful radio jets.

  6. Radiation-driven Outflows from and Radiative Support in Dusty Tori of Active Galactic Nuclei

    Chan, Chi-Ho; Krolik, Julian H.

    2016-07-01

    Substantial evidence points to dusty, geometrically thick tori obscuring the central engines of active galactic nuclei (AGNs), but so far no mechanism satisfactorily explains why cool dust in the torus remains in a puffy geometry. Near-Eddington infrared (IR) and ultraviolet (UV) luminosities coupled with high dust opacities at these frequencies suggest that radiation pressure on dust can play a significant role in shaping the torus. To explore the possible effects of radiation pressure, we perform three-dimensional radiative hydrodynamics simulations of an initially smooth torus. Our code solves the hydrodynamics equations, the time-dependent multi–angle group IR radiative transfer (RT) equation, and the time-independent UV RT equation. We find a highly dynamic situation. IR radiation is anisotropic, leaving primarily through the central hole. The torus inner surface exhibits a break in axisymmetry under the influence of radiation and differential rotation; clumping follows. In addition, UV radiation pressure on dust launches a strong wind along the inner surface; when scaled to realistic AGN parameters, this outflow travels at ˜ 5000 {(M/{10}7{M}ȯ )}1/4 {[{L}{UV}/(0.1{L}{{E}})]}1/4 {km} {{{s}}}-1 and carries ˜ 0.1 {(M/{10}7{M}ȯ )}3/4 {[{L}{UV}/(0.1{L}{{E}})]}3/4 M ⊙ yr‑1, where M, {L}{UV}, and {L}{{E}} are the mass, UV luminosity, and Eddington luminosity of the central object respectively.

  7. Constraints on the outer radius of the broad emission line region of active galactic nuclei

    Landt, Hermine; Elvis, Martin; Karovska, Margarita

    2014-01-01

    Here we present observational evidence that the broad emission line region (BELR) of active galactic nuclei (AGN) generally has an outer boundary. This was already clear for sources with an obvious transition between the broad and narrow components of their emission lines. We show that the narrow component of the higher-order Paschen lines is absent in all sources, revealing a broad emission line profile with a broad, flat top. This indicates that the BELR is kinematically separate from the narrow emission line region. We use the virial theorem to estimate the BELR outer radius from the flat top width of the unblended profiles of the strongest Paschen lines, Pa alpha and Pa beta, and find that it scales with the ionising continuum luminosity roughly as expected from photoionisation theory. The value of the incident continuum photon flux resulting from this relationship corresponds to that required for dust sublimation. A flat-topped broad emission line profile is produced by both a spherical gas distribution ...

  8. Tracing the Physical Conditions in Active Galactic Nuclei with Time-Dependent Chemistry

    Meijerink, Rowin; Kamp, Inga; Aresu, Giambattista; Thi, Wing-Fai; Woitke, Peter

    2013-01-01

    We present an extension of the code ProDiMo that allows for a modeling of processes pertinent to active galactic nuclei and to an ambient chemistry that is time dependent. We present a proof-of-concept and focus on a few astrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO and H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water is strongly suppressed and that this affects the bulk of the oxygen and carbon chemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly time-dependent, with ratios that vary over orders of magnitude for times longer than 10^4 years. Through ALMA observations this ratio can be used to probe how the narrow-line region evolves under large fluctuations in the SMBH accretion rate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also found in species such as H3O+, CO, and H2O. These reflect, respectively, time dependent effects in the ionization balance, the transient nature of the production of molecu...

  9. The location of the dust causing internal reddening of active galactic nuclei

    Heard, Clio Z P

    2016-01-01

    We use the Balmer decrements of the broad-line regions (BLRs) and narrow-line regions (NLRs) of active galactic nuclei (AGNs) as reddening indicators to investigate the location of the dust for four samples of AGNs with reliable estimates of the NLR contribution to the Balmer lines. Intercomparison of the NLR and BLR Balmer decrements indicates that the reddening of the NLR sets a lower limit to the reddening of the BLR. Almost no objects have high NLR reddening but low BLR reddening. The reddening of the BLR is often substantially greater than the reddening of the NLR. The BLR reddening is correlated with the equivalent widths of [O III] lines and the intensity of the [O III] lines relative to broad H\\beta. We find these relationships to be consistent with the predictions of a simple model where the additional dust reddening the BLR is interior to the NLR. We thus conclude that the dust causing the additional reddening of the accretion disc and BLR is mostly located at a smaller radius than the NLR.

  10. High-energy neutrino production from photo-hadronic interactions of gamma rays from Active Galactic Nuclei at source

    Arteaga-Velazquez, J C

    2013-01-01

    Recent astronomical observations reveal that Active Galactic Nuclei (AGN) are sources of high-energy radiation. For example, the Fermi-LAT and Hess telescopes have detected gamma-ray emissions from the cores of several types of AGN's. Even more, the Pierre Auger observatory has found a correlation of ultra-high energy cosmic ray events with the position of Active Galactic Nuclei, such as Centaurus A. In this way, according to particle physics, a flux of high-energy neutrinos should be expected from the interactions of cosmic and gamma-rays with the ambient matter and radiation at the source. In this work, estimations of the diffuse neutrino flux from AGN's arising from interactions of the gamma radiation with the gas and dust of the sources will be presented.

  11. Semianalytic Models of Two-Phase Disk Winds in Active Galactic Nuclei with Combined Hydromagnetic and Radiative Driving

    Everett, John E.

    2002-01-01

    (abridged) We present a semianalytic model of steady-state magnetically and radiatively driven disk outflows in Active Galactic Nuclei (AGNs) consisting of a continuous wind with embedded clouds. The continuous outflow is launched from the disk surface as a centrifugally driven wind, whereas the clouds are uplifted from the disk by the ram pressure of the continuous outflow. In addition, the continuous wind and clouds are subject to both line and continuum radiative acceleration. We describe ...

  12. Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?

    Cheung, Edmond; Athanassoula, E; Bamford, Steven P; Bell, Eric F; Bosma, A; Cardamone, Carolin N; Casteels, Kevin R V; Faber, S M; Fang, Jerome J; Fortson, Lucy F; Kocevski, Dale D; Koo, David C; Laine, Seppo; Lintott, Chris; Masters, Karen L; Melvin, Thomas; Nichol, Robert C; Schawinski, Kevin; Simmons, Brooke; Smethurst, Rebecca; Willett, Kyle W

    2014-01-01

    We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 1, our findings suggest that large-scale bars have likely never directly been a dominant fueling mechanism for supermassive black hole growth.

  13. KEPLER PHOTOMETRY OF FOUR RADIO-LOUD ACTIVE GALACTIC NUCLEI IN 2010-2012

    Wehrle, Ann E. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Wiita, Paul J.; Di Lorenzo, Paolo; Revalski, Mitchell; Silano, Daniel; Sprague, Dan [Department of Physics, The College of New Jersey, P.O. Box 7718, Ewing, NJ 08628 (United States); Unwin, Stephen C., E-mail: awehrle@spacescience.org [Jet Propulsion Laboratory, Mail Stop 321-100, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

    2013-08-20

    We have used Kepler photometry to characterize variability in four radio-loud active galactic nuclei (AGN; three quasars and one object tentatively identified as a Seyfert 1.5 galaxy) on timescales from minutes to months, comparable to the light crossing time of the accretion disk around the central supermassive black hole or the base of the relativistic jet. Kepler's almost continuous observations provide much better temporal coverage than is possible from ground-based observations. We report the first such data analyzed for quasars. We have constructed power spectral densities using eight Kepler quarters of long-cadence (30-minute) data for three AGN, six quarters for one AGN and two quarters of short-cadence (1-minute) data for all four AGN. On timescales longer than about 0.2-0.6 days, we find red noise with mean power-law slopes ranging from -1.8 to -1.2, consistent with the variability originating in turbulence either behind a shock or within an accretion disk. Each AGN has a range of red noise slopes which vary slightly by month and quarter of observation. No quasi-periodic oscillations of astrophysical origin were detected. We detected flares of several days long when brightness increased by 3%-7% in two objects. No flares on timescales of minutes to hours were detected. Our observations imply that the duty cycle for enhanced activity in these radio-loud AGN is small. These well-sampled AGN light curves provide an impetus to develop more detailed models of turbulence in jets and instabilities in accretion disks.

  14. XMM FOLLOW-UP OBSERVATIONS OF THREE SWIFT BAT-SELECTED ACTIVE GALACTIC NUCLEI

    We present XMM-Newton observations of three active galactic nuclei (AGNs) taken as part of a hunt to find very heavily obscured Compton-thick AGNs. For obscuring columns greater than 1025 cm-2, AGNs are only visible at energies below 10 keV via reflected/scattered radiation, characterized by a flat power law. We therefore selected three objects (ESO 417-G006, IRAS 05218-1212, and MCG -01-05-047) from the Swift Burst Alert Telescope (BAT) hard X-ray survey catalog with Swift X-ray Telescope (XRT) 0.5-10 keV spectra with flat power-law indices as candidate Compton-thick sources for follow-up observations with the more sensitive instruments on XMM-Newton. The XMM spectra, however, rule out reflection-dominated models based on the weakness of the observed Fe Kα lines. Instead, the spectra are well fit by a model of a power-law continuum obscured by a Compton-thin absorber plus a soft excess. This result is consistent with previous follow-up observations of two other flat-spectrum BAT-detected AGNs. Thus, out of the six AGNs in the 22 month BAT catalog with apparently flat Swift XRT spectra, all five that have had follow-up observations are not likely Compton thick. We also present new optical spectra of two of these objects, IRAS 05218-1212 and MCG -01-05-047. Interestingly, though both the AGNs have similar X-ray spectra, their optical spectra are completely different, adding evidence against the simplest form of the geometric unified model of AGNs. IRAS 05218-1212 appears in the optical as a Seyfert 1, despite the ∼8.5 x 1022 cm-2 line-of-sight absorbing column indicated by its X-ray spectrum. MCG -01-05-047's optical spectrum shows no sign of AGN activity; it appears as a normal galaxy.

  15. KEPLER PHOTOMETRY OF FOUR RADIO-LOUD ACTIVE GALACTIC NUCLEI IN 2010-2012

    We have used Kepler photometry to characterize variability in four radio-loud active galactic nuclei (AGN; three quasars and one object tentatively identified as a Seyfert 1.5 galaxy) on timescales from minutes to months, comparable to the light crossing time of the accretion disk around the central supermassive black hole or the base of the relativistic jet. Kepler's almost continuous observations provide much better temporal coverage than is possible from ground-based observations. We report the first such data analyzed for quasars. We have constructed power spectral densities using eight Kepler quarters of long-cadence (30-minute) data for three AGN, six quarters for one AGN and two quarters of short-cadence (1-minute) data for all four AGN. On timescales longer than about 0.2-0.6 days, we find red noise with mean power-law slopes ranging from –1.8 to –1.2, consistent with the variability originating in turbulence either behind a shock or within an accretion disk. Each AGN has a range of red noise slopes which vary slightly by month and quarter of observation. No quasi-periodic oscillations of astrophysical origin were detected. We detected flares of several days long when brightness increased by 3%-7% in two objects. No flares on timescales of minutes to hours were detected. Our observations imply that the duty cycle for enhanced activity in these radio-loud AGN is small. These well-sampled AGN light curves provide an impetus to develop more detailed models of turbulence in jets and instabilities in accretion disks

  16. ON THE 10 μm SILICATE FEATURE IN ACTIVE GALACTIC NUCLEI

    The 10 μm silicate feature observed with Spitzer in active galactic nuclei (AGNs) reveals some puzzling behavior. It (1) has been detected in emission in type 2 sources, (2) shows broad, flat-topped emission peaks shifted toward long wavelengths in several type 1 sources, and (3) is not seen in deep absorption in any source observed so far. We solve all three puzzles with our clumpy dust radiative transfer formalism. Addressing (1), we present the spectral energy distribution (SED) of SST1721+6012, the first type 2 quasar observed to show a clear 10 μm silicate feature in emission. Such emission arises in models of the AGN torus easily when its clumpy nature is taken into account. We constructed a large database of clumpy torus models and performed extensive fitting of the observed SED. We find that the cloud radial distribution varies as r -1.5 and the torus contains 2-4 clouds along radial equatorial rays, each with optical depth at visual ∼60-80. The source bolometric luminosity is ∼3 x 1012 Lsun. Our modeling suggests that ∼<35% of objects with tori sharing these characteristics and geometry would have their central engines obscured. This relatively low obscuration probability can explain the clear appearance of the 10 μm emission feature in SST1721+6012 together with its rarity among other QSO2. Investigating (2), we also fitted the SED of PG1211+143, one of the first type 1 QSOs with a 10 μm silicate feature detected in emission. Together with other similar sources, this QSO appears to display an unusually broadened feature whose peak is shifted toward longer wavelengths. Although this led to suggestions of non-standard dust chemistry in these sources, our analysis fits such SEDs with standard galactic dust; the apparent peak shifts arise from simple radiative transfer effects. Regarding (3), we find additionally that the distribution of silicate feature strengths among clumpy torus models closely resembles the observed distribution, and the feature

  17. X-ray variability and the inner region in active galactic nuclei

    We present theoretical models of X-ray variability attributable to orbital signatures from an accretion disk including emission region size, quasi-periodic oscillations (QPOs), and its quality factor Q, and the emergence of a break frequency in the power spectral density shape. We find a fractional variability amplitude of Fvar∝M∙−0.4. We conduct a time series analysis on X-ray light curves (0.3-10 keV) of a sample of active galactic nuclei (AGNs). A statistically significant bend frequency is inferred in 9 of 58 light curves (16%) from 3 AGNs for which the break timescale is consistent with the reported BH spin but not with the reported BH mass. Upper limits of 2.85 × 107 M ☉ in NGC 4051, 8.02 × 107 M ☉ in MRK 766, and 4.68 × 107 M ☉ in MCG-6-30-15 are inferred for maximally spinning BHs. For REJ 1034+396 where a QPO at 3733 s was reported, we obtain an emission region size of (6-6.5) M and a BH spin of a ≲ 0.08. The relativistic inner region of a thin disk, dominated by radiation pressure and electron scattering, is likely to host the orbital features as the simulated Q ranges from 6.3 × 10–2 to 4.25 × 106, containing the observed Q. The derived value of Q ∼ 32 for REJ 1034+396 therefore suggests that the AGN hosts a thin disk.

  18. X-ray variability and the inner region in active galactic nuclei

    Mohan, P.; Mangalam, A., E-mail: prashanth@iiap.res.in, E-mail: mangalam@iiap.res.in [Indian Institute of Astrophysics, Sarjapur Road, Koramangala, Bangalore 560034 (India)

    2014-08-20

    We present theoretical models of X-ray variability attributable to orbital signatures from an accretion disk including emission region size, quasi-periodic oscillations (QPOs), and its quality factor Q, and the emergence of a break frequency in the power spectral density shape. We find a fractional variability amplitude of F{sub var}∝M{sub ∙}{sup −0.4}. We conduct a time series analysis on X-ray light curves (0.3-10 keV) of a sample of active galactic nuclei (AGNs). A statistically significant bend frequency is inferred in 9 of 58 light curves (16%) from 3 AGNs for which the break timescale is consistent with the reported BH spin but not with the reported BH mass. Upper limits of 2.85 × 10{sup 7} M {sub ☉} in NGC 4051, 8.02 × 10{sup 7} M {sub ☉} in MRK 766, and 4.68 × 10{sup 7} M {sub ☉} in MCG-6-30-15 are inferred for maximally spinning BHs. For REJ 1034+396 where a QPO at 3733 s was reported, we obtain an emission region size of (6-6.5) M and a BH spin of a ≲ 0.08. The relativistic inner region of a thin disk, dominated by radiation pressure and electron scattering, is likely to host the orbital features as the simulated Q ranges from 6.3 × 10{sup –2} to 4.25 × 10{sup 6}, containing the observed Q. The derived value of Q ∼ 32 for REJ 1034+396 therefore suggests that the AGN hosts a thin disk.

  19. LONG-TERM OPTICAL CONTINUUM COLOR VARIABILITY OF NEARBY ACTIVE GALACTIC NUCLEI

    We examine whether the spectral energy distribution of optical continuum emission of active galactic nuclei (AGNs) changes during flux variation, based on accurate and frequent monitoring observations of 11 nearby Seyfert galaxies and QSOs carried out in the B, V, and I bands for seven years by the MAGNUM telescope. The multi-epoch flux data in any two different bands obtained on the same night show a very tight linear flux-to-flux relationship for all target AGNs. The flux of the host galaxy within the photometric aperture is carefully estimated by surface brightness fitting to available high-resolution Hubble Space Telescope images and MAGNUM images. The flux of narrow emission lines in the photometric bands is also estimated from available spectroscopic data. We find that the non-variable component of the host galaxy plus narrow emission lines for all target AGNs is located on the fainter extension of the linear regression line of multi-epoch flux data in the flux-to-flux diagram. This result strongly indicates that the spectral shape of AGN continuum emission in the optical region (∼4400-7900 A) does not systematically change during flux variation. The trend of spectral hardening that optical continuum emission becomes bluer as it becomes brighter, which has been reported by many studies, is therefore interpreted as the domination of the variable component of the nearly constant spectral shape of an AGN as it brightens over the non-variable component of the host galaxy plus narrow lines, which is usually redder than AGN continuum emission.

  20. MEASURING X-RAY VARIABILITY IN FAINT/SPARSELY SAMPLED ACTIVE GALACTIC NUCLEI

    Allevato, V. [Department of Physics, University of Helsinki, Gustaf Haellstroemin katu 2a, FI-00014 Helsinki (Finland); Paolillo, M. [Department of Physical Sciences, University Federico II, via Cinthia 6, I-80126 Naples (Italy); Papadakis, I. [Department of Physics and Institute of Theoretical and Computational Physics, University of Crete, 71003 Heraklion (Greece); Pinto, C. [SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584-CA Utrecht (Netherlands)

    2013-07-01

    We study the statistical properties of the normalized excess variance of variability process characterized by a ''red-noise'' power spectral density (PSD), as in the case of active galactic nuclei (AGNs). We perform Monte Carlo simulations of light curves, assuming both a continuous and a sparse sampling pattern and various signal-to-noise ratios (S/Ns). We show that the normalized excess variance is a biased estimate of the variance even in the case of continuously sampled light curves. The bias depends on the PSD slope and on the sampling pattern, but not on the S/N. We provide a simple formula to account for the bias, which yields unbiased estimates with an accuracy better than 15%. We show that the normalized excess variance estimates based on single light curves (especially for sparse sampling and S/N < 3) are highly uncertain (even if corrected for bias) and we propose instead the use of an ''ensemble estimate'', based on multiple light curves of the same object, or on the use of light curves of many objects. These estimates have symmetric distributions, known errors, and can also be corrected for biases. We use our results to estimate the ability to measure the intrinsic source variability in current data, and show that they could also be useful in the planning of the observing strategy of future surveys such as those provided by X-ray missions studying distant and/or faint AGN populations and, more in general, in the estimation of the variability amplitude of sources that will result from future surveys such as Pan-STARRS and LSST.

  1. Role of active galactic nuclei in the luminous infrared galaxy phase at z ≤ 3

    Lin, Ming-Yi; Hashimoto, Yasuhiro; Foucaud, Sébastien

    2016-03-01

    To understand the interactions between active galactic nuclei (AGNs) and star formation during the evolution of galaxies, we investigate 142 galaxies detected in both X-ray and 70 μm observations in the COSMOS (Cosmic Evolution Survey) field. All of our data are obtained from the archive X-ray point-source catalogues from Chandra and XMM-Newton observations, and the far-infrared 70 μm point-source catalogue from Spitzer-MIPS observations. Although the IRAC [3.6 μm]-[4.5 μm] versus [5.8 μm]-[8.0 μm] colours of our sample indicate that only ˜63 per cent of our sources would be classified as AGNs, the ratio of the rest-frame 2-10 keV luminosity to the total infrared luminosity (8-1000 μm) shows that the entire sample has comparatively higher X-ray luminosity than that expected from pure star-forming galaxies, suggesting the presence of an AGN in all of our sources. From an analysis of the X-ray hardness ratio, we find that sources with both 70 μm and X-ray detection tend to have a higher hardness ratio relative to the whole X-ray-selected source population, suggesting the presence of more X-ray absorption in the 70 μm detected sources. In addition, we find that the observed far-infrared colours of 70 μm detected sources with and without X-ray emission are similar, suggesting the far-infrared emission could be mainly powered by star formation.

  2. LINE SHIFTS, BROAD-LINE REGION INFLOW, AND THE FEEDING OF ACTIVE GALACTIC NUCLEI

    Velocity-resolved reverberation mapping suggests that the broad-line regions (BLRs) of active galactic nuclei (AGNs) can have significant net inflow. We use the STOKES radiative transfer code to show that electron and Rayleigh scattering off the BLR and torus naturally explains the blueshifted profiles of high-ionization lines and the ionization dependence of the blueshifts. This result is insensitive to the geometry of the scattering region. If correct, then this model resolves the long-standing conflict between the absence of outflow implied by velocity-resolved reverberation mapping and the need for outflow if the blueshifting is the result of obscuration. The accretion rate implied by the inflow is sufficient to power the AGN. We suggest that the BLR is part of the outer accretion disk and that similar magnetohydrodynamic processes are operating. In the scattering model, the blueshifting is proportional to the accretion rate so high-accretion-rate AGNs will show greater high-ionization line blueshifts, as is observed. Scattering can lead to systematically too high black hole mass estimates from the C IV line. We note many similarities between narrow-line region (NLR) and BLR blueshiftings, and suggest that NLR blueshiftings have a similar explanation. Our model explains the higher blueshifts of broad absorption line QSOs if they are more highly inclined. Rayleigh scattering from the BLR and torus could be more important in the UV than electron scattering for predominantly neutral material around AGNs. The importance of Rayleigh scattering versus electron scattering can be assessed by comparing line profiles at different wavelengths arising from the same emission-line region.

  3. IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA

    Spitzer/IRAC selection is a powerful tool for identifying luminous active galactic nuclei (AGNs). For deep IRAC data, however, the AGN selection wedges currently in use are heavily contaminated by star-forming galaxies, especially at high redshift. Using the large samples of luminous AGNs and high-redshift star-forming galaxies in COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys. The new IRAC criteria are designed to be both highly complete and reliable, and incorporate the best aspects of the current AGN selection wedges and of infrared power-law selection while excluding high-redshift star-forming galaxies selected via the BzK, distant red galaxy, Lyman-break galaxy, and submillimeter galaxy criteria. At QSO luminosities of log L2-10keV(erg s–1) ≥44, the new IRAC criteria recover 75% of the hard X-ray and IRAC-detected XMM-COSMOS sample, yet only 38% of the IRAC AGN candidates have X-ray counterparts, a fraction that rises to 52% in regions with Chandra exposures of 50-160 ks. X-ray stacking of the individually X-ray non-detected AGN candidates leads to a hard X-ray signal indicative of heavily obscured to mildly Compton-thick obscuration (log NH (cm–2) = 23.5 ± 0.4). While IRAC selection recovers a substantial fraction of luminous unobscured and obscured AGNs, it is incomplete to low-luminosity and host-dominated AGNs.

  4. HerMES: disentangling active galactic nuclei and star formation in the radio source population

    Rawlings, J. I.; Page, M. J.; Symeonidis, M.; Bock, J.; Cooray, A.; Farrah, D.; Guo, K.; Hatziminaoglou, E.; Ibar, E.; Oliver, S. J.; Roseboom, I. G.; Scott, Douglas; Seymour, N.; Vaccari, M.; Wardlow, J. L.

    2015-10-01

    We separate the extragalactic radio source population above ˜50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20-65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ˜1 mJy for the extragalactic radio source population.

  5. MEASURING X-RAY VARIABILITY IN FAINT/SPARSELY SAMPLED ACTIVE GALACTIC NUCLEI

    We study the statistical properties of the normalized excess variance of variability process characterized by a ''red-noise'' power spectral density (PSD), as in the case of active galactic nuclei (AGNs). We perform Monte Carlo simulations of light curves, assuming both a continuous and a sparse sampling pattern and various signal-to-noise ratios (S/Ns). We show that the normalized excess variance is a biased estimate of the variance even in the case of continuously sampled light curves. The bias depends on the PSD slope and on the sampling pattern, but not on the S/N. We provide a simple formula to account for the bias, which yields unbiased estimates with an accuracy better than 15%. We show that the normalized excess variance estimates based on single light curves (especially for sparse sampling and S/N < 3) are highly uncertain (even if corrected for bias) and we propose instead the use of an ''ensemble estimate'', based on multiple light curves of the same object, or on the use of light curves of many objects. These estimates have symmetric distributions, known errors, and can also be corrected for biases. We use our results to estimate the ability to measure the intrinsic source variability in current data, and show that they could also be useful in the planning of the observing strategy of future surveys such as those provided by X-ray missions studying distant and/or faint AGN populations and, more in general, in the estimation of the variability amplitude of sources that will result from future surveys such as Pan-STARRS and LSST.

  6. BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI

    Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of the central black holes (BHs) that power the radio-emitting jets. Using general relativistic magnetohydrodynamic simulations, we construct steady state axisymmetric numerical models for a wide range of BH spins (dimensionless spin parameter 0.1 ≤ a ≤ 0.9999) and a variety of jet geometries. We assume that the total magnetic flux through the BH horizon at radius rH(a) is held constant. If the BH is surrounded by a thin accretion disk, we find that the total BH power output depends approximately quadratically on the angular frequency of the hole, P ∝ Ω2H ∝ (a/rH)2. We conclude that, in this scenario, differences in the BH spin can produce power variations of only a few tens at most. However, if the disk is thick such that the jet subtends a narrow solid angle around the polar axis, then the power dependence becomes much steeper, P ∝ Ω4H or even ∝Ω6H. Power variations of 1000 are then possible for realistic BH spin distributions. We derive an analytic solution that accurately reproduces the steeper scaling of jet power with ΩH and we provide a numerical fitting formula that reproduces all our simulation results. We discuss other physical effects that might contribute to the observed radio loud/quiet dichotomy of AGNs.

  7. THE EVOLUTION OF ACTIVE GALACTIC NUCLEI IN WARM DARK MATTER COSMOLOGY

    Menci, N.; Fiore, F.; Lamastra, A. [INAF, Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio (Italy)

    2013-04-01

    Recent measurements of the abundance of active galactic nuclei (AGNs) with low luminosities (L{sub 2-10} {<=} 10{sup 44} erg s{sup -1} in the 2-10 keV energy band) at high redshifts (z {>=} 4) provide a serious challenge for cold dark matter (CDM) models based on interaction-driven fueling of AGNs. Using a semi-analytic model of galaxy formation we investigate how such observations fit in a warm dark matter (WDM) scenario of galaxy formation, and compare the results with those obtained in the standard CDM scenario with different efficiencies for the stellar feedback. Taking on our previous exploration of galaxy formation in WDM cosmology, we assume as a reference case a spectrum which is suppressed-compared to the standard CDM case-below a cutoff scale Almost-Equal-To 0.2 Mpc corresponding (for thermal relic WDM particles) to a mass m{sub X} = 0.75 keV. We run our fiducial semi-analytic model with such a WDM spectrum to derive AGN luminosity functions from z Almost-Equal-To 6 to the present over a wide range of luminosities (10{sup 43} {<=} L{sub 2-10}/erg s{sup -1} {<=} 10{sup 46} in the 2-10 keV X-ray band), to compare with recent observations and with the results in the CDM case. When compared with the standard CDM case, the luminosity distributions we obtain assuming a WDM spectrum are characterized by a similar behavior at low redshift, and by a flatter slope at faint magnitudes for z {>=} 3, which provide an excellent fit to present observations. We discuss how such a result compares with CDM models with maximized feedback efficiency, and how future deep AGN surveys will allow for a better discrimination between feedback and cosmological effects on the evolution of AGNs in interaction-driven models for AGN fueling.

  8. The INTEGRAL High-energy Cut-off Distribution of Type 1 Active Galactic Nuclei

    Malizia, A.; Molina, M.; Bassani, L.; Stephen, J. B.; Bazzano, A.; Ubertini, P.; Bird, A. J.

    2014-02-01

    In this Letter we present the primary continuum parameters, the photon index Γ, and the high-energy cut-off E c of 41 type-1 Seyfert galaxies extracted from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) complete sample of active galactic nuclei (AGNs). We performed broadband (0.3-100 keV) spectral analysis by simultaneously fitting the soft and hard X-ray spectra obtained by XMM and INTEGRAL/IBIS-Swift/BAT, respectively, in order to investigate the general properties of these parameters, in particular their distribution and mean values. We find a mean photon index of 1.73 with a standard deviation of 0.17 and a mean high-energy cut-off of 128 keV with a standard deviation of 46 keV for the whole sample. This is the first time that the cut-off energy is constrained in such a large number of AGNs. We have 26 measurements of the cut-off, which corresponds to 63% of the entire sample, distributed between 50 and 200 keV. There are a further 11 lower limits mostly below 300 keV. Using the main parameters of the primary continuum, we have been able to obtain the actual physical parameters of the Comptonizing region, i.e., the plasma temperature kT e from 20 to 100 keV and the optical depth τ < 4. Finally, with the high signal-to-noise ratio spectra starting to come from NuSTAR it will soon be possible to better constrain the cut-off values in many AGNs, allowing the determination of more physical models and thus better understand the continuum emission and geometry of the region surrounding black holes.

  9. INVISIBLE ACTIVE GALACTIC NUCLEI. I. SAMPLE SELECTION AND OPTICAL/NEAR-IR SPECTRAL ENERGY DISTRIBUTIONS

    In order to find more examples of the elusive high-redshift molecular absorbers, we have embarked on a systematic discovery program for highly obscured, radio-loud 'invisible active galactic nuclei' using the Very Large Array Faint Images of the Radio Sky at Twenty centimeters radio survey in conjunction with the Sloan Digital Sky Survey (SDSS) to identify 82 strong (≥300 mJy) radio sources positionally coincident with late-type, presumably gas-rich galaxies. In this first paper, the basic properties of this sample are described including the selection process and the analysis of the spectral energy distributions (SEDs) derived from the optical (SDSS) + near-IR (NIR) photometry obtained by us at the Apache Point Observatory 3.5 m. The NIR images confirm the late-type galaxy morphologies found by SDSS for these sources in all but a few (6 of 70) cases (12 previously well studied or misclassified sources were culled). Among 70 sources in the final sample, 33 show galaxy type SEDs, 17 have galaxy components to their SEDs, and 20 have quasar power-law continua. At least nine sources with galaxy SEDs have K-band flux densities too faint to be giant ellipticals if placed at their photometric redshifts. Photometric redshifts for this sample are analyzed and found to be too inaccurate for an efficient radio-frequency absorption line search; spectroscopic redshifts are required. A few new spectroscopic redshifts for these sources are presented here but more will be needed to make significant progress in this field. Subsequent papers will describe the radio continuum properties of the sample and the search for redshifted H I 21 cm absorption.

  10. CHARACTERIZING THE OPTICAL VARIABILITY OF BRIGHT BLAZARS: VARIABILITY-BASED SELECTION OF FERMI ACTIVE GALACTIC NUCLEI

    We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ∼30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales σ-circumflex. Imposing cuts on minimum τ and σ-circumflex allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ≥ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ∼3 years in the rest frame of the jet, in contrast with the ∼320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.

  11. An optical and near-infrared color-magnitude diagram for type I Active Galactic Nuclei

    Palmer, Robert J.; Gibbs, John; Gorjian, Varoujan; Pruett, Lee; Young, Diedre; Boyd, Robert; Byrd, Joy; Cheshier, Jaicie; Chung, Stephanie; Clark, Ruby; Fernandez, Joseph; Gonzales, Elyse; Kumar, Anika; McGinnis, Gillian; Palmer, John; Perrine, Luke; Phelps, Brittney; Reginio, Margaret; Richter, Kristi; Sanchez, Elias; Washburn, Claire

    2016-01-01

    This project is seeking another standard candle for measuring cosmic distances by trying to establish a color-magnitude diagram for active galactic nuclei (AGN). Type I AGN selected from the NASA/IPAC Extragalactic Database (NED) were used to establish a correlation between the color and the luminosity of AGN. This work builds on previous NASA/IPAC Teacher Archive Research Program team attempts to establish such a relationship. This is novel in that it uses both optical and 1-2 micron near-infrared (NIR) wavelengths as a better color discriminator of the transition between accretion-dominated and dust/torus-dominated emission.Photometric data from the Sloan Digital Sky Survey (SDSS) and the Two Micron All Sky Survey (2MASS) was extracted and analyzed for type I AGN with redshifts z < 0.20. Our color-magnitude diagram for the area where the dust vaporizes is analogous to a stellar Hertzsprung-Russell (HR) diagram. Data from SDSS and 2MASS were specifically selected to focus on the sublimation boundary between the coolest part of the accretion disk and the hottest region of the inner edge of the dusty torus surrounding the accretion disk to find the greatest ratio for the color. The more luminous the AGN, the more extended the dust sublimation radius, causing a larger hot dust emitting surface area, which corresponds to a greater NIR luminosity.Our findings suggest that the best correlations correspond to colors associated with the Sloan z band and any of the 2MASS bands with slight variations dependent on redshift. This may result in a tool for using AGN as a standard for cosmic distances. This research was made possible through the NASA/IPAC Teacher Archive Research Program (NITARP) and was funded by NASA Astrophysics Data Program.

  12. GPU-BASED MONTE CARLO DUST RADIATIVE TRANSFER SCHEME APPLIED TO ACTIVE GALACTIC NUCLEI

    A three-dimensional parallel Monte Carlo (MC) dust radiative transfer code is presented. To overcome the huge computing-time requirements of MC treatments, the computational power of vectorized hardware is used, utilizing either multi-core computer power or graphics processing units. The approach is a self-consistent way to solve the radiative transfer equation in arbitrary dust configurations. The code calculates the equilibrium temperatures of two populations of large grains and stochastic heated polycyclic aromatic hydrocarbons. Anisotropic scattering is treated applying the Heney-Greenstein phase function. The spectral energy distribution (SED) of the object is derived at low spatial resolution by a photon counting procedure and at high spatial resolution by a vectorized ray tracer. The latter allows computation of high signal-to-noise images of the objects at any frequencies and arbitrary viewing angles. We test the robustness of our approach against other radiative transfer codes. The SED and dust temperatures of one- and two-dimensional benchmarks are reproduced at high precision. The parallelization capability of various MC algorithms is analyzed and included in our treatment. We utilize the Lucy algorithm for the optical thin case where the Poisson noise is high, the iteration-free Bjorkman and Wood method to reduce the calculation time, and the Fleck and Canfield diffusion approximation for extreme optical thick cells. The code is applied to model the appearance of active galactic nuclei (AGNs) at optical and infrared wavelengths. The AGN torus is clumpy and includes fluffy composite grains of various sizes made up of silicates and carbon. The dependence of the SED on the number of clumps in the torus and the viewing angle is studied. The appearance of the 10 μm silicate features in absorption or emission is discussed. The SED of the radio-loud quasar 3C 249.1 is fit by the AGN model and a cirrus component to account for the far-infrared emission.

  13. The hadronic origin of multi-TeV gamma rays from low-luminosity active galactic nuclei: implications of past activities of the Galactic center

    Fujita, Yutaka; Murase, Kohta

    2015-01-01

    Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) have been suggested as cosmic-ray and neutrino sources, which may largely contribute to the observed diffuse neutrino intensity. We show that this scenario naturally predicts hadronic multi-TeV gamma-ray excesses around galactic centers. The protons accelerated in the RIAF in Sagittarius A* (Sgr A*) escape and interact with dense molecular gas surrounding Sgr A*, which is known as the Central Molecular Zone (CMZ), and produce gamma rays as well as neutrinos. Based on a theoretical model that is compatible with the IceCube data, we calculate gamma-ray spectra of the CMZ and find that the gamma rays with $\\gtrsim 1$~TeV may have already been detected with the High Energy Stereoscopic System (HESS), if Sgr A* was more active in the past than it is today as indicated by various observations. Our model predicts that neutrinos should come from the CMZ with a spectrum similar to the gamma-ray spectrum. We also show that...

  14. THE SUZAKU VIEW OF THE SWIFT/BAT ACTIVE GALACTIC NUCLEI. II. TIME VARIABILITY AND SPECTRA OF FIVE 'HIDDEN' ACTIVE GALACTIC NUCLEI

    The fraction of Compton-thick sources is one of the main uncertainties left in understanding the active galactic nucleus (AGN) population. The Swift Burst Alert Telescope (BAT) all-sky survey for the first time gives us an unbiased sample of AGNs for all but the most heavily absorbed sources N H > 1025 cm-2). Still, the BAT spectra (14-195 keV) are time averaged over months of observations and therefore hard to compare with softer spectra from the Swift XRT or other missions. This makes it difficult to distinguish between Compton-thin and Compton-thick models. With Suzaku, we have obtained simultaneous hard (>15 keV) and soft (0.3-10 keV) X-ray spectra for five Compton-thick candidate sources. We report on the spectra and a comparison with the BAT and earlier XMM observations. Based on both flux variability and spectral shape, we conclude that these hidden sources are not Compton thick. We also report on a possible correlation between excess variance and Swift BAT luminosity from the 16 day binned light curves, which holds true for a sample of both absorbed (four sources), unabsorbed (eight sources), and Compton-thick (Circinus) AGNs, but is weak in the 64 day binned BAT light curves.

  15. MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. I. CHARACTERIZING WISE-SELECTED ACTIVE GALACTIC NUCLEI IN COSMOS

    The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1 – W2 ≥ 0.8 (i.e., [3.4]–[4.6] ≥0.8, Vega), which identifies 61.9 ± 5.4 active galactic nucleus (AGN) candidates per deg2 to a depth of W2 ∼ 15.0. This implies a much larger census of luminous AGNs than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGNs. Optical and soft X-ray surveys alone are highly biased toward only unobscured AGNs, while this simple WISE selection likely identifies even heavily obscured, Compton-thick AGNs. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 μJy at 4.6 μm, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field.

  16. MOJAVE: monitoring of jets in active galactic nuclei with VLBA experiments. V. Multi-epoch VLBA images

    Lister, M. L.; Aller, H. D.; Aller, M. F.; Cohen, M. H.; Homan, D. C.; Kadler, M.; Kellermann, K. I.; Kovalev, Y. Y.; Ros, E.; Savolainen, T.; Zensus, J. A.; Vermeulen, R. C.

    2009-01-01

    We present images from a long-term program (MOJAVE: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observations consist of 2424 15 GHz Very Long Baseline Array (VLBA) images of a complete flux-density-limited sample of 135 AGNs above declination –20°, spanning the period 1994 August to 2007 September. These data were acquire...

  17. INFRARED CLASSIFICATION AND LUMINOSITIES FOR DUSTY ACTIVE GALACTIC NUCLEI AND THE MOST LUMINOUS QUASARS

    Mid-infrared spectroscopic measurements from the Infrared Spectrometer (IRS) on Spitzer are given for 125 hard X-ray active galactic nuclei (AGNs; 14-195 keV) from the Swift Burst Alert Telescope (BAT) sample and for 32 AGNs with black hole masses (BHMs) from reverberation mapping. The 9.7 μm silicate feature in emission or absorption defines an infrared AGN classification describing whether AGNs are observed through dust clouds, indicating that 55% of the BAT AGNs are observed through dust. The mid-infrared dust continuum luminosity is shown to be an excellent indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray luminosity, log νLν(7.8 μm)/L(X) = –0.31 ± 0.35, and independent of classification determined from silicate emission or absorption. Dust luminosity scales closely with BHM, log νLν(7.8 μm) = (37.2 ± 0.5) + 0.87 log BHM for luminosity in erg s–1 and BHM in M☉. The 100 most luminous type 1 quasars as measured in νLν(7.8 μm) are found by comparing Sloan Digital Sky Survey (SDSS) optically discovered quasars with photometry at 22 μm from the Wide-Field Infrared Survey Explorer (WISE), scaled to rest frame 7.8 μm using an empirical template determined from IRS spectra. The most luminous SDSS/WISE quasars have the same maximum infrared luminosities for all 1.5 IR = 1014.4 L☉. Comparing with dust-obscured galaxies from Spitzer and WISE surveys, we find no evidence of hyperluminous obscured quasars whose maximum infrared luminosities exceed the maximum infrared luminosities of optically discovered quasars. Bolometric luminosities Lbol estimated from rest-frame optical or ultraviolet luminosities are compared to LIR. For the local AGN, the median log LIR/Lbol = –0.35, consistent with a covering factor of 45% for the absorbing dust clouds. For the SDSS/WISE quasars, the median log LIR/Lbol = 0.1, with extremes indicating that ultraviolet-derived Lbol can be seriously underestimated even for type 1 quasars.

  18. Bursty stellar populations and obscured active galactic nuclei in galaxy bulges

    Wild, Vivienne; Kauffmann, Guinevere; Heckman, Tim; Charlot, Stéphane; Lemson, Gerard; Brinchmann, Jarle; Reichard, Tim; Pasquali, Anna

    2007-10-01

    We investigate trends between the recent star formation history and black hole growth in galaxy bulges in the Sloan Digital Sky Survey. The galaxies lie at 0.01 4.0 kpc diameter of the galaxy. We find strong trends between black hole growth, as measured by dust-attenuation-corrected [O III] luminosity, and the recent star formation history of the bulges. 56 per cent of the bulges are quiescent with no signs of recent or ongoing star formation and, while almost half of all active galactic nuclei (AGN) lie within these bulges, they contribute only ~10 per cent to the total black hole growth in the local Universe. At the other extreme, the AGN contained within the ~4 per cent of galaxy bulges that are undergoing or have recently undergone the strongest starbursts, contribute at least 10-20 per cent of the total black hole growth. Much of this growth occurs in AGN with high amounts of dust extinction and thus the precise numbers remain uncertain. The remainder of the black hole growth (>60 per cent) is contributed by bulges with more moderate recent or ongoing star formation. The strongest accreting black holes reside in bulges with a wide range in recent star formation history. We conclude that our results support the popular hypothesis for black hole growth occurring through gas inflow into the central regions of galaxies, followed by a starburst and triggering of the AGN. However, while this is a significant pathway for the growth of black holes, it is not the dominant one in the present-day Universe. More unspectacular processes are apparently responsible for the majority of this growth. In order to arrive at these conclusions we have developed a set of new high signal-to-noise ratio (S/N) optical spectral indicators, designed to allow a detailed study of stellar populations which have undergone recent enhanced star formation. Working in the rest-frame wavelength range 3750-4150 Å, ideally suited to many recent and ongoing spectroscopic surveys at low and high

  19. IceCube expectations for two high-energy neutrino production models at active galactic nuclei

    We have determined the currently allowed regions of the parameter spaces of two representative models of diffuse neutrino flux from active galactic nuclei (AGN): one by Koers and Tinyakov (KT) and another by Becker and Biermann (BB). Our observable has been the number of upgoing muon-neutrinos expected in the 86-string IceCube detector, after 5 years of exposure, in the range 105 ≤ Eν/GeV ≤ 108. We have used the latest estimated discovery potential of the IceCube-86 array at the 5σ level to determine the lower boundary of the regions, while for the upper boundary we have used either the AMANDA upper bound on the neutrino flux or the more recent preliminary upper bound given by the half-completed IceCube-40 array (IC40). We have varied the spectral index of the proposed power-law fluxes, α, and two parameters of the BB model: the ratio between the boost factors of neutrinos and cosmic rays, Γν/ΓCR, and the maximum redshift of the sources that contribute to the cosmic-ray flux, zCRmax. For the KT model, we have considered two scenarios: one in which the number density of AGN does not evolve with redshift and another in which it evolves strongly, following the star formation rate. Using the IC40 upper bound, we have found that the models are visible in IceCube-86 only inside very thin strips of parameter space and that both of them are discarded at the preferred value of α = 2.7 obtained from fits to cosmic-ray data. Lower values of α, notably the values 2.0 and 2.3 proposed in the literature, fare better. In addition, we have analysed the capacity of IceCube-86 to discriminate between the models within the small regions of parameter space where both of them give testable predictions. Within these regions, discrimination at the 5σ level or more is guaranteed

  20. A 3.5 mm POLARIMETRIC SURVEY OF RADIO-LOUD ACTIVE GALACTIC NUCLEI

    We present the results from the first large (>100 sources) 3.5 mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30 m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-300 (J2000.0) and flux density ∼>1 Jy at ∼86 GHz, as measured at the IRAM 30 m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. We detect linear and circular polarization (above minimum 3σ levels of ∼1.5% and ∼0.3%) for 76% and 6% of the sample, respectively. We find a clear excess in degree of linear polarization detected at 86 GHz with regard to that at 15 GHz by a factor of ∼2. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter γ-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. We do not find a clear relation between the linear polarization angle and the jet structural position angle for any source class in our sample. We interpret this as the consequence of a markedly non-axisymmetric character of the 3 mm emitting region in the jets. We find that intrinsic circular polarization is the most

  1. CO SPECTRAL LINE ENERGY DISTRIBUTIONS OF INFRARED-LUMINOUS GALAXIES AND ACTIVE GALACTIC NUCLEI

    We report on new sensitive CO J = 6-5 line observations of several luminous infrared galaxies (LIRGs; L IR(8-1000 μm) ∼> 1011 L sun), 36% (8/22) of them ultraluminous infrared galaxies (ULIRGs) (L IR>1012 L sun), and two powerful local active galactic nuclei (AGNs)-the optically luminous QSO PG 1119+120 and the powerful radio galaxy 3C 293-using the James Clerk Maxwell Telescope on Mauna Kea in Hawaii. We combine these observations with existing low-J CO data and dust emission spectral energy distributions in the far-infrared-submillimeter from the literature to constrain the properties of the star-forming interstellar medium (ISM) in these systems. We then build the first local CO spectral line energy distributions (SLEDs) for the global molecular gas reservoirs that reach up to high J-levels. These CO SLEDs are neither biased by strong lensing (which affects many of those constructed for high-redshift galaxies), nor suffer from undersampling of CO-bright regions (as most current high-J CO observations of nearby extended systems do). We find: (1) a significant influence of dust optical depths on the high-J CO lines, suppressing the J = 6-5 line emission in some of the most IR-luminous LIRGs, (2) low global CO line excitation possible even in vigorously star-forming systems, (3) the first case of a shock-powered high-excitation CO SLED in the radio galaxy 3C 293 where a powerful jet-ISM interaction occurs, and (4) unusually highly excitated gas in the optically powerful QSO PG 1119+120. In Arp 220 and possibly other (U)LIRGs very faint CO J = 6-5 lines can be attributed to significant dust optical depths at short submillimeter wavelengths immersing those lines in a strong dust continuum, and also causing the C+ line luminosity deficit often observed in such extreme starbursts. Re-analysis of the CO line ratios available for submillimeter galaxies suggests that similar dust opacities also may be present in these high-redshift starbursts, with genuinely low

  2. Observations of active galactic nuclei from radio to gamma-rays

    In this work, Active Galactic Nuclei (AGN) - the brightest persistent objects in the universe - are discussed. According to current knowledge they consist out of several components. The central object of such systems is a supermassive black hole located in the center of a galaxy. Estimated masses of such black holes range from millions to billions of solar masses. The enormous gravitational field of the black hole affects material in its surrounding. Matter, such as gas, dust particles or stellar wind virtually provides the fuel for the AGN. The accretion process is highly efficient and partly explains the extreme luminosities of Active Galactic Nuclei. The thermal emission of the accretion disk is, however, insufficient for explaining the total emission of AGN. Observations show that some of these objects are visible throughout the complete electromagnetic spectrum. The emission in the radio regime as well as, most likely, high-energy emission seem to originate from jets. Unlike material accreted by the black hole, jets are collimated outflows with velocities near the speed of light. AGN are not completely understood. There are numerous open questions remaining, such as the exact accretion geometry, the formation and composition of the relativistic jets, the interaction between different components of these systems, as well as the place of origin and the underlying physical processes of the emission in different energy ranges. In order to address these questions a multiwavelength analysis of AGN has been performed in this work. The different energy regimes and observational techniques allow for insights into different processes and properties of such objects. A study of the connection between the accretion disk and properties of the jet has been done based on the object NGC 1052 using radio and X-ray observations. This object is a galaxy with an active nucleus. In the radio regime a double-sided jet with a projected length of several kpc is visible. In addition

  3. The Subaru/XMM-Newton Deep Survey (SXDS) - VI. Properties of Active Galactic Nuclei Selected by Optical Variability

    Morokuma, Tomoki; Doi, Mamoru; Yasuda, Naoki; Akiyama, Masayuki; Sekiguchi, Kazuhiro; Furusawa, Hisanori; Ueda, Yoshihiro; Totani, Tomonori; Oda, Takeshi; Nagao, Tohru; Kashikawa, Nobunari; Murayama, Takashi; Ouchi, Masami; Watson, Mike G.

    2007-01-01

    We present the properties of active galactic nuclei (AGN) selected by optical variability in the Subaru/XMM-Newton Deep Field (SXDF). Based on the locations of variable components and light curves, 211 optically variable AGN were reliably selected. We made three AGN samples; X-ray detected optically non-variable AGN (XA), X-ray detected optically variable AGN (XVA), and X-ray undetected optically variable AGN (VA). In the VA sample, we found a bimodal distribution of the ratio between the var...

  4. The structure of the broad-line region in active galactic nuclei. I. Reconstructed velocity-delay maps

    Grier, C.J.; Peterson, B.M.; Pogge, R.W.;

    2013-01-01

    of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements. © 2013. The American......We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different...

  5. The OPTX Project II: Hard X-ray Luminosity Functions of Active Galactic Nuclei for z<5

    Yencho, B.; Barger, A. J.; Trouille, L.; Winter, L. M.

    2009-01-01

    We use the largest, most uniform, and most spectroscopically complete to faint X-ray flux limits Chandra sample to date to construct hard 2-8 keV rest-frame X-ray luminosity functions (HXLFs) of spectroscopically identified active galactic nuclei (AGNs) to z~5. In addition, we use a new 2-8 keV local sample selected by the very hard (14-195 keV) SWIFT 9-month Burst Alert Telescope (BAT) survey to construct the local 2-8 keV HXLF. We do maximum likelihood fits of the combined distant plus loca...

  6. The Hard X-ray Spectral Slope as an Accretion-Rate Indicator in Radio-Quiet Active Galactic Nuclei

    Shemmer, Ohad; Brandt, W. N.; Netzer, Hagai; Maiolino, Roberto; Kaspi, Shai

    2006-01-01

    We present new XMM-Newton observations of two luminous and high accretion-rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties as well as 25 moderate-luminosity radio-quiet AGNs at z~2 keV) X-ray power-law photon index on the broad H_beta emission-line width and on the accretion rate across ~3 orders of magnitude in AGN luminosity. Provided the accretion rates of the five luminous sources ca...

  7. Reddening of the narrow-line regions of active galactic nuclei and the intrinsic Balmer decrement II

    It has recently been claimed (Malkam, 1983) that the intrinsic H-alpha/H-beta ratio for narrow line regions (NLRs) in active galactic nuclei is significantly larger than the standard case B recombination values. Here, the data assembled by Malkan are reexamined, and it is shown that the de-reddened H-alpha/H-Beta ratios are consistent with a value only slightly greater than case B, with no clear evidence for intrinsic variation from object to object. The systematic errors in the methods used are discussed, and some differences between the NLRs of Seyfert 1 and Seyfert 2 galaxies are noted. 22 references

  8. Luminosity of ultrahigh energy cosmic rays and bounds on magnetic luminosity of radio-loud active galactic nuclei

    Coimbra-Araújo, C H

    2015-01-01

    We investigate the production of magnetic flux from rotating black holes in active galactic nuclei (AGNs) and compare it with the upper limit of ultrahigh energy cosmic ray (UHECR) luminosities, calculated from observed integral flux of GeV-TeV gamma rays for nine UHECR AGN sources. We find that, for the expected range of black hole rotations (0.44

  9. Galaxy Zoo: Are bars responsible for the feeding of active galactic nuclei at 0.2 < z < 1.0?

    Cheung, Edmond; Trump, Jonathan R.; Athanassoula, E.; Bamford, Steven P.; Bell, Eric F.; Bosma, A.; Cardamone, Carolin N.; Casteels, Kevin R. V.; Faber, S. M.; Fang, Jerome J.; Fortson, Lucy F.; Kocevski, Dale D.; Koo, David C.; Laine, Seppo; Lintott, Chris; Masters, Karen L.; Melvin, Thomas; Nichol, Robert C.; Schawinski, Kevin; Simmons, Brooke; Smethurst, Rebecca; Willett, Kyle W.

    2015-02-01

    We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS (All-wavelength Extended Groth strip International Survey), COSMOS (Cosmological Evolution Survey), and (Great Observatories Origins Deep Survey-South) GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 1, our findings suggest that large-scale bars have likely never directly been a dominant fuelling mechanism for supermassive black hole growth.

  10. The Black Hole Mass-Bulge Luminosity Relationship for Active Galactic Nuclei From Reverberation Mapping and Hubble Space Telescope Imaging

    Bentz, Misty C.; Peterson, Bradley M.; Pogge, Richard W.;

    2009-01-01

    We investigate the relationship between black hole mass and bulge luminosity for active galactic nuclei (AGNs) with reverberation-based black hole mass measurements and bulge luminosities from two-dimensional decompositions of Hubble Space Telescope host galaxy images. We find that the slope...... of the relationship for AGNs is 0.76-0.85 with an uncertainty of ~0.1, somewhat shallower than the M BH vprop L 1.0±0.1 relationship that has been fit to nearby quiescent galaxies with dynamical black hole mass measurements. This difference is somewhat perplexing, as the AGN black hole masses include an overall...

  11. RADIO-LOUD NARROW-LINE SEYFERT 1 AS A NEW CLASS OF GAMMA-RAY ACTIVE GALACTIC NUCLEI

    We report the discovery with Fermi/LAT of γ-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z = 0.409), 1H 0323+342 (z = 0.061), and PKS 2004 - 447 (z = 0.24). In addition to PMN J0948+0022 (z = 0.585), the first source of this type to be detected in γ rays, they may form an emerging new class of γ-ray active galactic nuclei (AGNs). These findings can have strong implications on our knowledge about relativistic jets and the unified model of the AGN.

  12. Age determination of the nuclear stellar population of Active Galactic Nuclei using Locally Weighted Regression

    Estrada-Piedra, T; Terlevich, R J; Fuentes, O; Terlevich, E; Estrada-Piedra, Trilce; Torres-Papaqui, Juan Pablo; Terlevich, Roberto; Fuentes, Olac; Terlevich, Elena

    2003-01-01

    We present a new technique to segregate old and young stellar populations in galactic spectra using machine learning methods. We used an ensemble of classifiers, each classifier in the ensemble specializes in young or old populations and was trained with locally weighted regression and tested using ten-fold cross-validation. Since the relevant information concentrates in certain regions of the spectra we used the method of sequential floating backward selection offline for feature selection. The application to Seyfert galaxies proved that this technique is very insensitive to the dilution by the Active Galactic Nucleus (AGN) continuum. Comparing with exhaustive search we concluded that both methods are similar in terms of accuracy but the machine learning method is faster by about two orders of magnitude.

  13. The Ultraviolet Emission Properties of Five Low-Redshift Active Galactic Nuclei at High Signal to Noise and Spectral Resolution

    Laor, A; Jannuzi, B T; Schneider, D P; Green, R F; Hartig, G F; Laor, Ari; Bahcall, John N.; Jannuzi, Buell T.; Schneider, Donald P.; Green, IAS; Richard F.; Hartig, NOAO; George F.; ScI, ST

    1994-01-01

    We analyze the ultraviolet (UV) emission line and continuum properties of five low-redshift active galactic nuclei (four luminous quasars: PKS~0405$-$123, H1821+643, PG~0953+414, and 3C273, and one bright Seyfert 1 galaxy: Mrk~205). The HST spectra have higher signal-to-noise ratios (typically $\\sim 60$ per resolution element) and spectral resolution ($R = 1300$) than all previously- published UV spectra used to study the emission characteristics of active galactic nuclei. We include in the analysis ground-based optical spectra covering \\hb\\ and the narrow [O~III]~$\\lambda\\lambda$4959,5007 doublet. The following new results are obtained: \\lyb/\\lya=0.03$-$0.12 for the four quasars, which is the first accurate measurement of the long-predicted \\lyb\\ intensity in QSOs. The cores of \\lya\\ and C~IV are symmetric to an accuracy of better than 2.5\\% within about 2000~km~s$^{-1}$ of the line peak. This high degree of symmetry of \\lya\\ argues against models in which the broad line cloud velocity field has a significan...

  14. The Galactic Center compared with nuclei of nearby galaxies

    Combes, F

    2016-01-01

    Understanding our Galactic Center is easier with insights from nearby galactic nuclei. Both the star formation activity in nuclear gas disks, driven by bars and nuclear bars, and the fueling of low-luminosity AGN, followed by feedback of jets, driving molecular outflows, were certainly present in our Galactic Center, which appears now quenched. Comparisons and diagnostics are reviewed, in particular of m=2 and m=1 modes, lopsidedness, different disk orientations, and fossil evidences of activity and feedback.

  15. An Axisymmetric, Hydrodynamical Model for the Torus Wind in Active Galactic Nuclei

    Dorodnitsyn, A.; Kallman, T.; Proga, D.

    2008-01-01

    We report on time-dependent axisymmetric simulations of an X-ray-excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad biconical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.

  16. Deep Chandra Observations of HCG 16 - I. Active Nuclei, Star formation and Galactic Winds

    O'Sullivan, E; Vrtilek, J M; Giacintucci, S; Trevisan, M; David, L P; Ponman, T J; Mamon, G A; Raychaudhury, S

    2014-01-01

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610~MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation and the high luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe-K$\\alpha$ emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infra-red and ultra-vio...

  17. Origin and properties of dual and offset active galactic nuclei in a cosmological simulation at z=2

    Steinborn, Lisa K.; Dolag, Klaus; Comerford, Julia M.; Hirschmann, Michaela; Remus, Rhea-Silvia; Teklu, Adelheid F.

    2016-05-01

    In the last few years, it became possible to observationally resolve galaxies with two distinct nuclei in their centre. For separations smaller than 10 kpc, dual and offset active galactic nuclei (AGN) are distinguished: in dual AGN, both nuclei are active, whereas in offset AGN only one nucleus is active. To study the origin of such AGN pairs, we employ a cosmological, hydrodynamic simulation with a large volume of (182 Mpc)3 from the set of Magneticum Pathfinder Simulations. The simulation self-consistently produces 35 resolved black hole (BH) pairs at redshift z = 2, with a comoving distance smaller than 10 kpc. 14 of them are offset AGN and nine are dual AGN, resulting in a fraction of (1.2 ± 0.3) per cent AGN pairs with respect to the total number of AGN. In this paper, we discuss fundamental differences between the BH and galaxy properties of dual AGN, offset AGN and inactive BH pairs and investigate their different triggering mechanisms. We find that in dual AGN the BHs have similar masses and the corresponding BH from the less massive progenitor galaxy always accretes with a higher Eddington ratio. In contrast, in offset AGN the active BH is typically more massive than its non-active counterpart. Furthermore, dual AGN in general accrete more gas from the intergalactic medium than offset AGN and non-active BH pairs. This highlights that merger events, particularly minor mergers, do not necessarily lead to strong gas inflows and thus, do not always drive strong nuclear activity.

  18. AEGIS: DEMOGRAPHICS OF X-RAY AND OPTICALLY SELECTED ACTIVE GALACTIC NUCLEI

    We develop a new diagnostic method to classify galaxies into active galactic nucleus (AGN) hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hβ ratio with rest-frame U - B color. This can be used to robustly select AGNs in galaxy samples at intermediate redshifts (z AB bol > 1044 erg s-1 in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2-7 keV detection rate of Seyfert 2s at z ∼ 0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.

  19. Penrose photoproduction processes: A high efficiency energy mechanism for active galactic nuclei and quasars

    Recent observations of NGC 4151 and 3C273 suggest that the nuclei of active galaxies have very high gamma ray efficiencies. In addition, optical studies of M87 have indicated the possibility of a massive Mapprox.5 x 109 M/sub sun/ black holes being present in its central region. The above facts have led us to study a new physical mechanism, Penrose Photoproduction Processes in the ergospheres of massive Kerr black holes, as a way to account for the fluctuating, high efficiency, energy production associated with active galaxies and quasars. Observational signatures, associated with this mechanism, occur in the form of approx.2 MeV and approx.2 GeV gamma ray cutoffs which might be corroborated by the observed spectra of NGC 4151 and 3C273, respectively

  20. Penrose photoproduction processes: A high efficiency energy mechanism for active galactic nuclei and quasars

    Leiter, D.; Kafatos, M.

    1979-11-01

    Recent observations of NGC 4151 and 3C273 suggest that the nuclei of active galaxies have very high gamma ray efficiencies. In addition, optical studies of M87 have indicated the possibility of a massive Mapprox.5 x 10/sup 9/ M/sub sun/ black holes being present in its central region. The above facts have led us to study a new physical mechanism, Penrose Photoproduction Processes in the ergospheres of massive Kerr black holes, as a way to account for the fluctuating, high efficiency, energy production associated with active galaxies and quasars. Observational signatures, associated with this mechanism, occur in the form of approx.2 MeV and approx.2 GeV gamma ray cutoffs which might be corroborated by the observed spectra of NGC 4151 and 3C273, respectively.

  1. Penrose photoproduction processes - A high efficiency energy mechanism for active galactic nuclei and quasars

    Leiter, D.; Kafatos, M.

    1979-01-01

    Recent observations of NGC 4151 and 3C273 suggest that the nuclei of active galaxies have very high gamma ray efficiencies. In addition, optical studies of M87 have indicated the possibility of a massive black hole in its central region. The above facts have led to study of a new physical mechanism, Penrose Photoproduction Processes, in the ergospheres of massive Kerr black holes, as a way to account for the fluctuating, high efficiency, energy production associated with active galaxies and quasars. Observational signatures, associated with this mechanism, occur in the form of approximately 2 MeV and approximately 2 GeV gamma ray cutoffs which might be corroborated by the observed spectra of NGC 4151 and 3C273, respectively.

  2. Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region

    Wang, J -M; Du, P; Ho, L C

    2014-01-01

    Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR), from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energy distributions depending on their location relative to the disk, resulting in diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components...

  3. Studying the X-ray/UV Variability of Active Galactic Nuclei with data from Swift and XMM archives

    Many efforts have been made in understanding the underlying origin of variability in Active Galactic Nuclei (AGN), but at present they could give still no conclusive answers. Since a deeper knowledge of variability will enable to understand better the accretion process onto supermassive black holes, here we present preliminary results of the first ensemble structure function analysis of the X-ray variability of samples of quasars with data from Swift and XMM-Newton archives. Moreover, it is known that UV and X-ray luminosities of quasars are correlated and recent studies quantified this relation across 5 orders of magnitude. In this context, we present here some preliminary results on the X-ray/UV ratio from simultaneous observations in UV and X-ray bands of a sample of quasars with data from XMM-Newton archive.

  4. Virilization of the Broad Line Region in Active Galactic Nuclei - connection between shifts and widths of broad emission lines

    Jonic, Sanja; Ilic, Dragana; Popovic, Luka C

    2016-01-01

    We investigate the virilization of the emission lines Hbeta and Mg II in the sample of 287 Type 1 Active Galactic Nuclei taken from the Sloan Digital Sky Survey database. We explore the connections between the intrinsic line shifts and full widths at different levels of maximal intensity. We found that: (i) Hbeta seems to be a good virial estimator of black hole masses, and an intrinsic redshift of Hbeta is dominantly caused by the gravitational effect, (ii) there is an anti-correlation between the redshift and width of the wings of the Mg II line, (iii) the broad Mg II line can be used as virial estimator only at 50% of the maximal intensity, while the widths and intrinsic shifts of the line wings can not be used for this purpose.

  5. The interaction of two nonplanar solitary waves in electron-positron-ion plasmas: An application in active galactic nuclei

    EL-Labany, S. K.; Khedr, D. M. [Department of Physics, Faculty of Science, Damietta University, Damietta El-Gedida 34517 (Egypt); El-Shamy, E. F. [Department of Physics, Faculty of Science, Damietta University, Damietta El-Gedida 34517 (Egypt); Department of Physics, College of Science, King Khalid University, P.O. 9004, Abha (Saudi Arabia); Sabry, R. [Department of Physics, Faculty of Science, Damietta University, Damietta El-Gedida 34517 (Egypt); Department of Physics, College of Science and Humanitarian Studies, Salman bin Abdulaziz University, Alkharj (Saudi Arabia)

    2013-01-15

    In the present research paper, the effect of bounded nonplanar (cylindrical and spherical) geometry on the interaction between two nonplanar electrostatic solitary waves (NESWs) in electron-positron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain nonplanar phase shifts after the interaction of the two NESWs. This study is a first attempt to investigate nonplanar phase shifts and trajectories for NESWs in a two-fluid plasma (a pair-plasma) consisting of electrons and positrons, as well as immobile background positive ions in nonplanar geometry. The change of phase shifts and trajectories for NESWs due to the effect of cylindrical geometry, spherical geometry, the physical processes (either isothermal or adiabatic), and the positions of two NESWs are discussed. The present investigation may be beneficial to understand the interaction between two NESWs that may occur in active galactic nuclei.

  6. A Tale of Two Populations: The Contribution of Merger and Secular Processes to the Evolution of Active Galactic Nuclei

    Draper, Aden R

    2012-01-01

    Due to the co-evolution of supermassive black holes and their host galaxies, understanding the mechanisms that trigger active galactic nuclei (AGN) are imperative to understanding galaxy evolution and the formation of massive galaxies. It is observationally difficult to determine the trigger of a given AGN due to the difference between the AGN lifetime and triggering timescales. Here, we utilize AGN population synthesis modeling to determine the importance of different AGN triggering mechanisms. An AGN population model is computed by combining an observationally motivated AGN triggering rate and a theoretical AGN light curve. The free parameters of the AGN light curve are constrained by minimizing a \\chi squared test with respect to the observed AGN hard X-ray luminosity function. The observed black hole space density, AGN number counts, and X-ray background spectrum are also considered as observational constraints. It is found that major mergers are not able to account for the entire AGN population. Therefor...

  7. Clustering, Cosmology and a New Era of Black Hole Demographics -- I. The Conditional Luminosity Function of Active Galactic Nuclei

    Ballantyne, D R

    2016-01-01

    Deep X-ray surveys have provided a comprehensive and largely unbiased view of active galactic nuclei (AGN) evolution stretching back to $z \\sim 5$. However, it has been challenging to use the survey results to connect this evolution to the cosmological environment that AGNs inhabit. Exploring this connection will be crucial to understanding the triggering mechanisms of AGNs and how these processes manifest in observations at all wavelengths. In anticipation of upcoming wide-field X-ray surveys that will allow quantitative analysis of AGN environments, this paper presents a method to observationally constrain the Conditional Luminosity Function (CLF) of AGNs at a specific $z$. Once measured, the CLF allows the calculation of the AGN bias, mean dark matter halo mass, AGN lifetime, halo occupation number, and AGN correlation function -- all as a function of luminosity. The CLF can be constrained using a measurement of the X-ray luminosity function and the correlation length at different luminosities. The method ...

  8. Formation of Turbulent Cones in Accretion Disk Outflows and Application to Broad Line Regions of Active Galactic Nuclei

    Poludnenko, A Y; Frank, A

    2002-01-01

    We consider the stability of an accretion disk wind to cloud formation when subject to a central radiation force. For a vertical launch velocity profile that is Keplerian or flatter and the presence of a significant radiation pressure, the wind flow streamlines cross in a conical layer. We argue that such regions are highly unstable, and are natural sites for supersonic turbulence and, consequently, density compressions. We suggest that combined with thermal instability these will all conspire to produce clouds. Such clouds can exist in dynamical equilibrium, constantly dissipating and reforming. As long as there is an inner truncation radius to the wind, our model emerges with a biconical structure similar to that inferred by Elvis (2000) for the broad line region (BLR) of active galactic nuclei (AGN). Our results may also apply to other disk-wind systems.

  9. A search for pair halos around active galactic nuclei through a temporal analysis of Fermi-LAT data

    Prokhorov, D A

    2015-01-01

    We develop a method to search for pair halos around active galactic nuclei (AGN) through a temporal analysis of gamma-ray data. The basis of our method is an analysis of the spatial distributions of photons coming from AGN flares and from AGN quiescent states and a further comparison of these two spatial distributions. This method can also be used for a reconstruction of a point spread function (PSF). We found no evidence for a pair halo component through this method by applying it to the Fermi-LAT data in the energy bands of 4.5-6, 6-10, and >10 GeV and set upper limits on the fraction of photons attributable to a pair halo component. An illustration of how to reconstruct the PSF of Fermi-LAT is given.

  10. The Intrinsic Eddington Ratio Distribution of Active Galactic Nuclei in Star-forming Galaxies from the Sloan Digital Sky Survey

    Jones, M L; Black, C S; Hainline, K N; DiPompeo, M A; Goulding, A D

    2016-01-01

    An important question in extragalactic astronomy concerns the distribution of black hole accretion rates of active galactic nuclei (AGN). Based on observations at X-ray wavelengths, the observed Eddington ratio distribution appears as a power law, while optical studies have often yielded a lognormal distribution. There is increasing evidence that these observed discrepancies may be due to contamination by star formation and other selection effects. Using a sample of galaxies from the Sloan Digital Sky Survey Data Release 7, we test if an intrinsic Eddington ratio distribution that takes the form of a Schechter function is consistent with previous work that suggests that young galaxies in optical surveys have an observed lognormal Eddington ratio distribution. We simulate the optical emission line properties of a population of galaxies and AGN using a broad instantaneous luminosity distribution described by a Schechter function near the Eddington limit. This simulated AGN population is then compared to observe...

  11. Asymmetry in the Spectrum of High-Velocity H2O Maser Emission Features in Active Galactic Nuclei

    Nesterenok, A V; 10.1134/S1063773710010019

    2010-01-01

    We suggest a mechanism for the amplification of high-velocity water-vapor maser emission features from the central regions of active galactic nuclei. The model of an emitting accretion disk is considered. The high-velocity emission features originate in the right and left wings of the Keplerian disk. The hyperfine splitting of the signal levels leads to an asymmetry in the spectral profile of the water vapor maser line at a frequency of 22.235 GHz. We show that the gain profile asymmetry must lead to an enhanced brightness of the blueshifted high-velocity emission features compared to the redshifted ones. Such a situation is observed in the source UGC 3789.

  12. Search for gamma-ray-emitting active galactic nuclei in the Fermi-LAT unassociated sample using machine learning

    The second Fermi-LAT source catalog (2FGL) is the deepest all-sky survey available in the gamma-ray band. It contains 1873 sources, of which 576 remain unassociated. Machine-learning algorithms can be trained on the gamma-ray properties of known active galactic nuclei (AGNs) to find objects with AGN-like properties in the unassociated sample. This analysis finds 231 high-confidence AGN candidates, with increased robustness provided by intersecting two complementary algorithms. A method to estimate the performance of the classification algorithm is also presented, that takes into account the differences between associated and unassociated gamma-ray sources. Follow-up observations targeting AGN candidates, or studies of multiwavelength archival data, will reduce the number of unassociated gamma-ray sources and contribute to a more complete characterization of the population of gamma-ray emitting AGNs.

  13. Iron Kα Emission Lines in Seyfert(-Like) Active Galactic Nuclei: Revelation of a Rapidly Spinning Central Black Hole

    马振国

    2002-01-01

    Fe Kα lines are superimposed upon the x-ray continuum in most Seyfert(-like) active galactic nuclei (AGNs).By a data-fitting study, previous authors have claimed that the central black hole (BH) is either rotating ornon-rotating according to the thin disc model. We develop the disc model to the torus model to determine thereal spin of the BH. With formulations of the motion of both torus particles and photons near a BH in Kerrmetric, we simulate iron emission linesfrom a thin luminous torus. It is found that only spinning BH galaxiescan radiate observable profiles. The data-fitting to Fe lines of four AGNs observed by ASCA predicts that thecentral BH is spinning rapidly with the dimensionless specific angular momentum approaching the maximalvalueof 1.

  14. A Search for Very High Energy Neutrinos from Active Galactic Nuclei

    Bolesta, J J; Camerini, U; Clem, J; Dye, S T; George, J; Gorham, P W; Grieder, P K F; Hauptman, J M; Hayashino, T; Jaworski, M; Kitamura, T; Kondo, S; Learned, J G; March, R H; Matsumoto, T; Matsuno, S; Mauritz, K M; Minkowski, Peter; Narita, T; O'Connor, D J; Ohashi, Y; Okada, A; Peterson, V; Stenger, Victor J; Uehara, S; Webster, M; Wilkes, R J; Young, K K; Yamaguchi, A

    1997-01-01

    We report the results of a search for neutrino-induced particle cascades using a deep ocean water Cherenkov detector. The effective mass of the detector, a string of seven 40 cm diameter photomultipliers at 5.2 m spacing, is found through simulation analysis to be surprisingly large: greater than 1 megaton of water at incident neutrino energies of 1 PeV. We find no evidence for neutrino-induced cascades in 18.6 hours of observation. Although the limit implied by this observation is the strongest yet for predictions of active galatic nuclei (AGN) neutrinos at energies above 100 TeV, perhaps the more intriguing result is that the power of these techniques can be exploited to test these AGN models in a relatively short time.

  15. DISCOVERY OF CANDIDATE H2O DISK MASERS IN ACTIVE GALACTIC NUCLEI AND ESTIMATIONS OF CENTRIPETAL ACCELERATIONS

    Based on spectroscopic signatures, about one-third of known H2O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These 'disk maser candidates' are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v sys -1). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s-1. Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) x107 M sun) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s-1 sys -1), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ∼0.1-1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGNs and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.

  16. The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements. II. The Full Sample of Reverberation-Mapped AGNs

    Bentz, Misty C.; Peterson, Bradley M.; Netzer, Hagai; Pogge, Richard W.; Vestergaard, Marianne

    2009-01-01

    We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to...

  17. Optical counterparts of undetermined type $\\gamma$-ray Active Galactic Nuclei with blazar-like Spectral Energy Distributions

    La Mura, G; Ciroi, S; Rafanelli, P; Salvetti, D; Berton, M; Cracco, V

    2015-01-01

    During its first four years of scientific observations, the Fermi Large Area Telescope (Fermi-LAT) detected 3033 $\\gamma$-ray sources above a 4$\\sigma$ significance level. Although most of the extra-Galactic sources are active galactic nuclei (AGN) of the blazar class, other families of AGNs are observed too, while a still high fraction of detections ($\\sim 30\\%$) remains with uncertain association or classification. According to the currently accepted interpretation, the AGN $\\gamma$-ray emission arises from inverse Compton (IC) scattering of low energy photons by relativistic particles confined in a jet that, in the case of blazars, is oriented very close to our line of sight. Taking advantage of data from radio and X-ray wavelengths, which we expect to be produced together with $\\gamma$-rays, providing a much better source localization potential, we focused our attention on a sample of $\\gamma$-ray Blazar Candidates of Undetermined Type (BCUs), starting a campaign of optical spectroscopic observations. The...

  18. POSSIBLE ORIGIN OF RADIO EMISSION FROM NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS FOR LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

    Liu, Hu; Wu, Qingwen, E-mail: qwwu@hust.edu.cn [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2013-02-10

    The two components of radio emission, above and below 86 GHz, respectively, from the Galactic center source Sgr A* can be naturally explained by the hybrid of thermal and nonthermal electrons in hot accretion flows (e.g., radiatively inefficient accretion flow; RIAF). We further apply this model to a sample of nearby low-luminosity active galactic nuclei (LLAGNs), which are also believed to be powered by RIAF. We selected LLAGNs with only compact radio cores according to high-resolution radio observations, and sources observed with jets or jet-like features are excluded. We find that the radio emission of LLAGNs is severely underpredicted by the pure RIAF model, but can be naturally explained by the RIAF model with a hybrid electron population consisting of both thermal and nonthermal particles. Our model can roughly reproduce the observed anticorrelation between the mass-corrected radio loudness and Eddington ratio for the LLAGNs in our sample. We further model the spectral energy distributions of each source in our sample and find that roughly all sources can be well fitted if a small fraction of the steady-state electron energy is ejected into the nonthermal electrons. The size of the radio emission region of our model is around several thousands of gravitational radii, which is also roughly consistent with recent high-resolution VLBI observations for some nearby LLAGNs.

  19. XMM-Newton Survey of Local O VII Absorption Lines in the Spectra of Active Galactic Nuclei

    Fang, Taotao; Bullock, James S; Ma, Renyi

    2015-01-01

    Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of background active galactic nuclei (AGNs) provide an effective method to probe the hot ($T\\sim10^6$ K) gas and its metal content in and around the Milky Way. We present an all-sky survey of the $K_{\\alpha}$ transition of the local O VII absorption lines obtained by Voigt-profile fitting archival XMM-Newton observations. A total of 43 AGNs were selected, among which 12 are BL Lac-type AGNs, and the rest are Seyfert 1 galaxies. At above the $3\\sigma$ level the local O VII absorption lines were detected in 21 AGNs, among which 7 were newly discovered in this work. The sky covering fraction, defined as the ratio between the number of detections and the sample size, increases from at about 40% for all targets to 100% for the brightest targets, suggesting a uniform distribution of the O VII absorbers. We correlate the line equivalent width with the Galactic coordinates and do not find any strong correlations between these quantities. Some AG...

  20. SPECTRAL ENERGY DISTRIBUTIONS OF TYPE 1 ACTIVE GALACTIC NUCLEI IN THE COSMOS SURVEY. I. THE XMM-COSMOS SAMPLE

    The 'Cosmic Evolution Survey' (COSMOS) enables the study of the spectral energy distributions (SEDs) of active galactic nuclei (AGNs) because of the deep coverage and rich sampling of frequencies from X-ray to radio. Here we present an SED catalog of 413 X-ray (XMM-Newton)-selected type 1 (emission line FWHM > 2000 km s–1) AGNs with Magellan, SDSS, or VLT spectrum. The SEDs are corrected for Galactic extinction, broad emission line contributions, constrained variability, and host galaxy contribution. We present the mean SED and the dispersion SEDs after the above corrections in the rest-frame 1.4 GHz to 40 keV, and show examples of the variety of SEDs encountered. In the near-infrared to optical (rest frame ∼8 μm-4000 Å), the photometry is complete for the whole sample and the mean SED is derived from detections only. Reddening and host galaxy contamination could account for a large fraction of the observed SED variety. The SEDs are all available online.

  1. LUMINOUS X-RAY ACTIVE GALACTIC NUCLEI IN CLUSTERS OF GALAXIES

    We present a study of X-ray active galactic nucleus (AGN) overdensities in 16 Abell clusters, within the redshift range 0.073 x ≥ 1042 erg s-1 (at the redshift of the clusters) and within an area of 1 h -172 Mpc radius (excluding the core). To investigate the presence or absence of a true enhancement of luminous X-ray AGNs in the cluster area, we also derived the corresponding optical galaxy overdensities, using a suitable range of r-band magnitudes. We always find the latter to be significantly higher (and only in two cases roughly equal) with respect to the corresponding X-ray overdensities. Over the whole cluster sample, the mean X-ray point-source overdensity is a factor of ∼4 less than that corresponding to bright optical galaxies, a difference which is significant at a >0.995 level, as indicated by an appropriate student's t-test. We conclude that the triggering of luminous X-ray AGNs in rich clusters is strongly suppressed. Furthermore, searching for optical Sloan Digital Sky Survey counterparts of all the X-ray sources, associated with our clusters, we found that about half appear to be background QSOs, while others are background and foreground AGNs or stars. The true overdensity of X-ray point sources, associated with the clusters, is therefore even smaller than what our statistical approach revealed.

  2. On the Scatter in the Radius - Luminosity Relationship for Active Galactic Nuclei

    Eser, E Kilerci; Peterson, B M; Denney, K D; Bentz, M C

    2014-01-01

    We investigate and quantify the observed scatter in the empirical relationship between the broad line region size R and the luminosity of the active galactic nucleus (AGN), in order to better understand its origin. This study is motivated by the indispensable role of this relationship in the mass estimation of cosmologically distant black holes, but may also be relevant to the recently proposed application of this relationship for measuring cosmic distances. We study six nearby reverberation-mapped AGN for which simultaneous UV and optical monitoring data exist. We also examine the long-term optical luminosity variations of Seyfert 1 galaxy NGC 5548 and employ Monte Carlo simulations to study the effects of the intrinsic variability of individual objects on the scatter in the global relationship for a sample of ~40 AGN. We find the scatter in this relationship has a correctable dependence on color. For individual AGN, the size of the Hbeta emitting region has a steeper dependence on the nuclear optical lumino...

  3. NGC5252: a pair of radio-emitting active galactic nuclei?

    Yang, Xiaolong; Paragi, Zsolt; Liu, Xiang; An, Tao; Bianchi, Stefano; Ho, Luis C; Cui, Lang; Zhao, Wei; Wu, Xiaocong

    2016-01-01

    The X-ray source CXO J133815.6+043255 has counterparts in the UV, optical, and radio bands. Based on the multi-band investigations, it has been recently proposed by Kim et al. (2015) as a rarely-seen off-nucleus ultraluminous X-ray (ULX) source with a black hole mass of >= 10^4 solar mass in the nearby Seyfert galaxy NGC 5252. To explore its radio properties at very high angular resolution, we performed very long-baseline interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.7 GHz. We find that the radio counterpart is remarkably compact among the known ULXs. It does not show a resolved structure with a resolution of a few milliarcsecond (mas), and the total recovered flux density is comparable to that measured in earlier sub-arcsecond-resolution images. The compact radio structure, the relatively flat spectrum, and the high radio luminosity are consistent with a weakly accreting supermassive black hole in a low-luminosity active galactic nucleus. The nucleus of NGC 5252 itself has simi...

  4. Clumpy tori around type II active galactic nuclei as revealed by X-ray fluorescent lines

    Liu, Jiren; Liu, Yuan; Li, Xiaobo; Xu, Weiwei; Gou, Lijun; Cheng, Cheng

    2016-06-01

    The reflection spectrum of a torus around an active galactic nucleus (AGN) is characterized by X-ray fluorescent lines, which are most prominent for type II AGNs. A clumpy torus allows photons reflected from the back-side of the torus to leak through the front regions that are free of obscuration. The observed X-ray fluorescent lines are therefore sensitive to the clumpiness of the torus. We analysed a sample of type II AGNs observed with the Chandra High Energy Transmission Grating Spectrometer (HETGS), and measured the fluxes for the Si Kα and Fe Kα lines. The measured Fe Kα/Si Kα ratios, spanning a range between 5 and 60, are far smaller than the ratios predicted from simulations of smooth tori, indicating that the tori of the studied sources have clumpy distributions rather than smooth ones. We compared the measured Fe Kα/Si Kα ratios with simulation results of clumpy tori. The Circinus galaxy has a Fe Kα/Si Kα ratio of ˜60, which is close to the simulation results for N = 5, where N is the average number of clumps along the line of sight. The Fe Kα/Si Kα ratios of the other sources are all below the simulation results for N = 2. Overall, this shows that the non-Fe fluorescent lines in the soft X-ray band are a potentially powerful probe of the clumpiness of tori around AGNs.

  5. The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei

    Bentz, Misty C; Grier, Catherine J; Barth, Aaron J; Peterson, Bradley M; Vestergaard, Marianne; Bennert, Vardha N; Canalizo, Gabriela; De Rosa, Gisella; Filippenko, Alexei V; Gates, Elinor L; Greene, Jenny E; Li, Weidong; Malkan, Matthew A; Pogge, Richard W; Stern, Daniel; Treu, Tommaso; Woo, Jong-Hak

    2013-01-01

    We present an updated and revised analysis of the relationship between the Hbeta broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of 9 new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create "AGN-free" images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the Hbeta time lag, which is assumed to yield the average Hbeta BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the R-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of alpha = 0.533 (+0.035/-0.033), consistent ...

  6. An X-ray spectral model for clumpy tori in active galactic nuclei

    Liu, Yuan

    2014-01-01

    We construct an X-ray spectral model for the clumpy torus in an active galactic nucleus (AGN) using Geant4, which includes the physical processes of the photoelectric effect, Compton scattering, Rayleigh scattering, $\\gamma$ conversion, fluorescence line, and Auger process. Since the electrons in the torus are expected to be bounded instead of free, the deviation of the scattering cross section from the Klein-Nishina cross section has also been included, which changes the X-ray spectra by up to 25% below $10$ keV. We have investigated the effect of the clumpiness parameters on the reflection spectra and the strength of the fluorescent line Fe K$\\alpha$. The volume filling factor of the clouds in the clumpy torus only slightly influences the reflection spectra, however, the total column density and the number of clouds along the line of sight significantly change the shapes and amplitudes of the reflection spectra. The effect of column density is similar to the case of a smooth torus, while a small number of c...

  7. Hubble Space Telescope Spectroscopic Observations of the Narrow-Line Region in Nearby Low-Luminosity Active Galactic Nuclei

    Walsh, Jonelle L; Ho, Luis C; Filippenko, Alexei V; Rix, Hans-Walter; Shields, Joseph C; Sarzi, Marc; Sargent, Wallace L W

    2008-01-01

    (Abridged) We present STIS observations of 14 nearby low-luminosity active galactic nuclei, including 13 LINERs and 1 Seyfert, taken at multiple parallel slit positions centered on the galaxy nuclei and covering the H-alpha spectral region. For each galaxy, we measure the emission-line velocities, line widths, and strengths, to map out the inner narrow-line region structure. There is a wide diversity among the velocity fields: in a few galaxies the gas is clearly in disk-like rotation, while in other galaxies the gas kinematics appear chaotic or are dominated by radial flows with multiple velocity components. The [S II] line ratio indicates a radial stratification in gas density, with a sharp increase within the inner 10-20 pc, in the majority of the Type 1 objects. We examine how the [N II] 6583 line width varies as a function of aperture size over a range of spatial scales, extending from scales comparable to the black hole's sphere of influence to scales dominated by the host galaxy's bulge. For most galax...

  8. Constraints on Two Active Galactic Nuclei in the Merger Remnant COSMOS J100043.15+020637.2

    Wrobel, J M; Middelberg, E

    2014-01-01

    COSMOS J100043.15+020637.2 is a merger remnant at z = 0.36 with two optical nuclei, NW and SE, offset by 500 mas (2.5 kpc). Prior studies suggest two competing scenarios for these nuclei: (1) SE is an active galactic nucleus (AGN) lost from NW due to a gravitational-wave recoil. (2) NW and SE each contain an AGN, signaling a gravitational-slingshot recoil or inspiralling AGNs. We present new images from the Very Large Array (VLA) at a frequency nu = 9.0 GHz and a FWHM resolution theta = 320 mas (1.6 kpc), and the Very Long Baseline Array (VLBA) at nu = 1.52 GHz and theta = 15 mas (75 pc). The VLA imaging is sensitive to emission driven by AGNs and/or star formation, while the VLBA imaging is sensitive only to AGN-driven emission. No radio emission is detected at these frequencies. Folding in prior results, we find: (a) The properties of SE and its adjacent X-ray feature resemble those of the unobscured AGN in NGC 4151, albeit with a much higher narrow emission-line luminosity. (b) The properties of NW are con...

  9. VARIABILITY AND MULTIWAVELENGTH-DETECTED ACTIVE GALACTIC NUCLEI IN THE GOODS FIELDS

    We identify 85 variable galaxies in the GOODS North and South fields using five epochs of Hubble Space Telescope Advance Camera for Survey V-band (F606W) images spanning 6 months. The variables are identified through significant flux changes in the galaxy's nucleus and represent ∼2% of the survey galaxies. With the aim of studying the active galaxy population in the GOODS fields, we compare the variability-selected sample with X-ray and mid-IR active galactic nucleus (AGN) candidates. Forty-nine percent of the variables are associated with X-ray sources identified in the 2Ms Chandra surveys. Twenty-four percent of X-ray sources likely to be AGNs are optical variables and this percentage increases with decreasing hardness ratio of the X-ray emission. Stacking of the non-X-ray-detected variables reveals marginally significant soft X-ray emission. Forty-eight percent of mid-IR power-law sources are optical variables, all but one of which is also X-ray detected. Thus, about half of the optical variables are associated with either X-ray or mid-IR power-law emission. The slope of the power-law fit through the Spitzer IRAC bands indicates that two-thirds of the variables have BLAGN-like spectral energy distributions. Among those galaxies spectroscopically identified as AGNs, we observe variability in 74% of broad-line AGNs and 15% of NLAGNs. The variables are found in galaxies extending to z∼ 3.6. We compare the variable galaxy colors and magnitudes to the X-ray and mid-IR sample and find that the non-X-ray-detected variable hosts extend to bluer colors and fainter intrinsic magnitudes. The variable AGN candidates have Eddington ratios similar to those of X-ray-selected AGNs.

  10. The typecasting of active galactic nuclei: Mrk 590 no longer fits the role

    Denney, K. D.; De Rosa, G.; Croxall, K.; Gupta, A.; Fausnaugh, M. M.; Grier, C. J.; Martini, P.; Mathur, S.; Peterson, B. M.; Pogge, R. W.; Shappee, B. J. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Bentz, M. C., E-mail: denney@astronomy.ohio-state.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States)

    2014-12-01

    We present multiwavelength observations that trace more than 40 yr in the life of the active galactic nucleus (AGN) in Mrk 590, traditionally known as a classic Seyfert 1 galaxy. From spectra recently obtained from Hubble Space Telescope, Chandra, and the Large Binocular Telescope, we find that the activity in the nucleus of Mrk 590 has diminished so significantly that the continuum luminosity is a factor of 100 lower than the peak luminosity probed by our long-baseline observations. Furthermore, the broad emission lines, once prominent in the UV/optical spectrum, have all but disappeared. Since AGN type is defined by the presence of broad emission lines in the optical spectrum, our observations demonstrate that Mrk 590 has now become a 'changing-look' AGN. If classified by recent optical spectra, Mrk 590 would be a Seyfert ∼1.9–2, where the only broad emission line still visible in the optical spectrum is a weak component of Hα. As an additional consequence of this change, we have definitively detected UV narrow-line components in a Type 1 AGN, allowing an analysis of these emission-line components with high-resolution COS spectra. These observations challenge the historical paradigm that AGN type is only a consequence of the line-of-sight viewing angle toward the nucleus in the presence of a geometrically flattened, obscuring medium (i.e., the torus). Our data instead suggest that the current state of Mrk 590 is a consequence of the change in luminosity, which implies the black hole accretion rate has significantly decreased.

  11. GOODS-HERSCHEL: IMPACT OF ACTIVE GALACTIC NUCLEI AND STAR FORMATION ACTIVITY ON INFRARED SPECTRAL ENERGY DISTRIBUTIONS AT HIGH REDSHIFT

    We explore the effects of active galactic nuclei (AGNs) and star formation activity on the infrared (0.3-1000 μm) spectral energy distributions (SEDs) of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 μm (S 24 ∼> 100 μJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (∼25%) of our sample is dominated by an AGN (>50% of the mid-IR luminosity) in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z ∼ 1 star-forming (SF) sources, z ∼ 2 SF sources, AGNs with clear 9.7 μm silicate absorption, and AGNs with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 μm, we use 95 galaxies with complete spectral coverage to create a composite SED for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (∼20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high-redshift systems. High-redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high-redshift IR luminous galaxies.

  12. THE LOW-LUMINOSITY END OF THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI

    We present an updated and revised analysis of the relationship between the Hβ broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of nine new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create ''AGN-free'' images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the Hβ time lag, which is assumed to yield the average Hβ BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the RBLR-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of α= 0.533+0.035-0.033, consistent with previous work and with simple photoionization arguments. Only two AGNs appear to be outliers from the relationship, but both of them have monitoring light curves that raise doubt regarding the accuracy of their reported time lags. The scatter around the relationship is found to be 0.19 ± 0.02 dex, but would be decreased to 0.13 dex by the removal of these two suspect measurements. A large fraction of the remaining scatter in the relationship is likely due to the inaccurate distances to the AGN host galaxies. Our results help support the possibility that the RBLR-L relationship could potentially be used to turn the BLRs of AGNs into standardizable candles. This would allow the cosmological expansion of the universe to be probed by a separate population of objects, and over a larger range of redshifts.

  13. ON THE DIVERSITY AND COMPLEXITY OF ABSORPTION LINE PROFILES PRODUCED BY OUTFLOWS IN ACTIVE GALACTIC NUCLEI

    Understanding the origin of active galactic nucleus (AGN) absorption line profiles and their diversity could help to explain the physical structure of the accretion flow, and also to assess the impact of accretion on the evolution of the AGN host galaxies. Here, we present our first attempt to systematically address the issue of the origin of the complexities observed in absorption profiles. Using a simple method, we compute absorption line profiles against a continuum point source for several simulations of accretion disk winds. We investigate the geometrical, ionization, and dynamical effects on the absorption line shapes. We find that significant complexity and diversity of the absorption line profile shapes can be produced by the non-monotonic distribution of the wind velocity, density, and ionization state. Non-monotonic distributions of such quantities are present even in steady-state, smooth disk winds, and naturally lead to the formation of multiple and detached absorption troughs. These results demonstrate that the part of a wind where an absorption line is formed is not representative of the entire wind. Thus, the information contained in the absorption line is incomplete if not even insufficient to well estimate gross properties of the wind such as the total mass and energy fluxes. In addition, the highly dynamical nature of certain portions of disk winds can have important effects on the estimates of the wind properties. For example, the mass outflow rates can be off by up to two orders of magnitude with respect to estimates based on a spherically symmetric, homogeneous, constant velocity wind.

  14. Soft X-Ray Excess from Shocked Accreting Plasma in Active Galactic Nuclei

    Fukumura, Keigo; Hendry, Douglas; Clark, Peter; Tombesi, Francesco; Takahashi, Masaaki

    2016-08-01

    We propose a novel theoretical model to describe the physical identity of the soft X-ray excess that is ubiquitously detected in many Seyfert galaxies, by considering a steady-state, axisymmetric plasma accretion within the innermost stable circular orbit around a black hole (BH) accretion disk. We extend our earlier theoretical investigations on general relativistic magnetohydrodynamic accretion, which implied that the accreting plasma can develop into a standing shock under suitable physical conditions, causing the downstream flow to be sufficiently hot due to shock compression. We perform numerical calculations to examine, for sets of fiducial plasma parameters, the physical nature of fast magnetohydrodynamic shocks under strong gravity for different BH spins. We show that thermal seed photons from the standard accretion disk can be effectively Compton up-scattered by the energized sub-relativistic electrons in the hot downstream plasma to produce the soft excess feature in X-rays. As a case study, we construct a three-parameter Comptonization model of inclination angle θ obs, disk photon temperature kT in, and downstream electron energy kT e to calculate the predicted spectra in comparison with a 60 ks XMM-Newton/EPIC-pn spectrum of a typical radio-quiet Seyfert 1 active galactic nucleus, Ark 120. Our χ 2-analyses demonstrate that the model is plausible for successfully describing data for both non-spinning and spinning BHs with derived ranges of 61.3 keV ≲ kT e ≲ 144.3 keV, 21.6 eV ≲ kT in ≲ 34.0 eV, and 17.°5 ≲ θ obs ≲ 42.°6, indicating a compact Comptonizing region of three to four gravitational radii that resembles the putative X-ray coronae.

  15. THE LOW-LUMINOSITY END OF THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI

    Bentz, Misty C. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Denney, Kelly D.; Vestergaard, Marianne [Dark Cosmology Center, Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Grier, Catherine J.; Peterson, Bradley M.; De Rosa, Gisella; Pogge, Richard W. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Barth, Aaron J. [Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States); Bennert, Vardha N. [Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407 (United States); Canalizo, Gabriela [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Filippenko, Alexei V.; Li Weidong [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Gates, Elinor L. [University of California Observatories/Lick Observatory, P.O. Box 85, Mount Hamilton, CA 95140 (United States); Greene, Jenny E. [Department of Astrophysical Sciences, Princeton University, Peyton Hall - Ivy Lane, Princeton, NJ 08544 (United States); Malkan, Matthew A. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Treu, Tommaso [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Woo, Jong-Hak, E-mail: bentz@chara.gsu.edu [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul (Korea, Republic of)

    2013-04-20

    We present an updated and revised analysis of the relationship between the H{beta} broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of nine new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create ''AGN-free'' images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the H{beta} time lag, which is assumed to yield the average H{beta} BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the R{sub BLR}-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of {alpha}= 0.533{sup +0.035}{sub -0.033}, consistent with previous work and with simple photoionization arguments. Only two AGNs appear to be outliers from the relationship, but both of them have monitoring light curves that raise doubt regarding the accuracy of their reported time lags. The scatter around the relationship is found to be 0.19 {+-} 0.02 dex, but would be decreased to 0.13 dex by the removal of these two suspect measurements. A large fraction of the remaining scatter in the relationship is likely due to the inaccurate distances to the AGN host galaxies. Our results help support the possibility that the R{sub BLR}-L relationship could potentially be used to turn the BLRs of AGNs into standardizable candles. This would allow the cosmological expansion of the universe to be probed by a separate population of objects, and over a larger range of redshifts.

  16. Iron Opacity Bump Changes the Stability and Structure of Accretion Disks in Active Galactic Nuclei

    Jiang, Yan-Fei; Davis, Shane W.; Stone, James M.

    2016-08-01

    Accretion disks around supermassive black holes have regions where the Rosseland mean opacity can be larger than the electron scattering opacity due to the large number of bound–bound transitions in iron. We study the effects of this iron opacity “bump” on the thermal stability and vertical structure of radiation-pressure-dominated accretion disks, utilizing three-dimensional radiation magnetohydrodynamic (MHD) simulations in the local shearing box approximation. The simulations self-consistently calculate the heating due to MHD turbulence caused by magneto-rotational instability and radiative cooling by using the radiative transfer module based on a variable Eddington tensor in Athena. For a 5 × 108 solar mass black hole with ˜3% of the Eddington luminosity, a model including the iron opacity bump maintains its structure for more than 10 thermal times without showing significant signs of thermal runaway. In contrast, if only electron scattering and free–free opacity are included as in the standard thin disk model, the disk collapses on the thermal timescale. The difference is caused by a combination of (1) an anti-correlation between the total optical depth and the midplane pressure, and (2) enhanced vertical advective energy transport. These results suggest that the iron opacity bump may have a strong impact on the stability and structure of active galactic nucleus (AGN) accretion disks, and may contribute to a dependence of AGN properties on metallicity. Since this opacity is relevant primarily in UV emitting regions of the flow, it may help to explain discrepancies between observation and theory that are unique to AGNs.

  17. An X-ray spectral model for clumpy tori in active galactic nuclei

    Liu, Yuan; Li, Xiaobo, E-mail: liuyuan@ihep.ac.cn, E-mail: lixb@ihep.ac.cn [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918-3, Beijing 100049 (China)

    2014-05-20

    We construct an X-ray spectral model for the clumpy torus in an active galactic nucleus (AGN) using Geant4, which includes the physical processes of the photoelectric effect, Compton scattering, Rayleigh scattering, γ conversion, fluorescence line, and Auger process. Since the electrons in the torus are expected to be bounded instead of free, the deviation of the scattering cross section from the Klein-Nishina cross section has also been included, which changes the X-ray spectra by up to 25% below 10 keV. We have investigated the effect of the clumpiness parameters on the reflection spectra and the strength of the fluorescent line Fe Kα. The volume filling factor of the clouds in the clumpy torus only slightly influences the reflection spectra, however, the total column density and the number of clouds along the line of sight significantly change the shapes and amplitudes of the reflection spectra. The effect of column density is similar to the case of a smooth torus, while a small number of clouds along the line of sight will smooth out the anisotropy of the reflection spectra and the fluorescent line Fe Kα. The smoothing effect is mild in the low column density case (N {sub H} = 10{sup 23} cm{sup –2}), whereas it is much more evident in the high column density case (N {sub H} = 10{sup 25} cm{sup –2}). Our model provides a quantitative tool for the spectral analysis of the clumpy torus. We suggest that the joint fits of the broad band spectral energy distributions of AGNs (from X-ray to infrared) should better constrain the structure of the torus.

  18. KILOPARSEC-SCALE SPATIAL OFFSETS IN DOUBLE-PEAKED NARROW-LINE ACTIVE GALACTIC NUCLEI. I. MARKERS FOR SELECTION OF COMPELLING DUAL ACTIVE GALACTIC NUCLEUS CANDIDATES

    Merger-remnant galaxies with kiloparsec (kpc) scale separation dual active galactic nuclei (AGNs) should be widespread as a consequence of galaxy mergers and triggered gas accretion onto supermassive black holes, yet very few dual AGNs have been observed. Galaxies with double-peaked narrow AGN emission lines in the Sloan Digital Sky Survey (SDSS) are plausible dual AGN candidates, but their double-peaked profiles could also be the result of gas kinematics or AGN-driven outflows and jets on small or large scales. To help distinguish between these scenarios, we have obtained spatial profiles of the AGN emission via follow-up long-slit spectroscopy of 81 double-peaked narrow-line AGNs in SDSS at 0.03 ≤ z ≤ 0.36 using Lick, Palomar, and MMT Observatories. We find that all 81 systems exhibit double AGN emission components with ∼kpc projected spatial separations on the sky (0.2 h–170 kpc –170 kpc; median Δx = 1.1 h–170 kpc), which suggests that they are produced by kiloparsec-scale dual AGNs or kiloparsec-scale outflows, jets, or rotating gaseous disks. Further, the objects split into two subpopulations based on the spatial extent of the double emission components and the correlation between projected spatial separations and line-of-sight velocity separations. These results suggest that the subsample (58+5–6%) of the objects with spatially compact emission components may be preferentially produced by dual AGNs, while the subsample (42+6–5%) with spatially extended emission components may be preferentially produced by AGN outflows. We also find that for 32+8–6% of the sample the two AGN emission components are preferentially aligned with the host galaxy major axis, as expected for dual AGNs orbiting in the host galaxy potential. Our results both narrow the list of possible physical mechanisms producing the double AGN components, and suggest several observational criteria for selecting the most promising dual AGN candidates from the full sample of double

  19. SPITZER MID-INFRARED SPECTROSCOPY OF COMPACT SYMMETRIC OBJECTS: WHAT POWERS RADIO-LOUD ACTIVE GALACTIC NUCLEI?

    We present low- and high-resolution mid-infrared (mid-IR) spectra and photometry for eight compact symmetric objects (CSOs) taken with the Infrared Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful radio galaxies show significant diversity in their mid-IR spectra. This includes multiple atomic fine-structure lines, H2 gas, polycyclic aromatic hydrocarbon (PAH) emission, warm dust from T = 50to150 K, and silicate features in both emission and absorption. There is no evidence in the mid-IR of a single template for CSO hosts, but 5/8 galaxies show similar moderate levels of star formation (sun yr-1 from PAH emission) and silicate dust in a clumpy torus. The total amount of extinction ranges from AV ∼ 10to30, and the high-ionization [Ne V] 14.3 and 24.3 μm transitions are not detected for any galaxy in the sample. Almost all CSOs show contributions both from star formation and active galactic nuclei (AGNs), suggesting that they occupy a continuum between pure starbursts and AGNs. This is consistent with the hypothesis that radio galaxies are created following a galactic merger; the timing of the radio activity onset means that contributions to the IR luminosity from both merger-induced star formation and the central AGN are likely. Bondi accretion is capable of powering the radio jets for almost all CSOs in the sample; the lack of [Ne V] emission suggests an advection-dominated accretion flow mode as a possible candidate. Merging black holes (BHs) with MBH > 108 Msun likely exist in all of the CSOs in the sample; however, there is no direct evidence from these data that BH spin energy is being tapped as an alternative mode for powering the radio jets.

  20. The Discovery of X-ray Emission from Active Galactic Nuclei

    Elvis, Martin

    2013-01-01

    Back in 1974 the UHURU catalog (3U) had been published with many UHGLS - unidentified high galactic latitude sources. Identifications were hampered by the square degree sized error boxes (positional uncertainties). Could these explain the cosmic X-ray background? Could UHGLS be "X-ray galaxies"? Only three active galaxies (AGNs) had been found as X-ray sources: 3C273, Cen A and NGC 4151, while others had upper limits. What was the difference between X-ray and non-X-ray AGNs? It turned out that the slightly better positioning capability and slightly deeper sensitivity of the Ariel V Sky Survey Instrument (SSI), launched in October 1974, were just enough to show that the UHGLS were Seyfert galaxies. And I was lucky enough that I'd joined the Leicester X-ray group and had taken on the UHGLS for my PhD thesis, with Ken Pounds as my supervisor. With the SSI we made a catalog of high latitude sources, the "2A" catalog, including about a dozen known Seyfert galaxies (lowish luminosity nearby AGNs) and, with Mike Penston and Martin Ward, we went on to identify many of them with both newly discovered normal broad emission line AGNs and a few new "narrow emission line galaxies", or NELGs, as we called them. We are now convinced that it is summation of many obscured NELGs that produce the flat spectrum of the X-ray background, and we are still searching for them in Chandra deep surveys and at higher energies with NuSTAR. There was an obvious connection between the X-ray obscuration and the optical reddening, which must lie outside the region emitting the broad optical spectral lines. Andy Lawrence and I, following a clue from Bill Keel, put this together into what we now call the Unified Scheme for AGN structure. This idea of a flattened torus obscuring the inner regions of the AGN was so dramatically confirmed a few years later -- by Ski Antonucci and Joe Miller's discovery of polarized broad emission lines in NGC1068 -- that the precursor papers became irrelevant. But Ariel

  1. X-ray Surface Brightness Profiles of Active Galactic Nuclei in the Extended Groth Strip: Implications for AGN Feedback

    Chatterjee, Suchetana; Jeltema, Tesla; Myers, Adam D; Aird, James; Coil, Alison L; Cooper, Michael; Finoguenov, Alexis; Laird, Elise; Montero-Dorta, Antonio; Nandra, Kripal; Willmer, Christopher; Yan, Renbin

    2013-01-01

    Using data from the All Wavelength Extended Groth Strip International Survey (AEGIS) we statistically detect the extended X-ray emission in the interstellar medium (ISM) in both active and normal galaxies at 0.3 < z < 1.3 at a scale of 40-60 kpc. We study the effect of feedback from active galactic nuclei (AGN) on the diffuse interstellar gas by comparing the stacked X-ray surface brightness profiles of active and normal galaxies in the same redshift range with identical properties in optical color--magnitude space. In accordance with theoretical studies we detect a slight deficit (< 1.5 \\sigma) of X-ray photons when averaged over a scale of 0-30 kpc in the profile of AGN host galaxies at 0.3 < z < 0.7. The equivalent flux deficit is (1.25 +/- 0.75) X 10^(-19) ergs/s/cm^(-2). When averaged over a scale of 30-60 kpc, beyond the PSF scales of our AGN sources, we observe a (~ 2 \\sigma) photon excess in the profile of the AGN host galaxies with an equivalent flux excess of (1.1 +/- 0.5) X 10^{-19} ...

  2. SUZAKU VIEW OF THE SWIFT/BAT ACTIVE GALACTIC NUCLEI. III. APPLICATION OF NUMERICAL TORUS MODELS TO TWO NEARLY COMPTON THICK ACTIVE GALACTIC NUCLEI (NGC 612 AND NGC 3081)

    The broadband spectra of two Swift/BAT active galactic nuclei (AGNs) obtained from Suzaku follow-up observations are studied: NGC 612 and NGC 3081. Fitting with standard models, we find that both sources show similar spectra characterized by heavy absorption with NH ≅ 1024 cm-2, and the fraction of scattered light is fscat = 0.5%-0.8%, and the solid angle of the reflection component is Ω/2π = 0.4-1.1. To investigate the geometry of the torus, we apply numerical spectral models utilizing Monte Carlo simulations by Ikeda et al. to the Suzaku spectra. We find that our data are well explained by this torus model, which has four geometrical parameters. The fit results suggest that NGC 612 has a torus half-opening angle of ≅60 deg. - 70 deg. and is observed from a nearly edge-on angle with a small amount of scattering gas, while NGC 3081 has a very small opening angle of ≅15 deg. and is observed on a face-on geometry, more like the deeply buried 'new type' AGNs found by Ueda et al. We demonstrate the potential power of direct application of such numerical simulations to high-quality broadband spectra to unveil the inner structure of AGNs.

  3. THE LONGEST TIMESCALE X-RAY VARIABILITY REVEALS EVIDENCE FOR ACTIVE GALACTIC NUCLEI IN THE HIGH ACCRETION STATE

    The All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer has continuously monitored a number of active galactic nuclei (AGNs) with similar sampling rates for 14 years, from 1996 January to 2009 December. Utilizing the archival ASM data of 27 AGNs, we calculate the normalized excess variances of the 300-day binned X-ray light curves on the longest timescale (between 300 days and 14 years) explored so far. The observed variance appears to be independent of AGN black-hole mass and bolometric luminosity. According to the scaling relation of black-hole mass (and bolometric luminosity) from galactic black hole X-ray binaries (GBHs) to AGNs, the break timescales that correspond to the break frequencies detected in the power spectral density (PSD) of our AGNs are larger than the binsize (300 days) of the ASM light curves. As a result, the singly broken power-law (soft-state) PSD predicts the variance to be independent of mass and luminosity. Nevertheless, the doubly broken power-law (hard-state) PSD predicts, with the widely accepted ratio of the two break frequencies, that the variance increases with increasing mass and decreases with increasing luminosity. Therefore, the independence of the observed variance on mass and luminosity suggests that AGNs should have soft-state PSDs. Taking into account the scaling of the break timescale with mass and luminosity synchronously, the observed variances are also more consistent with the soft-state than the hard-state PSD predictions. With the averaged variance of AGNs and the soft-state PSD assumption, we obtain a universal PSD amplitude of 0.030 ± 0.022. By analogy with the GBH PSDs in the high/soft state, the longest timescale variability supports the standpoint that AGNs are scaled-up GBHs in the high accretion state, as already implied by the direct PSD analysis.

  4. Supermassive black holes with high accretion rates in active galactic nuclei. II. The most luminous standard candles in the universe

    This is the second in a series of papers reporting on a large reverberation mapping (RM) campaign to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). The goal is to identify super-Eddington accreting massive black holes (SEAMBHs) and to use their unique properties to construct a new method for measuring cosmological distances. Based on theoretical models, the saturated bolometric luminosity of such sources is proportional to the BH mass, which can be used to obtain their distance. Here we report on five new RM measurements and show that in four of the cases, we can measure the BH mass and three of these sources are SEAMBHs. Together with the three sources from our earlier work, we now have six new sources of this type. We use a novel method based on a minimal radiation efficiency to identify nine additional SEAMBHs from earlier RM-based mass measurements. We use a Bayesian analysis to determine the parameters of the new distance expression and the method uncertainties from the observed properties of the objects in the sample. The ratio of the newly measured distances to the standard cosmological ones has a mean scatter of 0.14 dex, indicating that SEAMBHs can be use as cosmological distance probes. With their high luminosity, long period of activity, and large numbers at high redshifts, SEAMBHs have a potential to extend the cosmic distance ladder beyond the range now explored by Type Ia supernovae.

  5. Inefficient Driving of Bulk Turbulence by Active Galactic Nuclei in a Hydrodynamic Model of the Intracluster Medium

    Reynolds, Christopher S; Schekochihin, Alexander A

    2015-01-01

    Central jetted active galactic nuclei (AGN) appear to heat the core regions of the intracluster medium (ICM) in cooling-core galaxy clusters and groups, thereby preventing a cooling catastrophe. However, the physical mechanism(s) by which the directed flow of kinetic energy is thermalized throughout the ICM core remains unclear. We examine one widely discussed mechanism whereby the AGN induces subsonic turbulence in the ambient medium, the dissipation of which provides the ICM heat source. Through controlled inviscid 3-d hydrodynamic simulations, we verify that explosive AGN-like events can launch gravity waves (g-modes) into the ambient ICM which in turn decay to volume-filling turbulence. In our model, however, this process is found to be inefficient, with less than 1% of the energy injected by the AGN activity actually ending up in the turbulence of the ambient ICM. This efficiency is an order of magnitude or more too small to explain the observations of AGN-feedback in galaxy clusters and groups with shor...

  6. X-ray spectra and time variability of active galactic nuclei

    Mushotzky, Richard F.; Done, Christine; Pounds, Kenneth A.

    1993-01-01

    The history and the present status of X-ray observations of AGN are outlined with reference to Seyfert Is, Seyfert IIs, and quasars. Fe K emission lines, other distortions at E greater tha 6 keV, excess emission below 2 keV, absorption, and ionized material are discussed. The continuum flux variability and line variability in Seyfert Is and the continuum variability in Seyfert IIs are examined. Models and theories of the continuum are reviewed, and the total energy budget of AGN and their similarity to Galactic black holes are also discussed.

  7. Chandra and MMT observations of low-mass black hole active galactic nuclei accreting at low rates in dwarf galaxies

    We report on Chandra X-ray observations of four candidate low-mass black hole (M bh ≲ 106 M ☉) active galactic nuclei (AGNs) that have the estimated Eddington ratios among the lowest (∼10–2) found for this class. The aims are to validate the nature of their AGNs and to confirm the low Eddington ratios that are derived from the broad Hα line, and to explore this poorly studied regime in the AGN parameter space. Among them, two objects with the lowest significance of the broad lines are also observed with the Multi-Mirror Telescope, and the high-quality optical spectra taken confirm them as Seyfert 1 AGNs and as having small black hole masses. X-ray emission is detected from the nuclei of two of the galaxies, which is variable on timescales of ∼103 s, whereas no significant (or only marginal at best) detection is found for the remaining two. The X-ray luminosities are on the order of 1041 erg s–1 or even lower, on the order of 1040 erg s–1 for non-detections, which are among the lowest regimes ever probed for Seyfert galaxies. The low X-ray luminosities, compared to their black hole masses derived from Hα, confirm their low accretion rates assuming typical bolometric corrections. Our results hint at the existence of a possibly large population of under-luminous low-mass black holes in the local universe. An off-nucleus ultra-luminous X-ray source in one of the dwarf galaxies is detected serendipitously, with a luminosity (6-9)× 1039 erg s–1 in 2-10 keV.

  8. Constraints on two active galactic nuclei in the merger remnant cosmos J100043.15+020637.2

    COSMOS J100043.15+020637.2 is a merger remnant at z = 0.36 with two optical nuclei, NW and SE, offset by 500 mas (2.5 kpc). Prior studies suggest two competing scenarios for these nuclei: (1) SE is an active galactic nucleus (AGN) lost from NW due to a gravitational-wave recoil. (2) NW and SE each contain an AGN, signaling a gravitational-slingshot recoil or inspiralling AGNs. We present new images from the Very Large Array (VLA) at a frequency ν = 9.0 GHz and a FWHM resolution θ = 320 mas (1.6 kpc), and the Very Long Baseline Array (VLBA) at ν = 1.52 GHz and θ = 15 mas (75 pc). The VLA imaging is sensitive to emission driven by AGNs and/or star formation, while the VLBA imaging is sensitive only to AGN-driven emission. No radio emission is detected at these frequencies. Folding in prior results, we find: (a) The properties of SE and its adjacent X-ray feature resemble those of the Type 1 AGN in NGC 4151, albeit with a much higher narrow emission-line luminosity. (b) The properties of NW are consistent with it hosting a Compton-thick AGN that warms ambient dust, photoionizes narrow emission-line gas, and is free-free absorbed by that gas. Finding (a) is consistent with scenarios (a) and (b). Finding (b) weakens the case for scenario (a) and strengthens the case for scenario (b). Follow-up observations are suggested.

  9. Unification of Active Galactic Nuclei at X-rays and soft gamma-rays

    Through the work on X-ray and gamma-ray data of AGN I contributed significantly to the progress in the unification of AGN since I finished my PhD in 2000. The study of the evolutionary behaviour of X-ray selected N blazars (Beckmann and Wolter 2001; Beckmann et al. 2002, 2003b; Beckmann 2003) shows that their evolution is not as strongly negative as indicated by previous studies. The overall luminosity function is consistent with no evolution in the 0.1-2.4 keV band as seen by ROSAT/PSPC. There is still a difference compared to the luminosity function of FSRQ and LBL, which seem to show a positive evolution, indicating that they have been more luminous and/or numerous at cosmological distances. We indicated a scenario in order to explain this discrepancy, in which the high luminous FSRQ develop into the fainter LBL and finally into the BL Lac objects with high frequency peaks in their spectral energy distribution but overall low bolometric luminosity. Studying the variability pattern of hard X-ray selected Seyfert galaxies, we actually found differences between type 1 and type 2 objects, in the sense that type 2 seemed to be more variable (Beckmann et al. 2007a). This breaking of the unified model is caused by the different average luminosity of the absorbed and unabsorbed sources, as discussed in Sect. 4.7.3. This can be explained by a larger inner disk radius when the AGN core is most active (the so-called receding disc model). The work on the sample characteristics of hard X-ray detected AGN also led to the proof that the average intrinsic spectra of type 1 and type 2 objects are the same when reflection processes are taken into account (Beckmann et al. 2009d). This also explains why in the past Seyfert 2 objects were seen to have harder X-ray spectra than Seyfert 1, as the stronger reflection hump in the type 2 objects makes the spectra appear to be flatter, although the underlying continuum is the same. Further strong evidence for the unification scheme comes

  10. The Intrinsic Eddington Ratio Distribution of Active Galactic Nuclei in Star-forming Galaxies from the Sloan Digital Sky Survey

    Jones, Mackenzie L.; Hickox, Ryan C.; Black, Christine S.; Hainline, Kevin N.; DiPompeo, Michael A.; Goulding, Andy D.

    2016-07-01

    An important question in extragalactic astronomy concerns the distribution of black hole accretion rates of active galactic nuclei (AGNs). Based on observations at X-ray wavelengths, the observed Eddington ratio distribution appears as a power law, while optical studies have often yielded a lognormal distribution. There is increasing evidence that these observed discrepancies may be due to contamination by star formation and other selection effects. Using a sample of galaxies from the Sloan Digital Sky Survey Data Release 7, we test whether or not an intrinsic Eddington ratio distribution that takes the form of a Schechter function is consistent with previous work suggesting that young galaxies in optical surveys have an observed lognormal Eddington ratio distribution. We simulate the optical emission line properties of a population of galaxies and AGNs using a broad, instantaneous luminosity distribution described by a Schechter function near the Eddington limit. This simulated AGN population is then compared to observed galaxies via their positions on an emission line excitation diagram and Eddington ratio distributions. We present an improved method for extracting the AGN distribution using BPT diagnostics that allows us to probe over one order of magnitude lower in Eddington ratio, counteracting the effects of dilution by star formation. We conclude that for optically selected AGNs in young galaxies, the intrinsic Eddington ratio distribution is consistent with a possibly universal, broad power law with an exponential cutoff, as this distribution is observed in old, optically selected galaxies and X-rays.

  11. Active galactic nuclei at z~1.5: II. Black Hole Mass estimation by means of broad emission lines

    Mejía-Restrepo, Julián E; Lira, Paulina; Netzer, Hagai; Capellupo, Daniel M

    2016-01-01

    This is the second in a series of papers aiming to test how the mass ($M_{\\rm BH}$), accretion rate ($\\dot{M}$) and spin ($a_{*}$) of super massive black holes (SMBHs) determine the observed properties of type-I active galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at $z\\simeq1.55$ observed by VLT/X-shooter, selected to map a large range in $M_{\\rm BH}$ and $L/L_{\\rm edd}$ and covers the most prominent UV-optical (broad) emission lines, including H$\\alpha$, H$\\beta$, MgII, and CIV. This paper focuses on single-epoch, "virial" $M_{\\rm BH}$ determinations from broad emission lines and examines the implications of different continuum modeling approaches in line width measurements. We find that using a "local" power-law continuum instead of a physically-motivated thin disk continuum leads to only slight underestimation of the FWHM of the lines and the associated $M_{\\rm BH}\\left({\\rm FWHM}\\right)$. However, the line dispersion $\\sigma_{\\rm line}$ and associated $M_{\\rm BH}\\left(\\sigma_{...

  12. Determining inclinations of active galactic nuclei via their narrow-line region kinematics. II. Correlation with observed properties

    Active galactic nuclei (AGNs) are axisymmetric systems to first order; their observed properties are likely strong functions of inclination with respect to our line of sight, yet the specific inclinations of all but a few AGNs are generally unknown. By determining the inclinations and geometries of nearby Seyfert galaxies using the kinematics of their narrow-line regions (NLRs) and comparing them with observed properties, we find strong correlations between inclination and total hydrogen column density, infrared color, and Hβ FWHM. These correlations provide evidence that the orientation of AGNs with respect to our line of sight affects how we perceive them beyond the Seyfert 1/2 dichotomy. They can also be used to constrain three-dimensional models of AGN components such as the broad-line region and torus. Additionally, we find weak correlations between AGN luminosity and several modeled NLR parameters, which suggests that the NLR geometry and kinematics are dependent to some degree on the AGN's radiation field.

  13. Hierarchical Assembly of Supermassive Black Holes: Adaptive Optics Imaging of Double-Peaked [O III] Active Galactic Nuclei

    Fu, Hai; Djorgovski, S G; Yan, Lin

    2010-01-01

    Hierarchical galaxy assembly models predict the ubiquity of binary supermassive black holes (SMBHs). Nevertheless, observational confirmations of binary SMBHs are rare. We have obtained high-resolution near-infrared images of 50 double-peaked [O III] active galactic nuclei (AGNs) with Keck II laser guide star adaptive optics. The sample is compiled from the literature and consists of 17 type-1 and 33 type-2 AGNs over 0.03 < z < 0.56. Eight type-1 and eight type-2 sources are apparently undergoing mergers with multiple components of comparable luminosities, separated between 0.6 and 12 kpc. Disturbed morphologies are evident in most cases. The merger fractions of type-1s and type-2s differ because the fraction increases with redshift, f_merger \\propto (1+z)^4, which is consistent with the evolution of major merger fraction of L* galaxies at z < 1. We show that type-1 AGNs in compact merging systems are outliers of the M_BH-sigma relation since stellar velocity dispersions could be over-estimated becau...

  14. Constraining UV Continuum Slopes of Active Galactic Nuclei With CLOUDY Models of Broad Line Region EUV Emission Lines

    Moloney, Joshua

    2014-01-01

    Understanding the composition and structure of the broad-line region (BLR) of active galactic nuclei (AGN) is important for answering many outstanding questions in supermassive black hole evolution, galaxy evolution, and ionization of the intergalactic medium. We used single-epoch UV spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to measure EUV emission-line fluxes from four individual AGN with $0.49 \\le z \\le 0.64$, two AGN with $0.32 \\le z \\le 0.40$, and a composite of 159 AGN. With the Cloudy photoionization code, we calculated emission-line fluxes from BLR clouds with a range of density, hydrogen ionizing flux and incident continuum spectral indices. The photoionization grids were fit to the observations using single-component and locally optimally emitting cloud (LOC) models. The LOC models provide good fits to the measured fluxes, while the single-component models do not. The UV spectral indices preferred by our LOC models are consistent with those measured from COS spe...

  15. The subarcsecond mid-infrared view of local active galactic nuclei: I. The N- and Q-band imaging atlas

    Asmus, D; Gandhi, P; Smette, A; Duschl, W J

    2013-01-01

    We present the first subarcsecond-resolution mid-infrared (MIR) atlas of local active galactic nuclei (AGN) containing 253 objects with a median redshift of z = 0.016. It comprises all available MIR imaging observations performed to date with ground-based 8-meter class telescopes and includes in total 895 independent photometric measurements, of which more than 60% are previously unpublished.We detect extended nuclear emission in at least 21% of the objects, while another 19% appear clearly point-like, and the remaining objects cannot be constrained. Subarcsecond resolution allows us to isolate the emission of the AGN on scales of a few tens of parsecs for the bulk of the sample and obtain nuclear photometry in multiple filters for the objects. The photometry is used to construct median spectral energy distributions (SEDs) for the different optical AGN types and estimate the individual MIR 12 and 18 um continuum luminosities, which range over more than six orders of magnitude. We also analyse the arcsecond-sc...

  16. Three-dimensional Relativistic MHD Simulations of Active Galactic Nuclei Jets: Magnetic Kink Instability and Fanaroff-Riley Dichotomy

    Tchekhovskoy, Alexander

    2015-01-01

    Active galactic nuclei jets are thought to form in the immediate vicinity of the event horizons of supermassive black holes. Therefore, jets could be excellent probes of general relativity. However, in practice, using jets to infer near-black hole physics is not straightforward since the cause of their most basic morphological features is not understood. For instance, there is no agreement on the cause of the well-known Fanaroff-Riley (FR) morphological dichotomy of jets, with FRI jets being shorter and wiggly and FRII jets being longer and more stable. Here, we carry out 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic jets propagating through the ambient medium. Because in flat density cores of galaxies ($n \\propto r^{-\\alpha}$ with $\\alpha < 2$) the mass per unit distance ahead of the jets increases with distance, the jets slow down and collimate into smaller opening angles. This makes the jets more vulnerable to the 3D magnetic kink ("corkscrew") instability, which develops faster ...

  17. Optically-Selected BLR-less Active Galactic Nuclei from the SDSS Stripe82 Database I: The Sample

    Zhang, Xue Guang

    2013-01-01

    This is the first paper in a dedicated series to study the properties of the optically selected BLR-less AGNs (Active Galactic Nuclei with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136676 spectroscopic objects (galaxies and QSOs) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission $R_{AGN}>0.3$ and apparent stellar lights $R_{ssp}>0.3$. Then, using the properties of the photometry magnitude RMS ($RMS$) and the Pearson's coefficients ($R_{1, 2}$) between two different SDSS band light curves: $RMS_k>3\\times RMS_{M_k}$ and $R_{1, 2}>\\sim0.8$, the final 281 pure narrow objects with true photometry variabilities are our selected reliable candidates for t...

  18. Does the Iron K and Alpha: Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?

    You, J. H.; Liu, D. B.; Chen, W. P.; Chen, L.; Zhang, S. N.

    2003-01-01

    When thermal relativistic electrons with isotropic distribution of velocities move in a gas region or impinge upon the surface of a cloud that consists of a dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic emission lines, which is known as the Cerenkov line - like radiation. This newly recognized emission mechanism may find wide applications in high-energy astrophysics. In this paper we tentatively adopt this new line emission mechanism to discuss the origin of the iron Kα feature of active galactic nuclei (AGNs). The motivation of this research is to attempt a solution to a problem encountered by the "disk fluorescence line" model, i.e. , the lack of temporal response of the observed iron Kα line flux to the changes of the X-ray continuum flux. If the Cerenkov line emission is indeed responsible significant ly for the iron Kα feature, the conventional scenario around the central supermassive black holes of AGNs would need to be modified to accomodate more energetic, more violent, and much denser environments than previously thought.

  19. Tracing the evolution of active galactic nuclei host galaxies over the last 9 Gyr of cosmic time

    We present the results of a combined galaxy population analysis for the host galaxies of active galactic nuclei (AGN) identified at 0 < z < 1.4 within the Sloan Digital Sky Survey, Boötes, and DEEP2 surveys. We identified AGN in a uniform and unbiased manner at X-ray, infrared, and radio wavelengths. Supermassive black holes undergoing radiatively efficient accretion (detected as X-ray and/or infrared AGN) appear to be hosted in a separate and distinct galaxy population than AGN undergoing powerful mechanically dominated accretion (radio AGN). Consistent with some previous studies, radiatively efficient AGN appear to be preferentially hosted in modest star-forming galaxies, with little dependence on AGN or galaxy luminosity. AGN exhibiting radio-emitting jets due to mechanically dominated accretion are almost exclusively observed in massive, passive galaxies. Crucially, we now provide strong evidence that the observed host-galaxy trends are independent of redshift. In particular, these different accretion-mode AGN have remained as separate galaxy populations throughout the last 9 Gyr. Furthermore, it appears that galaxies hosting AGN have evolved along the same path as galaxies that are not hosting AGN with little evidence for distinctly separate evolution.

  20. The FeII emission in active galactic nuclei: excitation mechanisms and location of the emitting region

    Marinello, A O M; Garcia-Rissmann, A; Sigut, T A A; Pradhan, A K

    2016-01-01

    We present a study of FeII emission in the near-infrared region (NIR) for 25 active galactic nuclei (AGNs) to obtain information about the excitation mechanisms that power it and the location where it is formed. We employ a NIR FeII template derived in the literature and found that it successfully reproduces the observed FeII spectrum. The FeII bump at 9200 Angstroms detected in all objects studied confirms that Lyman-alpha fluorescence is always present in AGNs. The The correlation found between the flux of the 9200 Angstroms bump, the 1 micron lines and the optical FeII imply that Lyman-alpha fluorescence plays an important role in the FeII production. We determined that at least 18% of the optical FeII is due to this process while collisional excitation dominates the production of the observed FeII. The line profiles of FeII 10502, OI 11287, CaII 8664 and Paschen-beta were compared to gather information about the most likely location where they are emitted. We found that FeII, OI and CaII have similar widt...

  1. The radio/gamma-ray connection in Active Galactic Nuclei in the era of the Fermi Large Area Telescope

    Ackermann, M; Allafort, A; Angelakis, E; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bouvier, A; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Cannon, A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Ciprini, S; Claus, R; Cohen-Tanugi, J; Cutini, S; de Palma, F; Dermer, C D; Silva, E do Couto e; Drell, P S; Dubois, R; Dumora, D; Escande, L; Favuzzi, C; Fegan, S J; Focke, W B; Fortin, P; Frailis, M; Fuhrmann, L; Fukazawa, Y; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grandi, P; Grenier, I A; Guiriec, S; Hadasch, D; Hayashida, M; Hays, E; Healey, S E; J, G; Johnson, A S; Kamae, T; Katagiri, H; Kataoka, J; Kn, J; Kuss, M; Lande, J; Lee, S -H; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Makeev, A; Max-Moerbeck, W; Mazziotta, M N; McEnery, J E; Mehault, J; Michelson, P F; Mizuno, T; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Naumann-Godo, M; Nishino, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Pavlidou, V; Pelassa, V; Pepe, M; Pesce-Rollins, M; Pierbattista, M; Piron, F; Porter, T A; Rain, S; Razzano, M; Readhead, A; Reimer, A; Reimer, O; Richards, J L; Romani, R W; Sadrozinski, H F -W; Scargle, J D; Sgr, C; Siskind, E J; Smith, P D; Spandre, G; Spinelli, P; Strickman, M S; Suson, D J; Takahashi, H; Tanaka, T; Taylor, G B; Thayer, J G; Thayer, J B; Thompson, D J; Torres, D F; Tosti, G; Tramacere, A; Troja, E; Vandenbroucke, J; Vianello, G; Vitale, V; Waite, A P; Wang, P; Winer, B L; Wood, K S; Yang, Z; Ziegler, M

    2011-01-01

    We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the Active Galactic Nuclei (AGN) detected by Fermi during its first year of operation, with the largest datasets ever used for this purpose. We use both archival interferometric 8.4 GHz data (from the VLA and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate-data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the cm radio and the broad band (E>100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability <1e-7 for the correlation appearing by chance. Using the...

  2. Upholding the Unified Model for Active Galactic Nuclei: VLT/FORS2 Spectropolarimetry of Seyfert 2 galaxies

    Almeida, Cristina Ramos; Ramos, A Asensio; Acosta-Pulido, J A; Hönig, S F; Alonso-Herrero, A; Tadhunter, C N; González-Martín, O

    2016-01-01

    The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in 30-40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report >=4{\\sigma} detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing p...

  3. A TALE OF TWO POPULATIONS: THE CONTRIBUTION OF MERGER AND SECULAR PROCESSES TO THE EVOLUTION OF ACTIVE GALACTIC NUCLEI

    Due to the co-evolution of supermassive black holes and their host galaxies, understanding the mechanisms that trigger active galactic nuclei (AGNs) is imperative to understanding galaxy evolution and the formation of massive galaxies. It is observationally difficult to determine the trigger of a given AGN due to the difference between the AGN lifetime and triggering timescales. Here, we utilize AGN population synthesis modeling to determine the importance of different AGN triggering mechanisms. An AGN population model is computed by combining an observationally motivated AGN triggering rate and a theoretical AGN light curve. The free parameters of the AGN light curve are constrained by minimizing a χ2 test with respect to the observed AGN hard X-ray luminosity function. The observed black hole space density, AGN number counts, and X-ray background spectrum are also considered as observational constraints. It is found that major mergers are not able to account for the entire AGN population. Therefore, non-merger processes, such as secular mechanisms, must also trigger AGNs. Indeed, non-merger processes are the dominant AGN triggering mechanism at z ∼< 1-1.5. Furthermore, the shape and evolution of the black hole mass function of AGNs triggered by major mergers are intrinsically different from the shape and evolution of the black hole mass function of AGNs triggered by secular processes.

  4. The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

    Marsden, Danica; Marriage, Tobias A; Switzer, Eric R; Partridge, Bruce; Massardi, Marcella; Morales, Gustavo; Addison, Graeme; Bond, J Richard; Crichton, Devin; Das, Sudeep; Devlin, Mark; Dunner, Rolando; Hajian, Amir; Hilton, Matt; Hincks, Adam; Hughes, John P; Irwin, Kent; Kosowsky, Arthur; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael; Page, Lyman; Reese, Erik D; Schmitt, Benjamin; Sehgal, Neelima; Sievers, Jonathan; Staggs, Suzanne; Swetz, Daniel; Thornton, Robert; Wollack, Edward

    2013-01-01

    We present a catalog of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 GHz and/or 218 GHz in the 2008 Southern survey. Flux densities span 14-1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two sub-populations: 167 radio galaxies powered by central active galactic nuclei (AGN), and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97% of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogs. When combined with flux densities from the Australian Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index of 3.7+0.62-0.86, and includes both local galaxies and sources with redshifts as great as 5.6. Dusty ...

  5. The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

    Marsden, Danica; Gralla, Megan; Marriage, Tobias A.; Switzer, Eric R.; Partridge, Bruce; Massardi, Marcella; Morales, Gustavo; Addison, Graeme; Bond, J. Richard; Crighton, Devin; Das, Sudeep; Devlin, Mark; Dunner, Rolando; Hajian, Amir; Hilton, Matt; Hincks, Adam; Hughes, John P.; Irwin, Kent; Kosowsky, Arthur; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael; Page, Lyman; Reese, Erik D.; Schmitt, Benjamin; Sehgal, Neelima; Sievers, Johnathan; Staggs, Suzanne; Swetz, Daniel; Thornton, Robert; Wollack, Edward

    2014-01-01

    We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 -1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, A(sub 148-218), of 3.7 (+0.62 or -0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

  6. On the difference of torus geometry between hidden and non-hidden broad line active galactic nuclei

    Ichikawa, Kohei; Almeida, Cristina Ramos; Ramos, Andres Asensio; Alonso-Herrero, Almudena; Gonzalez-Martin, Omaira; Lopez-Rodriguez, Enrique; Ueda, Yoshihiro; Diaz-Santos, Tanio; Elitzur, Moshe; Hoenig, Sebastian F; Imanishi, Masatoshi; Levenson, Nancy A; Mason, Rachel E; Perlman, Eric S; Alsip, Crystal D

    2015-01-01

    We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGN) with clumpy torus models. We compiled high spatial resolution ($\\sim 0.3$--$0.7$ arcsec) mid-IR $N$-band spectroscopy, $Q$-band imaging and nuclear near- and mid-IR photometry from the literature. Combining these nuclear near- and mid-IR observations, far-IR photometry and clumpy torus models, enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties; type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGN have smaller torus opening angles and larger covering factors than those of HBLR AGN. This suggests that the chance to observe scattered (polarized) flux from the BLR in NH...

  7. The Black Hole-Bulge Relationship in Luminous Broad-Line Active Galactic Nuclei and Host Galaxies

    Shen, J; Schneider, D P; Hall, P B

    2007-01-01

    We have measured the stellar velocity dispersions (\\sigma_*) and estimated the central black hole (BH) masses for over 900 broad-line active galactic nuclei (AGNs) observed with the Sloan Digital Sky Survey. The sample includes objects which have redshifts up to z=0.452, high quality spectra, and host galaxy spectra dominated by an early-type (bulge) component. The AGN and host galaxy spectral components were decomposed using an eigenspectrum technique. The BH masses (M_BH) were estimated from the AGN broad-line widths, and the velocity dispersions were measured from the stellar absorption spectra of the host galaxies. The range of black hole masses covered by the sample is approximately 10^6 < M_BH < 10^9 M_Sun. The host galaxy luminosity-velocity dispersion relationship follows the well-known Faber-Jackson relation for early-type galaxies, with a power-law slope 4.33+-0.21. The estimated BH masses are correlated with both the host luminosities (L_{H}) and the stellar velocity dispersions (\\sigma_*), s...

  8. Probing Spectroscopic Variability of Galaxies & Narrow-Line Active Galactic Nuclei in the Sloan Digital Sky Survey

    Yip, Ching-Wa; Berk, Daniel Vanden; Scranton, Ryan; Krughoff, Simon; Szalay, Alex; Dobos, Laszlo; Tremonti, Christy; Taghizadeh-Popp, Manuchehr; Budavari, Tamas; Csabai, Istvan; Wyse, Rosemary; Ivezic, Zeljko

    2008-01-01

    Under the unified model for active galactic nuclei (AGNs), narrow-line (Type 2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured accretion disk. We would therefore expect the optical continuum emission from Type 2 AGN to be composed mainly of stellar light and non-variable on the time-scales of months to years. In this work we probe the spectroscopic variability of galaxies and narrow-line AGNs using the multi-epoch data in the Sloan Digital Sky Survey (SDSS) Data Release 6. The sample contains 18,435 sources for which there exist pairs of spectroscopic observations (with a maximum separation in time of ~700 days) covering a wavelength range of 3900-8900 Angstrom. To obtain a reliable repeatability measurement between each spectral pair, we consider a number of techniques for spectrophotometric calibration resulting in an improved spectrophotometric calibration of a factor of two. From these data we find that on average the spectroscopic variability of the continuum for narrow-line...

  9. Fermi-LAT γ-ray anisotropy and intensity explained by unresolved radio-loud active galactic nuclei

    Radio-loud active galactic nuclei (AGN) are expected to contribute substantially to both the intensity and anisotropy of the isotropic γ-ray background (IGRB). In turn, the measured properties of the IGRB can be used to constrain the characteristics of proposed contributing source classes. We consider individual subclasses of radio-loud AGN, including low-, intermediate-, and high-synchrotron-peaked BL Lacertae objects, flat-spectrum radio quasars, and misaligned AGN. Using updated models of the γ-ray luminosity functions of these populations, we evaluate the energy-dependent contribution of each source class to the intensity and anisotropy of the IGRB. We find that collectively radio-loud AGN can account for the entirety of the IGRB intensity and anisotropy as measured by the Fermi Large Area Telescope (LAT). Misaligned AGN provide the bulk of the measured intensity but a negligible contribution to the anisotropy, while high-synchrotron-peaked BL Lacertae objects provide the dominant contribution to the anisotropy. In anticipation of upcoming measurements with the Fermi-LAT and the forthcoming Cherenkov Telescope Array, we predict the anisotropy in the broader energy range that will be accessible to future observations

  10. The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation

    Asmus, D; Hoenig, S F; Smette, A; Duschl, W J

    2015-01-01

    We present an updated mid-infrared (MIR) versus X-ray correlation for the local active galactic nuclei (AGN) population based on the high angular resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and 2-10 keV and 14-195 keV data collected from the literature. We isolate a sample of 152 objects with reliable AGN nature and multi-epoch X-ray data and minimal MIR contribution from star formation. Although the sample is not homogeneous or complete, we show that our results are unlikely to be affected by biases. The MIR--X-ray correlation is nearly linear and within a factor of two independent of the AGN type and the wavebands used. The observed scatter is <0.4 dex. A possible flattening of the correlation slope at the highest luminosities probed (~ 10^45 erg/s) is indicated but not significant. Unobscured objects have, on average, an MIR--X-ray ratio that is only <= 0.15 dex higher than that of obscured objects. Objects with intermediate X-ray column densities (22 < log N_H <...

  11. Variability of the X-ray Broad Iron Spectral Features in Active Galactic Nuclei and Black-hole Binaries

    Mizumoto, Misaki; Tsujimoto, Masahiro; Inoue, Hajime

    2015-01-01

    The "broad iron spectral features" are often seen in X-ray spectra of Active Galactic Nuclei (AGN) and black-hole binaries (BHB). These features may be explained either by the "relativistic disc reflection" scenario or the "partial covering" scenario: It is hardly possible to determine which model is valid from time-averaged spectral analysis. Thus, X-ray spectral variability has been investigated to constrain spectral models. To that end, it is crucial to study iron structure of BHBs in detail at short time-scales, which is, for the first time, made possible with the Parallel-sum clocking (P-sum) mode of XIS detectors on board Suzaku. This observational mode has a time-resolution of 7.8~ms as well as a CCD energy-resolution. We have carried out systematic calibration of the P-sum mode, and investigated spectral variability of the BHB GRS 1915+105. Consequently, we found that the spectral variability of GRS 1915+105 does not show iron features at sub-seconds. This is totally different from variability of AGN ...

  12. HST-COS Observations of AGN. II. Extended Survey of Ultraviolet Composite Spectra from 159 Active Galactic Nuclei

    Stevans, Matthew L; Danforth, Charles W; Tilton, Evan M

    2014-01-01

    The ionizing fluxes from quasars and other active galactic nuclei (AGN) are critical for interpreting their emission-line spectra and for photoionizing and heating the intergalactic medium (IGM). Using far-ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we directly measure the rest-frame ionizing continua and emission lines for 159 AGN at redshifts 0.001 10^17.2 cm^-2) and 214 partial Lyman-limit systems (15.0 < log N_HI < 17.2). The 159 AGN exhibit a wide range of FUV/EUV spectral shapes, F_nu \\propto nu^(alpha_nu), typically with -2 < alpha_nu < 0 and no discernible continuum edges at 912A (H I) or 504A (He I). The composite rest-frame continuum shows a gradual break at 1000 A, with mean spectral index alpha_nu = -0.83 +/- 0.09 in the FUV (1200-2000A) steepening to alpha_nu = -1.41 +/- 0.15 in the EUV (500-1000A). We discuss the implications of the UV flux turnovers and lack of continuum edges for the structure of accretion disks, AGN mass inf...

  13. TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry I. First-Epoch 8.4 GHz Images

    Ojha, Roopesh; Böck, Moritz; Booth, Roy; Dutka, M S; Edwards, P G; Fey, A L; Fuhrmann, L; Gaume, R A; Hase, H; Horiuchi, S; Jauncey, D L; Johnston, K J; Katz, U; Lister, M; Lovell, J E J; Müller, C; Plötz, C; Quick, J F H; Ros, E; Taylor, G B; Thompson, D J; Tingay, S J; Tosti, G; Tzioumis, A K; Wilms, J; Zensus, J A

    2010-01-01

    We introduce the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) which is monitoring an initial sample of 43 extragalactic jets located south of -30 degrees declination at 8.4 GHz and 22 GHz since 2007. All aspects of the program are discussed. First epoch results at 8.4 GHz are presented along with physical parameters derived therefrom. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at http://pulsar.sternwarte.uni-erlangen.de/tanami/ We obtain reliable, high dynamic range images of the southern hemisphere AGN. All the quasars and BL Lac objects in the sample have a single-sided radio morphology. Galaxies are either double-sided, single-sided or irregular. About 28% of the TANAMI sample has been detected by LAT during its first three...

  14. COEXISTENCE OF GRAVITATIONALLY-BOUND AND RADIATION-DRIVEN C IV EMISSION LINE REGIONS IN ACTIVE GALACTIC NUCLEI

    There are mutually contradictory views in the literature of the kinematics and structure of high-ionization line (e.g., C IV) emitting regions in active galactic nuclei (AGNs). Two kinds of broad emission line region (BELR) models have been proposed, outflow and gravitationally-bound BELR, which are supported, respectively, by blueshift of the C IV line and reverberation mapping observations. To reconcile these two apparently different models, we present a detailed comparison study between the C IV and Mg II lines using a sample of AGNs selected from the Sloan Digital Sky Survey. We find that the kinematics of the C IV region is different from that of Mg II, which is thought to be controlled by gravity. A strong correlation is found between the blueshift and asymmetry of the C IV profile and the Eddington ratio. This provides strong observational support for the postulation that the outflow is driven by radiation pressure. In particular, we find robust evidence that the C IV line region is largely dominated by outflow at high Eddington ratios, while it is primarily gravitationally-bounded at low Eddington ratios. Our results indicate that these two emitting regions coexist in most AGNs. The emission strength from these two gases varies smoothly with Eddington ratio in opposite ways. This explanation naturally reconciles the apparently contradictory views proposed in previous studies. Finally, candidate models are discussed which can account for both the enhancement of outflow emission and suppression of normal BEL in AGNs with high Eddington ratios.

  15. A New Diagnostic of Active Galactic Nuclei: Revealing Highly-Absorbed Systems at Redshift>0.3

    Juneau, Stéphanie; Alexander, David M; Salim, Samir

    2011-01-01

    We introduce the Mass-Excitation (MEx) diagnostic to identify active galactic nuclei (AGN) in galaxies at intermediate redshift. In the absence of near-infrared spectroscopy, necessary to use traditional nebular line diagrams at z>0.4, we demonstrate that combining [OIII]5007/Hbeta and stellar mass successfully distinguishes between star formation and AGN emission. The MEx classification scheme relies on a novel probabilistic approach splitting galaxies into sub-categories with more confidence than alternative high-z diagnostic diagrams. It recognizes that galaxies near empirical boundaries on traditional diagrams have an uncertain classification and thus a non-zero probability of belonging to more than one category. An outcome of this work is a system of statistical weights that can be used to compute global properties of galaxy samples. We apply the MEx diagram to 2,812 galaxies at 0.3

  16. The Nature of the Stable Soft X-ray Emissions in Several Types of Active Galactic Nuclei Observed by Suzaku

    Noda, Hirofumi; Nakazawa, Kazuhiro; Uchiyama, Hideki; Yamada, Shin'ya; Sakurai, Soki

    2012-01-01

    To constrain the origin of the soft X-ray excess phenomenon seen in many active galactic nuclei, the intensity-correlated spectral analysis, developed by Noda et al. (2011b) for Markarian 509, was applied to wide-band (0.5-45 keV) Suzaku data of five representative objects with relatively weak reflection signature. They are the typical bare-nucleus type 1 Seyfert Fairall 9, the bright and typical type 1.5 Seyfert MCG-2-58-22, 3C382 which is one of the X-ray brightest broad line radio galaxies, the typical Seyfert-like radio loud quasar 4C+74.26, and the X-ray brightest radio quiet quasar MR2251-178. In all of them, soft X-ray intensities in energies below 3 keV were tightly correlated with that in 3-10 keV, but with significant positive offsets. These offsets, when calculated in finer energy bands, define a stable soft component in 0.5-3 keV. In each object, this component successfully explained the soft excess above a power-law fit. These components were interpreted in several alternative ways, including a t...

  17. A NEW SAMPLE OF BURIED ACTIVE GALACTIC NUCLEI SELECTED FROM THE SECOND XMM-NEWTON SERENDIPITOUS SOURCE CATALOGUE

    We present the results of X-ray spectral analysis of 22 active galactic nuclei (AGNs) with a small scattering fraction selected from the Second XMM-Newton Serendipitous Source Catalogue using hardness ratios. They are candidates of buried AGNs, since a scattering fraction, which is a fraction of scattered emission by the circumnuclear photoionized gas with respect to direct emission, can be used to estimate the size of the opening part of an obscuring torus. Their X-ray spectra are modeled by a combination of a power law with a photon index of 1.5-2 absorbed by a column density of ∼1023-24 cm-2, an unabsorbed power law, narrow Gaussian lines, and some additional soft components. We find that scattering fractions of 20 among 22 objects are less than a typical value (∼3%) for Seyfert 2s observed so far. In particular, those of eight objects are smaller than 0.5%, which are in the range for buried AGNs found in recent hard X-ray surveys. Moreover, [O III] λ5007 luminosities at given X-ray luminosities for some objects are smaller than those for Seyfert 2s previously known. This fact could be interpreted as a smaller size of optical narrow emission-line regions produced in the opening direction of the obscuring torus. These results indicate that they are strong candidates for the AGN buried in a very geometrically thick torus.

  18. THE MAGELLANIC QUASARS SURVEY. I. DOUBLING THE NUMBER OF KNOWN ACTIVE GALACTIC NUCLEI BEHIND THE SMALL MAGELLANIC CLOUD

    We report the spectroscopic confirmation of 29 new, 12 plausible, and three previously known quasars behind the central ∼1.5 deg2 region of the Small Magellanic Cloud (SMC). These were identified in a single 2DF/AAOMEGA observation on the Anglo-Australian Telescope of 268 candidates selected primarily based on their mid-IR colors, along with a smaller number of optically variable sources in OGLE-II close to known X-ray sources. The low detection efficiency was partly expected from the high surface density of SMC as compared with the Large Magellanic Cloud targets and the faintness of many of them (149 with I>20 mag). The expected number of I < 20 mag quasars in the field is ≅38, and we found 15 (40%). We did not attempt to determine the nature of the remaining sources, although several appear to be new planetary nebulae. The newly discovered active galactic nuclei can be used as reference points for future proper-motion studies, to study absorption in the SMC interstellar medium, and to study the physics of quasar variability with the existing long-term, highly cadenced OGLE light curves.

  19. Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy

    Wang, Deliang; Dong, Xiaobo

    2009-01-01

    Results are presented of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank (RGB) catalog which have been spectroscopically observed in the Sloan digital sky survey (SDSS) DR5. For 74 sources, the identifications for are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei (AGNs), particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies (NLRGs), as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs, based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to `weak line radio galaxies', are found have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as $10^{23}-10^{26}$ \\whz at 5 GHz, being among ...

  20. Tracing the evolution of active galactic nuclei host galaxies over the last 9 Gyr of cosmic time

    Goulding, A. D.; Forman, W. R.; Jones, C.; Murray, S. S.; Paggi, A.; Ashby, M. L. N.; Huang, J.-S.; Kraft, R.; Willner, S. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hickox, R. C. [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Coil, A. L. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, San Diego, CA 92093 (United States); Cooper, M. C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Newman, J. A. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); Weiner, B. J., E-mail: agoulding@cfa.harvard.edu [Steward Observatory, 933 North Cherry Street, University of Arizona, Tucson, AZ 85721 (United States)

    2014-03-01

    We present the results of a combined galaxy population analysis for the host galaxies of active galactic nuclei (AGN) identified at 0 < z < 1.4 within the Sloan Digital Sky Survey, Boötes, and DEEP2 surveys. We identified AGN in a uniform and unbiased manner at X-ray, infrared, and radio wavelengths. Supermassive black holes undergoing radiatively efficient accretion (detected as X-ray and/or infrared AGN) appear to be hosted in a separate and distinct galaxy population than AGN undergoing powerful mechanically dominated accretion (radio AGN). Consistent with some previous studies, radiatively efficient AGN appear to be preferentially hosted in modest star-forming galaxies, with little dependence on AGN or galaxy luminosity. AGN exhibiting radio-emitting jets due to mechanically dominated accretion are almost exclusively observed in massive, passive galaxies. Crucially, we now provide strong evidence that the observed host-galaxy trends are independent of redshift. In particular, these different accretion-mode AGN have remained as separate galaxy populations throughout the last 9 Gyr. Furthermore, it appears that galaxies hosting AGN have evolved along the same path as galaxies that are not hosting AGN with little evidence for distinctly separate evolution.

  1. The Radio/Gamma-Ray Connection in Active Galactic Nuclei in the Era of the Fermi Large Area Telescope

    Ackermann, M.; Ajello, M.; Allafort, A.; Angelakis, E.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Gehrels, N.; Hays, E.; MeEnery, J. E.; Scargle, J. D.; Thompson, D. J.

    2011-01-01

    We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose.We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the OwensValley RadioObservatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability < 10(exp -7)) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.

  2. Constraints on the broad line region from regularized linear inversion: Velocity-delay maps for five nearby active galactic nuclei

    Skielboe, Andreas; Treu, Tommaso; Park, Daeseong; Barth, Aaron J; Bentz, Misty C

    2015-01-01

    Reverberation mapping probes the structure of the broad emission-line region (BLR) in active galactic nuclei (AGN). The radius of the BLR along with the virial velocity of the BLR gas can be used to measure the mass of the supermassive black hole. The main systematic uncertainty affecting reverberation mapping is the unknown structure of the BLR. We develop a new method for analysing reverberation mapping data based on regularized linear inversion (RLI) that includes statistical modelling of the AGN continuum light curves. This method enables fast, flexible, and robust calculation of velocity-resolved response maps to probe BLR structure. Contrary to other methods, RLI allows for negative response in the BLR, such as when some areas of the BLR respond in inverse proportion to a change in ionizing continuum luminosity. We present time delays, integrated response functions, and velocity-delay maps for the H{\\beta} broad emission line in five nearby AGN, as well as H{\\alpha} and H{\\gamma} broad emission lines in...

  3. Improvement on the quality of the images obtained with adaptive optics and application to the study of the active galactic nuclei

    Exposito, Jonathan

    2013-01-01

    My work is connecting three areas in astrophysics: the study of active galactic nuclei (AGN), adaptive optics (AO) and the optimization of the methods for related data-processing. It focuses on the development of tools to obtain the best image quality in terms of resolution and contrast so as to maximize the scientific return especially for the study of AGN. Adaptive optics can compensate for the effects of atmospheric turbulence on the wavefront and thus to approach the theoretical resolutio...

  4. ADAPTIVE OPTICS IMAGING OF QUASI-STELLAR OBJECTS WITH DOUBLE-PEAKED NARROW LINES: ARE THEY DUAL ACTIVE GALACTIC NUCLEI?

    Active galaxies hosting two accreting and merging supermassive black holes (SMBHs)-dual active galactic nuclei (AGNs)-are predicted by many current and popular models of black-hole-galaxy co-evolution. We present here the results of a program that has identified a set of probable dual AGN candidates based on near-infrared laser guide star adaptive optics imaging with the Keck II telescope. These candidates are selected from a complete sample of radio-quiet quasi-stellar objects (QSOs) drawn from the Sloan Digital Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the 12 AGNs imaged, we find 6 with double galaxy structure, of which four are in galaxy mergers. We measure the ionization of the two velocity components in the narrow AGN lines to test the hypothesis that both velocity components come from an active nucleus. The combination of a well-defined parent sample and high-quality imaging allows us to place constraints on the fraction of SDSS QSOs that host dual accreting black holes separated on kiloparsec scales: ∼0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during a typical merger and find a value that is much lower than estimates that arise from QSO space densities and galaxy merger statistics. We discuss possible reasons for this difference. Finally, we compare the SMBH mass distributions of single and dual AGNs and find little difference between the two within the limited statistics of our program, hinting that most SMBH growth happens in the later stages of a merger process.

  5. FEEDBACK FROM MASS OUTFLOWS IN NEARBY ACTIVE GALACTIC NUCLEI. I. ULTRAVIOLET AND X-RAY ABSORBERS

    We present an investigation into the impact of feedback from outflowing UV and X-ray absorbers in nearby (z out) and kinetic luminosity (LKE) for each AGN, summed over all of its absorbers. These calculations make use of values (or limits) for the radial locations of the absorbers determined from variability, excited-state absorption, and other considerations. From a sample of 10 Seyfert 1 galaxies with detailed photoionization models for their absorbers, we find that 7 have sufficient constraints on the absorber locations to determine M-dotout and LKE. For the low-luminosity AGN NGC 4395, these values are low, although we do not have sufficient constraints on the X-ray absorbers to make definitive conclusions. At least five of the six Seyfert 1s with moderate bolometric luminosities (Lbol = 1043 – 1045 erg s–1) have mass outflow rates that are 10-1000 times the mass accretion rates needed to generate their observed luminosities, indicating that most of the mass outflow originates from outside the inner accretion disk. Three of these (NGC 4051, NGC 3516, and NGC 3783) have LKE in the range 0.5%-5% Lbol, which is the range typically required by feedback models for efficient self-regulation of black hole and galactic bulge growth. At least two of the other three (NGC 5548, NGC 4151, and NGC 7469) have LKE ∼> 0.1%Lbol, although these values may increase if radial locations can be determined for more of the absorbers. We conclude that the outflowing UV and X-ray absorbers in moderate-luminosity AGNs have the potential to deliver significant feedback to their environments.

  6. SUZAKU VIEW OF THE SWIFT/BAT ACTIVE GALACTIC NUCLEI. V. TORUS STRUCTURE OF TWO LUMINOUS RADIO-LOUD ACTIVE GALACTIC NUCLEI (3C 206 AND PKS 0707–35)

    We present the results from broadband X-ray spectral analysis of 3C 206 and PKS 0707–35 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei (AGNs) with hard X-ray luminosities of 1045.5 erg s–1 and 1044.9 erg s–1 (14-195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (∼60% in the 14-195 keV band) contribution from the jet, while it is negligible in PKS 0707–35. We can successfully model the spectra with the jet component (for 3C 206), the transmitted emission, and two reflection components from the torus and the accretion disk. The reflection strengths from the torus are found to be Rtorus(≡ Ω/2π) = 0.29 ± 0.18 and 0.41 ± 0.18 for 3C 206 and PKS 0707–35, respectively, which are smaller than those in typical Seyfert galaxies. Utilizing the torus model by Ikeda et al., we quantify the relation between the half-opening angle of a torus (θoa) and the equivalent width of an iron-K line. The observed equivalent width of 3C 206, Heq 23 cm–2, or the half-opening angle to θoa > 80° if NHeq =1024 cm–2 is assumed. That of PKS 0707–35, 72 ± 36 eV, is consistent with NHeq ∼1023 cm–2. Our results suggest that the tori in luminous radio-loud AGNs are only poorly developed. The trend is similar to that seen in radio-quiet AGNs, implying that the torus structure is not different between AGNs with jets and without jets

  7. PROBING SPECTROSCOPIC VARIABILITY OF GALAXIES AND NARROW-LINE ACTIVE GALACTIC NUCLEI IN THE SLOAN DIGITAL SKY SURVEY

    Under the unified model for active galactic nuclei (AGNs), narrow-line (Type 2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured accretion disk. We would therefore expect the optical continuum emission from Type 2 AGNs to be composed mainly of stellar light and nonvariable on the timescales of months to years. In this work we probe the spectroscopic variability of galaxies and narrow-line AGNs using the multiepoch data in the Sloan Digital Sky Survey Data Release 6. The sample contains 18,435 sources for which there exist pairs of spectroscopic observations (with a maximum separation in time of ∼700 days) covering a wavelength range of 3900-8900 A. To obtain a reliable repeatability measurement between each spectral pair, we consider a number of techniques for spectrophotometric calibration resulting in an improved spectrophotometric calibration of a factor of 2. From these data we find no obvious continuum and emission-line variability in the narrow-line AGNs on average-the spectroscopic variability of the continuum is 0.07 ± 0.26 mag in the g band and, for the emission-line ratios log10([N II]/Hα) and log10([O III]/Hβ), the variability is 0.02 ± 0.03 dex and 0.06 ± 0.08 dex, respectively. From the continuum variability measurement we set an upper limit on the ratio between the flux of the varying spectral component, presumably related to AGN activities, and that of the host galaxy to be ∼30%. We provide the corresponding upper limits for other spectral classes, including those from the BPT diagram, eClass galaxy classification, stars, and quasars.

  8. THE BLUESHIFTING AND BALDWIN EFFECTS FOR THE [O III] λ5007 EMISSION LINE IN TYPE 1 ACTIVE GALACTIC NUCLEI

    We use homogeneous samples of radio-quiet Seyfert 1 galaxies and QSOs selected from the Sloan Digital Sky Survey to investigate the connection between the velocity shift and the equivalent width (EW) of the [O III] λ5007 emission line, and their correlations with physical parameters of active galactic nuclei (AGNs). We find a significant and negative correlation between the EW of the core component, EW(core), and the blueshift of either the core (the peak), the wing, or the total profile of [O III] emission; it is fairly strong for the blueshift of the total profile in particular. However, both quantities (EW and velocity shift) generally have only weak, if any, correlations with fundamental AGN parameters such as the nuclear continuum luminosity at 5100 A (5100), black hole mass (MBH), and the Eddington ratio (L/LEdd); these correlations include the classical Baldwin effect of EW(core), an inverse Baldwin effect of EW(wing), and the relationship between velocity shifts and L/LEdd. Our findings suggest that both the large object-to-object variation in the strength of [O III] emission and the blueshift-EW(core) connection are not governed primarily by fundamental AGN parameters such as L5100, MBH, and L/LEdd. We propose that the interstellar medium conditions of the host galaxies play a major role instead in the diversity of the [O III] properties in active galaxies. This suggests that the use of [O III] λ5007 luminosity as a proxy of AGN luminosity does not depend strongly on the above-mentioned fundamental AGN parameters.

  9. On minor black holes in galactic nuclei

    McKernan, Barry; Ford, K. E. Saavik; Yaqoob, Tahir; Winter, Lisa M.

    2011-01-01

    Small and intermediate mass black holes should be expected in galactic nuclei as a result of stellar evolution, minor mergers and gravitational dynamical friction. If these minor black holes accrete as X-ray binaries or ultra-luminous X-ray sources, and are associated with star formation, they could account for observations of many low luminosity AGN or LINERs. Accreting and inspiralling intermediate mass black holes could provide a crucial electromagnetic counterpart to strong gravitational ...

  10. Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South

    Young, M.; Brandt, W. N.; Xue, Y. Q.; Paolillo, D. M.; Alexander, F. E.; Bauer, F. E.; Lehmer, B. D.; Luo, B.; Shemmer, O.; Schneider, D. P.; Vignail, C.

    2012-01-01

    The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGN). However, cosmologically distant low-luminosity AGN (LLAGN) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X ray variability (approx. month years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts approx equals 00.8 - 1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole. The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Gamma(sub Stack) approx equals 1.93 +/- 0.13, and arc therefore likely LLAGN. The LLAGN tend to lie it factor of approx equal 6-89 below the extrapolated linear variability-luminosity relation measured for luminous AGN. This may he explained by their lower accretion rates. Variability-independent black-hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black hole mass-accretion-rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGNs at the same redshift. We find that an empirical model based on a universal broken power-law power spectral density function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGNs.

  11. DEPENDENCE OF THE OPTICAL/ULTRAVIOLET VARIABILITY ON THE EMISSION-LINE PROPERTIES AND EDDINGTON RATIO IN ACTIVE GALACTIC NUCLEI

    The dependence of the long-term optical/UV variability on the spectral and fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch-repeated photometric scanning data in the Stripe-82 region of the Sloan Digital Sky Survey (SDSS) are exploited for two comparative AGN samples (mostly quasars) selected therein: a broad-line Seyfert 1 (BLS1) type sample and a narrow-line Seyfert 1 (NLS1) type AGN sample within redshifts 0.3-0.8. Their spectral parameters are derived from the SDSS spectroscopic data. It is found that on rest-frame timescales of several years the NLS1-type AGNs show systematically smaller variability compared to the BLS1-type AGNs. In fact, the variability amplitude is found to correlate, though only moderately, with the eigenvector 1 parameters, i.e., the smaller the Hβ linewidth, the weaker the [O III] and the stronger the Fe II emission, the smaller the variability amplitude. Moreover, an interesting inverse correlation is found between the variability and the Eddington ratio, which is perhaps more fundamental. The previously known dependence of the variability on luminosity is not significant, and the dependence on black hole mass-as claimed in recent papers and also present in our data-fades out when controlling for the Eddington ratio in the correlation analysis, though these may be partly due to the limited ranges of luminosity and black hole mass of our samples. Our result strongly supports that an accretion disk is likely to play a major role in producing the optical/UV variability.

  12. VARIABILITY-SELECTED LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI IN THE 4 Ms CHANDRA DEEP FIELD-SOUTH

    The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGNs). However, cosmologically distant low-luminosity AGNs (LLAGNs) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X-ray variability (∼month-years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts z ≈ 0.08-1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole (SMBH). The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Γstack ≈ 1.93 ± 0.13, and are therefore likely LLAGNs. The LLAGNs tend to lie a factor of ≈6-80 below the extrapolated linear variability-luminosity relation measured for luminous AGNs. This may be explained by their lower accretion rates. Variability-independent black hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black hole mass-accretion-rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGNs at the same redshift. We find that an empirical model based on a universal broken power-law power spectral density function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGNs.

  13. The development of a color-magnitude diagram for active galactic nuclei (AGN): hope for a new standard candle

    McGinnis, G.; Chung, S.; Gonzales, E. V.; Gorjian, V.; Pruett, L.

    2015-12-01

    Of the galaxies in our universe, only a small percentage currently have Active Galactic Nuclei (AGN). These galaxies tend to be further out in the universe and older, and are different from inactive galaxies in that they emit high amounts of energy from their central black holes. These AGN can be classified as either Seyferts or quasars, depending on the amount of energy emitted from the center (less or more). We are studying the correlation between the ratio of dust emission and accretion disk emission to luminosities of AGN in order to determine if there is a relationship strong enough to act as a predictive model for distance within the universe. This relationship can be used as a standard candle if luminosity is found to determine distances in space. We have created a color-magnitude diagram depicting this relationship between luminosity and wavelengths, similar to the Hertzsprung-Russell (HR) diagram. The more luminous the AGN, the more dust surface area over which to emit energy, which results in a greater near-infrared (NIR) luminosity. This differs from previous research because we use NIR to differentiate accretion from dust emission. Using data from the Sloan Digital Sky Survey (SDSS) and the Two Micron All Sky Survey (2MASS), we analyzed over one thousand Type 1 Seyferts and quasars. We studied data at different wavelengths in order to show the relationship between color (the ratio of one wavelength to another) and luminosity. It was found that plotting filters i-K (the visible and mid-infrared regions of the electromagnetic spectrum) against the magnitude absolute K (luminosity) showed a strong correlation. Furthermore, the redshift range between 0.14 and 0.15 was the most promising, with an R2 of 0.66.

  14. Upholding the unified model for active galactic nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies

    Ramos Almeida, C.; Martínez González, M. J.; Asensio Ramos, A.; Acosta-Pulido, J. A.; Hönig, S. F.; Alonso-Herrero, A.; Tadhunter, C. N.; González-Martín, O.

    2016-09-01

    The origin of the unification model for active galactic nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ˜30-40 per cent of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ≥4σ detections of a HBLR in 11 of these galaxies (73 per cent of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad Hα and Hβ components in polarized light for 10 targets, and just broad Hα for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s-1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components.

  15. Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy

    Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank (RGB) catalog are presented (Brinkmann et al. 1997) which have been spectroscopically observed in the Sloan Digital Sky Survey (SDSS) DR5. The SDSS spectra of the optical counterparts are modeled in a careful and self-consistent way by incorporating the host galaxy's starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4-5 GHz spectral indices estimated using (non-simultaneous) archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei (AGNs), particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies (NLRGs), as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs (low-ionization nuclear emission regions), based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to 'weak line radio galaxies', are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 1023 - 1026 W Hz-1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies (NLS1s), a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs (HBLs), as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.

  16. FROM THE BLAZAR SEQUENCE TO THE BLAZAR ENVELOPE: REVISITING THE RELATIVISTIC JET DICHOTOMY IN RADIO-LOUD ACTIVE GALACTIC NUCLEI

    We revisit the concept of a blazar sequence that relates the synchrotron peak frequency (νpeak) in blazars with synchrotron peak luminosity (Lpeak, in νLν) using a large sample of radio-loud active galactic nuclei. We present observational evidence that the blazar sequence is formed from two populations in the synchrotron νpeak-Lpeak plane, each forming an upper edge to an envelope of progressively misaligned blazars, and connecting to an adjacent group of radio galaxies having jets viewed at much larger angles to the line of sight. When binned by jet kinetic power (Lkin; as measured through a scaling relationship with extended radio power), we find that radio core dominance decreases with decreasing synchrotron Lpeak, revealing that sources in the envelope are generally more misaligned. We find population-based evidence of velocity gradients in jets at low kinetic powers (∼1042-1044.5 erg s-1), corresponding to Fanaroff-Riley (FR) I radio galaxies and most BL Lac objects. These low jet power 'weak-jet' sources, thought to exhibit radiatively inefficient accretion, are distinguished from the population of non-decelerating, low synchrotron-peaking (LSP) blazars and FR II radio galaxies ('strong' jets) which are thought to exhibit radiatively efficient accretion. The two-population interpretation explains the apparent contradiction of the existence of highly core-dominated, low-power blazars at both low and high synchrotron peak frequencies, and further implies that most intermediate synchrotron peak sources are not intermediate in intrinsic jet power between LSP and high synchrotron-peaking (HSP) sources, but are more misaligned versions of HSP sources with similar jet powers.

  17. Active galactic nuclei at z ˜ 1.5 - II. Black hole mass estimation by means of broad emission lines

    Mejía-Restrepo, J. E.; Trakhtenbrot, B.; Lira, P.; Netzer, H.; Capellupo, D. M.

    2016-07-01

    This is the second in a series of papers aiming to test how the mass (MBH), accretion rate (Ṁ) and spin (a*) of supermassive black holes (SMBHs) determine the observed properties of type I active galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at z ≃ 1.55 observed by Very Large Telescope/X-Shooter, selected to map a large range in MBH and L/LEdd and covers the most prominent UV-optical (broad) emission lines, including Hα, Hβ, Mg II λ2798 and C IV λ1549. This paper focuses on single-epoch, `virial' MBH determinations from broad emission lines and examines the implications of different continuum modelling approaches in line width measurements. We find that using a local power-law continuum instead of a physically motivated thin disc continuum leads to only slight underestimation of the full width at half-maximum (FWHM) of the lines and the associated MBH(FWHM). However, the line dispersion σline and associated MBH(σline) are strongly affected by the continuum placement and provides less reliable mass estimates than FWHM-based methods. Our analysis shows that Hα, Hβ and Mg II can be safely used for virial MBH estimation. The C IV line, on the other hand, is not reliable in the majority of the cases; this may indicate that the gas emitting this line is not virialized. While Hα and Hβ show very similar line widths, the mean FWHM(Mg II) is about 30 per cent narrower than FWHM(Hβ). We confirm several recent suggestions to improve the accuracy in C IV-based mass estimates, relying on other UV emission lines. Such improvements do not reduce the scatter between C IV-based and Balmer-line-based mass estimates.

  18. THE HALO OCCUPATION DISTRIBUTION OF X-RAY-BRIGHT ACTIVE GALACTIC NUCLEI: A COMPARISON WITH LUMINOUS QUASARS

    We perform halo occupation distribution (HOD) modeling of the projected two-point correlation function (2PCF) of high-redshift (z ∼ 1.2) X-ray-bright active galactic nuclei (AGNs) in the XMM-COSMOS field measured by Allevato et al. The HOD parameterization is based on low-luminosity AGNs in cosmological simulations. At the median redshift of z ∼ 1.2, we derive a median mass of 1.02-0.23+0.21×1013 h-1 Msun for halos hosting central AGNs and an upper limit of ∼10% on the AGN satellite fraction. Our modeling results indicate (at the 2.5σ level) that X-ray AGNs reside in more massive halos compared to more bolometrically luminous, optically selected quasars at similar redshift. The modeling also yields constraints on the duty cycle of the X-ray AGN, and we find that at z ∼ 1.2 the average duration of the X-ray AGN phase is two orders of magnitude longer than that of the quasar phase. Our inferred mean occupation function of X-ray AGNs is similar to recent empirical measurements with a group catalog and suggests that AGN halo occupancy increases with increasing halo mass. We project the XMM-COSMOS 2PCF measurements to forecast the required survey parameters needed in future AGN clustering studies to enable higher precision HOD constraints and determinations of key physical parameters like the satellite fraction and duty cycle. We find that N 2/A ∼ 5 × 106 deg–2 (with N the number of AGNs in a survey area of A deg2) is sufficient to constrain the HOD parameters at the 10% level, which is easily achievable by upcoming and proposed X-ray surveys

  19. Supermassive black holes with high accretion rates in active galactic nuclei. I. First results from a new reverberation mapping campaign

    We report first results from a large project to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). Such objects may be different from other AGNs in being powered by slim accretion disks and showing saturated accretion luminosities, but both are not yet fully understood. The results are part of a large reverberation mapping (RM) campaign using the 2.4 m Shangri-La telescope at the Yunnan Observatory in China. The goals are to investigate the gas distribution near the BH and the properties of the central accretion disks, to measure BH mass and Eddington ratios, and to test the feasibility of using such objects as a new type of cosmological candles. The paper presents results for three objects, Mrk 335, Mrk 142, and IRAS F12397+3333, with Hβ time lags relative to the 5100 Å continuum of 10.6−2.9+1.7, 6.4−2.2+0.8 and 11.4−1.9+2.9 days, respectively. The corresponding BH masses are (8.3−3.2+2.6)×106 M⊙, (3.4−1.2+0.5)×106 M⊙, and (7.5−4.1+4.3)×106 M⊙, and the lower limits on the Eddington ratios are 0.6, 2.3, and 4.6 for the minimal radiative efficiency of 0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from the currently known relation between Hβ lag and continuum luminosity. The three Eddington ratios are beyond the values expected in thin accretion disks and two of them are the largest measured so far among objects with RM-based BH masses. We briefly discuss implications for slim disks, BH growth, and cosmology.

  20. HST-COS observations of AGNs. II. Extended survey of ultraviolet composite spectra from 159 active galactic nuclei

    Stevans, Matthew L. [Present address: Astronomy Department, University of Texas, Austin, TX 78712, USA. (United States); Shull, J. Michael [Also at Institute of Astronomy, Cambridge University, Cambridge CB3 OHA, UK. (United Kingdom); Danforth, Charles W.; Tilton, Evan M., E-mail: stevans@astro.as.utexas.edu, E-mail: michael.shull@colorado.edu, E-mail: charles.danforth@colorado.edu, E-mail: evan.tilton@colorado.edu [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)

    2014-10-10

    The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting their emission-line spectra and for photoionizing and heating the intergalactic medium. Using far-ultraviolet (FUV) spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we directly measure the rest-frame ionizing continua and emission lines for 159 AGNs at redshifts 0.001 < z {sub AGN} < 1.476 and construct a composite spectrum from 475 to 1875 Å. We identify the underlying AGN continuum and strong extreme ultraviolet (EUV) emission lines from ions of oxygen, neon, and nitrogen after masking out absorption lines from the H I Lyα forest, 7 Lyman-limit systems (N{sub H} {sub I}≥10{sup 17.2} cm{sup –2}) and 214 partial Lyman-limit systems (14.5

  1. Active galactic nuclei at z ˜ 1.5: II. Black Hole Mass estimation by means of broad emission lines

    Mejia-Restrepo, J. E.; Trakhtenbrot, B.; Lira, P.; Netzer, H.; Capellupo, D. M.

    2016-03-01

    This is the second in a series of papers aiming to test how the mass (MBH), accretion rate (dot{M}) and spin (a★) of super massive black holes (SMBHs) determine the observed properties of type-I active galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at z ≃ 1.55 observed by VLT/X-shooter, selected to map a large range in MBH and L/LEddand covers the most prominent UV-optical (broad) emission lines, including Hα, Hβ, Mg II λ2798, and C IV λ1549. This paper focuses on single-epoch, "virial" MBH determinations from broad emission lines and examine the implications of different continuum modeling approaches in line width measurements. We find that using a local power-law continuum instead of a physically-motivated thin disk continuum leads to only slight underestimation of the FWHM of the lines and the associated MBH(FWHM). However, the line dispersion σline and associated MBH(σline) are strongly affected by the continuum placement and provides less reliable mass estimates than FWHM-based methods. Our analysis shows that Hα, Hβ and Mg II can be safely used for virial MBH estimation. The C IV line, on the other hand, is not reliable in the majority of the cases, this may indicate that the gas emitting this line is not virialized. While Hα and Hβ show very similar line widths, the mean FWHM(Mg II) is about 30% narrower than FWHM(Hβ). We confirm several recent suggestions to improve the accuracy in C IV-based mass estimates, relying on other UV emission lines. Such improvements do not reduce the scatter between C IV-based and Balmer-line-based mass estimates.

  2. A SEARCH FOR BINARY ACTIVE GALACTIC NUCLEI: DOUBLE-PEAKED [O III] AGNs IN THE SLOAN DIGITAL SKY SURVEY

    We present active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) having double-peaked profiles of [O III]λλ5007, 4959 and other narrow emission lines, motivated by the prospect of finding candidate binary AGNs. These objects were identified by means of a visual examination of 21,592 quasars at z < 0.7 in SDSS Data Release 7 (DR7). Of the spectra with adequate signal-to-noise, 148 spectra exhibit a double-peaked [O III] profile. Of these, 86 are Type 1 AGNs and 62 are Type 2 AGNs. Only two give the appearance of possibly being optically resolved double AGNs in the SDSS images, but many show close companions or signs of recent interaction. Radio-detected quasars are three times more likely to exhibit a double-peaked [O III] profile than quasars with no detected radio flux, suggesting a role for jet interactions in producing the double-peaked profiles. Of the 66 broad-line (Type 1) AGNs that are undetected in the FIRST survey, 0.9% show double-peaked [O III] profiles. We discuss statistical tests of the nature of the double-peaked objects. Further study is needed to determine which of them are binary AGNs rather than disturbed narrow line regions, and how many additional binaries may remain undetected because of insufficient line-of-sight velocity splitting. Previous studies indicate that 0.1% of SDSS quasars are spatially resolved binaries, with typical spacings of ∼10-100 kpc. If a substantial fraction of the double-peaked objects are indeed binaries, then our results imply that binaries occur more frequently at smaller separations (<10 kpc). This suggests that simultaneous fueling of both black holes is more common as the binary orbit decays through these spacings.

  3. X-ray Detected Active Galactic Nuclei in Dwarf Galaxies at $0

    Pardo, Kristina; Greene, Jenny E; Somerville, Rachel S; Gallo, Elena; Hickox, Ryan C; Miller, Brendan P; Reines, Amy E; Silverman, John D

    2016-01-01

    We present a sample of accreting supermassive black holes (SMBHs) in low-mass galaxies at $z200$ ks) archival \\textit{Chandra} X-ray data. From our sample of $\\sim 600$ low-mass galaxies, $10$ exhibit X-ray emission consistent with that arising from AGN activity. If black hole mass scales roughly with stellar mass, then we expect that these AGN are powered by SMBHs with masses of $\\sim 10^5-10^6 \\ M_{\\odot}$ and typical Eddington ratios $\\sim 5\\%$. Furthermore, we find an active fraction consistent with extrapolations of other searches of $\\sim 0.006-3\\%$ for $10^9 \\ M_{\\odot} \\leq M_{\\star} \\leq 3\\times 10^{9} \\ M_{\\odot}$ and $0.1active fraction has been directly measured outside of the local universe for these SMBH mass ranges. We find good agreement with semi-analytic models, suggesting that as we search larger volumes we may use comparisons between observed active fractions and models to understand seeding mechanisms in the early universe.

  4. On radio-bright Active Galactic Nuclei in a complete Spectroscopic Redshift Survey

    Reviglio, P; Reviglio, Pietro; Helfand, David J.

    2006-01-01

    Analysis of the frequency and physical properties of galaxies with star-formation and AGN activity in different environments in the local universe is a cornerstone for understanding structure formation and galaxy evolution. We have built a new multiwavelength catalog for galaxies in a complete redshift survey (the 15R Survey), gathering information on their H-alpha, R-band, radio, far-infrared, and X-ray emission, as well as their radio and optical morphologies, and have developed a classification scheme to compare different selection methods and to select accurately samples of radio emitting galaxies with AGN and star-forming activity. While alternative classification schemes do not lead to major differences for star-forming galaxies, we show that spectroscopic and photometric classifications of AGN lead to incomplete samples. In particular, a large population of AGN-containing galaxies with absorption-line spectra, and in many cases extended radio structures (jets, lobes), is missed in the standard Baldwin-...

  5. Variability of Active Galactic Nuclei from the Optical to X-ray Regions

    Gaskell, C. Martin; Klimek, Elizabeth S.

    2009-01-01

    Some progress in understanding AGN variability is reviewed. Reprocessing of X-ray radiation to produce significant amounts of longer-wavelength continua seems to be ruled out. In some objects where there has been correlated X-ray and optical variability, the amplitude of the optical variability has exceeded the amplitude of X-ray variability. We suggest that accelerated particles striking material could be linking X-ray and optical variability (as in activity in the solar chromosphere). Beami...

  6. Dynamical model for the central engine of QSOs and active galactic nuclei

    A model for the energy generation in quasars and active galaxies is proposed based on (quasi)spherical accretion and a shock as a means for randomizing the inflowing kinetic energy. According to the model, most of the accretion energy is converted into relativistic protons at the shock, which in turn can provide the necessary pressure to self-consistently support it if their energy loss time scale by nuclear collisions is longer than the free fall time scale. The shock can thus be characterized as a relativistic proton radiative shock in analogy with similar accretion shocks on white dwarfs. 27 references

  7. X-ray Spectroscopy of Low-Luminosity Active Galactic Nuclei with XMM

    DiMatteo, Tiziana; Mushotzky, Richard (Technical Monitor)

    2002-01-01

    The measurement of black hole masses in nearby galaxies has transformed our understanding of these systems, allowing us to quantify the relevant scales of power, length and time and explore how the activity of black holes is linked to their environments and to the evolution of their host galaxies. In this project, Dr. Tiziana Di Matteo has the primary responsibility for developing and investigating theoretical models for the origin of the X-ray emission observed in low-luminosity AGN. Dr. Di Matteo has been involved in interpreting X-ray data and assessing accretion models throughout the project.

  8. Alignments Of Black Holes With Their Warped Accretion Disks And Episodic Lifetimes Of Active Galactic Nuclei

    Li, Yan-Rong; Cheng, Cheng; Qiu, Jie

    2015-01-01

    Warped accretion disks have attracted intensive attention because of their critical role on shaping the spin of supermassive massive black holes (SMBHs) through the Bardeen-Petterson effect, a general relativistic effect that leads to final alignments or anti-alignments between black holes and warped accretion disks. We study such alignment processes by explicitly taking into account the finite sizes of accretion disks and the episodic lifetimes of AGNs that delineate the duration of gas fueling onto accretion disks. We employ an approximate global model to simulate the evolution of accretion disks, allowing to determine the gravitomagnetic torque that drives the alignments in a quite simple way. We then track down the evolutionary paths for mass and spin of black holes both in a single activity episode and over a series of episodes. Given with randomly and isotropically oriented gas fueling over episodes, we calculate the spin evolution with different episodic lifetimes and find that it is quite sensitive to...

  9. Mid- to far infrared properties of star-forming galaxies and active galactic nuclei

    Magdis, G E; Helou, G; Farrah, D; Hurley, P; Alonso-Herrero, A; Bock, J; Burgarella, D; Chapman, S; Charmandaris, V; Cooray, A; Dai, Y S; Dale, D; Elbaz, D; Feltre, A; Hatziminaoglou, E; Huang, J-S; Morrison, G; Oliver, S; Page, M; Scott, D; Shi, Y

    2013-01-01

    We study the mid- to far-IR properties of a 24um-selected flux-limited sample (S24 > 5mJy) of 154 intermediate redshift (~0.15), infrared luminous galaxies, drawn from the 5MUSES survey. By combining existing mid-IR spectroscopy and new Herschel SPIRE submm photometry from the HerMES program, we derived robust total infrared luminosity (LIR) and dust mass (Md) estimates and infered the relative contribution of the AGN to the infrared energy budget of the sources. We found that the total infrared emission of galaxies with weak 6.2um PAH emission (EW0.2um more than 50% of the LIR arises from star formation. We also found that for galaxies detected in the 250-500um Herschel bands an AGN has a statistically insignificant effect on the temperature of the cold dust and the far-IR colours of the host galaxy, which are primarily shaped by star formation activity. For star-forming galaxies we reveal an anti-correlation between the LIR-to-rest-frame 8um luminosity ratio, IR8 = LIR\\L8, and the strength of PAH features. ...

  10. Variability of Active Galactic Nuclei from the Optical to X-ray Regions

    Gaskell, C Martin; 10.1080/1055679031000153851

    2009-01-01

    Some progress in understanding AGN variability is reviewed. Reprocessing of X-ray radiation to produce significant amounts of longer-wavelength continua seems to be ruled out. In some objects where there has been correlated X-ray and optical variability, the amplitude of the optical variability has exceeded the amplitude of X-ray variability. We suggest that accelerated particles striking material could be linking X-ray and optical variability (as in activity in the solar chromosphere). Beaming effects could be significant in all types of AGN. The diversity in optical/X-ray relationships at different times in the same object, and between different objects, might be explained by changes in geometry and directions of motion relative to our line of sight. Linear shot-noise models of the variability are ruled out; instead there must be large-scale organization of variability. Variability occurs on light-crossing timescales rather than viscous timescales and this probably rules out the standard Shakura-Sunyaev acc...

  11. Quasars and active galactic nuclei in rich environments. II - The evolution of radio-loud quasars

    It is shown here that the environments of radio-loud quasars have a strong effect on the optical evolution of the quasars. Quasars in rich clusters of galaxies are found to fade at least four optical magnitudes between redshifts 0.65 and 0.3, corresponding to a statistical e-folding fading time of about 1.0 Gyr. This rapid decrease in quasar activity is about four times as fast as quasars in poor environments. Several physical mechanisms of this evolution are suggested, emphasizing dynamical evolution of the cluster core and evolution in the amount of gaseous fuel in the cluster environment. The environments of radio-loud and radio-quiet quasars are shown to be significantly different. Radio-quiet quasars are much less frequently situated in galaxy clusters as rich as Abell class I. This result is consistent with scenarios linking radio-loud quasars with elliptical host galaxies and radio-quiet quasars with spiral host galaxies. 49 refs

  12. X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution

    Johnson, Seth P; Wang, Danial Q; Williams, Christina C; Scott, Kim S; Yun, Min S; Pope, Alexandra; Lowenthal, James; Aretxaga, Itziar; Hughes, David; Kim, M J; Kim, Sungeun; Tamura, Yoichi; Kohno, Kotaro; Ezawa, Hajime; Kawabe, Ryohei; Oshima, Tai; 10.1093/mnras/stt197

    2013-01-01

    We present a large-scale study of the X-ray properties and near-IR-to-radio SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral modeling and SED fitting using Monte Carlo Markov Chain techniques to Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst) templates, we find that while star formation dominates the IR emission, with SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2. Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a prior to the NIR-to-radio SED effectively...

  13. The host galaxies of active galactic nuclei with powerful relativistic jets

    Olguín-Iglesias, A.; León-Tavares, J.; Kotilainen, J. K.; Chavushyan, V.; Tornikoski, M.; Valtaoja, E.; Añorve, C.; Valdés, J.; Carrasco, L.

    2016-08-01

    We present deep near-infrared (NIR) images of a sample of 19 intermediate-redshift (0.3 1027 W Hz-1), previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes for blazars from literature. The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities L1.4 GHz ˜ 1023.7-1028.3 W Hz-1, allowing us to divide our sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our sample are bright and seem to follow the μe-Reff relation for ellipticals and bulges. The two populations of blazars show different behaviours in the MK,nuclear -MK,bulge plane, where a statistically significant correlation is observed for HLBs. Although it may be affected by selection effects, this correlation suggests a close coupling between the accretion mode of the central supermassive black hole and its host galaxy, which could be interpreted in terms of AGN feedback. Our findings are consistent with semi-analytical models where low-luminosity AGN emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and high-luminosity AGN are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes.

  14. Suzaku View of the Swift/BAT Active Galactic Nuclei. V. Torus Structure of Two Luminous Radio-Loud Active Galactic Nuclei (3C 206 and PKS 0707-35)

    Tazaki, Fumie; Ueda, Yoshihiro; Terashima, Yuichi; Mushotzky, Richard F.; Tombesi, Francesco

    2013-01-01

    We present the results from broadband X-ray spectral analysis of 3C 206 and PKS 0707-35 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei (AGNs) with hard X-ray luminosities of 10(sup 45.5) erg per second and 10(sup 44.9) erg per second (14-195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (60% in the 14-195 keV band) contribution from the jet, while it is negligible in PKS 0707-35.We can successfully model the spectra with the jet component (for 3C 206), the transmitted emission, and two reflection components from the torus and the accretion disk. The reflection strengths from the torus are found to be R(sub torus)(=Omega/2pi) = 0.29 +/- 0.18 and 0.41 +/- 0.18 for 3C 206 and PKS 0707-35, respectively, which are smaller than those in typical Seyfert galaxies. Utilizing the torus model by Ikeda et al., we quantify the relation between the half-opening angle of a torus (theta(sub oa)) and the equivalent width of an iron-K line. The observed equivalent width of 3C 206, less than 71 eV, constrains the column density in the equatorial plane to N(sup eq)(sub H) lesst han 10(sup 23) per square centimeter, or the half-opening angle to theta(sub oa) greater than 80 deg. if N(sup eq)(sub H) = 10(sup 24) per square centimeter is assumed. That of PKS 0707-35, 72 +/- 36 eV, is consistent with N(sup eq)(sub H) 10(sup 23) per square centimeter. Our results suggest that the tori in luminous radio-loud AGNs are only poorly developed. The trend is similar to that seen in radio-quiet AGNs, implying that the torus structure is not different between AGNs with jets and without jets.

  15. CHARACTERIZATION OF A SAMPLE OF INTERMEDIATE-TYPE ACTIVE GALACTIC NUCLEI. II. HOST BULGE PROPERTIES AND BLACK HOLE MASS ESTIMATES

    Benitez, Erika; Cruz-Gonzalez, Irene; Martinez, Benoni; Jimenez-Bailon, Elena [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Apdo. Postal 70-264, Mexico D.F. 04510 (Mexico); Mendez-Abreu, Jairo; Lopez-Martin, Luis [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Fuentes-Carrera, Isaura [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional (ESFM-IPN), U.P. Adolfo Lopez Mateos, Mexico D.F. 07730 (Mexico); Chavushyan, Vahram [Instituto Nacional de Astrofisica, Optica y Electronica, Apdo. Postal 51-216, 72000 Puebla (Mexico); Leon-Tavares, Jonathan, E-mail: erika@astro.unam.mx [Aalto University Metsaehovi Radio Observatory, Metsaehovintie 114, 02540 Kylmaelae (Finland)

    2013-02-15

    We present a study of the host bulge properties and their relations with the black hole mass for a sample of 10 intermediate-type active galactic nuclei (AGNs). Our sample consists mainly of early-type spirals, four of them hosting a bar. For 70{sup +10} {sub -17}% of the galaxies, we have been able to determine the type of the bulge, and find that these objects probably harbor a pseudobulge or a combination of classical bulge/pseudobulge, suggesting that pseudobulges might be frequent in intermediate-type AGNs. In our sample, 50% {+-} 14% of the objects show double-peaked emission lines. Therefore, narrow double-peaked emission lines seem to be frequent in galaxies harboring a pseudobulge or a combination of classical bulge/pseudobulge. Depending on the bulge type, we estimated the black hole mass using the corresponding M {sub BH}-{sigma}* relation and found them within a range of 5.69 {+-} 0.21 < log M {sup {sigma}}*{sub BH} < 8.09 {+-} 0.24. Comparing these M {sup {sigma}}*{sub BH} values with masses derived from the FWHM of H{beta} and the continuum luminosity at 5100 A from their SDSS-DR7 spectra (M {sub BH}), we find that 8 out of 10 (80{sup +7} {sub -17}%) galaxies have black hole masses that are compatible within a factor of 3. This result would support that M {sub BH} and M {sup {sigma}}*{sub BH} are the same for intermediate-type AGNs, as has been found for type 1 AGNs. However, when the type of the bulge is taken into account, only three out of the seven (43{sup +18} {sub -15}%) objects of the sample have their M {sup {sigma}}*{sub BH} and M {sub BH} compatible within 3{sigma} errors. We also find that estimations based on the M {sub BH}-{sigma}* relation for pseudobulges are not compatible in 50% {+-} 20% of the objects.

  16. Invisible Active Galactic Nuclei. II. Radio Morphologies and Five New H i 21cm Absorption Line Detectors

    Yan, Ting; Stocke, John T.; Darling, Jeremy; Momjian, Emmanuel; Sharma, Soniya; Kanekar, Nissim

    2016-03-01

    This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Paper I. In this paper, we present both high-resolution radio continuum images for all of these sources and H i 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size 0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H i 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral “window” (i.e., the percentage of H i 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H i detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H i absorption may well be present but is masked by the RFI. Future searches for

  17. On the relationship between black hole mass and X-ray variability amplitude in the low-mass regime of active galactic nuclei

    Pan, H.; Yuan, W.; Zhou, X.-L.; Dong, X.; Liu, B.

    2016-02-01

    Recent studies of active galactic nuclei (AGN) found a statistical inverse scaling between the X-ray normalized excess variance σrms 2 (variability amplitude) and the black hole mass spanning over M BH = 106 - 109 M ⊙. We present a study of this relation by including AGN with M BH = 105 - 106 M ⊙. It is found that the relation is no longer a simple extrapolation of the known inverse proportion, but starts to flatten around 106 M ⊙. This behavior can be understood by the shape of the power spectrum density of AGN and its dependence on the black hole mass.

  18. A view of the narrow-line region in the infrared: active galactic nuclei with resolved fine-structure lines in the Spitzer archive

    Dasyra, K. M.; Ho, L. C.; Netzer, H.; Combes, F; Trakhtenbrot, B.; Sturm, E.; Armus, L.; Elbaz, D.

    2011-01-01

    We queried the Spitzer archive for high-resolution observations with the Infrared Spectrograph of optically selected active galactic nuclei (AGNs) for the purpose of identifying sources with resolved fine-structure lines that would enable studies of the narrow-line region (NLR) at mid-infrared wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory spectra, we present kinematic information of the NLR for 81, z ≾ 0.3 AGNs. We used the [Ne v], [O iv], [Ne iii], and...

  19. Chandra X-ray and Hubble Space Telescope Imaging of Optically Selected Kiloparsec-Scale Binary Active Galactic Nuclei II: Host Galaxy Morphology and AGN Activity

    Shangguan, Jinyi; Ho, Luis C; Shen, Yue; Peng, Chien Y; Greene, Jenny E; Strauss, Michael A

    2016-01-01

    Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a gas-rich environment. While significant effort has been invested in their identification, the detailed properties of binary AGNs and their host galaxies are still poorly constrained. In a companion paper, we examined the nature of ionizing sources in the double nuclei of four kpc-scale binary AGNs with redshifts between 0.1~0.2. Here, we present their host galaxy morphology based on F336W (U-band) and F105W (Y-band) images taken by the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. Our targets have double-peaked narrow emission lines and were confirmed to host binary AGNs with follow up observations. We find that kpc-scale binary AGNs occur in galaxy mergers with diverse morphological types. There are three major mergers with intermediate morphologies and a minor merger with a dominant disk component. We estimate the masses of the SMBHs from ...

  20. Finding binary active galactic nuclei candidates by the centroid shift in imaging surveys II. Testing the method with SDSS J233635.75-010733.7

    Liu, Yuan

    2016-01-01

    In Liu (2015), we propose selecting binary active galactic nuclei (AGNs) candidates using the centroid shift of the images, which is induced by the non-synchronous variations of the two nuclei. In this paper, a known binary AGN (SDSS J233635.75-010733.7) is employed to verify the ability of this method. Using 162 exposures in the $R$ band of \\textit{Palomar Transient Factory} (PTF), an excess of dispersion in the positional distribution of the binary AGN is detected, though the two nuclei cannot be resolved in the images of PTF. We also propose a new method to compare the position of the binary AGN in PTF $g$ and $R$ band and find the difference is highly significant even only with 20 exposures. This new method is efficient for two nuclei with different spectral energy distributions, e.g., type I + type II AGN or off-set AGN. Large-scale surveys, e.g., the Panoramic Survey Telescope and Rapid Response System and the Large Synoptic Survey Telescope, are expected to discover a large sample of binary AGN candida...

  1. Spitzer Observations of Deeply Obscured Galactic Nuclei

    Spoon, H W W; Cami, J; Lahuis, F; Tielens, A G G M; Armus, L; Charmandaris, V

    2005-01-01

    We report on our first results from a mid-infrared spectroscopic study of ISM features in a sample of deeply obscured ULIRG nuclei using the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. The spectra are extremely rich and complex, revealing absorption features of both amorphous and crystalline silicates, aliphatic hydrocarbons, water ice and gas phase bands of hot CO and warm C_2H_2, HCN and CO_2. PAH emission bands were found to be generally weak and in some cases absent. The features are probing a dense and warm environment in which crystalline silicates and water ice are able to survive but volatile ices, commonly detected in Galactic dense molecular clouds, cannot. If powered largely by star formation, the stellar density and conditions of the gas and dust have to be extreme not to give rise to the commonly detected emission features associated with starburst.

  2. Changing ionization conditions in SDSS galaxies with active galactic nuclei as a function of environment from pairs to clusters

    We study how active galactic nucleus (AGN) activity changes across environments from galaxy pairs to clusters using 143,843 galaxies with z < 0.2 from the Sloan Digital Sky Survey. Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([N II] λ6548/Hα, [O III] λ5007/Hβ) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.

  3. Active galactic nuclei flicker: an observational estimate of the duration of black hole growth phases of ~1e5 years

    Schawinski, Kevin; Berney, Simon; Sartori, Lia

    2015-01-01

    We present an observational constraint for the typical active galactic nucleus (AGN) phase lifetime. The argument is based on the time lag between an AGN central engine switching on and becoming visible in X-rays, and the time the AGN then requires to photoionize a large fraction of the host galaxy. Based on the typical light travel time across massive galaxies, and the observed fraction of X-ray selected AGN without AGN-photoionized narrow lines, we estimate that the AGN phase typically lasts $\\sim10^{5}$ years. This lifetime is short compared to the total growth time of $10^{7}-10^{9}$ years estimated from e.g. the Soltan argument and implies that black holes grow via many such short bursts and that AGN therefore "flicker" on and off. We discuss some consequences of this flickering behavior for AGN feedback and the analogy of X-ray binaries and AGN lifecycles.

  4. Active galactic nuclei flicker: an observational estimate of the duration of black hole growth phases of ˜105 yr

    Schawinski, Kevin; Koss, Michael; Berney, Simon; Sartori, Lia F.

    2015-08-01

    We present an observational constraint for the typical active galactic nucleus (AGN) phase lifetime. The argument is based on the time lag between an AGN central engine switching on and becoming visible in X-rays, and the time the AGN then requires to photoionize a large fraction of the host galaxy. Based on the typical light travel time across massive galaxies, and the observed fraction of X-ray-selected AGN without AGN-photoionized narrow lines, we estimate that the AGN phase typically lasts ˜105 yr. This lifetime is short compared to the total growth time of 107-109 yr estimated from e.g. the Soltan argument and implies that black holes grow via many such short bursts and that AGN therefore `flicker' on and off. We discuss some consequences of this flickering behaviour for AGN feedback and the analogy of X-ray binaries and AGN lifecycles.

  5. Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database

    Peterson, B. M.; Ferrarese, L.; Gilbert, K. M.;

    2004-01-01

    We present improved black hole masses for 35 active galactic nuclei (AGNs) based on a complete and consistent reanalysis of broad emission-line reverberation-mapping data. From objects with multiple line measurements, we find that the highest precision measure of the virial product is obtained by...... depends critically on avoiding contaminating features, in particular the narrow components of the emission lines. We find that the precision (or random component of the error) of reverberation-based black hole mass measurements is typically around 30%, comparable to the precision attained in measurement...... of black hole masses in quiescent galaxies by gas or stellar dynamical methods. Based on results presented in a companion paper by Onken et al., we provide a zero-point calibration for the reverberation-based black hole mass scale by using the relationship between black hole mass and host...

  6. ALMA observations of a z~3.1 Protocluster: Star Formation from Active Galactic Nuclei and Lyman-Alpha Blobs in an Overdense Environment

    Alexander, D M; Harrison, C M; Mullaney, J R; Smail, I; Geach, J E; Hickox, R C; Hine, N K; Karim, A; Kubo, M; Lehmer, B D; Matsuda, Y; Rosario, D J; Stanley, F; Swinbank, A M; Umehata, H; Yamada, T

    2016-01-01

    We exploit ALMA 870um observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z~3.1 protocluster, four of which reside in extended Ly-alpha haloes (often termed Ly-alpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ~220-410~M_sun/yr; the non detection of the other five AGNs places SFR upper limits of 100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Ly-alpha emission. We use these results to discuss star formation as the power source of LABs.

  7. The NuSTAR Extragalactic Surveys: The Number Counts of Active Galactic Nuclei and the Resolved Fraction of the Cosmic X-ray Background

    Harrison, F A; Civano, F; Lansbury, G; Mullaney, J R; Ballantyne, D R; Alexander, D M; Stern, D; Ajello, M; Barret, D; Bauer, F E; Balokovic, M; Brandt, W N; Brightman, M; Boggs, S E; Christensen, F E; Comastri, A; Craig, W W; Del Moro, A; Forster, K; Gandhi, P; Giommi, P; Grefenstette, B W; Hailey, C J; Hickox, R C; Hornstrup, A; Kitaguchi, T; Koglin, J; Luo, B; Madsen, K K; Mao, P H; Miyasaka, H; Mori, K; Perri, M; Pivovaroff, M; Puccetti, S; Rana, V; Treister, E; Walton, D; Westergaard, N J; Wik, D; Zappacosta, L; Zhang, W W; Zoglauer, A

    2015-01-01

    We present the 3-8 keV and 8-24 keV number counts of active galactic nuclei (AGN) identified in the NuSTAR extragalactic surveys. NuSTAR has now resolved approximately 35% of the X-ray background in the 8-24 keV band, directly identifying AGN with obscuring columns up to 1e25 / cm2. In the softer 3-8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5e-15 1e-11 erg/cm2/s, for any realistic AGN spectral model. The most natural explanation for the difference is an evolution in the AGN poulation between the very local objects seen by BAT and the more distant (0.5 < z < 1) NuSTAR sample that is not accounted for in the current models.

  8. A CENSUS OF BROAD-LINE ACTIVE GALACTIC NUCLEI IN NEARBY GALAXIES: COEVAL STAR FORMATION AND RAPID BLACK HOLE GROWTH

    We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey are used to disentangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.

  9. A Census of Broad-Line Active Galactic Nuclei in Nearby Galaxies: Coeval Star Formation and Rapid Black Hole Growth

    Trump, Jonathan R; Fang, Jerome J; Faber, S M; Koo, David C; Kocevski, Dale D

    2012-01-01

    We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey (SDSS) are used to dis- entangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid superm...

  10. Delayed triggering of radio Active Galactic Nuclei in gas-rich minor mergers in the local Universe

    Shabala, Stanislav; Kaviraj, Sugata; Middelberg, Enno; Turner, Ross; Ting, Yuan-Sen; Allison, James; Davis, Tim

    2016-01-01

    We examine the processes triggering star formation and Active Galactic Nucleus (AGN) activity in a sample of 25 low redshift ($z10^7$ K) brightness temperature required for an mJIVE-20 detection allows us to unambiguously identify the radio AGN in our sample. We find three such objects. Our VLBI AGN identifications are classified as Seyferts or LINERs in narrow line optical diagnostic plots; mid-infrared colours of our targets and the comparison of H$\\alpha$ star formation rates with integrated radio luminosity are also consistent with the VLBI identifications. We reconstruct star formation histories in our galaxies using optical and UV photometry, and find that these radio AGN are not triggered promptly in the merger process, consistent with previous findings for non-VLBI samples of radio AGN. This delay can significantly limit the efficiency of feedback by radio AGN triggered in galaxy mergers. We find that radio AGN hosts have lower star formation rates than non-AGN radio-selected galaxies at the same star...

  11. The NuSTAR Extragalactic Survey: First Direct Measurements of the Greater Than Or Similar To 10 Kev X-Ray Luminosity Function For Active Galactic Nuclei At z > 0.1

    Aird, J.; Alexander, D. M.; Ballantyne, D. R.;

    2015-01-01

    We present the first direct measurements of the rest-frame 10-40 keV X-ray luminosity function (XLF) of active galactic nuclei (AGNs) based on a sample of 94 sources at 0.1

  12. A mid-infrared spectroscopic atlas of local active galactic nuclei on sub-arcsecond resolution using GTC/CanariCam

    Alonso-Herrero, A; Roche, P F; Almeida, C Ramos; Gonzalez-Martin, O; Packham, C; Levenson, N A; Mason, R E; Hernan-Caballero, A; Pereira-Santaella, M; Alvarez, C; Aretxaga, I; Lopez-Rodriguez, E; Colina, L; Diaz-Santos, T; Imanishi, M; Espinosa, J M Rodriguez; Perlman, E

    2015-01-01

    We present an atlas of mid-infrared (mid-IR) ~7.5-13micron spectra of 45 local active galactic nuclei (AGN) obtained with CanariCam on the 10.4m Gran Telescopio CANARIAS (GTC) as part of an ESO/GTC large program. The sample includes Seyferts and other low luminosity AGN (LLAGN) at a median distance of 35Mpc and luminous AGN, namely PG quasars, (U)LIRGs, and radio galaxies (RG) at a median distance of 254Mpc. To date, this is the largest mid-IR spectroscopic catalog of local AGN at sub-arcsecond resolution (median 0.3arcsec). The goal of this work is to give an overview of the spectroscopic properties of the sample. The nuclear 12micron luminosities of the AGN span more than four orders of magnitude, nu*Lnu(12micron)~ 3e41-1e46erg/s. In a simple mid-IR spectral index vs. strength of the 9.7micron silicate feature diagram most LLAGN, Seyfert nuclei, PG quasars, and RGs lie in the region occupied by clumpy torus model tracks. However, the mid-IR spectra of some might include contributions from other mechanisms. ...

  13. Chandra X-Ray and Hubble Space Telescope Imaging of Optically Selected Kiloparsec-scale Binary Active Galactic Nuclei. II. Host Galaxy Morphology and AGN Activity

    Shangguan, Jinyi; Liu, Xin; Ho, Luis C.; Shen, Yue; Peng, Chien Y.; Greene, Jenny E.; Strauss, Michael A.

    2016-05-01

    Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a gas-rich environment. While significant effort has been invested in their identification, the detailed properties of binary AGNs and their host galaxies are still poorly constrained. In a companion paper, we examined the nature of ionizing sources in the double nuclei of four kiloparsec-scale binary AGNs with redshifts between 0.1 and 0.2. Here, we present their host galaxy morphology based on F336W (U-band) and F105W (Y-band) images taken by the Wide Field Camera 3 on board the Hubble Space Telescope. Our targets have double-peaked narrow emission lines and were confirmed to host binary AGNs with follow-up observations. We find that kiloparsec-scale binary AGNs occur in galaxy mergers with diverse morphological types. There are three major mergers with intermediate morphologies and a minor merger with a dominant disk component. We estimate the masses of the SMBHs from their host bulge stellar masses and obtain Eddington ratios for each AGN. Compared with a representative control sample drawn at the same redshift and stellar mass, the AGN luminosities and Eddington ratios of our binary AGNs are similar to those of single AGNs. The U ‑ Y color maps indicate that clumpy star-forming regions could significantly affect the X-ray detection of binary AGNs, e.g., the hardness ratio. Considering the weak X-ray emission in AGNs triggered in merger systems, we suggest that samples of X-ray-selected AGNs may be biased against gas-rich mergers. Based, in part, on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program number GO 12363.

  14. THE OBSCURED FRACTION OF ACTIVE GALACTIC NUCLEI IN THE XMM-COSMOS SURVEY: A SPECTRAL ENERGY DISTRIBUTION PERSPECTIVE

    The fraction of active galactic nucleus (AGN) luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type 1) AGNs, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We use this technique to estimate the obscured AGN fraction as a function of luminosity and redshift for 513 Type 1 AGNs from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18 band COSMOS photometry with a custom spectral energy distribution fitting code, which jointly models emission from hot dust in the AGN torus, from the accretion disk, and from the host galaxy. We find a relatively shallow decrease of the luminosity ratio as a function of Lbol, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGNs, our measurements require a torus height that increases with luminosity as h ∝ Lbol0.3-0.4. Our obscured-fraction-luminosity relation agrees with determinations from Sloan Digital Sky Survey censuses of Type 1 and Type 2 quasars and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of the obscured fraction on 2-10 keV luminosity than previous determinations from X-ray surveys and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGNs. Our analysis shows no clear evidence for evolution of the obscured fraction with redshift

  15. On the virialization of disk winds: Implications for the black hole mass estimates in active galactic nuclei

    Estimating the mass of a supermassive black hole in an active galactic nucleus usually relies on the assumption that the broad line region (BLR) is virialized. However, this assumption seems to be invalid in BLR models that consist of an accretion disk and its wind. The disk is likely Keplerian and therefore virialized. However, beyond a certain point, the wind material must be dominated by an outward force that is stronger than gravity. Here, we analyze hydrodynamic simulations of four different disk winds: an isothermal wind, a thermal wind from an X-ray-heated disk, and two line-driven winds, one with and the other without X-ray heating and cooling. For each model, we determine whether gravity governs the flow properties by computing and analyzing the volume-integrated quantities that appear in the virial theorem: internal, kinetic, and gravitational energies. We find that in the first two models, the winds are non-virialized, whereas the two line-driven disk winds are virialized up to a relatively large distance. The line-driven winds are virialized because they accelerate slowly so that the rotational velocity is dominant and the wind base is very dense. For the two virialized winds, the so-called projected virial factor scales with inclination angle as 1/sin 2 i. Finally, we demonstrate that an outflow from a Keplerian disk becomes unvirialized more slowly when it conserves the gas specific angular momentum, as in the models considered here, than when it conserves the angular velocity, as in the so-called magneto-centrifugal winds.

  16. On the virialization of disk winds: Implications for the black hole mass estimates in active galactic nuclei

    Kashi, Amit; Proga, Daniel; Nagamine, Kentaro [Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154-4002 (United States); Greene, Jenny [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Barth, Aaron J., E-mail: kashia@physics.unlv.edu [Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697 (United States)

    2013-11-20

    Estimating the mass of a supermassive black hole in an active galactic nucleus usually relies on the assumption that the broad line region (BLR) is virialized. However, this assumption seems to be invalid in BLR models that consist of an accretion disk and its wind. The disk is likely Keplerian and therefore virialized. However, beyond a certain point, the wind material must be dominated by an outward force that is stronger than gravity. Here, we analyze hydrodynamic simulations of four different disk winds: an isothermal wind, a thermal wind from an X-ray-heated disk, and two line-driven winds, one with and the other without X-ray heating and cooling. For each model, we determine whether gravity governs the flow properties by computing and analyzing the volume-integrated quantities that appear in the virial theorem: internal, kinetic, and gravitational energies. We find that in the first two models, the winds are non-virialized, whereas the two line-driven disk winds are virialized up to a relatively large distance. The line-driven winds are virialized because they accelerate slowly so that the rotational velocity is dominant and the wind base is very dense. For the two virialized winds, the so-called projected virial factor scales with inclination angle as 1/sin {sup 2} i. Finally, we demonstrate that an outflow from a Keplerian disk becomes unvirialized more slowly when it conserves the gas specific angular momentum, as in the models considered here, than when it conserves the angular velocity, as in the so-called magneto-centrifugal winds.

  17. THE SPITZER MID-INFRARED ACTIVE GALACTIC NUCLEUS SURVEY. I. OPTICAL AND NEAR-INFRARED SPECTROSCOPY OF OBSCURED CANDIDATES AND NORMAL ACTIVE GALACTIC NUCLEI SELECTED IN THE MID-INFRARED

    Lacy, M. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Ridgway, S. E. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Gates, E. L. [UCO/Lick Observatory, P.O. Box 85, Mount Hamilton, CA 95140 (United States); Nielsen, D. M. [Department of Astronomy, University of Wisconsin, 475 N. Charter Street, Madison, WI 53706 (United States); Petric, A. O. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Sajina, A. [Department of Physics and Astronomy, Tuffs University, 212 College Avenue, Medford, MA 02155 (United States); Urrutia, T. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Cox Drews, S. [946 Mangrove Avenue 102, Sunnyvale, CA 94086 (United States); Harrison, C. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Seymour, N. [CSIRO, P.O. Box 76, Epping, NSW 1710 (Australia); Storrie-Lombardi, L. J. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-10-01

    We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate active galactic nuclei (AGNs) selected in the mid-infrared. This survey selects both normal and obscured AGNs closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L {sub bol} ∼ 10{sup 10} L {sub ☉} to highly luminous quasars (L {sub bol} ∼ 10{sup 14} L {sub ☉}), all with redshifts ranging from 0 to 4.3. Samples of candidate AGNs were selected with mid-infrared color cuts at several different 24 μm flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGNs and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type 1 AGNs with blue continua, 294 (44%) are type 2 objects with extinctions A{sub V} ∼> 5 toward their AGNs, 96 (14%) are AGNs with lower extinctions (A{sub V} ∼ 1), and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. Of the survey objects 50% have L {sub bol} > 10{sup 12} L {sub ☉}, in the quasar regime. We present composite spectra for type 2 quasars and objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared—emission-line luminosity correlation and present the results of cross correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) mid-infrared selected AGN candidates exist which lack AGN signatures in their optical spectra but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGNs often differ.

  18. Herschel far-infrared photometry of the swift burst alert telescope active galactic nuclei sample of the local universe. I. PACS observations

    Far-Infrared (FIR) photometry from the Photodetector Array Camera and Spectrometer on the Herschel Space Observatory is presented for 313 nearby, hard X-ray selected galaxies from the 58 month Swift Burst Alert Telescope (BAT) Active Galactic Nuclei catalog. The present data do not distinguish between the FIR luminosity distributions at 70 and 160 μm for Seyfert 1 and Seyfert 2 galaxies. This result suggests that if the FIR emission is from the nuclear obscuring material surrounding the accretion disk, then it emits isotropically, independent of orientation. Alternatively, a significant fraction of the 70 and 160 μm luminosity could be from star formation, independent of active galactic nucleus (AGN) type. Using a non-parametric test for partial correlation with censored data, we find a statistically significant correlation between the AGN intrinsic power (in the 14-195 keV band) and the FIR emission at 70 and 160 μm for Seyfert 1 galaxies. We find no correlation between the 14-195 keV and FIR luminosities in Seyfert 2 galaxies. The observed correlations suggest two possible scenarios: (1) if we assume that the FIR luminosity is a good tracer of star formation, then there is a connection between star formation and the AGN at sub-kiloparsec scales, or (2) dust heated by the AGN has a statistically significant contribution to the FIR emission. Using a Spearman rank-order analysis, the 14-195 keV luminosities for the Seyfert 1 and 2 galaxies are weakly statistically correlated with the F 70/F 160 ratios.

  19. X-ray variability of 104 active galactic nuclei. XMM-Newton power-spectrum density profiles

    Gonzalez-Martin, O.; Vaughan, S

    2012-01-01

    AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. We have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z

  20. Observations, with the H.E.S.S. telescopes, of the gamma emission by the Active Galactic Nuclei PKS 2155-304 above 100 GeV

    The H.E.S.S. (High Energy Stereoscopic System) experiment consists of four imaging Atmospheric Cerenkov detectors dedicated to the study of southern hemisphere sources emitting photons above 100 GeV. This thesis presents the instrument and also the analysis chain. First the calibration of the cameras is presented using 'classical methods' (pulsed light systems, pedestals positions...) but also real Cerenkov signal coming from atmospheric muons. An extraction method for gamma ray signals then presented with the spectral shape determination, which is applied to the Crab Nebula. All these techniques were applied to confirm the emission above 100 GeV from the Active Galactic Nuclei PKS 2155-304. The different observation periods in 2002 and 2003 show a quasi-stable source activity which allowed to postulate the first detection of a quiescent state for this type of object in the TeV range. This confirm the gain in sensitivity reached by H.E.S.S. compared to the previous experiments. The spectrum of PKS 2155-304 allows the study of the extragalactic background light using absorption of the very high energy emission from the source. This study leads to incoherencies between a pure SSC scenario for BL Lac objects and high EBL densities. (author)

  1. ACTIVE GALACTIC NUCLEI AS MAIN CONTRIBUTORS TO THE ULTRAVIOLET IONIZING EMISSIVITY AT HIGH REDSHIFTS: PREDICTIONS FROM A {Lambda}-CDM MODEL WITH LINKED AGN/GALAXY EVOLUTION

    Giallongo, E.; Menci, N.; Fiore, F.; Castellano, M.; Fontana, A.; Grazian, A.; Pentericci, L. [INAF-Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio (Italy)

    2012-08-20

    We have evaluated the contribution of the active galactic nuclei (AGN) population to the ionization history of the universe based on a semi-analytic model of galaxy formation and evolution in the cold dark matter cosmological scenario. The model connects the growth of black holes and of the ensuing AGN activity to galaxy interactions. In the model we have included a self-consistent physical description of the escape of ionizing UV photons; this is based on the blast-wave model for the AGN feedback we developed in a previous paper to explain the distribution of hydrogen column densities in AGNs of various redshifts and luminosities, due to absorption by the host galaxy gas. The model predicts UV luminosity functions for AGNs that are in good agreement with those derived from the observations especially at low and intermediate redshifts (z {approx} 3). At higher redshifts (z > 5), the model tends to overestimate the data at faint luminosities. Critical biases in both the data and in the model are discussed to explain such apparent discrepancies. The predicted hydrogen photoionization rate as a function of redshift is found to be consistent with that derived from the observations. All of the above suggests that we should reconsider the role of the AGNs as the main driver of the ionization history of the universe.

  2. The NuSTAR view of nearby Compton-thick active galactic nuclei: the cases of NGC 424, NGC 1320, and IC 2560

    We present X-ray spectral analyses for three Seyfert 2 active galactic nuclei (AGNs), NGC 424, NGC 1320, and IC 2560, observed by NuSTAR in the 3-79 keV band. The high quality hard X-ray spectra allow detailed modeling of the Compton reflection component for the first time in these sources. Using quasi-simultaneous NuSTAR and Swift/XRT data, as well as archival XMM-Newton data, we find that all three nuclei are obscured by Compton-thick material with column densities in excess of ∼5 × 1024 cm–2, and that their X-ray spectra above 3 keV are dominated by reflection of the intrinsic continuum on Compton-thick material. Due to the very high obscuration, absorbed intrinsic continuum components are not formally required by the data in any of the sources. We constrain the intrinsic photon indices and the column density of the reflecting medium through the shape of the reflection spectra. Using archival multi-wavelength data we recover the intrinsic X-ray luminosities consistent with the broadband spectral energy distributions. Our results are consistent with the reflecting medium being an edge-on clumpy torus with a relatively large global covering factor and overall reflection efficiency of the order of 1%. Given the unambiguous confirmation of the Compton-thick nature of the sources, we investigate whether similar sources are likely to be missed by commonly used selection criteria for Compton-thick AGNs, and explore the possibility of finding their high-redshift counterparts.

  3. The NuSTAR View of Nearby Compton-thick Active Galactic Nuclei: The Cases of NGC 424, NGC 1320, and IC 2560

    Baloković, M.; Comastri, A.; Harrison, F. A.; Alexander, D. M.; Ballantyne, D. R.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Moro, A. Del; Gandhi, P.; Hailey, C. J.; Koss, M.; Lansbury, G. B.; Luo, B.; Madejski, G. M.; Marinucci, A.; Matt, G.; Markwardt, C. B.; Puccetti, S.; Reynolds, C. S.; Risaliti, G.; Rivers, E.; Stern, D.; Walton, D. J.; Zhang, W. W.

    2014-09-30

    We present X-ray spectral analyses for three Seyfert 2 active galactic nuclei, NGC 424, NGC 1320, and IC 2560, observed by NuSTAR in the 3-79 keV band. The high quality hard X-ray spectra allow detailed modeling of the Compton reflection component for the first time in these sources. Using quasi-simultaneous NuSTAR and Swift/XRT data, as well as archival XMM-Newton data, we find that all three nuclei are obscured by Compton-thick material with column densities in excess of ~ 5 x 1024 cm-2, and that their X-ray spectra above 3 keV are dominated by reflection of the intrinsic continuum on Compton-thick material. Due to the very high obscuration, absorbed intrinsic continuum components are not formally required by the data in any of the sources. We constrain the intrinsic photon indices and the column density of the reflecting medium through the shape of the reflection spectra. Using archival multi-wavelength data we recover the intrinsic X-ray luminosities consistent with the broadband spectral energy distributions. Our results are consistent with the reflecting medium being an edge-on clumpy torus with a relatively large global covering factor and overall reflection efficiency of the order of 1%. Given the unambiguous confirmation of the Compton-thick nature of the sources, we investigate whether similar sources are likely to be missed by commonly used selection criteria for Compton-thick AGN, and explore the possibility of finding their high-redshift counterparts.

  4. A NEW EXTENSIVE CATALOG OF OPTICALLY VARIABLE ACTIVE GALACTIC NUCLEI IN THE GOODS FIELDS AND A NEW STATISTICAL APPROACH TO VARIABILITY SELECTION

    Variability is a property shared by practically all active galactic nuclei (AGNs). This makes variability selection a possible technique for identifying AGNs. Given that variability selection makes no prior assumption about spectral properties, it is a powerful technique for detecting both low-luminosity AGNs in which the host galaxy emission is dominating and AGNs with unusual spectral properties. In this paper, we will discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates. We will apply these methods to the GOODS North and South fields and present a catalog of variable sources in the z band in both GOODS fields. Out of the 11,931 objects checked, we find 155 variable sources at a significance level of 99.9%, corresponding to about 1.3% of all objects. After rejection of stars and supernovae, 139 variability-selected AGNs remain. Their magnitudes reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for 22 of the variability-selected AGNs, ranging from 0.046 to 3.7. The absolute magnitudes in the rest-frame z band range from ∼-18 to -24, reaching substantially fainter than the typical luminosities probed by traditional X-ray and spectroscopic AGN selection in these fields. Therefore, this is a powerful technique for future exploration of the evolution of the faint end of the AGN luminosity function up to high redshifts.

  5. Clustering, Cosmology and a New Era of Black Hole Demographics -- II. The Conditional Luminosity Functions of Type 2 and Type 1 Active Galactic Nuclei

    Ballantyne, D R

    2016-01-01

    The orientation-based unification model of active galactic nuclei (AGNs) posits that the principle difference between obscured (Type 2) and unobscured (Type 1) AGNs is the line-of-sight into the central engine. If this model is correct than there should be no difference in many of the properties of AGN host galaxies (e.g., the mass of the surrounding dark matter haloes). However, recent clustering analyses of Type 1 and Type 2 AGNs have provided some evidence for a difference in the halo mass, in conflict with the orientation-based unified model. In this work, a method to compute the Conditional Luminosity Function (CLF) of Type 2 and Type 1 AGNs is presented. The CLF allows many fundamental halo properties to be computed as a function of AGN luminosity, which we apply to the question of the host halo masses of Type 1 and 2 AGNs. By making use of the total AGN CLF, the Type 1 X-ray luminosity function, and the luminosity-dependent Type 2 AGN fraction, the CLFs of Type 1 and 2 AGNs are calculated at $z\\approx ...

  6. The spatial clustering of ROSAT All-Sky Survey Active Galactic Nuclei IV. More massive black holes reside in more massive dark matter halos

    Krumpe, Mirko; Husemann, Bernd; Fanidakis, Nikos; Coil, Alison L; Aceves, Hector

    2015-01-01

    This is the fourth paper in a series that reports on our investigation of the clustering properties of active galactic nuclei (AGN) identified in the ROSAT All-Sky Survey (RASS) and Sloan Digital Sky Survey (SDSS). In this paper we investigate the cause of the X-ray luminosity dependence of the clustering of broad-line, luminous AGN at 0.16

  7. The Origin of Double-peaked Narrow Lines in Active Galactic Nuclei II: Kinematic Classifications for the Population at z < 0.1

    Nevin, Rebecca; Müller-Sánchez, Francisco; Barrows, R Scott; Cooper, Michael

    2016-01-01

    We present optical longslit observations of the complete sample of 71 Type 2 active galactic nuclei (AGNs) with double-peaked narrow emission lines at $z < 0.1$ in the Sloan Digital Sky Survey. Double-peaked emission lines are produced by a variety of mechanisms including disk rotation, kpc-scale dual AGNs, and NLR kinematics (outflows or inflows). We develop a novel kinematic classification technique to determine the nature of these objects using longslit spectroscopy alone. We determine that 86% of the double-peaked profiles are produced by moderate luminosity AGN outflows, 6% are produced by rotation, and 8% are ambiguous. While we are unable to directly identify dual AGNs with longslit data alone, we explore their potential kinematic classifications with this method. We also find a positive correlation between the narrow-line region (NLR) size and luminosity of the AGN NLRs (R$_{\\mathrm{NLR}}\\propto \\; {\\mathrm{L}_{\\mathrm{[OIII]}}}^{0.21 \\pm 0.05}$), indicating a clumpy two-zone ionization model for t...

  8. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. III. Detection of Fe II Reverberation in Nine Narrow-Line Seyfert 1 Galaxies

    Hu, Chen; Lu, Kai-Xing; Li, Yan-Rong; Wang, Fang; Qiu, Jie; Bai, Jin-Ming; Kaspi, Shai; Ho, Luis C; Netzer, Hagai; Wang, Jian-Min

    2015-01-01

    This is the third in a series of papers reporting on a large reverberation-mapping campaign aimed to study the properties of active galactic nuclei (AGNs) with high accretion rates. We present new results on the variability of the optical Fe II emission lines in 10 AGNs observed by the Yunnan Observatory 2.4m telescope during 2012--2013. We detect statistically significant time lags, relative to the AGN continuum, in nine of the sources. This accurate measurement is achieved by using a sophisticated spectral fitting scheme that allows for apparent flux variations of the host galaxy, and several narrow lines, due to the changing observing conditions. Six of the newly detected lags are indistinguishable from the Hbeta lags measured in the same sources. Two are significantly longer and one is slightly shorter. Combining with Fe II lags reported in previous studies, we find a Fe II radius--luminosity relationship similar to the one for Hbeta, although our sample by itself shows no clear correlation. The results s...

  9. THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI: THE EFFECT OF HOST-GALAXY STARLIGHT ON LUMINOSITY MEASUREMENTS. II. THE FULL SAMPLE OF REVERBERATION-MAPPED AGNs

    We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to ground-based spectroscopic luminosity measurements at 5100 A. After correcting the luminosities of the AGNs for the contribution from starlight, we re-examine the Hβ R BLR-L relationship. Our best fit for the relationship gives a power-law slope of 0.52 with a range of 0.45-0.59 allowed by the uncertainties. This is consistent with our previous findings, and thus still consistent with the naive assumption that all AGNs are simply luminosity-scaled versions of each other. We discuss various consistency checks relating to the galaxy modeling and starlight contributions, as well as possible systematic errors in the current set of reverberation measurements from which we determine the form of the R BLR-L relationship.

  10. Active galactic nuclei cores in infrared-faint radio sources: Very long baseline interferometry observations using the Very Long Baseline Array

    Herzog, Andreas; Norris, Ray P; Spitler, Lee R; Deller, Adam T; Collier, Jordan D; Parker, Quentin A

    2015-01-01

    Infrared-faint radio sources (IFRS) form a new class of galaxies characterised by radio flux densities between tenths and tens of mJy and faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs) at significant redshifts (z >~ 2). Whereas the high redshifts of IFRS have been recently confirmed based on spectroscopic data, the evidence for the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs have been unquestionably confirmed in IFRS based on very long baseline interferometry (VLBI) observations. In this work, we test the hypothesis that IFRS contain AGNs in a large sample of sources using VLBI. We observed 57 IFRS with the Very Long Baseline Array (VLBA) down to a detection sensitivity in the sub-mJy regime and detected compact cores in 35 sources. Our VLBA detections increase the number of VLBI-detected IFRS from 2 to 37 and provide strong evidence that most - if not all - IFRS contain AGNs. We find that IFRS have a marginal...

  11. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. V. A New Size-Luminosity Scaling Relation for the Broad-Line Region

    Du, Pu; Zhang, Zhi-Xiang; Huang, Ying-Ke; Wang, Kai; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Fan, Xu-Liang; Fang, Xiang-Er; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Ho, Luis C; Wang, Jian-Min

    2016-01-01

    This paper reports results of the third-year campaign of monitoring super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs) between 2014-2015. Ten new targets were selected from quasar sample of Sloan Digital Sky Survey (SDSS), which are generally more luminous than the SEAMBH candidates in last two years. H$\\beta$ lags ($\\tau_{_{\\rm H\\beta}}$) in five of the 10 quasars have been successfully measured in this monitoring season. We find that the lags are generally shorter, by large factors, than those of objects with same optical luminosity, in light of the well-known $R_{_{\\rm H\\beta}}-L_{5100}$ relation. The five quasars have dimensionless accretion rates of $\\dot{\\mathscr{M}}=10-10^3$. Combining measurements of the previous SEAMBHs, we find that the reduction of H$\\beta$ lags tightly depends on accretion rates, $\\tau_{_{\\rm H\\beta}}/\\tau_{_{R-L}}\\propto\\dot{\\mathscr{M}}^{-0.42}$, where $\\tau_{_{R-L}}$ is the H$\\beta$ lag from the normal $R_{_{\\rm H\\beta}}-L_{5100}$ relation....

  12. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VI. Velocity-resolved Reverberation Mapping of H$\\beta$ Line

    Du, Pu; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Huang, Ying-Ke; Wang, Fang; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Ho, Luis C; Wang, Jian-Min

    2016-01-01

    In the sixth of the series of papers reporting on a large reverberation mapping (RM) campaign of active galactic nuclei (AGNs) with high accretion rates, we present velocity-resolved time lags of H$\\beta$ emission lines for nine objects observed in the campaign during 2012$-$2013. In order to correct the line-broadening caused by seeing and instruments before the analysis of velocity-resolved RM, we adopt Richardson-Lucy deconvolution to reconstruct their H$\\beta$ profiles. The validity and effectiveness of the deconvolution are checked out by Monte Carlo simulation. Five among the nine objects show clear dependence of time delay on velocity. Mrk 335 and Mrk 486 show signatures of gas inflow whereas the clouds in the broad-line regions (BLRs) of Mrk 142 and MCG +06-26-012 tend to be radial outflowing. Mrk 1044 is consistent with the case of virialized motions. The lags of the rest four are not velocity-resolvable. The velocity-resolved RM of super-Eddington accreting massive black holes (SEAMBHs) shows that t...

  13. The Biases of Optical Line-Ratio Selection for Active Galactic Nuclei, and the Intrinsic Relationship between Black Hole Accretion and Galaxy Star Formation

    Trump, Jonathan R; Zeimann, Gregory R; Luck, Cuyler; Bridge, Joanna S; Grier, Catherine J; Hagen, Alex; Juneau, Stephanie; Montero-Dorta, Antonio; Rosario, David J; Brandt, W Niel; Ciardullo, Robin; Schneider, Donald P

    2015-01-01

    We use 317,000 emission-line galaxies from the Sloan Digital Sky Survey to investigate line-ratio selection of active galactic nuclei (AGNs). In particular, we demonstrate that "star formation dilution" by HII regions causes a significant bias against AGN selection in low-mass, blue, star-forming, disk-dominated galaxies. This bias is responsible for the observed preference of AGNs among high-mass, green, moderately star-forming, bulge-dominated hosts. We account for the bias and simulate the intrinsic population of emission-line AGNs using a physically-motivated Eddington ratio distribution, intrinsic AGN narrow line region line ratios, a luminosity-dependent Lbol/L[OIII] bolometric correction, and the observed Mbh-sigma relation. These simulations indicate that, in massive (log(M*/Msun) > 10) galaxies, AGN accretion is correlated with specific star formation rate but is otherwise uniform with stellar mass. There is some hint of lower black hole occupation in low-mass (log(M*/Msun) < 10) hosts, although o...

  14. A Radial Velocity Test for Supermassive Black Hole Binaries as an Explanation for Broad, Double-Peaked Emission Lines in Active Galactic Nuclei

    Liu, Jia; Halpern, Jules P

    2015-01-01

    One of the proposed explanations for the broad, double-peaked Balmer emission lines observed in the spectra of some active galactic nuclei (AGNs) is that they are associated with sub-parsec supermassive black hole (SMBH) binaries. Here, we test the binary broad-line region hypothesis through several decades of monitoring of the velocity structure of double-peaked H-alpha emission lines in 13 low-redshift, mostly radio-loud AGNs. This is a much larger set of objects compared to an earlier test by Eracleous et al. (1997) and we use much longer time series for the three objects studied in that paper. Although systematic changes in radial velocity can be traced in many of their lines, they are demonstrably not like those of a spectroscopic binary in a circular orbit. Any spectroscopic binary period must therefore be much longer than the span of the monitoring (assuming a circular orbit), which in turn would require black hole masses that exceed by 1-2 orders of magnitude the values obtained for these objects usin...

  15. Suzaku follow-up of heavily obscured active galactic nuclei detected in Swift/BAT survey: NGC 1106, UGC 03752, and NGC 2788A

    Tanimoto, Atsushi; Ueda, Yoshihiro; Kawamuro, Taiki; Ricci, Claudio

    2016-03-01

    We present the broad-band (0.5-100 keV) spectra of three heavily obscured active galactic nuclei (AGNs), NGC 1106, UGC 03752, and NGC 2788A, observed with Suzaku and the Swift/Burst Alert Telescope (BAT). The targets are selected from the Swift/BAT 70-month catalog on the basis of their high hardness ratio between above and below 10 keV, and their X-ray spectra are reported here for the first time. We apply three models: a conventional model utilizing an analytic reflection code, and two Monte Carlo based torus models with a doughnut-like geometry (MYTorus: Murphy & Yaqoob, 2009, MNRAS, 397, 1549) and with a nearly spherical geometry (Ikeda torus: Ikeda et al., 2009, ApJ, 692, 608). The three models can successfully reproduce the spectra, and the Ikeda torus model gives a better description than the MYTorus model in all targets. We identify NGC 1106 and NGC 2788A as Compton-thick AGNs. We point out that the common presence of unabsorbed reflection components below 7.1 keV in obscured AGNs, as observed from UGC 03752, is evidence for clumpy tori. This implies that detailed studies utilizing clumpy torus models are required to reach correct interpretation of the X-ray spectra of AGNs.

  16. Suzaku View of the Swift/BAT Active Galactic Nuclei. V. Torus Structure of Two Luminous Radio-loud AGNs (3C 206 and PKS 0707-35)

    Tazaki, Fumie; Terashima, Yuichi; Mushotzky, Richard; Tombesi, Francesco

    2013-01-01

    We present the results from broad-band X-ray spectral analysis of 3C 206 and PKS 0707-35 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei with hard X-ray luminosities of 10^{45.5} erg s^{-1} and 10^{44.9} erg s^{-1} (14--195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (~ 60% in the 14--195 keV band) contribution from the jet, while it is negligible in PKS 0707-35. We can successfully model the spectra with the jet component (for 3C 206), the transmitted emission, and two reflection components from the torus and the accretion disk. The reflection strengths from the torus are found to be R_{torus} (= \\Omega/2\\pi) = 0.29 +- 0.18 and 0.41 +- 0.18 for 3C 206 and PKS 0707-35, respectively, which are smaller than those in typical Seyfert galaxies. Utilizing the torus model by Ikeda et al. (2009), we quantify the relation between the half opening angle of a torus (\\theta_{oa}) ...

  17. Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array

    Jorstad, S G; Lister, M L; Stirling, A M; Cawthorne, T V; Gear, W K; Gómez, J L; Stevens, J A; Smith, P S; Forster, J R; Gabuzda, D C; Robson, E I; Jorstad, Svetlana G.; Marscher, Alan P.; Lister, Matthew L.; Stirling, Alastair M.; Cawthorne, Timothy V.; Gear, Walter K.; Gomez, Jose L.; Stevens, Jason A.; Smith, Paul S.; Forster, James R.; Gabuzda, Denise C.

    2005-01-01

    We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7 mm at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3 mm, 1.35/0.85 mm, and optical wavelengths. Here we analyze the 7 mm images to define the properties of the jets of two radio galaxies, five BL Lac objects, and eight quasars on angular scales $\\gtrsim 0.1$ milliarcseconds. We determine the apparent velocities of 109 features in the jets; for many of the features we derive Doppler factors using a new method based on comparison of timescale of decline in flux density with the light-travel time across the emitting region. This allows us to estimate the Lorentz factors, intrinsic brightness temperatures, and viewing angles of 77 superluminal knots, as well as the opening angle of the jet for each source. We analyze the derived physical parameters of the jets. In nine sources we detect statistically m...

  18. The case for cases B and C: intrinsic hydrogen line ratios of the broad-line region of active galactic nuclei, reddenings, and accretion disc sizes

    Gaskell, C Martin

    2016-01-01

    Low-redshift active galactic nuclei (AGNs) with extremely blue optical spectral indices are shown to have a mean, velocity-averaged, broad-line H$\\alpha$/H$\\beta$ ratio of $\\thickapprox 2.72 \\pm 0.04$, consistent with the Baker-Menzel Case B value. Comparison of a wide range of properties of the very bluest AGNs with those of a luminosity-matched subset of the Dong et al. blue AGN sample indicates that the only difference is the internal reddening. Ultraviolet fluxes are brighter for the bluest AGNs by an amount consistent with the flat AGN reddening curve of Gaskell et al. (2004). The lack of a significant difference in the GALEX (FUV--NUV) colour index strongly rules out a steep SMC-like reddening curve and also argues against an intrinsically harder spectrum. For very blue AGNs the Ly$\\alpha$/H$\\beta$ ratio is also consistent with being the Case B value. The Case B ratios provide strong support for the self-shielded broad-line model of Gaskell, Klimek & Nazarova. It is proposed that the greatly enhance...

  19. A view of the narrow-line region in the infrared: active galactic nuclei with resolved fine-structure lines in the Spitzer archive

    Dasyra, K M; Netzer, H; Combes, F; Traktenbrot, B; Sturm, E; Armus, L; Elbaz, D

    2011-01-01

    We queried the Spitzer archive for high-resolution observations with the Infrared Spectrograph of optically selected active galactic nuclei (AGN) for the purpose of identifying sources with resolved fine-structure lines that would enable studies of the narrow-line region (NLR) at mid-infrared wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory spectra, we present kinematic information of the NLR for 81 z<=0.3 AGNs. We used the [NeV], [OIV], [NeIII], and [SIV] lines, whose fluxes correlate well with each other, to probe gas photoionized by the AGN. We found that the widths of the lines are, on average, increasing with the ionization potential of the species that emit them. No correlation of the line width with the critical density of the corresponding transition was found. The velocity dispersion of the gas, sigma, is systematically higher than that of the stars, sigma_*, in the AGN host galaxy, and it scales with the mass of the central black hole, M_BH. Further correlations bet...

  20. Constraining UV continuum slopes of active galactic nuclei with cloudy models of broad-line region extreme-ultraviolet emission lines

    Moloney, Joshua [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States); Michael Shull, J., E-mail: joshua.moloney@colorado.edu, E-mail: michael.shull@colorado.edu [Also at Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK. (United Kingdom)

    2014-10-01

    Understanding the composition and structure of the broad-line region (BLR) of active galactic nuclei (AGNs) is important for answering many outstanding questions in supermassive black hole evolution, galaxy evolution, and ionization of the intergalactic medium. We used single-epoch UV spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to measure EUV emission-line fluxes from four individual AGNs with 0.49 ≤ z ≤ 0.64, two AGNs with 0.32 ≤ z ≤ 0.40, and a composite of 159 AGNs. With the CLOUDY photoionization code, we calculated emission-line fluxes from BLR clouds with a range of density, hydrogen ionizing flux, and incident continuum spectral indices. The photoionization grids were fit to the observations using single-component and locally optimally emitting cloud (LOC) models. The LOC models provide good fits to the measured fluxes, while the single-component models do not. The UV spectral indices preferred by our LOC models are consistent with those measured from COS spectra. EUV emission lines such as N IV λ765, O II λ833, and O III λ834 originate primarily from gas with electron temperatures between 37,000 K and 55,000 K. This gas is found in BLR clouds with high hydrogen densities (n {sub H} ≥ 10{sup 12} cm{sup –3}) and hydrogen ionizing photon fluxes (Φ{sub H} ≥ 10{sup 22} cm{sup –2} s{sup –1}).

  1. No more active galactic nuclei in clumpy disks than in smooth galaxies at z ∼ 2 in CANDELS/3D-HST

    Trump, Jonathan R.; Luo, Bin; Brandt, W. N. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Barro, Guillermo; Guo, Yicheng; Koo, David C.; Faber, S. M. [University of California Observatories/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Juneau, Stéphanie [Irfu/Service d' Astrophysique, CEA-Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France); Weiner, Benjamin J. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Brammer, Gabriel B.; Ferguson, Henry C.; Grogin, Norman A.; Kartaltepe, Jeyhan; Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Dekel, Avishai [Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Hopkins, Philip F. [California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Kocevski, Dale D. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); McIntosh, Daniel H. [Department of Physics and Astronomy, University of Missouri-Kansas City, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Momcheva, Ivelina [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); and others

    2014-10-01

    We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to investigate if active galactic nuclei (AGNs) are preferentially fueled by violent disk instabilities funneling gas into galaxy centers at 1.3 < z < 2.4. We select galaxies undergoing gravitational instabilities using the number of clumps and degree of patchiness as proxies. The CANDELS visual classification system is used to identify 44 clumpy disk galaxies, along with mass-matched comparison samples of smooth and intermediate morphology galaxies. We note that despite being mass-matched and having similar star formation rates, the smoother galaxies tend to be smaller disks with more prominent bulges compared to the clumpy galaxies. The lack of smooth extended disks is probably a general feature of the z ∼ 2 galaxy population, and means we cannot directly compare with the clumpy and smooth extended disks observed at lower redshift. We find that z ∼ 2 clumpy galaxies have slightly enhanced AGN fractions selected by integrated line ratios (in the mass-excitation method), but the spatially resolved line ratios indicate this is likely due to extended phenomena rather than nuclear AGNs. Meanwhile, the X-ray data show that clumpy, smooth, and intermediate galaxies have nearly indistinguishable AGN fractions derived from both individual detections and stacked non-detections. The data demonstrate that AGN fueling modes at z ∼ 1.85—whether violent disk instabilities or secular processes—are as efficient in smooth galaxies as they are in clumpy galaxies.

  2. Time Series Analysis of Active Galactic Nuclei: The case of Arp 102B, 3C 390.3, NGC 5548 and NGC 4051

    Kovacevic, A; Shapovalova, A I; Ilic, D; Burenkov, A N; Chavushyan, V H

    2014-01-01

    We used the Z-transformed Discrete Correlation Function (ZDCF) and the Stochastic Process Estimation for AGN Reverberation (SPEAR) methods for the time series analysis of the continuum and the H${\\alpha}$ and H${\\beta}$ line fluxes of a sample of well known type 1 active galactic nuclei (AGNs): Arp 102B, 3C 390.3, NGC 5548, and NGC 4051, where the first two objects are showing double-peaked emission line profiles. The aim of this work is to compare the time lag measurements from these two methods, and check if there is a connection with other emission line properties. We found that the obtained time lags from H$\\beta$ are larger than those derived from the H$\\alpha$ analysis for Arp 102B, 3C 390.3 and NGC 5548. This may indicate that the H$\\beta$ line originates at larger radii in these objects. Moreover, we found that the ZDCF and SPEAR time lags are highly correlated ($r \\sim0.87$), and that the error ranges of both ZDCF and SPEAR time lags are correlated with the FWHM of used emission lines ($r\\sim 0.7$). ...

  3. No more active galactic nuclei in clumpy disks than in smooth galaxies at z ∼ 2 in CANDELS/3D-HST

    We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to investigate if active galactic nuclei (AGNs) are preferentially fueled by violent disk instabilities funneling gas into galaxy centers at 1.3 < z < 2.4. We select galaxies undergoing gravitational instabilities using the number of clumps and degree of patchiness as proxies. The CANDELS visual classification system is used to identify 44 clumpy disk galaxies, along with mass-matched comparison samples of smooth and intermediate morphology galaxies. We note that despite being mass-matched and having similar star formation rates, the smoother galaxies tend to be smaller disks with more prominent bulges compared to the clumpy galaxies. The lack of smooth extended disks is probably a general feature of the z ∼ 2 galaxy population, and means we cannot directly compare with the clumpy and smooth extended disks observed at lower redshift. We find that z ∼ 2 clumpy galaxies have slightly enhanced AGN fractions selected by integrated line ratios (in the mass-excitation method), but the spatially resolved line ratios indicate this is likely due to extended phenomena rather than nuclear AGNs. Meanwhile, the X-ray data show that clumpy, smooth, and intermediate galaxies have nearly indistinguishable AGN fractions derived from both individual detections and stacked non-detections. The data demonstrate that AGN fueling modes at z ∼ 1.85—whether violent disk instabilities or secular processes—are as efficient in smooth galaxies as they are in clumpy galaxies.

  4. Suzaku follow-up of heavily obscured active galactic nuclei detected in Swift/BAT survey: NGC 1106, UGC 03752, and NGC 2788A

    Tanimoto, Atsushi; Ueda, Yoshihiro; Kawamuro, Taiki; Ricci, Claudio

    2016-06-01

    We present the broad-band (0.5-100 keV) spectra of three heavily obscured active galactic nuclei (AGNs), NGC 1106, UGC 03752, and NGC 2788A, observed with Suzaku and the Swift/Burst Alert Telescope (BAT). The targets are selected from the Swift/BAT 70-month catalog on the basis of their high hardness ratio between above and below 10 keV, and their X-ray spectra are reported here for the first time. We apply three models: a conventional model utilizing an analytic reflection code, and two Monte Carlo based torus models with a doughnut-like geometry (MYTorus: Murphy & Yaqoob, 2009, MNRAS, 397, 1549) and with a nearly spherical geometry (Ikeda torus: Ikeda et al., 2009, ApJ, 692, 608). The three models can successfully reproduce the spectra, and the Ikeda torus model gives a better description than the MYTorus model in all targets. We identify NGC 1106 and NGC 2788A as Compton-thick AGNs. We point out that the common presence of unabsorbed reflection components below 7.1 keV in obscured AGNs, as observed from UGC 03752, is evidence for clumpy tori. This implies that detailed studies utilizing clumpy torus models are required to reach correct interpretation of the X-ray spectra of AGNs.

  5. Suzaku Follow-up of Heavily Obscured Active Galactic Nuclei Detected in Swift/BAT Survey: NGC 1106, UGC 03752, and NGC 2788A

    Tanimoto, Atsushi; Kawamuro, Taiki; Ricci, Claudio

    2016-01-01

    We present the broadband (0.5-100 keV) spectra of three heavily obscured Active Galactic Nuclei (AGNs), NGC 1106, UGC 03752, and NGC 2788A, observed with Suzaku and Swift/Burst Alert Telescope (BAT). The targets are selected from the Swift/BAT 70-month catalog on the basis of high hardness ratio between above and below 10 keV, and their X-ray spectra are reported here for the first time. We apply three models, a conventional model utilizing an analytic reflection code and two Monte-Carlo based torus models with a doughnut-like geometry (MYTorus) and with a nearly spherical geometry (Ikeda torus). The three models can successfully reproduce the spectra, while the Ikeda torus model gives better description than the MYTorus model in all targets. We identify that NGC 1106 and NGC 2788A as Compton-thick AGNs. We point out that the common presence of unabsorbed reflection components below 7.1 keV in obscured AGNs, as observed from UGC 03752, is evidence for clumpy tori. This implies that detailed studies utilizing ...

  6. Herschel Far-Infrared Photometry of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. II. SPIRE Observations

    Shimizu, T Taro; Mushotzky, Richard F; Koss, Michael J; Barger, Amy J; Cowie, Lennox L

    2015-01-01

    We present far-infrared (FIR) and submillimeter photometry from the Herschel Space Observatory's Spectral and Photometric Imaging Receiver (SPIRE) for 313 nearby z<0.05 active galactic nuclei (AGN). We selected AGN from the 58 month Swift Burst Alert Telescope (BAT) catalog, the result of an all-sky survey in the 14-195 keV energy band, allowing for a reduction in AGN selection effects due to obscuration and host galaxy contamination. We find 46% (143/313) of our sample is detected at all three wavebands and combined with our PACS observations represents the most complete FIR spectral energy distributions of local, moderate luminosity AGN. We find no correlation between the 250, 350, and 500 micron luminosities with 14-195 keV luminosity, indicating the bulk of the FIR emission is not related to the AGN. However, Seyfert 1s do show a very weak correlation with X-ray luminosity compared to Seyfert 2s and we discuss possible explanations. We compare the SPIRE colors (F250/F350 and F350/F500) to a sample of n...

  7. DETERMINATION OF THE POINT-SPREAD FUNCTION FOR THE FERMI LARGE AREA TELESCOPE FROM ON-ORBIT DATA AND LIMITS ON PAIR HALOS OF ACTIVE GALACTIC NUCLEI

    Ackermann, M. [Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany); Ajello, M.; Allafort, A.; Bechtol, K.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Buehler, R. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Asano, K. [Interactive Research Center of Science, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551 (Japan); Atwood, W. B. [Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Baldini, L.; Bellazzini, R.; Bregeon, J. [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Ballet, J. [Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d' Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France); Barbiellini, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy); Bastieri, D. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy); Bonamente, E. [Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); Brandt, T. J. [CNRS, IRAP, F-31028 Toulouse cedex 4 (France); Brigida, M. [Dipartimento di Fisica ' M. Merlin' dell' Universita e del Politecnico di Bari, I-70126 Bari (Italy); Bruel, P., E-mail: mdwood@slac.stanford.edu, E-mail: mar0@uw.edu [Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France); and others

    2013-03-01

    The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from Almost-Equal-To 20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of {gamma} rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of {gamma}-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347-121.

  8. DETERMINATION OF THE POINT-SPREAD FUNCTION FOR THE FERMI LARGE AREA TELESCOPE FROM ON-ORBIT DATA AND LIMITS ON PAIR HALOS OF ACTIVE GALACTIC NUCLEI

    The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from ≈20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of γ rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of γ-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347–121.

  9. On the Black Hole Mass---X-ray Excess Variance Scaling Relation for Active Galactic Nuclei in the Low-mass Regime

    Pan, Hai-Wu; Zhou, Xin-Lin; Dong, Xiao-Bo; Liu, Bifang

    2015-01-01

    Recent studies of active galactic nuclei (AGN) found a statistical inverse linear scaling between the X-ray normalized excess variance $\\sigma_{\\rm rms}^2$ (variability amplitude) and the black hole mass spanning over $M_{\\rm BH}=10^6- 10^9\\ M_{\\odot}$. Being suggested to have a small scatter, this scaling relation may provide a novel method to estimate the black hole mass of AGN. However, a question arises as to whether this relation can be extended to the low-mass regime below $\\sim10^6\\ M_{\\odot}$. If confirmed, it would provide an efficient tool to search for AGN with low-mass black holes using X-ray variability. This paper presents a study of the X-ray excess variances for a sample of AGN with black hole masses in the range of $10^5- 10^6\\ M_{\\odot}$ observed with {\\it XMM-Newton} and {\\it ROSAT}, including data both from the archives and from newly preformed observations. It is found that the relation is no longer a simple extrapolation of the linear scaling; instead, the relation starts to flatten at $...

  10. The X-Ray Zurich Environmental Study (X-ZENS). I. Chandra and XMM-Newton Observations of Active Galactic Nuclei in Galaxies in nearby Groups

    Silverman, J. D.; Miniati, F.; Finoguenov, A.; Carollo, C. M.; Cibinel, A.; Lilly, S. J.; Schawinski, K.

    2014-01-01

    We describe X-ray observations with Chandra and XMM-Newton of 18 M group ~ 1-6 × 1013 M ⊙, z ~ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f 0.5 - 8 keV ~ 5 × 10-15 erg cm-2 s-1, corresponding to a limiting luminosity of L 0.5 - 8 keV ~ 3 × 1040 erg s-1. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L Edd >~ 10-4), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <1011 M ⊙, central galaxies appear to be a factor of ~4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.

  11. The X-ray Zurich environmental study (X-zens). I. Chandra and XMM-Newton observations of active galactic nuclei in galaxies in nearby groups

    We describe X-ray observations with Chandra and XMM-Newton of 18 M group ∼ 1-6 × 1013 M ☉, z ∼ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f 0.5 – 8 keV ∼ 5 × 10–15 erg cm–2 s–1, corresponding to a limiting luminosity of L 0.5 – 8 keV ∼ 3 × 1040 erg s–1. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L Edd ≳ 10–4), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <1011 M ☉, central galaxies appear to be a factor of ∼4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.

  12. Exploring the Active Galactic Nuclei population with extreme X-ray to optical flux ratios (Fx/Fo >50)

    Della Ceca, R; Caccianiga, A; Severgnini, P; Ballo, L; Braito, V; Corral, A; Del Moro, A; Mateos, S; Ruiz, A; Watson, M G

    2015-01-01

    The cosmic history of the growth of supermassive black holes in galactic centers parallels that of star-formation in the Universe. However, an important fraction of this growth occurs inconspicuously in obscured objects, where ultraviolet/optical/near-infrared emission is heavily obscured by dust. Since the X-ray flux is less attenuated, a high X-ray-to-optical flux ratio (Fx/Fo) is expected to be an efficient tool to find out these obscured accreting sources. We explore here via optical spectroscopy, X-ray spectroscopy and infrared photometry the most extreme cases of this population (those with Fx/Fo >50, EXO50 sources hereafter), using a well defined sample of seven X-ray sources extracted from the 2XMM catalogue. Five EXO50 sources (about 70 percent of the sample) in the bright flux regime explored by our survey (f(2-10 keV) > 1.5E-13 cgs) are associated with obscured AGN (Nh > 1.0E22 cm-2), spanning a redshift range between 0.75 and 1 and characterised by 2-10 keV intrinsic luminosities in the QSO regime...

  13. Galactic Nuclei Formation Via Globular Cluster Merging

    Capuzzo-Dolcetta, R

    2009-01-01

    Preliminary results are presented about a fully self-consistent N-body simulation of a sample of four massive globular clusters in close interaction within the central region of a galaxy. The N-body representation (with N=1.5x10^6 particles in total) of both the clusters and the galaxy allows to include in a natural and self-consistent way dynamical friction and tidal interactions. The results confirm the decay and merging of globulars as a viable scenario for the formation/accretion of compact nuclear clusters. Specifically: i) the frictional orbital decay is about 2 times faster than that predicted by the generalized Chandrasekhar formula; ii) the progenitor clusters merge in less than 20 galactic core-crossing times; iii) the NC configuration keeps quasi-stable at least within 70 galactic core-crossing times.

  14. THE AKARI 2.5-5.0 μm SPECTRAL ATLAS OF TYPE-1 ACTIVE GALACTIC NUCLEI: BLACK HOLE MASS ESTIMATOR, LINE RATIO, AND HOT DUST TEMPERATURE

    Kim, Dohyeong; Im, Myungshin; Kim, Ji Hoon; Jun, Hyunsung David; Lee, Seong-Kook [Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Shillim-Dong, Kwanak-Gu, Seoul 151-742 (Korea, Republic of); Woo, Jong-Hak; Lee, Hyung Mok; Lee, Myung Gyoon [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Shillim-Dong, Kwanak-Gu, Seoul 151-742 (Korea, Republic of); Nakagawa, Takao; Matsuhara, Hideo; Wada, Takehiko; Takagi, Toshinobu [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210 (Japan); Oyabu, Shinki [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Ohyama, Youichi, E-mail: dohyeong@astro.snu.ac.kr, E-mail: mim@astro.snu.ac.kr [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China)

    2015-01-01

    We present 2.5-5.0 μm spectra of 83 nearby (0.002 < z < 0.48) and bright (K < 14 mag) type-1 active galactic nuclei (AGNs) taken with the Infrared Camera on board AKARI. The 2.5-5.0 μm spectral region contains emission lines such as Brβ (2.63 μm), Brα (4.05 μm), and polycyclic aromatic hydrocarbons (3.3 μm), which can be used for studying the black hole (BH) masses and star formation activity in the host galaxies of AGNs. The spectral region also suffers less dust extinction than in the ultra violet (UV) or optical wavelengths, which may provide an unobscured view of dusty AGNs. Our sample is selected from bright quasar surveys of Palomar-Green and SNUQSO, and AGNs with reverberation-mapped BH masses from Peterson et al. Using 11 AGNs with reliable detection of Brackett lines, we derive the Brackett-line-based BH mass estimators. We also find that the observed Brackett line ratios can be explained with the commonly adopted physical conditions of the broad line region. Moreover, we fit the hot and warm dust components of the dust torus by adding photometric data of SDSS, 2MASS, WISE, and ISO to the AKARI spectra, finding hot and warm dust temperatures of ∼1100 K and ∼220 K, respectively, rather than the commonly cited hot dust temperature of 1500 K.

  15. The Biases of Optical Line-Ratio Selection for Active Galactic Nuclei and the Intrinsic Relationship between Black Hole Accretion and Galaxy Star Formation

    Trump, Jonathan R.; Sun, Mouyuan; Zeimann, Gregory R.; Luck, Cuyler; Bridge, Joanna S.; Grier, Catherine J.; Hagen, Alex; Juneau, Stephanie; Montero-Dorta, Antonio; Rosario, David J.; Brandt, W. Niel; Ciardullo, Robin; Schneider, Donald P.

    2015-09-01

    We use 317,000 emission-line galaxies from the Sloan Digital Sky Survey to investigate line-ratio selection of active galactic nuclei (AGNs). In particular, we demonstrate that “star formation (SF) dilution” by H ii regions causes a significant bias against AGN selection in low-mass, blue, star-forming, disk-dominated galaxies. This bias is responsible for the observed preference of AGNs among high-mass, green, moderately star-forming, bulge-dominated hosts. We account for the bias and simulate the intrinsic population of emission-line AGNs using a physically motivated Eddington ratio distribution, intrinsic AGN narrow line region line ratios, a luminosity-dependent {L}{bol}/L[{{O}} {{III}}] bolometric correction, and the observed {M}{BH}-σ relation. These simulations indicate that, in massive ({log}({M}*/{M}⊙ )≳ 10) galaxies, AGN accretion is correlated with specific star formation rate (SFR) but is otherwise uniform with stellar mass. There is some hint of lower black hole occupation in low-mass ({log}({M}*/{M}⊙ )≲ 10) hosts, although our modeling is limited by uncertainties in measuring and interpreting the velocity dispersions of low-mass galaxies. The presence of SF dilution means that AGNs contribute little to the observed strong optical emission lines (e.g., [{{O}} {{III}}] and {{H}}α ) in low-mass and star-forming hosts. However the AGN population recovered by our modeling indicates that feedback by typical (low- to moderate-accretion) low-redshift AGNs has nearly uniform efficiency at all stellar masses, SFRs, and morphologies. Taken together, our characterization of the observational bias and resultant AGN occupation function suggest that AGNs are unlikely to be the dominant source of SF quenching in galaxies, but instead are fueled by the same gas which drives SF activity.

  16. CHANDRA X-RAY AND HUBBLE SPACE TELESCOPE IMAGING OF OPTICALLY SELECTED KILOPARSEC-SCALE BINARY ACTIVE GALACTIC NUCLEI. I. NATURE OF THE NUCLEAR IONIZING SOURCES

    Kiloparsec-scale binary active galactic nuclei (AGNs) signal active supermassive black hole (SMBH) pairs in merging galaxies. Despite their significance, unambiguously confirmed cases remain scarce and most have been discovered serendipitously. In a previous systematic search, we optically identified four kpc-scale binary AGNs from candidates selected with double-peaked narrow emission lines at z = 0.1-0.2. Here, we present Chandra and Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging of these four systems. We critically examine and confirm the binary-AGN scenario for two of the four targets, by combining high angular resolution X-ray imaging spectroscopy with Chandra ACIS-S, better nuclear position constraints from WFC3 F105W imaging, and direct starburst estimates from WFC3 F336W imaging; for the other two targets, the existing data are still consistent with the binary-AGN scenario, but we cannot rule out the possibility of only one AGN ionizing gas in both merging galaxies. We find tentative evidence for a systematically smaller X-ray-to-[O III] luminosity ratio and/or higher Compton-thick fraction in optically selected kpc-scale binary AGNs than in single AGNs, possibly caused by a higher nuclear gas column due to mergers and/or a viewing angle bias related to the double-peak narrow-line selection. While our result lends some further support to the general approach of optically identifying kpc-scale binary AGNs, it also highlights the challenge and ambiguity of X-ray confirmation.

  17. Nebular excitation in z ∼ 2 star-forming galaxies from the SINS and LUCI surveys: The influence of shocks and active galactic nuclei

    Newman, Sarah F.; Genzel, Reinhard [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States); Buschkamp, Peter; Förster Schreiber, Natascha M.; Kurk, Jaron; Rosario, David; Davies, Ric; Eisenhauer, Frank; Lutz, Dieter [Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); Sternberg, Amiel [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Gnat, Orly [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Mancini, Chiara; Renzini, Alvio [Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Lilly, Simon J.; Carollo, C. Marcella [Institute of Astronomy, Department of Physics, Eidgenössische Technische Hochschule, ETH, CH-8093 Zürich (Switzerland); Burkert, Andreas [Universitäts-Sternwarte Ludwig-Maximilians-Universität (USM), Scheinerstr. 1, D-81679 München (Germany); Cresci, Giovanni [Istituto Nazionale di Astrofisica Osservatorio di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Genel, Shy [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Shapiro Griffin, Kristen [Space Sciences Research Group, Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278 (United States); Hicks, Erin K. S., E-mail: sfnewman@berkeley.edu [Department of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580 (United States); and others

    2014-01-20

    Based on high-resolution, spatially resolved data of 10 z ∼ 2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGNs), shocks, and photoionization. We explore how these spatially resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the 'composite' region of the z ∼ 0 [N II]/Hα versus [O III]/Hβ diagnostic (BPT) diagram, between star-forming galaxies and those with AGNs. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from an enhanced ionization parameter as compared with H II regions in normal, local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [O III]/Hβ versus stellar mass plane, does not properly separate z ∼ 2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z ∼ 2 mass-metallicity relation (i.e., to the mass they would have at z ∼ 0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [N II]/Hα are more biased by shocks and AGNs at high-z than the [O III]/Hβ/[N II]/Hα calibration.

  18. A MULTI-WAVELENGTH STUDY OF LOW-REDSHIFT CLUSTERS OF GALAXIES. I. COMPARISON OF X-RAY AND MID-INFRARED SELECTED ACTIVE GALACTIC NUCLEI

    Clusters of galaxies have long been used as laboratories for the study of galaxy evolution, but despite intense, recent interest in feedback between active galactic nuclei (AGNs) and their hosts, the impact of environment on these relationships remains poorly constrained. We present results from a study of AGNs and their host galaxies found in low-redshift galaxy clusters. We fit model spectral energy distributions (SEDs) to the combined visible and mid-infrared (MIR) photometry of cluster members and use these model SEDs to determine stellar masses and star formation rates (SFRs). We identify two populations of AGNs, the first based on their X-ray luminosities (X-ray AGNs) and the second based on the presence of a significant AGN component in their model SEDs (IR AGNs). We find that the two AGN populations are nearly disjoint; only 8 out of 44 AGNs are identified with both techniques. We further find that IR AGNs are hosted by galaxies with similar masses and SFRs but higher specific SFRs (sSFRs) than X-ray AGN hosts. The relationship between AGN accretion and host star formation in cluster AGN hosts shows no significant difference compared to the relationship between field AGNs and their hosts. The projected radial distributions of both AGN populations are consistent with the distribution of other cluster members. We argue that the apparent dichotomy between X-ray and IR AGNs can be understood as a combination of differing extinction due to cold gas in the host galaxies of the two classes of AGNs and the presence of weak star formation in X-ray AGN hosts.

  19. The Spatial Clustering of ROSAT All-Sky Survey Active Galactic Nuclei. IV. More Massive Black Holes Reside in More Massive Dark Matter Halos

    Krumpe, Mirko; Miyaji, Takamitsu; Husemann, Bernd; Fanidakis, Nikos; Coil, Alison L.; Aceves, Hector

    2015-12-01

    This is the fourth paper in a series that reports on our investigation of the clustering properties of active galactic nuclei (AGNs) identified in the ROSAT All-Sky Survey and Sloan Digital Sky Survey (SDSS). In this paper we investigate the cause of the X-ray luminosity dependence of the clustering of broad-line, luminous AGNs at 0.16\\lt z\\lt 0.36. We fit the Hα line profile in the SDSS spectra for all X-ray and optically selected broad-line AGNs, determine the mass of the supermassive black hole (SMBH), {M}{BH}, and infer the accretion rate relative to Eddington (L/{L}{EDD}). Since {M}{BH} and L/{L}{EDD} are correlated, we create AGN subsamples in one parameter while maintaining the same distribution in the other parameter. In both the X-ray and optically selected AGN samples, we detect a weak clustering dependence with {M}{BH} and no statistically significant dependence on L/{L}{EDD}. We find a difference of up to 2.7σ when comparing the objects that belong to the 30% least and 30% most massive {M}{BH} subsamples, in that luminous broad-line AGNs with more massive black holes reside in more massive parent dark matter halos at these redshifts. These results provide evidence that higher accretion rates in AGNs do not necessarily require dense galaxy environments, in which more galaxy mergers and interactions are expected to channel large amounts of gas onto the SMBH. We also present semianalytic models that predict a positive {M}{DMH} dependence on {M}{BH}, which is most prominent at {M}{BH}˜ {10}8-9 {M}⊙ .

  20. Active galactic nuclei emission line diagnostics and the mass-metallicity relation up to redshift z ∼ 2: The impact of selection effects and evolution

    Emission line diagnostic diagrams probing the ionization sources in galaxies, such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used extensively to distinguish active galactic nuclei (AGN) from purely star-forming galaxies. However, they remain poorly understood at higher redshifts. We shed light on this issue with an empirical approach based on a z ∼ 0 reference sample built from ∼300,000 Sloan Digital Sky Survey galaxies, from which we mimic selection effects due to typical emission line detection limits at higher redshift. We combine this low-redshift reference sample with a simple prescription for luminosity evolution of the global galaxy population to predict the loci of high-redshift galaxies on the BPT and Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate distributions agree remarkably well with direct observations of galaxies out to z ∼ 1.5, including the observed stellar mass-metallicity (MZ) relation evolution. As a result, we infer that high-redshift star-forming galaxies are consistent with having normal interstellar medium (ISM) properties out to z ∼ 1.5, after accounting for selection effects and line luminosity evolution. Namely, their optical line ratios and gas-phase metallicities are comparable to that of low-redshift galaxies with equivalent emission-line luminosities. In contrast, AGN narrow-line regions may show a shift toward lower metallicities at higher redshift. While a physical evolution of the ISM conditions is not ruled out for purely star-forming galaxies and may be more important starting at z ≳ 2, we find that reliably quantifying this evolution is hindered by selections effects. The recipes provided here may serve as a basis for future studies toward this goal. Code to predict the loci of galaxies on the BPT and MEx diagnostic diagrams and the MZ relation as a function of emission line luminosity limits is made publicly available.

  1. GALAXY CLUSTERS AROUND RADIO-LOUD ACTIVE GALACTIC NUCLEI AT 1.3 < z < 3.2 AS SEEN BY SPITZER

    We report the first results from the Clusters Around Radio-Loud AGN program, a Cycle 7 and 8 Spitzer Space Telescope snapshot program to investigate the environments of a large sample of obscured and unobscured luminous radio-loud active galactic nuclei (AGNs) at 1.2 AB = 22.6 and [4.5]AB = 22.9 at the 95% completeness level, which is two to three times fainter than L* in this redshift range. By using the color cut [3.6] – [4.5] > –0.1 (AB), which efficiently selects high-redshift (z > 1.3) galaxies of all types, we identify galaxy cluster member candidates in the fields of the radio-loud AGN. The local density of these Infrared Array Camera (IRAC)-selected sources is compared to the density of similarly selected sources in blank fields. We find that 92% of the radio-loud AGN reside in environments richer than average. The majority (55%) of the radio-loud AGN fields are found to be overdense at a ≥2σ level; 10% are overdense at a ≥5σ level. A clear rise in surface density of IRAC-selected sources toward the position of the radio-loud AGN strongly supports an association of the majority of the IRAC-selected sources with the radio-loud AGN. Our results provide solid statistical evidence that radio-loud AGN are likely beacons for finding high-redshift galaxy (proto-)clusters. We investigate how environment depends on AGN type (unobscured radio-loud quasars versus obscured radio galaxies), radio luminosity and redshift, finding no correlation with either AGN type or radio luminosity. We find a decrease in density with redshift, consistent with galaxy evolution for this uniform, flux-limited survey. These results are consistent with expectations from the orientation-driven AGN unification model, at least for the high radio luminosity regimes considered in this sample.

  2. RADIATION MECHANISM AND JET COMPOSITION OF GAMMA-RAY BURSTS AND GeV-TeV-SELECTED RADIO-LOUD ACTIVE GALACTIC NUCLEI

    Gamma-ray bursts (GRBs) and GeV-TeV-selected radio-loud active galactic nuclei (AGNs) are compared based on our systematic modeling of the observed spectral energy distributions of a sample of AGNs with a single-zone leptonic model. We show that the correlation between the jet power (Pjet) and the prompt gamma-ray luminosity (Ljet) of GRBs is consistent, within the uncertainties, with the correlation between jet power and the synchrotron peak luminosity (Ls,jet) of flat spectrum radio quasars (FSRQs). Their radiation efficiencies (ε) are also comparable (>10% for most sources), which increase with the bolometric jet luminosity (Lbol,jet) for FSRQs and with the Ljet for GRBs with similar power-law indices. BL Lac objects (BL Lacs) do not follow the Pjet-Ls,jet relation of FSRQs. They have lower ε and Lbol,jet values than FSRQs, and a tentative Lbol,jet-ε relation is also found, with a power-law index different from that of the FSRQs. The magnetization parameters (σ) of FSRQs are on average larger than that of BL Lacs. They are anti-correlated with ε for the FSRQs, but positively correlated with ε for the BL Lacs. GeV narrow-line Seyfert 1 galaxies potentially share similar properties with FSRQs. Based on the analogy between GRBs and FSRQs, we suggest that the prompt gamma-ray emission of GRBs is likely produced by the synchrotron process in a magnetized jet with high radiation efficiency, similar to FSRQs. The jets of BL Lacs, on the other hand, are less efficient and are likely more matter-dominated

  3. A COMPARATIVE STUDY OF OPTICAL/ULTRAVIOLET VARIABILITY OF NARROW-LINE SEYFERT 1 AND BROAD-LINE SEYFERT 1 ACTIVE GALACTIC NUCLEI

    The ensemble optical/ultraviolet (UV) variability of narrow-line Seyfert 1 (NLS1)-type active galactic nuclei (AGNs) is investigated, based on a sample selected from the Sloan Digital Sky Survey (SDSS) Stripe 82 region with multi-epoch photometric scanning data. As a comparison, a control sample of broad-line Seyfert 1 (BLS1)-type AGNs is also incorporated. To quantify properly the intrinsic variation amplitudes and their uncertainties, a novel method of parametric maximum likelihood is introduced that has, as we argued, certain virtues over previously used methods. The majority of NLS1-type AGNs exhibit significant variability on timescales from about 10 days to a few years with, however, smaller amplitudes on average compared to BLS1-type AGNs. About 20 NLS1-type AGNs that show relatively large variations are presented and may deserve future monitoring observations, for instance, reverberation mapping. The averaged structure functions of variability, constructed using the same maximum likelihood method, show remarkable similarity in shape for the two types of AGNs on timescales longer than about 10 days, which can be approximated by a power law or an exponential function. This, along with other similar properties, such as the wavelength-dependent variability, is indicative of a common dominant mechanism responsible for the long-term optical/UV variability of both NLS1- and BLS1-type AGNs. Toward the short timescales, however, there is tentative evidence that the structure function of NLS1-type AGNs continues to decline, whereas that of BLS1-type AGNs flattens with some residual variability on timescales of days. If this can be confirmed, it may suggest that an alternative mechanism, such as X-ray reprocessing, starts to dominate in BLS1-type AGNs, but not in NLS1-type AGNs, on such timescales.

  4. Active galactic nuclei emission line diagnostics and the mass-metallicity relation up to redshift z ∼ 2: The impact of selection effects and evolution

    Juneau, Stéphanie; Bournaud, Frédéric; Daddi, Emanuele; Elbaz, David; Duc, Pierre-Alain; Gobat, Raphael; Jean-Baptiste, Ingrid; Le Floc' h, Émeric; Pannella, Maurilio; Schreiber, Corentin [CEA-Saclay, DSM/IRFU/SAp, F-91191 Gif-sur-Yvette (France); Charlot, Stéphane; Lehnert, M. D.; Pacifici, Camilla [UPMC-CNRS, UMR 7095, Institut d' Astrophysique de Paris, F-75014 Paris (France); Trump, Jonathan R. [University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Brinchmann, Jarle [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Dickinson, Mark, E-mail: stephanie.juneau@cea.fr [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

    2014-06-10

    Emission line diagnostic diagrams probing the ionization sources in galaxies, such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used extensively to distinguish active galactic nuclei (AGN) from purely star-forming galaxies. However, they remain poorly understood at higher redshifts. We shed light on this issue with an empirical approach based on a z ∼ 0 reference sample built from ∼300,000 Sloan Digital Sky Survey galaxies, from which we mimic selection effects due to typical emission line detection limits at higher redshift. We combine this low-redshift reference sample with a simple prescription for luminosity evolution of the global galaxy population to predict the loci of high-redshift galaxies on the BPT and Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate distributions agree remarkably well with direct observations of galaxies out to z ∼ 1.5, including the observed stellar mass-metallicity (MZ) relation evolution. As a result, we infer that high-redshift star-forming galaxies are consistent with having normal interstellar medium (ISM) properties out to z ∼ 1.5, after accounting for selection effects and line luminosity evolution. Namely, their optical line ratios and gas-phase metallicities are comparable to that of low-redshift galaxies with equivalent emission-line luminosities. In contrast, AGN narrow-line regions may show a shift toward lower metallicities at higher redshift. While a physical evolution of the ISM conditions is not ruled out for purely star-forming galaxies and may be more important starting at z ≳ 2, we find that reliably quantifying this evolution is hindered by selections effects. The recipes provided here may serve as a basis for future studies toward this goal. Code to predict the loci of galaxies on the BPT and MEx diagnostic diagrams and the MZ relation as a function of emission line luminosity limits is made publicly available.

  5. Active galactic nuclei cores in infrared-faint radio sources. Very long baseline interferometry observations using the Very Long Baseline Array

    Herzog, A.; Middelberg, E.; Norris, R. P.; Spitler, L. R.; Deller, A. T.; Collier, J. D.; Parker, Q. A.

    2015-06-01

    Context. Infrared-faint radio sources (IFRS) form a new class of galaxies characterised by radio flux densities between tenths and tens of mJy and faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs) at significant redshifts (z ≳ 2). Aims: Whereas the high redshifts of IFRS have been recently confirmed based on spectroscopic data, the evidence for the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs have been unquestionably confirmed in IFRS based on very long baseline interferometry (VLBI) observations. In this work, we test the hypothesis that IFRS contain AGNs in a large sample of sources using VLBI. Methods: We observed 57 IFRS with the Very Long Baseline Array (VLBA) down to a detection sensitivity in the sub-mJy regime and detected compact cores in 35 sources. Results: Our VLBA detections increase the number of VLBI-detected IFRS from 2 to 37 and provide strong evidence that most - if not all - IFRS contain AGNs. We find that IFRS have a marginally higher VLBI detection fraction than randomly selected sources with mJy flux densities at arcsec-scales. Moreover, our data provide a positive correlation between compactness - defined as the ratio of milliarcsec- to arcsec-scale flux density - and redshift for IFRS, but suggest a decreasing mean compactness with increasing arcsec-scale radio flux density. Based on these findings, we suggest that IFRS tend to contain young AGNs whose jets have not formed yet or have not expanded, equivalent to very compact objects. We found two IFRS that are resolved into two components. The two components are spatially separated by a few hundred milliarcseconds in both cases. They might be components of one AGN, a binary black hole, or the result of gravitational lensing.

  6. Self-shadowing effects of slim accretion disks in active galactic nuclei: the diverse appearance of the broad-line region

    Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR) from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energy distributions depending on their location relative to the disk, resulting in the diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components of the broad Hβ line profile with different line widths and fluxes, which jointly account for the Lorentzian profile generally observed in narrow-line Seyfert 1 galaxies. In the time domain, these two components are expected to reverberate with different time lags with respect to the varying ionizing continuum, depending on the accretion rate and the viewing angle of the observer. The diverse appearance of the BLR due to the anisotropic ionizing energy source can be tested by reverberation mapping of Hβ and other broad emission lines (e.g., Fe II), providing a new tool to diagnose the structure and dynamics of the BLR. Other observational consequences of our model are also explored.

  7. THE MAGELLANIC QUASARS SURVEY. II. CONFIRMATION OF 144 NEW ACTIVE GALACTIC NUCLEI BEHIND THE SOUTHERN EDGE OF THE LARGE MAGELLANIC CLOUD

    We quadruple the number of quasars known behind the Large Magellanic Cloud (LMC) from 56 (42 in the Optical Gravitational Lensing Experiment (OGLE)-III LMC fields) to 200 by spectroscopically confirming 169 (144 new) quasars from a sample of 845 observed candidates in four ∼3 deg2 Anglo-Australian Telescope/AAOmega fields south of the LMC center. The candidates were selected based on their Spitzer mid-infrared colors, X-ray emission, and/or optical variability properties in the database of the OGLE microlensing survey. The contaminating sources can be divided into 115 young stellar objects (YSOs), 17 planetary nebulae (PNe), 39 Be and 24 blue stars, 68 red stars, and 12 objects classed as either YSO/PN or blue star/YSO. There are also 402 targets with either featureless spectra or too low signal-to-noise ratios for source classification. Our quasar sample is 50% (30%) complete at I = 18.6 mag (19.3 mag). The newly discovered active galactic nuclei (AGNs) provide many additional reference points for proper motion studies of the LMC, and the sample includes 10 bright AGNs (I < 18 mag) that are potentially suitable for absorption line studies. Their primary use, however, is for detailed studies of quasar variability, as they all have long-term, high cadence, continuously growing light curves from the microlensing surveys of the LMC. Completing the existing Magellanic Quasars Survey fields in the LMC and Small Magellanic Cloud should yield a sample of ∼700 well-monitored AGNs, and expanding it to the larger regions covered by the OGLE-IV survey should yield a sample of ∼3600 AGNs.

  8. COMOVING SPACE DENSITY AND OBSCURED FRACTION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE SUBARU/XMM-NEWTON DEEP SURVEY

    We study the comoving space density of X-ray-selected luminous active galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts (3 3 with intrinsic (de-absorbed and rest-frame 2-10 keV) luminosities of LX = 1044-45 erg s–1 detected in the 0.5-2 keV band, consisting of 20 and 10 objects with spectroscopic and photometric redshifts, respectively. Utilizing the 1/Vmax method, we confirm that the comoving space density of luminous AGNs decreases with redshift above z > 3. When combined with the Chandra-COSMOS result of Civano et al., the density decline of AGNs with LX = 1044-45 erg s–1 is well represented by a power law of (1 + z)–6.2±0.9. We also determine the fraction of X-ray obscured AGNs with NH > 1022 cm–2 in the Compton-thin population to be 0.54+0.17–0.19, by carefully taking into account observational biases including the effects of photon statistics for each source. This result is consistent with an independent determination of the type-2 AGN fraction based on optical properties, for which the fraction is found to be 0.59 ± 0.09. Comparing our result with that obtained in the local universe, we conclude that the obscured fraction of luminous AGNs increases significantly from z = 0 to z > 3 by a factor of 2.5 ± 1.1.

  9. BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY

    The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b|>10 deg. with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b| < 10 deg., were previously detected with Energetic Gamma-Ray Experiment Telescope(EGRET), probably due to variability. The analysis of the γ-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak γ-ray fluxes is observed. Blazar log N-log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic γ-ray intensity is estimated.

  10. [C ii] emission from galactic nuclei in the presence of X-rays

    Langer, W. D.; Pineda, J. L.

    2015-08-01

    Context. The luminosity of [C ii] is used as a probe of the star formation rate in galaxies, but the correlation breaks down in some active galactic nuclei (AGNs). Models of the [C ii] emission from galactic nuclei do not include the influence of X-rays on the carbon ionization balance, which may be a factor in reducing the [C ii] luminosity. Aims: We aim to determine the properties of the ionized carbon and its distribution among highly ionized states in the interstellar gas in galactic nuclei under the influence of X-ray sources. We calculate the [C ii] luminosity in galactic nuclei under the influence of bright sources of soft X-rays. Methods: We solve the balance equation of the ionization states of carbon as a function of X-ray flux, electron, atomic hydrogen, and molecular hydrogen density. These are input to models of [C ii] emission from the interstellar medium (ISM) in galactic nuclei representing conditions in the Galactic central molecular zone and a higher density AGN model. The behavior of the [C ii] luminosity is calculated as a function of the X-ray luminosity. We also solve the distribution of the ionization states of oxygen and nitrogen in highly ionized regions. Results: We find that the dense warm ionized medium (WIM) and dense photon dominated regions (PDRs) dominate the [C ii] emission when no X-rays are present. The X-rays in galactic nuclei can affect strongly the C+ abundance in the WIM, converting some fraction to C2+ and higher ionization states and thus reducing its [C ii] luminosity. For an X-ray luminosity L(X-ray) ≳ 1043 erg s-1 the [C ii] luminosity can be suppressed by a factor of a few, and for very strong sources, L(X-ray) >1044 erg s-1 such as found for many AGNs, the [C ii] luminosity is significantly depressed. Comparison of the model with several extragalactic sources shows that the [C ii] to far-infrared ratio declines for L(X-ray) ≳ 1043 erg s-1, in reasonable agreement with our model. Conclusions: We conclude that X

  11. Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei III. Kinematics of Parsec-Scale Radio Jets

    Kellermann, K I; Homan, D C; Vermeulen, R C; Cohen, M H; Ros, E; Kadler, M; Zensus, J A; Kovalev, Y Y

    2004-01-01

    We report the results of a 15 GHz (2 cm) multi-epoch VLBA program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies. The observed flow of 208 distinct features measured in 110 quasars, active galaxies, and BL Lac objects shows highly collimated relativistic motion with apparent transverse velocities typically between zero and about 15c, with a tail extending up to about 34c. Within individual jets, different features appear to move with a similar characteristic velocity which may represent an underlying continuous jet flow, but we also see some stationary and even apparently inward moving features which co-exist with the main features. Comparison of our observations with published data at other wavelengths suggests that there is a systematic decrease in apparent velocity with increasing wavelength, probably because the observations at different wavelengths sample different parts of the jet structure. The observed distribution of linear velocities is not consistent with...

  12. Fate of Dead Radio-loud Active Galactic Nuclei: New Prediction of Long-lived Shell Emission

    Ito, Hirotaka; Kawakatu, Nozomu; Orienti, Monica

    2015-01-01

    We examine the fate of a dead radio source in which jet injection from central engine has stopped at early stage of its evolution ($t = t_j \\lesssim 10^5$ yr). To this aim, we theoretically evaluate the evolution of the emission from both lobe and shell which are composed of shocked jet matter and shocked ambient medium, respectively. Based on a simple dynamical model of expanding lobe and shell, we clarify how the broadband spectrum of each component evolves before and after the cessation of the jet activity. It is shown that the spectrum is strongly dominated by the lobe emission while the jet is active ($t \\leq t_j$). On the other hand, once the jet activity has ceased ($t > t_j$), the lobe emission fades out rapidly, since fresh electrons are no longer supplied from the jet. Meanwhile, shell emission only shows gradual decrease, since accelerated electrons are continuously supplied from the bow shock that is propagating into the ambient medium. As a result, overall emission from the shell overwhelms that ...

  13. Probing Stellar Dynamics in Galactic Nuclei

    Miller, M Coleman; Amaro-Seoane, Pau; Barth, Aaron J; Cutler, Curt; Gair, Jonathan R; Hopman, Clovis; Merritt, David; Phinney, E Sterl; Richstone, Douglas O

    2009-01-01

    Electromagnetic observations over the last 15 years have yielded a growing appreciation for the importance of supermassive black holes (SMBH) to the evolution of galaxies, and for the intricacies of dynamical interactions in our own Galactic center. Here we show that future low-frequency gravitational wave observations, alone or in combination with electromagnetic data, will open up unique windows to these processes. In particular, gravitational wave detections in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to unprecedented precision and will provide clues to the properties of the otherwise undetectable stellar remnants expected to populate the centers of galaxies. Such observations are therefore keys to understanding the interplay between SMBHs and their environments.

  14. Star clusters as tracers of galactic nuclei properties

    Arca-Sedda, Manuel

    2016-01-01

    We present a series of $N$-body simulations representing the evolution of a galactic nucleus and its stellar content in a nearly one-to-one representation. The aim of this suite of simulations is to shed light on the interplay between nuclear clusters (NCs), super-massive black holes (SMBH) and the galactic nuclei in which they are contained. We modelled galaxies with masses from few times $10^8$ to $10^{11}$ M$_\\odot$, hosting in their nucleus a number of globular clusters and, in some cases, a central SMBH.

  15. The X-ray Zurich environmental study (X-zens). I. Chandra and XMM-Newton observations of active galactic nuclei in galaxies in nearby groups

    Silverman, J. D. [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo (Kavli IPMU, WPI), Kashiwa 277-8583 (Japan); Miniati, F.; Carollo, C. M.; Cibinel, A.; Lilly, S. J.; Schawinski, K. [Institute for Astronomy, ETH Zürich, CH-8093, Zürich (Switzerland); Finoguenov, A., E-mail: john.silverman@ipmu.jp [Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-00014 Helsinki (Finland)

    2014-01-01

    We describe X-ray observations with Chandra and XMM-Newton of 18 M {sub group} ∼ 1-6 × 10{sup 13} M {sub ☉}, z ∼ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f {sub 0.5} {sub –} {sub 8} {sub keV} ∼ 5 × 10{sup –15} erg cm{sup –2} s{sup –1}, corresponding to a limiting luminosity of L {sub 0.5} {sub –} {sub 8} {sub keV} ∼ 3 × 10{sup 40} erg s{sup –1}. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L {sub Edd} ≳ 10{sup –4}), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <10{sup 11} M {sub ☉}, central galaxies appear to be a factor of ∼4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.

  16. BALANCING THE ENERGY BUDGET BETWEEN STAR FORMATION AND ACTIVE GALACTIC NUCLEI IN HIGH-REDSHIFT INFRARED LUMINOUS GALAXIES

    We present deep Spitzer mid-infrared spectroscopy, along with 16, 24, 70, and 850 μm photometry, for 22 galaxies located in the Great Observatories Origins Deep Survey-North (GOODS-N) field. The sample spans a redshift range of 0.6 ∼AB > 25 mag) sources. We find that infrared (IR; 8-1000 μm) luminosities derived by fitting local spectral energy distributions (SEDs) with 24 μm photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data are used for galaxies having z ∼12 L sun. However, for galaxies in the redshift range between 1.4 ∼3 x 1012 L sun, IR luminosities are overestimated by an average factor of ∼5 when SED fitting with 24 μm photometry alone. This result arises partly due to the fact that high-redshift galaxies exhibit aromatic feature equivalent widths that are large compared to local galaxies of similar luminosities. Using improved estimates for the IR luminosities of these sources, we investigate whether their infrared emission is found to be in excess relative to that expected based on extinction-corrected UV star formation rates (SFRs), possibly suggesting the presence of an obscured AGN. Through a spectral decomposition of mid-infrared spectroscopic data, we are able to isolate the fraction of IR luminosity arising from an AGN as opposed to star formation activity. This fraction is only able to account for ∼30% of the total IR luminosity among the entire sample and ∼35% of the 'excess' IR emission among these sources, on average, suggesting that AGNs are not the dominant cause of the inferred 'mid-infrared excesses' in these systems. Of the sources identified as having mid-infrared excesses, half are accounted for by using proper bolometric corrections while half show the presence of obscured AGNs. This implies sky and space densities for Compton-thick AGNs of ∼1600 deg.-2 and ∼1.3 x 10-4 Mpc-3, respectively. We also note that IR luminosities derived from SED

  17. Jets from black hole binaries and Galactic Nuclei

    Mirabel, I.F.

    2000-01-01

    Relativistic outflows are a common phenomenon in accreting black holes. Despite the enormous differences in scale, stellar-mass black holes in binaries and supermassive black holes in Galactic Nuclei produce jets with analogous properties. In both are observed two types of relativistic outflows: 1) steady compact jets with flat-spectrum, and 2) sporadic extended jets with steep-spectrum and apparent superluminal motions. Besides, the most common class of gamma-ray bursts are afterglows from u...

  18. The advection-dominated accretion flow+thin accretion disk model for two low-luminosity active galactic nuclei: M81 and NGC 4579

    Ya-Di Xu; Xin-Wu Cao

    2009-01-01

    It was found that advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SEDs) of two low- luminosity active galactic nuclei (AGNs), provided they are accreting at ~ 0.01 - 0.03 Eddington rates and the thin disks are truncated to ADAFs at~ 100Rs (Rs is the Schwarzschild radius) for M81 and NGC 4579 (Quataert et al. 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two low- luminosity AGNs, if the black hole is accreting at 2.5 × 10-4 Eddington rates with the thin disk truncated at Rtr = 120Rs for M81 ((m) = 3.3 × 10-3 and Rtr = 80Rs are required for NGC 4579). The transition zones with temperature from the thin disk with 104 - 105 to~109 - 1010 K in the ADAF will inevitably emit thermal X-ray lines, which provides a useful diagnosis of their physical properties. The observed widths of the thermal X-ray iron lines at(~)6.8 keV are consistent with Doppler broadening by Keplerian motion of the gases in the transition zones at~100Rs. We use the structure of the transition zone between the ADAF and the thin disk derived by assuming the turbulent diffusive heat mechanism to calculate their thermal X-ray line emission with the standard software package Astrophysical Plasma Emission Code (APEC). Comparing them with the equivalent widths of the observed thermal X-ray iron lines in these two sources, we find that the turbulent diffusive heat mechanism seems to be unable to reproduce the ob- served thermal X-ray line emission. The test of the evaporation model for the accretion mode transition with the observed thermal X-ray line emission is briefly discussed.

  19. EVIDENCE FOR ULTRA-FAST OUTFLOWS IN RADIO-QUIET ACTIVE GALACTIC NUCLEI. II. DETAILED PHOTOIONIZATION MODELING OF Fe K-SHELL ABSORPTION LINES

    X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially through blueshifted Fe XXV/XXVI K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s–1 and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe XXV/XXVI transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from ∼10,000 km s–1 (∼0.03c) up to ∼100,000 km s–1 (∼0.3c), with a peak and mean value of ∼42,000 km s–1 (∼0.14c). The ionization parameter is very high and in the range log ξ ∼ 3-6 erg s–1 cm, with a mean value of log ξ ∼ 4.2 erg s–1 cm. The associated column densities are also large, in the range NH ∼ 1022-1024 cm–2, with a mean value of NH ∼ 1023 cm–2. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback

  20. Evidence for Ultra-fast Outflows in Radio-quiet Active Galactic Nuclei. II. Detailed Photoionization Modeling of Fe K-shell Absorption Lines

    Tombesi, F.; Cappi, M.; Reeves, J. N.; Palumbo, G. G. C.; Braito, V.; Dadina, M.

    2011-11-01

    X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially through blueshifted Fe XXV/XXVI K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s-1 and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe XXV/XXVI transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from ~10,000 km s-1 (~0.03c) up to ~100,000 km s-1 (~0.3c), with a peak and mean value of ~42,000 km s-1 (~0.14c). The ionization parameter is very high and in the range log ξ ~ 3-6 erg s-1 cm, with a mean value of log ξ ~ 4.2 erg s-1 cm. The associated column densities are also large, in the range N H ~ 1022-1024 cm-2, with a mean value of N H ~ 1023 cm-2. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can

  1. Suzaku Observations of Moderately Obscured (Compton-thin) Active Galactic Nuclei Selected by Swift/BAT Hard X-ray Survey

    Kawamuro, Taiki; Ueda, Yoshihiro; Tazaki, Fumie; Ricci, Claudio; Terashima, Yuichi

    2016-07-01

    We report the results obtained by a systematic, broadband (0.5–150 keV) X-ray spectral analysis of moderately obscured (Compton-thin, 22≤slant {log}{N}{{H}}\\lt 24) active galactic nuclei (AGNs) observed with Suzaku and Swift/Burst Alert Telescope (BAT). Our sample consists of 45 local AGNs at z\\lt 0.1 with {log}{L}14-195{keV}\\gt 42 detected in the Swift/BAT 70-month survey, whose Suzaku archival data are available as of 2015 December. All spectra are uniformly fit with a baseline model composed of an absorbed cutoff power-law component, reflected emission accompanied by a narrow fluorescent iron-Kα line from cold matter (torus), and scattered emission. The main results based on the above analysis are as follows. (1) The photon index is correlated with Eddington ratio, but not with luminosity or black hole mass. (2) The ratio of the luminosity of the iron-Kα line to the X-ray luminosity an indicator of the covering fraction of the torus, shows significant anticorrelation with luminosity. (3) The averaged reflection strength derived from stacked spectra above 14 keV is larger in less luminous ({log}{L}10-50{keV}≤slant 43.3, R={1.04}-0.19+0.17) or highly obscured ({log}{N}{{H}}\\gt 23, R={1.03}-0.17+0.15) AGNs than in more luminous ({log}{L}10-50{keV}\\gt 43.3, R={0.46}-0.09+0.08) or lightly obscured ({log}{N}{{H}}≤slant 23, R={0.59}-0.10+0.09) objects. (4) The ratio of the luminosity of the [{{O}} {{IV}}] 25.89 μm line to the X-ray luminosity is significantly smaller in AGNs with lower soft X-ray scattering fractions, suggesting that the former luminosity underestimates the intrinsic power of an AGN buried in a torus of small opening angle.

  2. Relativistic reflection in the average X-ray spectrum of active galactic nuclei in the Véron-Cetty and Véron catalogue

    Falocco, S.; Carrera, F. J.; Barcons, X.; Miniutti, G.; Corral, A.

    2014-08-01

    Context. The X-ray spectra of active galactic nuclei (AGN) unveil properties of matter around the super-massive black hole (SMBH). Aims: We investigate the X-ray spectra of AGN focusing on Compton reflection and fluorescence. These are two of the most important processes of interaction between primary radiation and circumnuclear material that is located far away from the SMBH, as indicated by the unresolved spectral emission lines (most notably the Fe line) in the X-ray spectra of AGN. Contributions from the inner accretion disk, affected by relativistic effects as expected, have also been detected in several cases. Methods: We studied the average X-ray spectrum of a sample of 263 X-ray unabsorbed AGN that yield 419 023 counts in the 2-12 keV rest-frame band distributed among 388 XMM-Newton spectra. Results: We fitted the average spectrum using a (basically) unabsorbed power law (representing the primary radiation). From a second model that represents the interaction (through Compton reflection and fluorescence) of this primary radiation with matter located far away from the central engine (e.g. the putative torus), we found that it was very significantly detected. Finally, we added a contribution from interaction with neutral material in the accretion disk close to the central SMBH, which is therefore smeared by relativistic effects, which improved the fit at a 6 sigma. The reflection factors are 0.65 for the accretion disk and 0.25 for the torus. Replacing the neutral disk-reflection with low-ionisation disk reflection, also relativistically smeared, fits the data equally well, suggesting that we do not find evidence for significant ionisation of the accretion disk. Conclusions: We detect distant neutral reflection associated with a narrow Fe line in the average spectrum of unabsorbed AGN with ⟨ z ⟩ = 0.8. Adding the disk-reflection component associated with a relativistic Fe line improves the data description at a 6 sigma confidence level, suggesting that

  3. Escape probability methods versus ``exact" transfer for modelling the X-ray spectrum of Active Galactic Nuclei and X-ray binaries

    Dumont, A.-M.; Collin, S.; Paletou, F.; Coupé, S.; Godet, O.; Pelat, D.

    2003-08-01

    In the era of XMM-Newton and Chandra missions, it is crucial to use codes able to compute correctly the line spectrum of X-ray irradiated thick media (Thomson thickness of the order of unity), in order to build models for the structure and the emission of the central regions of Active Galactic Nuclei (AGN), or of X-ray binaries. In all photoionized codes except in our code Titan, the line intensities are computed with the so-called ``escape probability approximation". In its last version, Titan solves the transfer of a thousand lines and of the continuum with the ``Accelerated Lambda Iteration" method, which is one of the most efficient and at the same time the most secure for line transfer. We first review the escape probability formalism and mention various reasons why it should lead to wrong results concerning the line fluxes. Then we check several approximations commonly used instead of line transfer in photoionization codes, by comparing them to the full transfer computation. We find that for conditions typical of the AGN or X-ray binary emission medium, all approximations lead to an overestimation of the emitted X-ray line spectrum, which can reach more than one order of magnitude. We show that it is due mainly to the local treatment of line photons, implying a delicate balance between excitations of X-ray transitions by the very intense underlying diffuse X-ray continuum (which are not taken properly into account in escape probability approximations) and the net rate of excitations by the diffuse line flux. The most affected lines are those in the soft X-ray range. Such processes are much less important in cooler and thinner media (like the Broad Line Region of AGN), as the most intense lines lie in the optical and near ultraviolet range where the diffuse continuum is small. We conclude that it is very important to treat correctly the transfer of the continuum to get the best results for the line spectrum. On the other hand the approximations used for the

  4. Black holes in binary stellar systems and galactic nuclei

    Cherepashchuk, A. M.

    2014-04-01

    In the last 40 years, following pioneering papers by Ya B Zeldovich and E E Salpeter, in which a powerful energy release from nonspherical accretion of matter onto a black hole (BH) was predicted, many observational studies of black holes in the Universe have been carried out. To date, the masses of several dozen stellar-mass black holes (M_BH = (4{-}20) M_\\odot) in X-ray binary systems and of several hundred supermassive black holes (M_BH = (10^{6}{-}10^{10}) M_\\odot) in galactic nuclei have been measured. The estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozen supermassive black holes, the values of the dimensionless angular momentum a_* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a_* = 0.998. A new field of astrophysics, so-called black hole demography, which studies the birth and growth of black holes and their evolutionary connection to other objects in the Universe, namely stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. The evolutionary relations between supermassive black holes in galactic centers and spheroidal stellar components (bulges) of galaxies, as well as dark-matter galactic haloes are brought out. The launch into Earth's orbit of the space radio interferometer RadioAstron opened up the real possibility of finally proving that numerous discovered massive and highly compact objects with properties very similar to those of black holes make up real black holes in the sense of Albert Einstein's General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths \\lambda \\lesssim 1 mm (the international program, Event Horizon Telescope).

  5. An instability of feedback regulated star formation in galactic nuclei

    Torrey, Paul; Faucher-Giguère, Claude-André; Vogelsberger, Mark; Quataert, Eliot; Kereš, Dušan; Murray, Norman

    2016-01-01

    We examine the stability of feedback-regulated star formation (SF) in galactic nuclei and contrast it to SF in extended discs. In galactic nuclei the dynamical time becomes shorter than the time over which feedback from young stars evolves. We argue analytically that the balance between stellar feedback and gravity is unstable in this regime. We study this using numerical simulations with pc-scale resolution and explicit stellar feedback taken from stellar evolution models. The nuclear gas mass, young stellar mass, and SFR within the central ~100 pc (the short-timescale regime) never reach steady-state, but instead go through dramatic, oscillatory cycles. Stars form until a critical surface density of young stars is present (such that feedback overwhelms gravity), at which point they begin to expel gas from the nucleus. Since the dynamical times are shorter than the stellar evolution times, the stars do not die as the gas is expelled, but continue to push, triggering a runaway quenching of star formation in t...

  6. Dense Molecular Gas Around Protostars and in Galactic Nuclei European Workshop on Astronomical Molecules 2004

    Baan, W A; Langevelde, H J

    2004-01-01

    The phenomena observed in young stellar objects (YSO), circumstellar regions and extra-galactic nuclei show some similarity in their morphology, dynamical and physical processes, though they may differ in scale and energy. The European Workshop on Astronomical Molecules 2004 gave astronomers a unique opportunity to discuss the links among the observational results and to generate common interpretations of the phenomena in stars and galaxies, using the available diagnostic tools such as masers and dense molecular gas. Their theoretical understanding involves physics, numerical simulations and chemistry. Including a dozen introductory reviews, topics of papers in this book also cover: maser and dense gas diagnostics and related phenomena, evolution of circumstellar regions around protostars, evolution of circumnuclear regions of active galaxies, diagnostics of the circumnuclear gas in stars and galactic nuclei. This book summarizes our present knowledge in these topics, highlights major problems to be addressed...

  7. X-ray Spectral Model of Reprocessing by Smooth and Clumpy Molecular Tori in Active Galactic Nuclei with the MONACO framework

    Furui, Shun'ya; Odaka, Hirokazu; Kawaguchi, Toshihiro; Ohno, Masanori; Hayashi, Kazuma

    2016-01-01

    We construct an X-ray spectral model of reprocessing by a torus in an active galactic nucleus (AGN) with a Monte Carlo simulation framework MONACO. Two torus geometries of smooth and clumpy cases are considered and compared. In order to reproduce a Compton shoulder accurately, MONACO includes not only free electron scattering but also bound electron scattering. Raman and Reyleigh scattering are also treated, and scattering cross sections dependent on chemical states of hydrogen and helium are included. Doppler broadening by turbulence velocity can be implemented. Our model gives consistent results with other available models, such as MYTorus, except for differences due to different physical parameters and assumptions. We studied the dependence on torus parameters for Compton shoulder, and found that a intensity ratio of Compton shoulder to line core mainly depends on the column density, inclination angle, and metal abundance. For instance, an increase of metal abundance makes the Compton shoulder relatively w...

  8. Star formation rates from [C II] 158 μm and mid-infrared emission lines for starbursts and active galactic nuclei

    Sargsyan, L.; Lebouteiller, V.; Weedman, D.; Barry, D.; Spoon, H. [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States); Samsonyan, A. [Byurakan Astrophysical Observatory, Byurakan 0213 (Armenia); Bernard-Salas, J. [Department of Physical Sciences, Open University, Milton Keynes MK7 6AA (United Kingdom); Houck, J., E-mail: sargsyan@isc.astro.cornell.edu, E-mail: dweedman@isc.astro.cornell.edu [Astronomy Department, Cornell University, Ithaca, NY 14853 (United States)

    2014-07-20

    A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)]) – 7.0, for SFR in M{sub ☉} yr{sup –1} and L([C II]) in L{sub ☉}. We conclude that L([C II]) can be used to measure SFR in any source to a precision of ∼50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL{sub ν}(158 μm) – 42.8 for SFR in M{sub ☉} yr{sup –1} and νL{sub ν}(158 μm) in erg s{sup –1}.

  9. Physical conditions in photodissociation regions - Application to galactic nuclei

    Wolfire, Mark G.; Tielens, A. G. G. M.; Hollenbach, David

    1990-01-01

    A procedure is outlined which determines the physical characteristics of the neutral interstellar medium in the nuclei of luminous galaxies. The method uses millimeter and IR observations to find the mass and density of the molecular and atomic gas components as well as the UV flux incident on clouds. The area and volume filling factors and approximate number of clouds and cloud radii are also found. For the Galactic center, about 100 clouds of radius about 0.4 pc and density about 100,000/cu cm are found within about 5 pc. The atomic gas temperature is about 700 K and the FUV field on clouds is about 100,000 times the local Galactic FUV field. The flux is consistent with a central source of luminosity of 2-3 x 10 to the 7th solar. Roughly 100,000 clouds of radius roughly 0.4 pc are found within the roughly 330 pc nuclear region of M82. The large number of clouds produces a projected area filling factor approaching unity. Cloud heating may be dominated by an intense interstellar UV flux.

  10. Gas flows in galactic nuclei: observational constraints on BH-galaxy coevolution

    Garcia-Burillo, Santiago

    2016-01-01

    Galaxy nuclei are a unique laboratory to study gas flows. High-resolution imaging of the gas flows in galactic nuclei are instrumental in the study of the fueling and the feedback of star formation and nuclear activity in nearby galaxies. Several fueling mechanisms can be now confronted in detail with observations done with state-of-the-art interferometers. Furthermore, the study of gas flows in galactic nuclei can probe the feedback of activity on the interstellar medium of galaxies. Feedback action from star formation and AGN activity is invoked to prevent galaxies from becoming overly massive, but also to explain scaling laws like black hole (BH)-bulge mass correlations and the bimodal color distribution of galaxies. This close relationship between galaxies and their central supermassive BH can be described as co-evolution. There is mounting observational evidence for the existence of gas outflows in different populations of starbursts and active galaxies, a manifestation of the feedback of activity. We su...

  11. EXPLORING THE DISK-JET CONNECTION FROM THE PROPERTIES OF NARROW-LINE REGIONS IN POWERFUL YOUNG RADIO-LOUD ACTIVE GALACTIC NUCLEI

    We investigate the optical emission-line flux ratios of narrow-line regions in order to determine whether the formation of active galactic nucleus (AGN) jets requires specific accretion conditions. We find that bright compact radio galaxies, which are powerful radio galaxies in the early stage of the jet activity, exhibit systematically larger flux ratios of [O I]λ6300/[O III]λ5007 and smaller flux ratios of [O III]λ5007/[O III]λ4363 than radio-quiet (RQ) Seyfert 2 galaxies. Comparing the observed line ratios with photoionization models, it is found that the difference in the flux ratio of low- to high-ionization lines (e.g., [O I]λ6300/[O III]λ5007) can be well understood by the difference in the spectral energy distribution (SED) of ionizing sources. Powerful young radio-loud (YRL) AGNs favor SED without a strong big blue bump (BBB), i.e., a radiatively inefficient accretion flow (RIAF), while RQ AGNs are consistent with the models adopting SED with a strong BBB, i.e., a geometrically thin, optically thick disk. These findings imply that the formation of powerful AGN jets requires the accretion disk with harder ionizing SED (i.e., an RIAF). We discuss the obscuring structure of YRL AGNs as a plausible origin of the difference in flux ratios of [O III]λ5007/[O III]λ4363.

  12. Herschel Far-Infrared Photometry of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. PACS Observations

    Meléndez, M; Shimizu, T T; Barger, A J; Cowie, L L

    2014-01-01

    Far-Infrared (FIR) photometry from the the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory is presented for 313 nearby, hard X-ray selected galaxies from the 58-month Swift Burst Alert Telescope (BAT) Active Galactic catalog. The present data do not distinguish between the FIR luminosity distributions at 70 and 160um for Seyfert 1 and Seyfert 2 galaxies. This result suggests that if the FIR emission is from the nuclear obscuring material surrounding the accretion disk, then it emits isotropically, independent of orientation. Alternatively, a significant fraction of the 70 and 160um could be from star formation, independent of AGN type. Using a non-parametric test for partial correlation with censored data, we find a statistically significant correlation between the AGN intrinsic power (in the 14-195 keV band ) and the FIR emission at 70 and 160um for Seyfert 1 galaxies. We find no correlation between the 14-195 keV and FIR luminosities in Seyfert 2 galaxies. The observed c...

  13. Co-evolution of galactic nuclei and globular cluster systems

    We revisit the hypothesis that dense galactic nuclei are formed from inspiraling globular clusters. Recent advances in the understanding of the continuous formation of globular clusters over cosmic time and the concurrent evolution of the galaxy stellar distribution allow us to construct a simple model that matches the observed spatial and mass distributions of clusters in the Galaxy and the giant elliptical galaxy M87. In order to compare with observations, we model the effects of dynamical friction and dynamical evolution, including stellar mass loss, tidal stripping of stars, and tidal disruption of clusters by the growing galactic nucleus. We find that inspiraling globular clusters form a dense central structure, with mass and radius comparable to the typical values in observed nuclear star clusters (NSCs) in late-type and low-mass early-type galaxies. The density contrast associated with the NSC is less pronounced in giant elliptical galaxies. Our results indicate that the NSC mass as a fraction of mass of the galaxy stellar spheroid scales as MNSC/M∗≈0.0025 M∗,11−0.5. Thus disrupted globular clusters could contribute most of the mass of NSCs in galaxies with stellar mass below 1011 M ☉. The inner part of the accumulated cluster may seed the growth of a central black hole via stellar dynamical core collapse, thereby relieving the problem of how to form luminous quasars at high redshift. The seed black hole may reach ∼105 M ☉ within ≲ 1 Gyr of the beginning of globular cluster formation.

  14. The Potential for Cubesats to Determine Black Holes Masses in Nearby Active Galactic Nuclei and Contribute to Other Time Domain Science

    Gorjian, Varoujan; Ardila, David R.; Barth, Aaron J.; Janson, Siegfried; Kochanek, Christopher S.; Malkan, Matthew Arnold; Peterson, Bradley M.; Rowen, Darren; Seager, Sara; Shkolnik, Evgenya L.

    2016-01-01

    A 3U (30cmx10cmx10cm) CubeSat with a 9cm diameter aperture telescope can deliver unprecedented time domain coverage in the ultraviolet (UV) for the purposes of Active Galactic Nucleus (AGN) reverberation mapping to determine supermassive black hole (SMBH) masses. SMBH's reside at the centers of most, if not all, massive galaxies and accretion onto those black holes generates a great deal of emission peaking in the UV. These accretion disks are also surrounded by a nearby, fast moving gas region called the Broad Line Region (BLR). As light pulses generated near the black hole spread out, they first illuminate the accretion disk, and then the BLR. For a sample of bright AGN, a dedicated cubesat can follow these changes in brightness on a daily basis for up to 100 days from low Earth orbit. With such monitoring of changes in the accretion disk and then the BLR, an accurate distance between the two regions can be determined. Combining this UV coverage with optical emission-line spectroscopy from the ground allows for a direct measurement of the mass of the central black hole. This exchange of time resolution for spatial resolution can also be used to determine the structure of the central region of the AGN. Ground-based photometric and spectroscopic measurements will complement the UV by tracing the optically emitting and hence cooler regions of the AGN to provide one of the best measurements of supermassive black hole masses.In addition to the primary science mission, the long observing campaigns and the large field of view required to get comparison stars for relative photometry allow for other competitive science. We have identified UV activity in M dwarfs as ancillary science that can be addressed with such a cubesat. This activity will have a strong impact on the habitability of any possible planet around the star.

  15. SECULAR DYNAMICAL ANTI-FRICTION IN GALACTIC NUCLEI

    We identify a gravitational-dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole. We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as 'secular dynamical anti-friction' (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity; (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration; and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

  16. Physical conditions in photodissociation regions: Application to galactic nuclei

    Wolfire, M. G.; Tielens, A. G. G. M.; Hollenbach, David J.

    1990-01-01

    Infrared and sub-millimeter observations are used in a simple procedure to determine average physical properties of the neutral interstellar medium in Galactic photodissociation regions as well as in ensembles of clouds which exist in the nuclei of luminous infrared galaxies. The relevant observations include the Infrared Astronomy Satellite (IRAS) infrared continuum measurements, infrared spectroscopy of the fine-structure lines of SiII 35 microns, OI 63 microns, and CII 158 microns, and the 2.6 mm CO (J=1-0) rotational transition. The diagnostic capabilities of the OI 145 microns line is also addressed. Researchers attribute these emission lines as well as the continuum to the atomic/molecular photodissociation region on the surfaces of molecular clouds which are illuminated by strong ultraviolet fields. They use the theoretical photodissociation region models of Tielens and Hollenbach (1985, Ap. J., 291, 722) to construct simple diagrams which utilize line ratios and line to continuum ratios to determine the average gas density n, the average incident far-ultraviolet flux G sub o, and the temperature of the atomic gas T.

  17. The History of Tidal Disruption Events in Galactic Nuclei

    Aharon, Danor; Perets, Hagai B

    2015-01-01

    The tidal disruption of a star by a massive black hole (MBH) is thought to produce a transient luminous event. Such tidal disruption events (TDEs) may play an important role in detecting and characterizing MBHs and probe the properties and dynamics of their nuclear stellar clusters (NSCs) hosts. Previous studies estimated the recent rates of TDEs in the local universe. However, the long-term evolution of the TDEs rate throughout the history of the universe have been hardly explored. Here we consider the TDEs history, using simple evolutionary models for the formation and evolution of galactic nuclei. We use a 1D Fokker-Planck approach to explore the evolution of MBH-hosting NSCs, and obtain the disruption rates of stars during their evolution. We complement these with an analysis of TDEs history based on N-body simulation data, and find them to be comparable. We consider NSCs that are built-up from close-in star formation or from star formation/clusters-dispersal far-out, a few pc from the MBH. We also explor...

  18. SPITZER SPECTROSCOPY OF INFRARED-LUMINOUS GALAXIES: DIAGNOSTICS OF ACTIVE GALACTIC NUCLEI AND STAR FORMATION AND CONTRIBUTION TO TOTAL INFRARED LUMINOSITY

    We use mid-infrared (MIR) spectroscopy from the Spitzer Infrared Spectrograph to study the nature of star-formation and supermassive black hole accretion for a sample of 65 IR-luminous galaxies at 0.02 1.2 mJy. The MIR spectra cover wavelengths 5-38 μm, spanning the polycyclic aromatic hydrocarbon (PAH) features and important atomic diagnostic lines. Our sample of galaxies corresponds to a range of total IR luminosity, LIR = L(8-1000 μm) = 1010-1012 L☉ (median LIR of 3.0 × 1011 L☉). We divide our sample into a subsample of galaxies with Spitzer Infrared Array Camera 3.6-8.0 μm colors indicative of warm dust heated by an active galactic nucleus (AGN; IRAGN) and those galaxies whose colors indicate star-formation processes (non-IRAGN). Compared to the non-IRAGN, the IRAGN show smaller PAH emission equivalent widths, which we attribute to an increase in mid-IR continuum from the AGN. We find that in both the IRAGN and star-forming samples, the luminosity in the PAH features correlates strongly with [Ne II] λ12.8 μm emission line, from which we conclude that the PAH luminosity directly traces the instantaneous star-formation rate (SFR) in both the IRAGN and star-forming galaxies. We compare the ratio of PAH luminosity to the total IR luminosity, and we show that for most IRAGN star-formation accounts for 10%-50% of the total IR luminosity. We also find no measurable difference between the PAH luminosity ratios of L11.3/L7.7 and L6.2/L7.7 for the IRAGN and non-IRAGN, suggesting that AGN do not significantly excite or destroy PAH molecules on galaxy-wide scales. Interestingly, a small subset of galaxies (8 of 65 galaxies) show a strong excess of [O IV] λ25.9 μm emission compared to their PAH emission, which indicates the presence of heavily-obscured AGN, including 3 galaxies that are not otherwise selected as IRAGN. The low PAH emission and low [Ne II] emission of the IRAGN and [O IV]-excess objects imply the IR luminosity of these objects is dominated by

  19. The History of Tidal Disruption Events in Galactic Nuclei

    Aharon, Danor; Mastrobuono Battisti, Alessandra; Perets, Hagai B.

    2016-06-01

    The tidal disruption of a star by a massive black hole (MBH) is thought to produce a transient luminous event. Such tidal disruption events (TDEs) may play an important role in the detection and characterization of MBHs, and in probing the properties and dynamics of their nuclear stellar cluster (NSC) hosts. Previous studies estimated the recent rates of TDEs in the local universe. However, the long-term evolution of the rates throughout the history of the universe has been little explored. Here we consider TDE history, using evolutionary models for the evolution of galactic nuclei. We use a 1D Fokker–Planck approach to explore the evolution of MBH-hosting NSCs, and obtain the disruption rates of stars during their evolution. We complement these with an analysis of TDE history based on N-body simulation data, and find them to be comparable. We consider NSCs that are built up from close-in star formation (SF) or from far-out SF/cluster-dispersal, a few pc from the MBH. We also explore cases where primordial NSCs exist and later evolve through additional SF/cluster-dispersal processes. We study the dependence of the TDE history on the type of galaxy, as well as the dependence on the MBH mass. These provide several scenarios, with a continuous increase of the TDE rates over time for cases of far-out SF and a more complex behavior for the close-in SF cases. Finally, we integrate the TDE histories of the various scenarios to provide a total TDE history of the universe, which can be potentially probed with future large surveys (e.g., LSST).

  20. IFU spectroscopy of 10 early-type galactic nuclei - II. Nuclear emission line properties

    Ricci, T. V.; Steiner, J. E.; Menezes, R. B.

    2014-05-01

    Although it is well known that massive galaxies have central black holes, most of them accreting at low Eddington ratios, many important questions still remain open. Among them are the nature of the ionizing source, the characteristics and frequencies of the broad-line region and of the dusty torus. We report observations of 10 early-type galactic nuclei, observed with the Gemini Multi Object Spectrograph in integral field unit mode, installed on the Gemini South telescope, analysed with standard techniques for spectral treatment and compared with results obtained with principal component analysis Tomography (Paper I). We performed spectral synthesis of each spaxel of the data cubes and subtracted the stellar component from the original cube, leaving a data cube with emission lines only. The emission lines were decomposed in multi-Gaussian components. We show here that, for eight galaxies previously known to have emission lines, the narrow-line region can be decomposed in two components with distinct line widths. In addition to this, broad Hα emission was detected in six galaxies. The two galaxies not previously known to have emission lines show weak Hα+[N II] lines. All 10 galaxies may be classified as low-ionization nuclear emission regions in diagnostic diagrams and seven of them have bona fide active galactic nuclei with luminosities between 1040 and 1043 erg s-1. Eddington ratios are always <10-3.