Galaxy growth in a massive halo in the first billion years of cosmic history

Science.gov (United States)

Marrone, D. P.; Spilker, J. S.; Hayward, C. C.; Vieira, J. D.; Aravena, M.; Ashby, M. L. N.; Bayliss, M. B.; Béthermin, M.; Brodwin, M.; Bothwell, M. S.; Carlstrom, J. E.; Chapman, S. C.; Chen, Chian-Chou; Crawford, T. M.; Cunningham, D. J. M.; De Breuck, C.; Fassnacht, C. D.; Gonzalez, A. H.; Greve, T. R.; Hezaveh, Y. D.; Lacaille, K.; Litke, K. C.; Lower, S.; Ma, J.; Malkan, M.; Miller, T. B.; Morningstar, W. R.; Murphy, E. J.; Narayanan, D.; Phadke, K. A.; Rotermund, K. M.; Sreevani, J.; Stalder, B.; Stark, A. A.; Strandet, M. L.; Tang, M.; Weiß, A.

2018-01-01

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.

AXIAL RATIO OF EDGE-ON SPIRAL GALAXIES AS A TEST FOR BRIGHT RADIO HALOS

International Nuclear Information System (INIS)

Singal, J.; Jones, E.; Dunlap, H.; Kogut, A.

2015-01-01

We use surface brightness contour maps of nearby edge-on spiral galaxies to determine whether extended bright radio halos are common. In particular, we test a recent model of the spatial structure of the diffuse radio continuum by Subrahmanyan and Cowsik which posits that a substantial fraction of the observed high-latitude surface brightness originates from an extended Galactic halo of uniform emissivity. Measurements of the axial ratio of emission contours within a sample of normal spiral galaxies at 1500 MHz and below show no evidence for such a bright, extended radio halo. Either the Galaxy is atypical compared to nearby quiescent spirals or the bulk of the observed high-latitude emission does not originate from this type of extended halo. (letters)

DISCOVERY OF A GIANT RADIO HALO IN A NEW PLANCK GALAXY CLUSTER PLCKG171.9-40.7

Energy Technology Data Exchange (ETDEWEB)

Giacintucci, Simona [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Kale, Ruta; Venturi, Tiziana [INAF-Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy); Wik, Daniel R.; Markevitch, Maxim, E-mail: simona@astro.umd.edu [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-03-20

We report the discovery of a giant radio halo in a new, hot, X-ray luminous galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was found using Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz, and in the 1.4 GHz data from an NRAO Very Large Array Sky Survey pointing that we have reanalyzed. The diffuse radio emission is coincident with the cluster X-ray emission, and has an extent of {approx}1 Mpc and a radio power of {approx}5 Multiplication-Sign 10{sup 24} W Hz{sup -1} at 1.4 GHz. Its integrated radio spectrum has a slope of {alpha} Almost-Equal-To 1.8 between 235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of the archival XMM-Newton X-ray data shows that the cluster is hot ({approx}10 keV) and disturbed, consistent with X-ray-selected clusters hosting radio halos. This is the first giant radio halo discovered in one of the new clusters found by Planck.

A Hidden Radio Halo in the Galaxy Cluster A 1682? T. Venturi1 ...

Indian Academy of Sciences (India)

Abstract. High sensitivity observations of radio halos in galaxy clus- ters at frequencies ν ≤ 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos imaged down to 150–240 MHz show a considerable spread in size, mor- phology and spectral properties.

VizieR Online Data Catalog: Galaxy clusters: radio halos, relics and parameters (Yuan+, 2015)

Science.gov (United States)

Yuan, Z. S.; Han, J. L.; Wen, Z. L.

2017-10-01

A large number of radio halos, relics, and mini-halos have been discovered and measured in recent decades through observations with VLA (e.g., Giovannini & Feretti 2000NewA....5..335G; van Weeren et al. 2011A&A...533A..35V), GMRT (e.g., Venturi et al. 2007A&A...463..937V; Kale et al. 2015A&A...579A..92K), WSRT (e.g., van Weeren et al. 2010Sci...330..347V; Trasatti et al. 2015A&A...575A..45T), and also ATCA (e.g., Shimwell et al. 2014MNRAS.440.2901S, 2015MNRAS.449.1486S). We have checked the radio images of radio halos, relics, and mini-halos in the literature and collected in Table 1 the radio flux Sν at frequencies within a few per cent around 1.4 GHz, 610 MHz, and 325 MHz; we have interpolated the flux at an intermediate frequency if measurements are available at higher and lower frequencies. To establish reliable scaling relations, we include only the very firm detection of diffuse radio emission in galaxy clusters, and omit questionable detections or flux estimates due to problematic point-source subtraction. (3 data files).

STOCHASTIC MODEL OF THE SPIN DISTRIBUTION OF DARK MATTER HALOS

Energy Technology Data Exchange (ETDEWEB)

Kim, Juhan [Center for Advanced Computation, Korea Institute for Advanced Study, Heogiro 85, Seoul 130-722 (Korea, Republic of); Choi, Yun-Young [Department of Astronomy and Space Science, Kyung Hee University, Gyeonggi 446-701 (Korea, Republic of); Kim, Sungsoo S.; Lee, Jeong-Eun [School of Space Research, Kyung Hee University, Gyeonggi 446-701 (Korea, Republic of)

2015-09-15

We employ a stochastic approach to probing the origin of the log-normal distributions of halo spin in N-body simulations. After analyzing spin evolution in halo merging trees, it was found that a spin change can be characterized by a stochastic random walk of angular momentum. Also, spin distributions generated by random walks are fairly consistent with those directly obtained from N-body simulations. We derived a stochastic differential equation from a widely used spin definition and measured the probability distributions of the derived angular momentum change from a massive set of halo merging trees. The roles of major merging and accretion are also statistically analyzed in evolving spin distributions. Several factors (local environment, halo mass, merging mass ratio, and redshift) are found to influence the angular momentum change. The spin distributions generated in the mean-field or void regions tend to shift slightly to a higher spin value compared with simulated spin distributions, which seems to be caused by the correlated random walks. We verified the assumption of randomness in the angular momentum change observed in the N-body simulation and detected several degrees of correlation between walks, which may provide a clue for the discrepancies between the simulated and generated spin distributions in the voids. However, the generated spin distributions in the group and cluster regions successfully match the simulated spin distribution. We also demonstrated that the log-normality of the spin distribution is a natural consequence of the stochastic differential equation of the halo spin, which is well described by the Geometric Brownian Motion model.

Discovery of megaparsec-scale, low surface brightness nonthermal emission in merging galaxy clusters using the green bank telescope

Energy Technology Data Exchange (ETDEWEB)

Farnsworth, Damon; Rudnick, Lawrence [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street S.E., Minneapolis, MN 55455 (United States); Brown, Shea [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, IA 52242 (United States); Brunetti, Gianfranco [INAF/Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy)

2013-12-20

We present results from a study of 12 X-ray bright clusters at 1.4 GHz with the 100 m Green Bank Telescope. After subtraction of point sources using existing interferometer data, we reach a median (best) 1σ rms sensitivity level of 0.01 (0.006) μJy arcsec{sup –2}, and find a significant excess of diffuse, low surface brightness emission in 11 of 12 Abell clusters observed. We also present initial results at 1.4 GHz of A2319 from the Very Large Array. In particular, we find: (1) four new detections of diffuse structures tentatively classified as two halos (A2065, A2069) and two relics (A2067, A2073); (2) the first detection of the radio halo in A2061 at 1.4 GHz, which qualifies this as a possible ultra-steep spectrum halo source with a synchrotron spectral index of α ∼ 1.8 between 327 MHz and 1.4 GHz; (3) a ∼2 Mpc radio halo in the sloshing, minor-merger cluster A2142; (4) a >2× increase of the giant radio halo extent and luminosity in the merging cluster A2319; (5) a ∼7× increase to the integrated radio flux and >4× increase to the observed extent of the peripheral radio relic in A1367 to ∼600 kpc, which we also observe to be polarized on a similar scale; (6) significant excess emission of ambiguous nature in three clusters with embedded tailed radio galaxies (A119, A400, A3744). Our radio halo detections agree with the well-known X-ray/radio luminosity correlation, but they are larger and fainter than current radio power correlation studies would predict. The corresponding volume-averaged synchrotron emissivities are 1-2 orders of magnitude below the characteristic value found in previous studies. Some of the halo-like detections may be some type of previously unseen, low surface brightness radio halo or blend of unresolved shock structures and sub-Mpc-scale turbulent regions associated with their respective cluster merging activity. Four of the five tentative halos contain one or more X-ray cold fronts, suggesting a possible connection between gas

An Analysis Framework for Understanding the Origin of Nuclear Activity in Low-power Radio Galaxies

Science.gov (United States)

Lin, Yen-Ting; Huang, Hung-Jin; Chen, Yen-Chi

2018-05-01

Using large samples containing nearly 2300 active galaxies of low radio luminosity (1.4 GHz luminosity between 2 × 1023 and 3 × 1025 W Hz‑1, essentially low-excitation radio galaxies) at z ≲ 0.3, we present a self-contained analysis of the dependence of the nuclear radio activity on both intrinsic and extrinsic properties of galaxies, with the goal of identifying the best predictors of the nuclear radio activity. While confirming the established result that stellar mass must play a key role on the triggering of radio activities, we point out that for the central, most massive galaxies, the radio activity also shows a strong dependence on halo mass, which is not likely due to enhanced interaction rates in denser regions in massive, cluster-scale halos. We thus further investigate the effects of various properties of the intracluster medium (ICM) in massive clusters on the radio activities, employing two standard statistical tools, principle component analysis and logistic regression. It is found that ICM entropy, local cooling time, and pressure are the most effective in predicting the radio activity, pointing to the accretion of gas cooling out of a hot atmosphere to be the likely origin in triggering such activities in galaxies residing in massive dark matter halos. Our analysis framework enables us to logically discern the mechanisms responsible for the radio activity separately for central and satellite galaxies.

TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES

International Nuclear Information System (INIS)

Fujita, Yutaka; Takizawa, Motokazu; Yamazaki, Ryo; Akamatsu, Hiroki; Ohno, Hiroshi

2015-01-01

Radio relics are synchrotron emission found on the periphery of galaxy clusters. From the position and the morphology, it is often believed that the relics are generated by cosmic-ray (CR) electrons accelerated at shocks through a diffusive shock acceleration (DSA) mechanism. However, some radio relics have harder spectra than the prediction of the standard DSA model. One example is observed in the cluster 1RXS J0603.3+4214, which is often called the “Toothbrush Cluster.” Interestingly, the position of the relic is shifted from that of a possible shock. In this study, we show that these discrepancies in the spectrum and the position can be solved if turbulent (re)acceleration is very effective behind the shock. This means that for some relics turbulent reacceleration may be the main mechanism to produce high-energy electrons, contrary to the common belief that it is the DSA. Moreover, we show that for efficient reacceleration, the effective mean free path of the electrons has to be much smaller than their Coulomb mean free path. We also study the merging cluster 1E 0657−56, or the “Bullet Cluster,” in which a radio relic has not been found at the position of the prominent shock ahead of the bullet. We indicate that a possible relic at the shock is obscured by the observed large radio halo that is generated by strong turbulence behind the shock. We propose a simple explanation of the morphological differences of radio emission among the Toothbrush, the Bullet, and the Sausage (CIZA J2242.8+5301) Clusters

Giant Radio Halos in Galaxy Clusters as Probes of Particle ...

Indian Academy of Sciences (India)

scenario still remain poorly understood. ... to test models with future observations. ... A popular scenario for the origin of radio halos assumes that relativis- ..... based on particle acceleration by merger-driven turbulence in galaxy clusters shows.

Observations and Modeling of Merging Galaxy Clusters

Science.gov (United States)

Golovich, Nathan Ryan

Context: Galaxy clusters grow hierarchically with continuous accretion bookended by major merging events that release immense gravitational potential energy (as much as ˜1065 erg). This energy creates an environment for rich astrophysics. Precise measurements of the dark matter halo, intracluster medium, and galaxy population have resulted in a number of important results including dark matter constraints and explanations of the generation of cosmic rays. However, since the timescale of major mergers (˜several Gyr) relegates observations of individual systems to mere snapshots, these results are difficult to understand under a consistent dynamical framework. While computationally expensive simulations are vital in this regard, the vastness of parameter space has necessitated simulations of idealized mergers that are unlikely to capture the full richness. Merger speeds, geometries, and timescales each have a profound consequential effect, but even these simple dynamical properties of the mergers are often poorly understood. A method to identify and constrain the best systems for probing the rich astrophysics of merging clusters is needed. Such a method could then be utilized to prioritize observational follow up and best inform proper exploration of dynamical phase space. Task: In order to identify and model a large number of systems, in this dissertation, we compile an ensemble of major mergers each containing radio relics. We then complete a pan-chromatic study of these 29 systems including wide field optical photometry, targeted optical spectroscopy of member galaxies, radio, and X-ray observations. We use the optical observations to model the galaxy substructure and estimate line of sight motion. In conjunction with the radio and X-ray data, these substructure models helped elucidate the most likely merger scenario for each system and further constrain the dynamical properties of each system. We demonstrate the power of this technique through detailed analyses

The radio halo and active galaxies in the Coma cluster

International Nuclear Information System (INIS)

Cordey, R.A.

1985-01-01

The Cambridge Low-Frequency Synthesis Telescope has been used to map the Coma cluster at 151 MHz. Two new extended sources are found, associated with the cluster galaxies NGC4839 and NGC4849. The central halo radio source is shown not to have a simple symmetrical structure but to be distorted, with separate centres of brightening near the radio galaxies NGC4874 and IC4040. The structure cannot be accounted for by cluster-wide acceleration processes but implies a close connection with current radio galaxies and, in particular, models requiring diffusion of electrons out of radio sources seem to be favoured. The other large source, near Coma A, is detected and higher resolution data at 1407 MHz are used to clarify its structure. (author)

First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

Science.gov (United States)

Savini, F.; Bonafede, A.; Brüggen, M.; van Weeren, R.; Brunetti, G.; Intema, H.; Botteon, A.; Shimwell, T.; Wilber, A.; Rafferty, D.; Giacintucci, S.; Cassano, R.; Cuciti, V.; de Gasperin, F.; Röttgering, H.; Hoeft, M.; White, G.

2018-05-01

Diffuse synchrotron radio emission from cosmic-ray electrons is observed at the center of a number of galaxy clusters. These sources can be classified either as giant radio halos, which occur in merging clusters, or as mini halos, which are found only in cool-core clusters. In this paper, we present the first discovery of a cool-core cluster with an associated mini halo that also shows ultra-steep-spectrum emission extending well beyond the core that resembles radio halo emission. The large-scale component is discovered thanks to LOFAR observations at 144 MHz. We also analyse GMRT observations at 610 MHz to characterise the spectrum of the radio emission. An X-ray analysis reveals that the cluster is slightly disturbed, and we suggest that the steep-spectrum radio emission outside the core could be produced by a minor merger that powers electron re-acceleration without disrupting the cool core. This discovery suggests that, under particular circumstances, both a mini and giant halo could co-exist in a single cluster, opening new perspectives for particle acceleration mechanisms in galaxy clusters.

Individual stellar haloes of massive galaxies measured to 100 kpc at 0.3 < z < 0.5 using Hyper Suprime-Cam

Science.gov (United States)

Huang, Song; Leauthaud, Alexie; Greene, Jenny E.; Bundy, Kevin; Lin, Yen-Ting; Tanaka, Masayuki; Miyazaki, Satoshi; Komiyama, Yutaka

2018-04-01

Massive galaxies display extended light profiles that can reach several hundreds of kiloparsecs. We use data from the Hyper Suprime-Cam (HSC) survey that is simultaneously wide (˜100 deg2) and deep (>28.5 mag arcsec-2 in i band) to study the stellar haloes of a sample of ˜7000 massive galaxies at z ˜ 0.4. The depth of the HSC data enables us to measure surface mass density profiles to 100 kpc for individual galaxies without stacking. As in previous work, we find that more massive galaxies exhibit more extended outer profiles than smaller galaxies. When this extended light is not properly accounted for (because of shallow imaging and/or inadequate profile modelling), the derived stellar mass function can be significantly underestimated at the high-mass end. Across our sample, the ellipticity of outer light profile increases substantially with radius. We show for the first time that these ellipticity gradients steepen dramatically as a function of galaxy mass, but we detect no mass dependence in outer colour gradients. Our results support the two-phase formation scenario for massive galaxies in which outer envelopes are built up at a later time from a series of merging events. We provide surface mass density profiles in a convenient tabulated format to facilitate comparisons with predictions from numerical simulations of galaxy formation.

Giant Radio Halos in Galaxy Clusters as Probes of Particle ...

Indian Academy of Sciences (India)

2016-01-27

Jan 27, 2016 ... Giant radio halos in galaxy clusters probe mechanisms of particle acceleration connected with cluster merger events. Shocks and turbulence are driven in the inter-galactic medium (IGM) during clusters mergers and may have a deep impact on the non-thermal properties of galaxy clusters. Models of ...

Dark-matter halo mergers as a fertile environment for low-mass Population III star formation

DEFF Research Database (Denmark)

Bovino, S.; Latif, M. A.; Grassi, Tommaso

2014-01-01

While Population III (Pop III) stars are typically thought to be massive, pathways towards lower mass Pop III stars may exist when the cooling of the gas is particularly enhanced. A possible route is enhanced HD cooling during the merging of dark-matter haloes. The mergers can lead to a high ioni...

FRESH ACTIVITY IN OLD SYSTEMS: RADIO AGNs IN FOSSIL GROUPS OF GALAXIES

International Nuclear Information System (INIS)

Hess, Kelley M.; Wilcots, Eric M.; Hartwick, Victoria L.

2012-01-01

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from Sloan Digital Sky Survey Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L 1.4GHz > 10 23 W Hz –1 ) active galactic nucleus (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray-selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.

Massively Parallel Sort-Merge Joins in Main Memory Multi-Core Database Systems

OpenAIRE

Albutiu, Martina-Cezara; Kemper, Alfons; Neumann, Thomas

2012-01-01

Two emerging hardware trends will dominate the database system technology in the near future: increasing main memory capacities of several TB per server and massively parallel multi-core processing. Many algorithmic and control techniques in current database technology were devised for disk-based systems where I/O dominated the performance. In this work we take a new look at the well-known sort-merge join which, so far, has not been in the focus of research in scalable massively parallel mult...

Radio haloes in nearby galaxies modelled with 1D cosmic ray transport using SPINNAKER

Science.gov (United States)

Heesen, V.; Krause, M.; Beck, R.; Adebahr, B.; Bomans, D. J.; Carretti, E.; Dumke, M.; Heald, G.; Irwin, J.; Koribalski, B. S.; Mulcahy, D. D.; Westmeier, T.; Dettmar, R.-J.

2018-05-01

We present radio continuum maps of 12 nearby (D ≤ 27 Mpc), edge-on (i ≥ 76°), late-type spiral galaxies mostly at 1.4 and 5 GHz, observed with the Australia Telescope Compact Array, Very Large Array, Westerbork Synthesis Radio Telescope, Effelsberg 100-m, and Parkes 64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detection in the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick disc that can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER (SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmic ray transport models to the vertical model profiles of the non-thermal intensity and to the non-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (or diffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scale heights range from 2 to 8 kpc with an average across the sample of 3.0 ± 1.7 kpc; they show no correlation with either star formation rate (SFR), SFR surface density (ΣSFR), or rotation speed (Vrot). The advection speeds range from 100 to 700 km s - 1 and display correlations of V∝SFR0.36 ± 0.06 and V∝ Σ _SFR^{0.39± 0.09}; they agree remarkably well with the escape velocities (0.5 ≤ V/Vesc ≤ 2), which can be explained by cosmic ray-driven winds. Radio haloes show the presence of disc winds in galaxies with ΣSFR > 10 - 3 M⊙ yr - 1 kpc - 2 that extend over several kpc and are driven by processes related to the distributed star formation in the disc.

The role of Dark Matter sub-halos in the non-thermal emission of galaxy clusters

Energy Technology Data Exchange (ETDEWEB)

Marchegiani, Paolo; Colafrancesco, Sergio, E-mail: Paolo.Marchegiani@wits.ac.za, E-mail: Sergio.Colafrancesco@wits.ac.za [School of Physics, University of the Witwatersrand, Private Bag 3, WITS-2050, Johannesburg (South Africa)

2016-11-01

Annihilation of Dark Matter (DM) particles has been recognized as one of the possible mechanisms for the production of non-thermal particles and radiation in galaxy clusters. Previous studies have shown that, while DM models can reproduce the spectral properties of the radio halo in the Coma cluster, they fail in reproducing the shape of the radio halo surface brightness because they produce a shape that is too concentrated towards the center of the cluster with respect to the observed one. However, in previous studies the DM distribution was modeled as a single spherically symmetric halo, while the DM distribution in Coma is found to have a complex and elongated shape. In this work we calculate a range of non-thermal emissions in the Coma cluster by using the observed distribution of DM sub-halos. We find that, by including the observed sub-halos in the DM model, we obtain a radio surface brightness with a shape similar to the observed one, and that the sub-halos boost the radio emission by a factor between 5 and 20%, thus allowing to reduce the gap between the annihilation cross section required to reproduce the radio halo flux and the upper limits derived from other observations, and that this gap can be explained by realistic values of the boosting factor due to smaller substructures. Models with neutralino mass of 9 GeV and composition τ{sup +} τ{sup −}, and mass of 43 GeV and composition b b-bar can fit the radio halo spectrum using the observed properties of the magnetic field in Coma, and do not predict a gamma-ray emission in excess compared to the recent Fermi-LAT upper limits. These findings make these DM models viable candidate to explain the origin of radio halos in galaxy clusters, avoiding the problems connected to the excessive gamma-ray emission expected from proton acceleration in most of the currently proposed models, where the acceleration of particles is directly or indirectly connected to events related to clusters merging. Therefore, DM

Detecting Massive, High-Redshift Galaxy Clusters Using the Thermal Sunyaev-Zel'dovich Effect

Science.gov (United States)

Adams, Carson; Steinhardt, Charles L.; Loeb, Abraham; Karim, Alexander; Staguhn, Johannes; Erler, Jens; Capak, Peter L.

2017-01-01

We develop the thermal Sunyaev-Zel'dovich (SZ) effect as a direct astrophysical measure of the mass distribution of dark matter halos. The SZ effect increases with cosmological distance, a unique astronomical property, and is highly sensitive to halo mass. We find that this presents a powerful methodology for distinguishing between competing models of the halo mass function distribution, particularly in the high-redshift domain just a few hundred million years after the Big Bang. Recent surveys designed to probe this epoch of initial galaxy formation such as CANDELS and SPLASH report an over-abundance of highly massive halos as inferred from stellar ultraviolet (UV) luminosities and the stellar mass to halo mass ratio estimated from nearby galaxies. If these UV luminosity to halo mass relations hold to high-redshift, observations estimate several orders of magnitude more highly massive halos than predicted by hierarchical merging and the standard cosmological paradigm. Strong constraints on the masses of these galaxy clusters are essential to resolving the current tension between observation and theory. We conclude that detections of thermal SZ sources are plausible at high-redshift only for the halo masses inferred from observation. Therefore, future SZ surveys will provide a robust determination between theoretical and observational predictions.

Journal of Astrophysics and Astronomy | Indian Academy of Sciences

Indian Academy of Sciences (India)

We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443, is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4 keV band of 2.9 × 1045 erg s-1. Recent observations from GMRT at ...

GALAXIES IN X-RAY GROUPS. II. A WEAK LENSING STUDY OF HALO CENTERING

Energy Technology Data Exchange (ETDEWEB)

George, Matthew R.; Ma, Chung-Pei [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Leauthaud, Alexie; Bundy, Kevin [Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8583 (Japan); Finoguenov, Alexis [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Rykoff, Eli S. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Tinker, Jeremy L. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Wechsler, Risa H. [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Massey, Richard [Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Mei, Simona, E-mail: mgeorge@astro.berkeley.edu [Bureau des Galaxies, Etoiles, Physique, Instrumentation (GEPI), University of Paris Denis Diderot, F-75205 Paris Cedex 13 (France)

2012-09-20

Locating the centers of dark matter halos is critical for understanding the mass profiles of halos, as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper, we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray-selected galaxy groups in the COSMOS field with redshifts 0 < z < 1 and halo masses in the range 10{sup 13}-10{sup 14} M{sub Sun }. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to {approx}< 75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically {approx}50-150 kpc). Approximately 30% of groups in our sample have ambiguous centers with multiple bright or massive galaxies, and some of these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5%-30% if inaccurate centers are used and the issue of miscentering is not addressed.

Journal of Astrophysics and Astronomy | Indian Academy of Sciences

Indian Academy of Sciences (India)

Home; Journals; Journal of Astrophysics and Astronomy. Siddharth Malu. Articles written in Journal of Astrophysics and Astronomy. Volume 32 Issue 4 December 2011 pp 529-532. Discovery of a Giant Radio Halo in a Massive Merging Cluster at = 0.443 · K. S. Dwarakanath Siddharth Malu Ruta Kale · More Details ...

Journal of Astrophysics and Astronomy | Indian Academy of Sciences

Indian Academy of Sciences (India)

Home; Journals; Journal of Astrophysics and Astronomy. Ruta Kale. Articles written in Journal of Astrophysics and Astronomy. Volume 32 Issue 4 December 2011 pp 529-532. Discovery of a Giant Radio Halo in a Massive Merging Cluster at = 0.443 · K. S. Dwarakanath Siddharth Malu Ruta Kale · More Details Abstract ...

TURBULENCE AND RADIO MINI-HALOS IN THE SLOSHING CORES OF GALAXY CLUSTERS

International Nuclear Information System (INIS)

ZuHone, J. A.; Markevitch, M.; Brunetti, G.; Giacintucci, S.

2013-01-01

A number of relaxed, cool-core galaxy clusters exhibit diffuse, steep-spectrum radio sources in their central regions, known as radio mini-halos. It has been proposed that the relativistic electrons responsible for the emission have been reaccelerated by turbulence generated by the sloshing of the cool core gas. We present a high-resolution MHD simulation of gas sloshing in a galaxy cluster coupled with subgrid simulations of relativistic electron acceleration to test this hypothesis. Our simulation shows that the sloshing motions generate turbulence on the order of δv ∼ 50-200 km s –1 on spatial scales of ∼50-100 kpc and below in the cool core region within the envelope of the sloshing cold fronts, whereas outside the cold fronts, there is negligible turbulence. This turbulence is potentially strong enough to reaccelerate relativistic electron seeds (with initial γ ∼ 100-500) to γ ∼ 10 4 via damping of magnetosonic waves and non-resonant compression. The seed electrons could remain in the cluster from, e.g., past active galactic nucleus activity. In combination with the magnetic field amplification in the core, these electrons then produce diffuse radio synchrotron emission that is coincident with the region bounded by the sloshing cold fronts, as indeed observed in X-rays and the radio. The result holds for different initial spatial distributions of pre-existing relativistic electrons. The power and the steep spectral index (α ≈ 1-2) of the resulting radio emission are consistent with observations of mini-halos, though the theoretical uncertainties of the acceleration mechanisms are high. We also produce simulated maps of inverse-Compton hard X-ray emission from the same population of relativistic electrons.

PSR J1755-2550: a young radio pulsar with a massive, compact companion

Science.gov (United States)

Ng, C.; Kruckow, M. U.; Tauris, T. M.; Lyne, A. G.; Freire, P. C. C.; Ridolfi, A.; Caiazzo, I.; Heyl, J.; Kramer, M.; Cameron, A. D.; Champion, D. J.; Stappers, B.

2018-06-01

Radio pulsars found in binary systems with short orbital periods are usually fast spinning as a consequence of recycling via mass transfer from their companion stars; this process is also thought to decrease the magnetic field of the neutron star being recycled. Here, we report on timing observations of the recently discovered binary PSR J1755-2550 and find that this pulsar is an exception: with a characteristic age of 2.1 Myr, it is relatively young; furthermore, with a spin period of 315 ms and a surface magnetic field strength at its poles of 0.88 × 1012 G, the pulsar shows no sign of having been recycled. Based on its timing and orbital characteristics, the pulsar either has a massive white dwarf (WD) or a neutron star (NS) companion. To distinguish between these two cases, we searched radio observations for a potential recycled pulsar companion and analysed archival optical data for a potential WD companion. Neither work returned conclusive detections. We apply population synthesis modelling and find that both solutions are roughly equally probable. Our population synthesis also predicts a minimum mass of 0.90 M⊙ for the companion star to PSR J1755-2550 and we simulate the systemic runaway velocities for the resulting WDNS systems which may merge and possibly produce Ca-rich supernovae. Whether PSR J1755-2550 hosts a WD or a NS companion star, it is certainly a member of a rare subpopulation of binary radio pulsars.

The gaseous haloes of evolving galaxies: a probe using the linear sizes of radio sources

International Nuclear Information System (INIS)

Subramanian, K.; Swarup, G.

1990-01-01

As galaxies form and evolve, their gaseous haloes are expected to undergo corresponding evolution. We examine here whether observations of the linear sizes of radio sources can be used to probe such evolution. For this purpose we first represent the gas density at various stages of galaxy formation and evolution by means of simple model density profiles, and then work out the expected linear sizes (l) of radio sources in these models. (author)

Massively Parallel Sort-Merge Joins in Main Memory Multi-Core Database Systems

OpenAIRE

Martina-Cezara Albutiu, Alfons Kemper, Thomas Neumann

2012-01-01

Two emerging hardware trends will dominate the database system technology in the near future: increasing main memory capacities of several TB per server and massively parallel multi-core processing. Many algorithmic and control techniques in current database technology were devised for disk-based systems where I/O dominated the performance. In this work we take a new look at the well-known sort-merge join which, so far, has not been in the focus of research ...

SIMULATIONS OF RECOILING MASSIVE BLACK HOLES IN THE VIA LACTEA HALO

International Nuclear Information System (INIS)

Guedes, J.; Madau, P.; Diemand, J.; Kuhlen, M.; Zemp, M.

2009-01-01

The coalescence of a massive black hole (MBH) binary leads to the gravitational-wave recoil of the system and its ejection from the galaxy core. We have carried out N-body simulations of the motion of a M BH = 3.7 x 10 6 M sun MBH remnant in the 'Via Lactea I' simulation, a Milky Way-sized dark matter halo. The black hole receives a recoil velocity of V kick = 80, 120, 200, 300, and 400 km s -1 at redshift 1.5, and its orbit is followed for over 1 Gyr within a 'live' host halo, subject only to gravity and dynamical friction against the dark matter background. We show that, owing to asphericities in the dark matter potential, the orbit of the MBH is highly nonradial, resulting in a significantly increased decay timescale compared to a spherical halo. The simulations are used to construct a semi-analytic model of the motion of the MBH in a time-varying triaxial Navarro-Frenk-White dark matter halo plus a spherical stellar bulge, where the dynamical friction force is calculated directly from the velocity dispersion tensor. Such a model should offer a realistic picture of the dynamics of kicked MBHs in situations where gas drag, friction by disk stars, and the flattening of the central cusp by the returning black hole are all negligible effects. We find that MBHs ejected with initial recoil velocities V kick ∼> 500 km s -1 do not return to the host center within a Hubble time. In a Milky Way-sized galaxy, a recoiling hole carrying a gaseous disk of initial mass ∼M BH may shine as a quasar for a substantial fraction of its 'wandering' phase. The long decay timescales of kicked MBHs predicted by this study may thus be favorable to the detection of off-nuclear quasar activity.

HALO EXPANSION IN COSMOLOGICAL HYDRO SIMULATIONS: TOWARD A BARYONIC SOLUTION OF THE CUSP/CORE PROBLEM IN MASSIVE SPIRALS

Energy Technology Data Exchange (ETDEWEB)

Maccio, A. V.; Stinson, G. [Max-Planck-Institut fuer Astronomie, 69117 Heidelberg (Germany); Brook, C. B.; Gibson, B. K. [University of Central Lancashire, Jeremiah Horrocks Institute for Astrophysics and Supercomputing, Preston PR1 2HE (United Kingdom); Wadsley, J.; Couchman, H. M. P. [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1 (Canada); Shen, S. [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 95064 (United States); Quinn, T., E-mail: maccio@mpia.de, E-mail: stinson@mpia.de [Astronomy Department, University of Washington, Seattle, WA 98195-1580 (United States)

2012-01-15

A clear prediction of the cold dark matter (CDM) model is the existence of cuspy dark matter halo density profiles on all mass scales. This is not in agreement with the observed rotation curves of spiral galaxies, challenging on small scales the otherwise successful CDM paradigm. In this work we employ high-resolution cosmological hydrodynamical simulations to study the effects of dissipative processes on the inner distribution of dark matter in Milky Way like objects (M Almost-Equal-To 10{sup 12} M{sub Sun }). Our simulations include supernova feedback, and the effects of the radiation pressure of massive stars before they explode as supernovae. The increased stellar feedback results in the expansion of the dark matter halo instead of contraction with respect to N-body simulations. Baryons are able to erase the dark matter cuspy distribution, creating a flat, cored, dark matter density profile in the central several kiloparsecs of a massive Milky-Way-like halo. The profile is well fit by a Burkert profile, with fitting parameters consistent with the observations. In addition, we obtain flat rotation curves as well as extended, exponential stellar disk profiles. While the stellar disk we obtain is still partially too thick to resemble the Milky Way thin disk, this pilot study shows that there is enough energy available in the baryonic component to alter the dark matter distribution even in massive disk galaxies, providing a possible solution to the long-standing problem of cusps versus cores.

The Impact of Assembly Bias on the Galaxy Content of Dark Matter Halos

Science.gov (United States)

Zehavi, Idit; Contreras, Sergio; Padilla, Nelson; Smith, Nicholas J.; Baugh, Carlton M.; Norberg, Peder

2018-01-01

We study the dependence of the galaxy content of dark matter halos on large-scale environment and halo formation time using semi-analytic galaxy models applied to the Millennium simulation. We analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. We find distinct differences among these occupation functions. The main effect with environment is that central galaxies (and in one model, also the satellites) in denser regions start populating lower-mass halos. A similar, but significantly stronger, trend exists with halo age, where early-forming halos are more likely to host central galaxies at lower halo mass. We discuss the origin of these trends and the connection to the stellar mass–halo mass relation. We find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, we see a reverse trend for the occupation of satellite galaxies where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. We describe these occupancy variations in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy samples. Finally, we study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. Our results can inform theoretical modeling of galaxy assembly bias and attempts to detect it in the real universe.

The “Building Blocks” of Stellar Halos

Directory of Open Access Journals (Sweden)

Kyle A. Oman

2017-08-01

Full Text Available The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the apostle project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ∼0.2–0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.

THE ELM SURVEY. V. MERGING MASSIVE WHITE DWARF BINARIES

International Nuclear Information System (INIS)

Brown, Warren R.; Kenyon, Scott J.; Kilic, Mukremin; Gianninas, A.; Allende Prieto, Carlos

2013-01-01

We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P ≤ 1 day) binaries. Our sample includes four objects with remarkable log g ≅ 5 surface gravities and orbital solutions that require them to be double degenerate binaries. All of the lowest surface gravity WDs have metal lines in their spectra implying long gravitational settling times or ongoing accretion. Notably, six of the WDs in our sample have binary merger times 0.9 M ☉ companions. If the companions are massive WDs, these four binaries will evolve into stable mass transfer AM CVn systems and possibly explode as underluminous supernovae. If the companions are neutron stars, then these may be millisecond pulsar binaries. These discoveries increase the number of detached, double degenerate binaries in the ELM Survey to 54; 31 of these binaries will merge within a Hubble time.

THE ELM SURVEY. V. MERGING MASSIVE WHITE DWARF BINARIES

Energy Technology Data Exchange (ETDEWEB)

Brown, Warren R.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden St, Cambridge, MA 02138 (United States); Kilic, Mukremin; Gianninas, A. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK, 73019 (United States); Allende Prieto, Carlos, E-mail: wbrown@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: kilic@ou.edu, E-mail: alexg@nhn.ou.edu, E-mail: callende@iac.es [Instituto de Astrofisica de Canarias, E-38205, La Laguna, Tenerife (Spain)

2013-05-20

We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P {<=} 1 day) binaries. Our sample includes four objects with remarkable log g {approx_equal} 5 surface gravities and orbital solutions that require them to be double degenerate binaries. All of the lowest surface gravity WDs have metal lines in their spectra implying long gravitational settling times or ongoing accretion. Notably, six of the WDs in our sample have binary merger times <10 Gyr. Four have {approx}>0.9 M{sub Sun} companions. If the companions are massive WDs, these four binaries will evolve into stable mass transfer AM CVn systems and possibly explode as underluminous supernovae. If the companions are neutron stars, then these may be millisecond pulsar binaries. These discoveries increase the number of detached, double degenerate binaries in the ELM Survey to 54; 31 of these binaries will merge within a Hubble time.

How Very Massive Metal Free Stars Start Cosmological Reionization

International Nuclear Information System (INIS)

Wise, John H.; Abel, Tom

2007-01-01

The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include non-equilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the Case B approximation using adaptively ray traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of ∼10 6 . These first sources of reionization are highly intermittent and anisotropic and first photoionize the small scales voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately 5 ionizing photons are needed per sustained ionization when star formation in 10 6 M · halos are dominant in the calculation. As the halos become larger than ∼10 7 M # circle d ot#, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15--50, in calculations with stellar feedback only. Supernova feedback in these more massive halos creates a more diffuse medium, allowing the stellar radiation to escape more easily and maintaining the ratio of 5 ionizing photons per sustained ionization

The Atacama Cosmology Telescope: ACT-CL J0102-4915 'EL GORDO', A Massive Merging Cluster at Redshift 0.87

Science.gov (United States)

Menanteau, Felipe; Hughes, John P.; Sifon, Cristobal; Hilton, Matt; Gonzalez, Jorge; Infante, Leopoldo; Barrientos, L. Felipe; Baker, Andrew J.; Bond, John R.; Das, Sudeep;

Metal enriched gaseous halos around distant radio galaxies: Clues to feedback in galaxy formation

Energy Technology Data Exchange (ETDEWEB)

Reuland, M; van Breugel, W; de Vries, W; Dopita, A; Dey, A; Miley, G; Rottgering, H; Venemans, B; Stanford, S A; Lacy, M; Spinrad, H; Dawson, S; Stern, D; Bunker, A

2006-08-01

We present the results of an optical and near-IR spectroscopic study of giant nebular emission line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07 and B2 0902+34. Previous deep narrow band Ly{alpha} imaging had revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s{sup -1}, and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions >1000 km s{sup -1}. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of {approx} 60 kpc along the radio-axis. The dynamical structures traced in the Ly{alpha} line are, in most cases, closely echoed in the Carbon and Oxygen lines. This shows that the Ly{alpha} line is produced in a highly clumped medium of small filling factor, and can therefore be used as a tracer of the dynamics of HzRGs. We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming 'red and dead' Elliptical galaxies.

THE ATACAMA COSMOLOGY TELESCOPE: ACT-CL J0102–4915 'EL GORDO', A MASSIVE MERGING CLUSTER AT REDSHIFT 0.87

International Nuclear Information System (INIS)

Menanteau, Felipe; Hughes, John P.; Baker, Andrew J.; Sifón, Cristóbal; González, Jorge; Infante, Leopoldo; Felipe Barrientos, L.; Hilton, Matt; Bond, John R.; Hajian, Amir; Nolta, Michael R.; Das, Sudeep; Devlin, Mark J.; Marsden, Danica; Dunkley, Joanna; Hincks, Adam D.; Kosowsky, Arthur; Marriage, Tobias A.; Moodley, Kavilan; Niemack, Michael D.

2012-01-01

We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102–4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102–4915 as the most significant SZ decrement in a sky survey area of 755 deg 2 . Our Very Large Telescope (VLT)/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, σ gal = 1321 ± 106 km s –1 . Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T X = 14.5 ± 0.1 keV and 0.5-2.0 keV band luminosity of L X = (2.19 ± 0.11) × 10 45 h –2 70 erg s –1 . We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y X , and integrated SZ distortion, we estimate a cluster mass of M 200a = (2.16 ± 0.32) × 10 15 h –1 70 M ☉ . We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102–4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6 ± 0.7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22 ± 6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other. Archival radio data at 843 MHz reveal diffuse radio emission that, if associated with the cluster, indicates the presence of an intense double radio relic, hosted by the highest redshift cluster yet. ACT-CL J0102–4915 is possibly a high-redshift analog of the famous Bullet cluster. Such a massive cluster at this redshift is rare, although consistent

`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C 35.06, a peculiar radio galaxy with dancing radio jets

Science.gov (United States)

Biju, K. G.; Bagchi, Joydeep; Ishwara-Chandra, C. H.; Pandey-Pommier, M.; Jacob, Joe; Patil, M. K.; Kumar, P. Sunil; Pandge, Mahadev; Dabhade, Pratik; Gaikwad, Madhuri; Dhurde, Samir; Abraham, Sheelu; Vivek, M.; Mahabal, Ashish A.; Djorgovski, S. G.

2017-10-01

We report the results of our radio, optical and infrared studies of a peculiar radio source 4C 35.06, an extended radio-loud active galactic nucleus (AGN) at the centre of galaxy cluster Abell 407 (z = 0.047). The central region of this cluster hosts a remarkably tight ensemble of nine galaxies, the spectra of which resemble those of passive red ellipticals, embedded within a diffuse stellar halo of ˜1 arcmin size. This system (named 'Zwicky's Nonet') provides unique and compelling evidence for a multiple-nucleus cD galaxy precursor. Multifrequency radio observations of 4C 35.06 with the Giant Meterwave Radio Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400-kpc scale helically twisted and kinked radio jets and outer diffuse lobes. The outer extremities of jets contain extremely steep-spectrum (spectral index -1.7 to -2.5) relic/fossil radio plasma with a spectral age of a few ×(107-108) yr. Such ultra-steep spectrum relic radio lobes without definitive hotspots are rare and they provide an opportunity to understand the life cycle of relativistic jets and physics of black hole mergers in dense environments. We interpret our observations of this radio source in the context of growth of its central black hole, triggering of its AGN activity and jet precession, all possibly caused by galaxy mergers in this dense galactic system. A slow conical precession of the jet axis due to gravitational perturbation between interacting black holes is invoked to explain the unusual jet morphology.

THE ATACAMA COSMOLOGY TELESCOPE: ACT-CL J0102-4915 'EL GORDO', A MASSIVE MERGING CLUSTER AT REDSHIFT 0.87

Energy Technology Data Exchange (ETDEWEB)

Menanteau, Felipe; Hughes, John P.; Baker, Andrew J. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Rd, Piscataway, NJ 08854 (United States); Sifon, Cristobal; Gonzalez, Jorge; Infante, Leopoldo; Felipe Barrientos, L. [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Hilton, Matt [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Bond, John R.; Hajian, Amir; Nolta, Michael R. [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada); Das, Sudeep [Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA 94720 (United States); Devlin, Mark J.; Marsden, Danica [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Dunkley, Joanna [Department of Astrophysics, Oxford University, Oxford, OX1 3RH (United Kingdom); Hincks, Adam D. [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Kosowsky, Arthur [Physics and Astronomy Department, University of Pittsburgh, 100 Allen Hall, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); Marriage, Tobias A. [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218-2686 (United States); Moodley, Kavilan [Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban 4041 (South Africa); Niemack, Michael D. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305 (United States); and others

2012-03-20

We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102-4915 as the most significant SZ decrement in a sky survey area of 755 deg{sup 2}. Our Very Large Telescope (VLT)/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, {sigma}{sub gal} = 1321 {+-} 106 km s{sup -1}. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T{sub X} = 14.5 {+-} 0.1 keV and 0.5-2.0 keV band luminosity of L{sub X} = (2.19 {+-} 0.11) Multiplication-Sign 10{sup 45} h{sup -2}{sub 70} erg s{sup -1}. We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y{sub X}, and integrated SZ distortion, we estimate a cluster mass of M{sub 200a} = (2.16 {+-} 0.32) Multiplication-Sign 10{sup 15} h{sup -1}{sub 70} M{sub Sun }. We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102-4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6 {+-} 0.7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22 {+-} 6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other. Archival radio data at 843 MHz reveal diffuse radio emission that, if associated with the cluster, indicates the presence of an intense double radio relic, hosted by the highest redshift cluster yet. ACT-CL J0102-4915 is possibly a high

THE UBIQUITOUS RADIO CONTINUUM EMISSION FROM THE MOST MASSIVE EARLY-TYPE GALAXIES

International Nuclear Information System (INIS)

Brown, Michael J. I.; Jannuzi, Buell T.; Floyd, David J. E.; Mould, Jeremy R.

2011-01-01

We have measured the radio continuum emission of 396 early-type galaxies brighter than K = 9, using 1.4 GHz imagery from the NRAO Very Large Array Sky Survey, Green Bank 300 ft Telescope, and 64 m Parkes Radio Telescope. For M K K < -25.5 early-type galaxies are greater than zero in all cases. It is thus highly likely that the most massive galaxies always host an active galactic nucleus or have recently undergone star formation.

Chameleon halo modeling in f(R) gravity

International Nuclear Information System (INIS)

Li Yin; Hu, Wayne

2011-01-01

We model the chameleon effect on cosmological statistics for the modified gravity f(R) model of cosmic acceleration. The chameleon effect, required to make the model compatible with local tests of gravity, reduces force enhancement as a function of the depth of the gravitational potential wells of collapsed structure and so is readily incorporated into a halo model by including parameters for the chameleon mass threshold and rapidity of transition. We show that the abundance of halos around the chameleon mass threshold is enhanced by both the merging from below and the lack of merging to larger masses. This property also controls the power spectrum in the nonlinear regime and we provide a description of the transition to the linear regime that is valid for a wide range of f(R) models.

Exploring the liminality: properties of haloes and subhaloes in borderline f(R) gravity

Science.gov (United States)

Shi, Difu; Li, Baojiu; Han, Jiaxin; Gao, Liang; Hellwing, Wojciech A.

2015-09-01

We investigate the properties of dark matter haloes and subhaloes in an f(R) gravity model with |fR0| = 10-6, using a very-high-resolution N-body simulation. The model is a borderline between being cosmologically interesting and yet still consistent with current data. We find that the halo mass function in this model has a maximum 20 per cent enhancement compared with the Λ-cold-dark-matter (ΛCDM) predictions between z = 1 and 0. Because of the chameleon mechanism which screens the deviation from standard gravity in dense environments, haloes more massive than 1013 h-1 M⊙ in this f(R) model have very similar properties to haloes of similar mass in ΛCDM, while less massive haloes, such as that of the Milky Way, can have steeper inner density profiles and higher velocity dispersions due to their weaker screening. The halo concentration is remarkably enhanced for low-mass haloes in this model due to a deepening of the total gravitational potential. Contrary to the naive expectation, the halo formation time zf is later for low-mass haloes in this model, a consequence of these haloes growing faster than their counterparts in ΛCDM at late times and the definition of zf. Subhaloes, especially those less massive than 1011 h-1 M⊙, are substantially more abundant in this f(R) model for host haloes less massive than 1013 h-1 M⊙. We discuss the implications of these results for the Milky Way satellite abundance problem. Although the overall halo and subhalo properties in this borderline f(R) model are close to their ΛCDM predictions, our results suggest that studies of the Local Group and astrophysical systems, aided by high-resolution simulations, can be valuable for further tests of it.

Satellites of radio AGN in SDSS: Insights into agn triggering and feedback

Energy Technology Data Exchange (ETDEWEB)

Pace, Cameron; Salim, Samir, E-mail: cjpace@indiana.edu, E-mail: salims@indiana.edu [Indiana University, Department of Astronomy, Swain Hall West 319, Bloomington, IN 47405-7105 (United States)

2014-04-10

We study the effects of radio jets on galaxies in their vicinity (satellites) and the role of satellites in triggering radio-loud active galactic nuclei (AGNs). The study compares the aggregate properties of satellites of a sample of 7220 radio AGNs at z < 0.3 (identified by Best and Heckman from the SDSS and NVSS+FIRST surveys) to the satellites of a control sample of radio-quiet galaxies, which are matched in redshift, color, luminosity, and axis ratio, as well as by environment type: field galaxies, cluster members, and brightest cluster galaxies (BCGs). Remarkably, we find that radio AGNs exhibit on average a 50% excess (17σ significance) in the number of satellites within 100 kpc even though the cluster membership was controlled (e.g., radio BCGs have more satellites than radio-quiet BCGs, etc.). Satellite excess is not confirmed for high-excitation sources, which are only 2% of radio AGN. Extra satellites may be responsible for raising the probability for hot gas AGN accretion via tidal effects or may otherwise enhance the intensity or duration of the radio-emitting phase. Furthermore, we find that the incidence of radio AGNs among potential hosts (massive ellipticals) is similar for field galaxies and for non-BCG cluster members, suggesting that AGN fueling depends primarily on conditions in the host halo rather than the parent, cluster halo. Regarding feedback, we find that radio AGNs, either high or low excitation, have no detectable effect on star formation in their satellites, as neither induced star formation nor star formation quenching is present in more than ∼1% of radio AGN.

Satellites of radio AGN in SDSS: Insights into agn triggering and feedback

International Nuclear Information System (INIS)

Pace, Cameron; Salim, Samir

2014-01-01

We study the effects of radio jets on galaxies in their vicinity (satellites) and the role of satellites in triggering radio-loud active galactic nuclei (AGNs). The study compares the aggregate properties of satellites of a sample of 7220 radio AGNs at z < 0.3 (identified by Best and Heckman from the SDSS and NVSS+FIRST surveys) to the satellites of a control sample of radio-quiet galaxies, which are matched in redshift, color, luminosity, and axis ratio, as well as by environment type: field galaxies, cluster members, and brightest cluster galaxies (BCGs). Remarkably, we find that radio AGNs exhibit on average a 50% excess (17σ significance) in the number of satellites within 100 kpc even though the cluster membership was controlled (e.g., radio BCGs have more satellites than radio-quiet BCGs, etc.). Satellite excess is not confirmed for high-excitation sources, which are only 2% of radio AGN. Extra satellites may be responsible for raising the probability for hot gas AGN accretion via tidal effects or may otherwise enhance the intensity or duration of the radio-emitting phase. Furthermore, we find that the incidence of radio AGNs among potential hosts (massive ellipticals) is similar for field galaxies and for non-BCG cluster members, suggesting that AGN fueling depends primarily on conditions in the host halo rather than the parent, cluster halo. Regarding feedback, we find that radio AGNs, either high or low excitation, have no detectable effect on star formation in their satellites, as neither induced star formation nor star formation quenching is present in more than ∼1% of radio AGN.

X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

Energy Technology Data Exchange (ETDEWEB)

Montes, V. A.; Hofner, P.; Anderson, C.; Rosero, V. [Physics Department, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801 (United States)

2015-08-15

We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.

Understanding the core-halo relation of quantum wave dark matter from 3D simulations.

Science.gov (United States)

Schive, Hsi-Yu; Liao, Ming-Hsuan; Woo, Tak-Pong; Wong, Shing-Kwong; Chiueh, Tzihong; Broadhurst, Tom; Hwang, W-Y Pauchy

2014-12-31

We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle mass ∼10(-22)  eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our 3D cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60  pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars.

Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

Science.gov (United States)

Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

2017-09-01

We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

Halo models of HI selected galaxies

Science.gov (United States)

Paul, Niladri; Choudhury, Tirthankar Roy; Paranjape, Aseem

2018-06-01

Modelling the distribution of neutral hydrogen (HI) in dark matter halos is important for studying galaxy evolution in the cosmological context. We use a novel approach to infer the HI-dark matter connection at the massive end (m_H{I} > 10^{9.8} M_{⊙}) from radio HI emission surveys, using optical properties of low-redshift galaxies as an intermediary. In particular, we use a previously calibrated optical HOD describing the luminosity- and colour-dependent clustering of SDSS galaxies and describe the HI content using a statistical scaling relation between the optical properties and HI mass. This allows us to compute the abundance and clustering properties of HI-selected galaxies and compare with data from the ALFALFA survey. We apply an MCMC-based statistical analysis to constrain the free parameters related to the scaling relation. The resulting best-fit scaling relation identifies massive HI galaxies primarily with optically faint blue centrals, consistent with expectations from galaxy formation models. We compare the Hi-stellar mass relation predicted by our model with independent observations from matched Hi-optical galaxy samples, finding reasonable agreement. As a further application, we make some preliminary forecasts for future observations of HI and optical galaxies in the expected overlap volume of SKA and Euclid/LSST.

Self-consistent construction of virialized wave dark matter halos

Science.gov (United States)

Lin, Shan-Chang; Schive, Hsi-Yu; Wong, Shing-Kwong; Chiueh, Tzihong

2018-05-01

Wave dark matter (ψ DM ), which satisfies the Schrödinger-Poisson equation, has recently attracted substantial attention as a possible dark matter candidate. Numerical simulations have, in the past, provided a powerful tool to explore this new territory of possibility. Despite their successes in revealing several key features of ψ DM , further progress in simulations is limited, in that cosmological simulations so far can only address formation of halos below ˜2 ×1011 M⊙ and substantially more massive halos have become computationally very challenging to obtain. For this reason, the present work adopts a different approach in assessing massive halos by constructing wave-halo solutions directly from the wave distribution function. This approach bears certain similarities with the analytical construction of the particle-halo (cold dark matter model). Instead of many collisionless particles, one deals with one single wave that has many noninteracting eigenstates. The key ingredient in the wave-halo construction is the distribution function of the wave power, and we use several halos produced by structure formation simulations as templates to determine the wave distribution function. Among different models, we find the fermionic King model presents the best fits and we use it for our wave-halo construction. We have devised an iteration method for constructing the nonlinear halo and demonstrate its stability by three-dimensional simulations. A Milky Way-sized halo has also been constructed, and the inner halo is found to be flatter than the NFW profile. These wave-halos have small-scale interferences both in space and time producing time-dependent granules. While the spatial scale of granules varies little, the correlation time is found to increase with radius by 1 order of magnitude across the halo.

Emulating Dynamic Radio Channels for Radiated Testing of Massive MIMO Devices

DEFF Research Database (Denmark)

Kyösti, Pekka; Hentilä, Lassi; Kyröläinen, Jukka

2018-01-01

This paper discusses a multi-probe anechoic chamber based (MPAC) setup, capable of reconstructing non-stationary radio propagation environments for testing of mm-wave and massive MIMO devices. The test setup is aimed for evaluation of end to end performance of devices, including hybrid beamforming...... operations of antenna arrays and base band processing, in highly time variant channel conditions. In this work we present simulated comparison of an ideal reference radio channel model and corresponding model implemented with limited resources of MPAC components. We give a qualitative analysis of the results...... with non-line of sight (NLOS) channel models, without quantitative evaluation. The example device under test (DUT) is a 8x8 planar array with half wavelength inter-element spacing....

On the building blocks of the M31 and Milky Way halos

Directory of Open Access Journals (Sweden)

Monelli Matteo

2017-01-01

Full Text Available We discuss the formation of the halo of M31 and the Milky Way as traced by the population of RR Lyrae stars, in comparison with the population of such stars preent in satellite dwarf galaxies. We find that both halos and the massive dwarf host a population of high amplitude short period RRab stars, absent in low-mass dwarfs. These stars are explained as the metal-rich tail of the RR Lyrae distribution ([Fe/H] ∼ - 1.5, and thus their existence imply fast chemical enrichment in the host system. Their presence in both halos implies that massive building blocks had an important role in their formation.

Galaxies Grow Their Bulges and Black Holes in Diverse Ways

Energy Technology Data Exchange (ETDEWEB)

Bell, Eric F.; Harmsen, Benjamin; D’Souza, Richard [Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109-1107 (United States); Monachesi, Antonela [Max Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, D-85741 Garching (Germany); Jong, Roelof S. de [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Bailin, Jeremy [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487-0324 (United States); Radburn-Smith, David J. [Department of Astronomy, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195 (United States); Holwerda, Benne W., E-mail: ericbell@umich.edu [Department of Physics and Astronomy, University of Louisville, 102 Natural Science Building, Louisville, KY 40292 (United States)

2017-03-01

Galaxies with Milky Way–like stellar masses have a wide range of bulge and black hole masses; in turn, these correlate with other properties such as star formation history. While many processes may drive bulge formation, major and minor mergers are expected to play a crucial role. Stellar halos offer a novel and robust measurement of galactic merger history; cosmologically motivated models predict that mergers with larger satellites produce more massive, higher-metallicity stellar halos, reproducing the recently observed stellar halo metallicity–mass relation. We quantify the relationship between stellar halo mass and bulge or black hole prominence using a sample of 18 Milky Way-mass galaxies with newly available measurements of (or limits on) stellar halo properties. There is an order of magnitude range in bulge mass, and two orders of magnitude in black hole mass, at a given stellar halo mass (or, equivalently, merger history). Galaxies with low-mass bulges show a wide range of quiet merger histories, implying formation mechanisms that do not require intense merging activity. Galaxies with massive “classical” bulges and central black holes also show a wide range of merger histories. While three of these galaxies have massive stellar halos consistent with a merger origin, two do not—merging appears to have had little impact on making these two massive “classical” bulges. Such galaxies may be ideal laboratories to study massive bulge formation through pathways such as early gas-rich accretion, violent disk instabilities, or misaligned infall of gas throughout cosmic time.

Gravitational lens effect and pregalactic halo objects

International Nuclear Information System (INIS)

Bontz, R.J.

1979-01-01

The changes in flux, position, and size of a distant extended (galaxy, etc.) source that result from the gravitational lens action of a massive opaque object are discussed. The flux increase is described by a single function of two parameters. One of these parameters characterizes the strength of the gravitational lens, the other describes the alignment of source and lens object. This function also describes the relative intensity of the images formed by lens. ( A similar formalism is discussed by Bourassa et al. for a point source). The formalism is applied to the problem of the galactic halo. It appears that a massive (10 1 2 M/sub sun/) spherical halo surrounding the visible part of the galaxy is consistent with the observable properties of extragalactic sources

Earth-mass haloes and the emergence of NFW density profiles

Science.gov (United States)

Angulo, Raul E.; Hahn, Oliver; Ludlow, Aaron D.; Bonoli, Silvia

2017-11-01

We simulate neutralino dark matter (χDM) haloes from their initial collapse, at ˜ earth mass, up to a few percent solar. Our results confirm that the density profiles of the first haloes are described by a ˜r-1.5 power law. As haloes grow in mass, their density profiles evolve significantly. In the central regions, they become shallower and reach on average ˜r-1, the asymptotic form of an NFW profile. Using non-cosmological controlled simulations, we observe that temporal variations in the gravitational potential caused by major mergers lead to a shallowing of the inner profile. This transformation is more significant for shallower initial profiles and for a higher number of merging systems. Depending on the merger details, the resulting profiles can be shallower or steeper than NFW in their inner regions. Interestingly, mergers have a much weaker effect when the profile is given by a broken power law with an inner slope of -1 (such as NFW or Hernquist profiles). This offers an explanation for the emergence of NFW-like profiles: after their initial collapse, r-1.5 χDM haloes suffer copious major mergers, which progressively shallows the profile. Once an NFW-like profile is established, subsequent merging does not change the profile anymore. This suggests that halo profiles are not universal but rather a combination of (1) the physics of the formation of the microhaloes and (2) their early merger history - both set by the properties of the dark matter particle - as well as (3) the resilience of NFW-like profiles to perturbations.

Dynamics of massive black holes as a possible candidate of Galactic dark matter

Science.gov (United States)

Xu, Guohong; Ostriker, Jeremiah P.

1994-01-01

If the dark halo of the Galaxy is comprised of massive black holes (MBHs), then those within approximately 1 kpc will spiral to the center, where they will interact with one another, forming binaries which contract, owing to further dynamical friction, and then possibly merge to become more massive objects by emission of gravitational radiation. If successive mergers would invariably lead, as has been proposed by various authors, to the formation of a very massive nucleus of 10(exp 8) solar mass, then the idea of MBHs as a dark matter candidate could be excluded on observational grounds, since the observed limit (or value) for a Galactic central black hole is approximately 10(exp 6.5) solar mass. But, if successive mergers are delayed or prevented by other processes, such as the gravitational slingshot or rocket effect of gravitational radiation, then a large mass accumulation will not occur. In order to resolve this issue, we perform detailed N-body simulations using a modfied Aarseth code to explore the dynamical behavior of the MBHs, and we find that for a 'best estimate' model of the Galaxy a runaway does not occur. The code treates the MBHs as subject to the primary gravitational forces of one another and to the smooth stellar distribution, as well as the secondary perturbations in their orbits due to another and to the smooth stellar distribution, as well as the secondary perturbations in their orbits due to dynamical friction and gravitational radiation. Instead of a runaway, three-body interactions between hard binaries and single MBHs eject massive objects before accumulation of more than a few units, so that typically the center will contain zero, one, or two MBHs. We study how the situation depends in detail on the mass per MBH, the rotation of the halo, the mass distribution within the Galaxy, and other parameters. A runaway will most sensitively depend on the ratio of initial (spheroid/halo) central mass densities and secondarily on the typical values

On the core-halo structure of NGC 604

CERN Document Server

Melnick, Yu M

1980-01-01

A detailed study is presented of the core-halo structure of the largest H II region in M 33, NGC 604, using newly obtained multi- aperture H/sub beta / photometry and Fabry-Perot interferometry, in conjunction with published radio continuum observations. Based on a comparison between the radio continuum and H/sub beta / luminosities of NGC 604, a dust density of rho /sub d/=6 10/sup -25/ g cm/sup -3/ is derived for the nebular core, in good agreement with published far- infrared results. By contrast, the halo of NGC 604 appears to contain virtually no dust. It is also shown that the turbulent component of the H/sub alpha /-line profile width of the halo of NGC 604 is significantly lower than that of the nebular core. This result is found to be inconsistent with models in which the highly supersonic velocities implied by the observed emission line profile widths in both nebular components are interpreted in terms of expansion motions. (14 refs).

Probing the shape and internal structure of dark matter haloes with the halo-shear-shear three-point correlation function

Science.gov (United States)

Shirasaki, Masato; Yoshida, Naoki

2018-04-01

Weak lensing three-point statistics are powerful probes of the structure of dark matter haloes. We propose to use the correlation of the positions of galaxies with the shapes of background galaxy pairs, known as the halo-shear-shear correlation (HSSC), to measure the mean halo ellipticity and the abundance of subhaloes in a statistical manner. We run high-resolution cosmological N-body simulations and use the outputs to measure the HSSC for galaxy haloes and cluster haloes. Non-spherical haloes cause a characteristic azimuthal variation of the HSSC, and massive subhaloes in the outer region near the virial radius contribute to ˜ 10 per cent of the HSSC amplitude. Using the HSSC and its covariance estimated from our N-body simulations, we make forecast for constraining the internal structure of dark matter haloes with future galaxy surveys. With 1000 galaxy groups with mass greater than 1013.5 h-1M⊙, the average halo ellipticity can be measured with an accuracy of 10 percent. A spherical, smooth mass distribution can be ruled out at a ˜5σ significance level. The existence of subhaloes whose masses are in 1-10 percent of the main halo mass can be detected with ˜104 galaxies/clusters. We conclude that the HSSC provides valuable information on the structure of dark haloes and hence on the nature of dark matter.

Low frequency radio observations of five rich clusters of galaxies

International Nuclear Information System (INIS)

Hanisch, R.J.; Erickson, W.C.

1980-01-01

Observations have been made at 43.0 and 73.8 MHz of five rich x-ray emitting clusters of galaxies: Abell 399/401, Abell 426 (the Perseus cluster), Abell 1367, Abell 1656 (the Coma cluster), and the Virgo cluster. A fan beam synthesis system has been used to search for extended radio emission, i.e., radio halos, in these clusters. Radio halos were detected in the Coma and Virgo clusters. No evidence was found for the existence of 3C84B, the halo source previously thought to exist in the Perseus cluster. If halo sources exist in Abell 399/401 or Abell 1367, they must be quite weak at frequencies less than 100 MHz. The observed sizes of the extended sources in Coma and Virgo imply that the rate of particle propagation away from strong radio galaxies greatly exceeds the Alfven velocity and is probably independent of particle energy

Density profile of dark matter haloes and galaxies in the HORIZON-AGN simulation: the impact of AGN feedback

Science.gov (United States)

Peirani, Sébastien; Dubois, Yohan; Volonteri, Marta; Devriendt, Julien; Bundy, Kevin; Silk, Joe; Pichon, Christophe; Kaviraj, Sugata; Gavazzi, Raphaël; Habouzit, Mélanie

2017-12-01

Using a suite of three large cosmological hydrodynamical simulations, HORIZON-AGN, HORIZON–NOAGN (no AGN feedback) and HORIZON-DM (no baryons), we investigate how a typical sub-grid model for AGN feedback affects the evolution of the inner density profiles of massive dark matter haloes and galaxies. Based on direct object-to-object comparisons, we find that the integrated inner mass and density slope differences between objects formed in these three simulations (hereafter, HAGN, HnoAGN and HDM) significantly evolve with time. More specifically, at high redshift (z ∼ 5), the mean central density profiles of HAGN and HnoAGN dark matter haloes tend to be much steeper than their HDM counterparts owing to the rapidly growing baryonic component and ensuing adiabatic contraction. By z ∼ 1.5, these mean halo density profiles in HAGN have flattened, pummelled by powerful AGN activity ('quasar mode'): the integrated inner mass difference gaps with HnoAGN haloes have widened, and those with HDM haloes have narrowed. Fast forward 9.5 billion years, down to z = 0, and the trend reverses: HAGN halo mean density profiles drift back to a more cusped shape as AGN feedback efficiency dwindles ('radio mode'), and the gaps in integrated central mass difference with HnoAGN and HDM close and broaden, respectively. On the galaxy side, the story differs noticeably. Averaged stellar profile central densities and inner slopes are monotonically reduced by AGN activity as a function of cosmic time, resulting in better agreement with local observations.

THE UNIFICATION OF POWERFUL QUASARS AND RADIO GALAXIES AND THEIR RELATION TO OTHER MASSIVE GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Podigachoski, Pece; Barthel, Peter [Kapteyn Astronomical Institute, University of Groningen, 9747 AD Groningen (Netherlands); Haas, Martin [Astronomisches Institut, Ruhr Universität, D-44801 Bochum (Germany); Leipski, Christian [Max-Planck Institut für Astronomie (MPIA), D-69117 Heidelberg (Germany); Wilkes, Belinda, E-mail: podigachoski@astro.rug.nl [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2015-06-10

The unification model for powerful radio galaxies (RGs) and radio-loud quasars postulates that these objects are intrinsically the same but viewed along different angles. Herschel Space Observatory data permit the assessment of that model in the far-infrared spectral window. We analyze photometry from Spitzer and Herschel for the distant 3CR hosts, and find that RGs and quasars have different mid-infrared, but indistinguishable far-infrared colors. Both these properties, the former being orientation dependent and the latter orientation invariant, are in line with expectations from the unification model. Adding powerful radio-quiet active galaxies and typical massive star-forming (SF) galaxies to the analysis, we demonstrate that infrared colors not only provide an orientation indicator, but can also distinguish active from SF galaxies.

THE UNIFICATION OF POWERFUL QUASARS AND RADIO GALAXIES AND THEIR RELATION TO OTHER MASSIVE GALAXIES

International Nuclear Information System (INIS)

Podigachoski, Pece; Barthel, Peter; Haas, Martin; Leipski, Christian; Wilkes, Belinda

2015-01-01

The unification model for powerful radio galaxies (RGs) and radio-loud quasars postulates that these objects are intrinsically the same but viewed along different angles. Herschel Space Observatory data permit the assessment of that model in the far-infrared spectral window. We analyze photometry from Spitzer and Herschel for the distant 3CR hosts, and find that RGs and quasars have different mid-infrared, but indistinguishable far-infrared colors. Both these properties, the former being orientation dependent and the latter orientation invariant, are in line with expectations from the unification model. Adding powerful radio-quiet active galaxies and typical massive star-forming (SF) galaxies to the analysis, we demonstrate that infrared colors not only provide an orientation indicator, but can also distinguish active from SF galaxies

Massive neutrinos in astrophysics

International Nuclear Information System (INIS)

Qadir, A.

1982-08-01

Massive neutrinos are among the big hopes of cosmologists. If they happen to have the right mass they can close the Universe, explain the motion of galaxies in clusters, provide galactic halos and even, possibly, explain galaxy formation. Tremaine and Gunn have argued that massive neutrinos cannot do all these things. I will explain, here, what some of us believe is wrong with their arguments. (author)

How Very Massive Metal-Free Stars Start Cosmological Reionization

Science.gov (United States)

Wise, John H.; Abel, Tom

2008-01-01

The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include nonequilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the case B approximation using adaptively ray-traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of approx.10(exp 6). These first sources of reionization are highly intermittent and anisotropic and first photoionize the small-scale voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf-sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies, making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately five ionizing photons are needed per sustained ionization when star formation in 10(exp 6) stellar Mass halos is dominant in the calculation. As the halos become larger than approx.10(exp 7) Stellar Mass, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Radiative feedback decreases clumping factors by 25% when compared to simulations without star formation and increases the average temperature of ionized gas to values between 3000 and 10,000 K.

Hot Gas Halos in Galaxies

Science.gov (United States)

Mulchaey, John

Most galaxy formation models predict that massive low-redshift disk galaxies are embedded in extended hot halos of externally accreted gas. Such gas appears necessary to maintain ongoing star formation in isolated spirals like the Milky Way. To explain the large population of red galaxies in rich groups and clusters, most galaxy evolution models assume that these hot gas halos are stripped completely when a galaxy enters a denser environment. This simple model has been remarkably successful at reproducing many observed properties of galaxies. Although theoretical arguments suggest hot gas halos are an important component in galaxies, we know very little about this gas from an observational standpoint. In fact, previous observations have failed to detect soft X-ray emission from such halos in disk galaxies. Furthermore, the assumption that hot gas halos are stripped completely when a galaxy enters a group or cluster has not been verified. We propose to combine proprietary and archival XMM-Newton observations of galaxies in the field, groups and clusters to study how hot gas halos are impacted by environment. Our proposed program has three components: 1) The deepest search to date for a hot gas halo in a quiescent spiral galaxy. A detection will confirm a basic tenet of disk galaxy formation models, whereas a non-detection will seriously challenge these models and impose new constraints on the growth mode and feedback history of disk galaxies. 2) A detailed study of the hot gas halos properties of field early-type galaxies. As environmental processes such as stripping are not expected to be important in the field, a study of hot gas halos in this environment will allow us to better understand how feedback and other internal processes impact hot gas halos. 3) A study of hot gas halos in the outskirts of groups and clusters. By comparing observations with our suite of simulations we can begin to understand what role the stripping of hot gas halos plays in galaxy

Shock Heating of the Merging Galaxy Cluster A521

Science.gov (United States)

Bourdin, H.; Mazzotta, P.; Markevitch, M.; Giacintucci, S.; Brunetti, G.

2013-01-01

A521 is an interacting galaxy cluster located at z = 0.247, hosting a low-frequency radio halo connected to an eastern radio relic. Previous Chandra observations hinted at the presence of an X-ray brightness edge at the position of the relic, which may be a shock front. We analyze a deep observation of A521 recently performed with XMM-Newton in order to probe the cluster structure up to the outermost regions covered by the radio emission. The cluster atmosphere exhibits various brightness and temperature anisotropies. In particular, two cluster cores appear to be separated by two cold fronts. We find two shock fronts, one that was suggested by Chandra and that is propagating to the east, and another to the southwestern cluster outskirt. The two main interacting clusters appear to be separated by a shock-heated region, which exhibits a spatial correlation with the radio halo. The outer edge of the radio relic coincides spatially with a shock front, suggesting that this shock is responsible for the generation of cosmic-ray electrons in the relic. The propagation direction and Mach number of the shock front derived from the gas density jump, M = 2.4 +/- 0.2, are consistent with expectations from the radio spectral index, under the assumption of Fermi I acceleration mechanism.

Halo Intrinsic Alignment: Dependence on Mass, Formation Time, and Environment

Energy Technology Data Exchange (ETDEWEB)

Xia, Qianli; Kang, Xi; Wang, Peng; Luo, Yu [Purple Mountain Observatory, the Partner Group of MPI für Astronomie, 2 West Beijing Road, Nanjing 210008 (China); Yang, Xiaohu; Jing, Yipeng [Center for Astronomy and Astrophysics, Shanghai Jiao Tong University, Shanghai 200240 (China); Wang, Huiyuan [Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China); Mo, Houjun, E-mail: kangxi@pmo.ac.cn [Astronomy Department and Center for Astrophysics, Tsinghua University, Beijing 10084 (China)

2017-10-10

In this paper we use high-resolution cosmological simulations to study halo intrinsic alignment and its dependence on mass, formation time, and large-scale environment. In agreement with previous studies using N -body simulations, it is found that massive halos have stronger alignment. For the first time, we find that for a given halo mass older halos have stronger alignment and halos in cluster regions also have stronger alignment than those in filaments. To model these dependencies, we extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias. However, the model cannot account for the environment dependence, as it is found that halo bias is lower in clusters and higher in filaments. Our results suggest that halo bias and environment are independent factors in determining halo alignment. We also study the halo alignment correlation function and find that halos are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scales as large as 100 h {sup −1} Mpc, where its feature is mainly driven by the baryon acoustic oscillation effect.

Radio observations of the double-relic galaxy cluster Abell 1240

Science.gov (United States)

Hoang, D. N.; Shimwell, T. W.; van Weeren, R. J.; Intema, H. T.; Röttgering, H. J. A.; Andrade-Santos, F.; Akamatsu, H.; Bonafede, A.; Brunetti, G.; Dawson, W. A.; Golovich, N.; Best, P. N.; Botteon, A.; Brüggen, M.; Cassano, R.; de Gasperin, F.; Hoeft, M.; Stroe, A.; White, G. J.

2018-05-01

We present LOFAR 120 - 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 - 629 MHz and VLA 2 - 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M=2.4 and 2.3 for the northern and southern shocks, respectively. For M≲ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (>10 per cent) particle acceleration efficiency required. However, for M≳ 4 shocks the required efficiency is ≳ 1% and ≳ 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥53 ± 3° and ≥39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (˜1.8 Mpc) our upper limit on the power is P1.4GHz = (1.4 ± 0.6) × 1023 W Hz-1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.

Emerging Massive Star Clusters Revealed: High-Resolution Imaging of NGC 4449 from the Radio to the Ultraviolet

Science.gov (United States)

Reines, Amy E.; Johnson, Kelsey E.; Goss, W. M.

2008-06-01

We present a multi-wavelength study of embedded massive clusters in the nearby (3.9 Mpc) starburst galaxy NGC 4449 in an effort to uncover the earliest phases of massive cluster evolution. By combining high-resolution imaging from the radio to the ultraviolet, we reveal these clusters to be in the process of emerging from their gaseous and dusty birth cocoons. We use Very Large Array (VLA) observations at centimeter wavelengths to identify young clusters surrounded by ultra-dense H II regions, detectable via their production of thermal free-free radio continuum. Ultraviolet, optical and infrared observations are obtained from the Hubble and Spitzer Space Telescope archives for comparison. We detect 39 compact radio sources toward NGC 4449 at 3.6 cm using the highest resolution (1farcs3) and sensitivity (~12 μJy) VLA image of the galaxy to date. We reliably identify 13 thermal radio sources and derive their physical properties using both nebular emission from the H II regions and spectral energy distribution fitting to the stellar continuum. These radio-detected clusters have ages lsim5 Myr and stellar masses of order 104 M sun. The measured extinctions are quite low: 12 of the 13 thermal radio sources have A V lsim 1.5, while the most obscured source has A V ≈ 4.3. By combining results from the nebular and stellar emission, we find an I-band excess that is anti-correlated with cluster age and an apparent mass-age correlation. Additionally, we find evidence that local processes such as supernovae and stellar winds likely play an important role in triggering the current bursts of star formation within NGC 4449.

The effect of gas dynamics on semi-analytic modelling of cluster galaxies

Science.gov (United States)

Saro, A.; De Lucia, G.; Dolag, K.; Borgani, S.

2008-12-01

We study the degree to which non-radiative gas dynamics affect the merger histories of haloes along with subsequent predictions from a semi-analytic model (SAM) of galaxy formation. To this aim, we use a sample of dark matter only and non-radiative smooth particle hydrodynamics (SPH) simulations of four massive clusters. The presence of gas-dynamical processes (e.g. ram pressure from the hot intra-cluster atmosphere) makes haloes more fragile in the runs which include gas. This results in a 25 per cent decrease in the total number of subhaloes at z = 0. The impact on the galaxy population predicted by SAMs is complicated by the presence of `orphan' galaxies, i.e. galaxies whose parent substructures are reduced below the resolution limit of the simulation. In the model employed in our study, these galaxies survive (unaffected by the tidal stripping process) for a residual merging time that is computed using a variation of the Chandrasekhar formula. Due to ram-pressure stripping, haloes in gas simulations tend to be less massive than their counterparts in the dark matter simulations. The resulting merging times for satellite galaxies are then longer in these simulations. On the other hand, the presence of gas influences the orbits of haloes making them on average more circular and therefore reducing the estimated merging times with respect to the dark matter only simulation. This effect is particularly significant for the most massive satellites and is (at least in part) responsible for the fact that brightest cluster galaxies in runs with gas have stellar masses which are about 25 per cent larger than those obtained from dark matter only simulations. Our results show that gas dynamics has only a marginal impact on the statistical properties of the galaxy population, but that its impact on the orbits and merging times of haloes strongly influences the assembly of the most massive galaxies.

Observations of a nearby filament of galaxy clusters with the Sardinia Radio Telescope

Science.gov (United States)

Vacca, Valentina; Murgia, M.; Loi, F. Govoni F.; Vazza, F.; Finoguenov, A.; Carretti, E.; Feretti, L.; Giovannini, G.; Concu, R.; Melis, A.; Gheller, C.; Paladino, R.; Poppi, S.; Valente, G.; Bernardi, G.; Boschin, W.; Brienza, M.; Clarke, T. E.; Colafrancesco, S.; Enßlin, T.; Ferrari, C.; de Gasperin, F.; Gastaldello, F.; Girardi, M.; Gregorini, L.; Johnston-Hollitt, M.; Junklewitz, H.; Orrù, E.; Parma, P.; Perley, R.; Taylor, G. B.

2018-05-01

We report the detection of diffuse radio emission which might be connected to a large-scale filament of the cosmic web covering a 8° × 8° area in the sky, likely associated with a z≈0.1 over-density traced by nine massive galaxy clusters. In this work, we present radio observations of this region taken with the Sardinia Radio Telescope. Two of the clusters in the field host a powerful radio halo sustained by violent ongoing mergers and provide direct proof of intra-cluster magnetic fields. In order to investigate the presence of large-scale diffuse radio synchrotron emission in and beyond the galaxy clusters in this complex system, we combined the data taken at 1.4 GHz with the Sardinia Radio Telescope with higher resolution data taken with the NRAO VLA Sky Survey. We found 28 candidate new sources with a size larger and X-ray emission fainter than known diffuse large-scale synchrotron cluster sources for a given radio power. This new population is potentially the tip of the iceberg of a class of diffuse large-scale synchrotron sources associated with the filaments of the cosmic web. In addition, we found in the field a candidate new giant radio galaxy.

Localized massive halo properties in BAHAMAS and MACSIS simulations: scalings, log-normality, and covariance

Science.gov (United States)

Farahi, Arya; Evrard, August E.; McCarthy, Ian; Barnes, David J.; Kay, Scott T.

2018-05-01

Using tens of thousands of halos realized in the BAHAMAS and MACSIS simulations produced with a consistent astrophysics treatment that includes AGN feedback, we validate a multi-property statistical model for the stellar and hot gas mass behavior in halos hosting groups and clusters of galaxies. The large sample size allows us to extract fine-scale mass-property relations (MPRs) by performing local linear regression (LLR) on individual halo stellar mass (Mstar) and hot gas mass (Mgas) as a function of total halo mass (Mhalo). We find that: 1) both the local slope and variance of the MPRs run with mass (primarily) and redshift (secondarily); 2) the conditional likelihood, p(Mstar, Mgas| Mhalo, z) is accurately described by a multivariate, log-normal distribution, and; 3) the covariance of Mstar and Mgas at fixed Mhalo is generally negative, reflecting a partially closed baryon box model for high mass halos. We validate the analytical population model of Evrard et al. (2014), finding sub-percent accuracy in the log-mean halo mass selected at fixed property, ⟨ln Mhalo|Mgas⟩ or ⟨ln Mhalo|Mstar⟩, when scale-dependent MPR parameters are employed. This work highlights the potential importance of allowing for running in the slope and scatter of MPRs when modeling cluster counts for cosmological studies. We tabulate LLR fit parameters as a function of halo mass at z = 0, 0.5 and 1 for two popular mass conventions.

The build up of the correlation between halo spin and the large-scale structure

Science.gov (United States)

Wang, Peng; Kang, Xi

2018-01-01

Both simulations and observations have confirmed that the spin of haloes/galaxies is correlated with the large-scale structure (LSS) with a mass dependence such that the spin of low-mass haloes/galaxies tend to be parallel with the LSS, while that of massive haloes/galaxies tend to be perpendicular with the LSS. It is still unclear how this mass dependence is built up over time. We use N-body simulations to trace the evolution of the halo spin-LSS correlation and find that at early times the spin of all halo progenitors is parallel with the LSS. As time goes on, mass collapsing around massive halo is more isotropic, especially the recent mass accretion along the slowest collapsing direction is significant and it brings the halo spin to be perpendicular with the LSS. Adopting the fractional anisotropy (FA) parameter to describe the degree of anisotropy of the large-scale environment, we find that the spin-LSS correlation is a strong function of the environment such that a higher FA (more anisotropic environment) leads to an aligned signal, and a lower anisotropy leads to a misaligned signal. In general, our results show that the spin-LSS correlation is a combined consequence of mass flow and halo growth within the cosmic web. Our predicted environmental dependence between spin and large-scale structure can be further tested using galaxy surveys.

MAPPING THE GALACTIC HALO. VIII. QUANTIFYING SUBSTRUCTURE

International Nuclear Information System (INIS)

Starkenburg, Else; Helmi, Amina; Van Woerden, Hugo; Morrison, Heather L.; Harding, Paul; Frey, Lucy; Oravetz, Dan; Mateo, Mario; Dohm-Palmer, R. C.; Olszewski, Edward W.; Sivarani, Thirupathi; Norris, John E.; Freeman, Kenneth C.; Shectman, Stephen A.

2009-01-01

We have measured the amount of kinematic substructure in the Galactic halo using the final data set from the Spaghetti project, a pencil-beam high-latitude sky survey. Our sample contains 101 photometrically selected and spectroscopically confirmed giants with accurate distance, radial velocity, and metallicity information. We have developed a new clustering estimator: the '4distance' measure, which when applied to our data set leads to the identification of one group and seven pairs of clumped stars. The group, with six members, can confidently be matched to tidal debris of the Sagittarius dwarf galaxy. Two pairs match the properties of known Virgo structures. Using models of the disruption of Sagittarius in Galactic potentials with different degrees of dark halo flattening, we show that this favors a spherical or prolate halo shape, as demonstrated by Newberg et al. using the Sloan Digital Sky Survey data. One additional pair can be linked to older Sagittarius debris. We find that 20% of the stars in the Spaghetti data set are in substructures. From comparison with random data sets, we derive a very conservative lower limit of 10% to the amount of substructure in the halo. However, comparison to numerical simulations shows that our results are also consistent with a halo entirely built up from disrupted satellites, provided that the dominating features are relatively broad due to early merging or relatively heavy progenitor satellites.

A multiwavelength view of the galaxy cluster Abell 523 and its peculiar diffuse radio source

Science.gov (United States)

Girardi, M.; Boschin, W.; Gastaldello, F.; Giovannini, G.; Govoni, F.; Murgia, M.; Barrena, R.; Ettori, S.; Trasatti, M.; Vacca, V.

2016-03-01

We study the structure of the galaxy cluster Abell 523 (A523) at z = 0.104 using new spectroscopic data for 132 galaxies acquired at the Telescopio Nazionale Galileo, new photometric data from the Isaac Newton Telescope, and X-ray and radio data from the Chandra and Very Large Array archives. We estimate the velocity dispersion of the galaxy population, σ _V=949_{-60}^{+80} km s-1, and the X-ray temperature of the hot intracluster medium, kT = 5.3 ± 0.3 keV. We infer that A523 is a massive system: M200 ˜ 7-9 × 1014 M⊙. The analysis of the optical data confirms the presence of two subclusters, 0.75 Mpc apart, tracing the SSW-NNE direction and dominated by the two brightest cluster galaxies (BCG1 and BCG2). The X-ray surface brightness is strongly elongated towards the NNE direction, and its peak is clearly offset from both the brightest cluster galaxies (BCGs). We confirm the presence of a 1.3 Mpc large radio halo, elongated in the ESE-WNW direction and perpendicular to the optical/X-ray elongation. We detect a significant radio/X-ray offset and radio polarization, two features which might be the result of a magnetic field energy spread on large spatial scales. A523 is found consistent with most scaling relations followed by clusters hosting radio haloes, but quite peculiar in the Pradio-LX relation: it is underluminous in the X-rays or overluminous in radio. A523 can be described as a binary head-on merger caught after a collision along the SSW-NNE direction. However, minor optical and radio features suggest a more complex cluster structure, with A523 forming at the crossing of two filaments along the SSW-NNE and ESE-WNW directions.

Effective description of dark matter self-interactions in small dark matter haloes

International Nuclear Information System (INIS)

Kummer, Janis

2017-07-01

Self-interacting dark matter may have striking astrophysical signatures, such as observ- able offsets between galaxies and dark matter in merging galaxy clusters. Numerical N-body simulations used to predict such observables typically treat the galaxies as collisionless test particles, a questionable assumption given that each galaxy is embedded in its own dark matter halo. To enable a more accurate treatment we develop an effective description of small dark matter haloes taking into account the two major effects due to dark matter self-scatterings: deceleration and evaporation. We point out that self-scatterings can have a sizeable impact on the trajectories of galaxies, diminishing the separation between galaxies and dark matter in merging clusters. This effect depends sensitively on the underlying particle physics, in particular the angular dependence of the self-scattering cross section, and cannot be predicted from the momentum transfer cross section alone.

The Evolution of the Stellar Hosts of Radio Galaxies

International Nuclear Information System (INIS)

Lacy, Mark; Bunker, Andrew J.; Ridgway, Susan E.

2000-01-01

We present new near-infrared images of z>0.8 radio galaxies from the flux-limited 7C-iii sample of radio sources for which we have recently obtained almost complete spectroscopic redshifts. The 7C objects have radio luminosities ≅20 times fainter than 3C radio galaxies at a given redshift. The absolute magnitudes of the underlying host galaxies and their scale sizes are only weakly dependent on radio luminosity. Radio galaxy hosts at z∼2 are significantly brighter than the hosts of radio-quiet quasars at similar redshifts and the recent model AGN hosts of Kauffmann and Haehnelt. There is no evidence for strong evolution in scale size, which shows a large scatter at all redshifts. The hosts brighten significantly with redshift, consistent with the passive evolution of a stellar population that formed at z(greater-or-similar sign)3. This scenario is consistent with studies of host galaxy morphology and submillimeter continuum emission, both of which show strong evolution at z(greater-or-similar sign)2.5. The lack of a strong ''redshift cutoff'' in the radio luminosity function to z>4 suggests that the formation epoch of the radio galaxy host population lasts (greater-or-similar sign)1 Gyr, from z(greater-or-similar sign)5 to z∼3. We suggest these facts are best explained by models in which the most massive galaxies and their associated AGN form early because of high baryon densities in the centers of their dark matter haloes. (c) 2000 The American Astronomical Society

Gas infall into atomic cooling haloes: on the formation of protogalactic disks and supermassive black holes at z > 10

CERN Document Server

Prieto, Joaquin; Haiman, Zoltan

2013-01-01

We have performed cosmo-hydro simulations using the RAMSES code to study atomic cooling (ACHs) haloes at z=10 with masses 5E7Msun10 to date. We examine the morphology, angular momentum (AM), thermodynamic, and turbulence of these haloes, in order to assess the prevalence of disks and supermassive black holes (SMBHs). We find no correlation between either the magnitude or the direction of the AM of the gas and its parent DM halo. Only 3 haloes form rotationally supported cores. Two of the most massive haloes form massive, compact overdense blobs. These blobs have an accretion rate ~0.5 Msun/yr (at a distance of 100 pc), and are possible sites of SMBH formation. Our results suggest that the degree of rotational support and the fate of the gas in a halo is determined by its large-scale environment and merger history. In particular, the two haloes forming blobs are located at knots of the cosmic web, cooled early on, and experienced many mergers. The gas in these haloes is lumpy and highly turbulent, with Mach N....

Galactic warps and the shape of heavy halos

International Nuclear Information System (INIS)

Sparke, L.S.

1984-01-01

The outer disks of many spiral galaxies are bent away from the plane of the inner disk; the abundance of these warps suggests that they are long-lived. Isolated galactic disks have long been thought to have no discrete modes of vertical oscillation under their own gravity, and so to be incapable of sustaining persistent warps. However, the visible disk contains only a fraction of the galactic mass; an invisible galactic halo makes up the rest. This paper presents an investigation of vertical warping modes in self-gravitating disks, in the imposed potential due to an axisymmetric unseen massive halo. If the halo matter is distributed so that the free precession rate of a test particle decreases with radius near the edge of the disk, then the disk has a discrete mode of vibration; oblate halos which become rapidly more flattened at large radii, and uniformly prolate halos, satisfy this requirement. Otherwise, the disk has no discrete modes and so cannot maintain a long-lived warp, unless the edge is sharply truncated. Computed mode shapes which resemble the observed warps can be found for halo masses consistent with those inferred from galactic rotation curves

Morphological Evolution in High-Redshift Radio Galaxies and the Formation of Giant Elliptical Galaxies

International Nuclear Information System (INIS)

Breugel, W.J. van; Stanford, S.A.; Spinrad, H.; Stern, D.; Graham, J.R.

1998-01-01

We present deep near-infrared images of high-redshift radio galaxies (HzRGs) obtained with the near-infrared camera (NIRC) on the Keck I telescope. In most cases, the near-IR data sample rest wavelengths that are free of contamination from strong emission lines and at λ rest > 4000 Angstrom, where older stellar populations, if present, might dominate the observed flux. At z > 3, the rest-frame optical morphologies generally have faint, large-scale (∼50 kpc) emission surrounding multiple, ∼10 kpc components. The brightest of these components are often aligned with the radio structures. These morphologies change dramatically at 2 rest ) ∼ -20 to -22] of the individual components in the z > 3 HzRGs are similar to the total sizes and luminosities of normal radio-quiet star forming galaxies at z = 3 - 4. For objects where such data are available, our observations show that the line-free, near-IR colors of the z > 3 galaxies are very blue, consistent with models in which recent star formation dominates the observed light. Direct spectroscopic evidence for massive star formation in one of the z > 3 HzRGs exists (4C 41.17). Our results suggest that the z > 3 HzRGs evolve into much more massive systems than the radio-quiet galaxies and that they are qualitatively consistent with models in which massive galaxies form in hierarchical fashion through the merging of smaller star-forming systems. The presence of relatively luminous subcomponents along the radio axes of the z > 3 galaxies suggests a causal connection with the AGN. We compare the radio and near-IR sizes as a function of redshift and suggest that this parameter may be a measure of the degree to which the radio sources have induced star formation in the parent objects. We also discuss the Hubble diagram of radio galaxies, the possibility of a radio power dependence in the K-z relation, and its implications for radio galaxy formation. Finally, we present for the first time in published format basic radio and

FRONTIER FIELDS CLUSTERS: DEEP CHANDRA OBSERVATIONS OF THE COMPLEX MERGER MACS J1149.6+2223

Energy Technology Data Exchange (ETDEWEB)

Ogrean, G. A.; Weeren, R. J. van; Jones, C.; Forman, W.; Andrade-Santos, F.; Murray, S. S.; Nulsen, P.; Bulbul, E.; Kraft, R.; Randall, S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Dawson, W. A. [Lawrence Livermore National Lab, 7000 East Avenue, Livermore, CA 94550 (United States); Golovich, N. [University of California, One Shields Avenue, Davis, CA 95616 (United States); Roediger, E. [Astronomy and Astrophysics Section, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); Zitrin, A.; Sayers, J. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Goulding, A. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Umetsu, K. [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Mroczkowski, T. [U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); Bonafede, A. [Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg (Germany); Churazov, E., E-mail: gogrean@cfa.harvard.edu [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741, Garching (Germany); and others

2016-03-10

The Hubble Space Telescope Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z  =  0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.

Hierarchical formation of dark matter halos and the free streaming scale

International Nuclear Information System (INIS)

Ishiyama, Tomoaki

2014-01-01

The smallest dark matter halos are formed first in the early universe. According to recent studies, the central density cusp is much steeper in these halos than in larger halos and scales as ρ∝r –(1.5-1.3) . We present the results of very large cosmological N-body simulations of the hierarchical formation and evolution of halos over a wide mass range, beginning from the formation of the smallest halos. We confirmed early studies that the inner density cusps are steeper in halos at the free streaming scale. The cusp slope gradually becomes shallower as the halo mass increases. The slope of halos 50 times more massive than the smallest halo is approximately –1.3. No strong correlation exists between the inner slope and the collapse epoch. The cusp slope of halos above the free streaming scale seems to be reduced primarily due to major merger processes. The concentration, estimated at the present universe, is predicted to be 60-70, consistent with theoretical models and earlier simulations, and ruling out simple power law mass-concentration relations. Microhalos could still exist in the present universe with the same steep density profiles.

A STRING OF RADIO EMISSION ASSOCIATED WITH IRAS 16562-3959: A COLLIMATED JET EMANATING FROM A LUMINOUS MASSIVE YOUNG STELLAR OBJECT

International Nuclear Information System (INIS)

Guzman, Andres E.; Garay, Guido; Brooks, Kate J.

2010-01-01

We report the discovery, made using the Australia Telescope Compact Array, of a remarkable string of radio emission toward IRAS 16562-3959, a luminous infrared source with a bolometric luminosity of 7.0 x 10 4 L sun . The radio emission arises from a compact, bright central component, two inner lobes which are separated by about 7'' and symmetrically offset from the central source, and two outer lobes which are separated by about 45''. The emission from the central object has a spectral index between 1.4 and 8.6 GHz of 0.85 ± 0.15, consistent with free-free emission from a thermal jet. The radio emission from the lobes has spectral indices in the range characteristic of thermal emission. We suggest that the emission from the lobes arises in shocks resulting from the interaction of a collimated wind with the surrounding medium. The radio string is located within a massive dense molecular core, and is associated with extended green emission (Spitzer three-color), Herbig-Haro-type emission (2MASS K s band), and OH maser sites-all phenomena readily observed toward sites of massive star formation. We conclude that the massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a powerful collimated stellar wind, showing that jets found in the formation of low-mass stars are also produced in high-mass stars.

DARK MATTER CONTRACTION AND THE STELLAR CONTENT OF MASSIVE EARLY-TYPE GALAXIES: DISFAVORING 'LIGHT' INITIAL MASS FUNCTIONS

International Nuclear Information System (INIS)

Auger, M. W.; Treu, T.; Gavazzi, R.; Bolton, A. S.; Koopmans, L. V. E.; Marshall, P. J.

2010-01-01

We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo models (unperturbed Navarro, Frenk, and White (NFW) halos and the adiabatic contraction models of Blumenthal and Gnedin) and impose a model for the relationship between the stellar and virial mass (i.e., a relationship for the star formation efficiency as a function of halo mass). We show that, given our model assumptions, the data clearly prefer a Salpeter-like initial mass function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of the choice of DM halo. In addition, we find that the data prefer at most a moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is strongly disfavored) and are only consistent with no adiabatic contraction (i.e., an NFW halo) if a mass-dependent IMF is assumed, in the sense of a more massive normalization of the IMF for more massive halos.

Stellar Mass-gap as a Probe of Halo Assembly History and Concentration: Youth Hidden among Old Fossils

Science.gov (United States)

Deason, A. J.; Conroy, C.; Wetzel, A. R.; Tinker, J. L.

2013-11-01

We investigate the use of the halo mass-gap statistic—defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo—as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ~ 25, 000 group/cluster-sized halos in the mass range 1012.5 time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration relation over a similar dynamic range. However, there is a large amount of scatter owing to the transitory nature of the satellite subhalo population, which limits the use of the halo mass-gap statistic on an object-by-object basis. For example, we find that 20% of very large halo mass-gap systems (akin to "fossil groups") are young and have likely experienced a recent merger between a massive satellite subhalo and the central subhalo. We relate halo mass-gap to the observable stellar mass-gap via abundance matching. Using a galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 7, we find that the star formation and structural properties of galaxies at fixed mass show no trend with stellar mass-gap. This is despite a variation in halo age of ≈2.5 Gyr over ≈1.2 dex in stellar mass-gap. Thus, we find no evidence to suggest that the halo formation history significantly affects galaxy properties.

Optimized distributed systems achieve significant performance improvement on sorted merging of massive VCF files.

Science.gov (United States)

Sun, Xiaobo; Gao, Jingjing; Jin, Peng; Eng, Celeste; Burchard, Esteban G; Beaty, Terri H; Ruczinski, Ingo; Mathias, Rasika A; Barnes, Kathleen; Wang, Fusheng; Qin, Zhaohui S

2018-06-01

Sorted merging of genomic data is a common data operation necessary in many sequencing-based studies. It involves sorting and merging genomic data from different subjects by their genomic locations. In particular, merging a large number of variant call format (VCF) files is frequently required in large-scale whole-genome sequencing or whole-exome sequencing projects. Traditional single-machine based methods become increasingly inefficient when processing large numbers of files due to the excessive computation time and Input/Output bottleneck. Distributed systems and more recent cloud-based systems offer an attractive solution. However, carefully designed and optimized workflow patterns and execution plans (schemas) are required to take full advantage of the increased computing power while overcoming bottlenecks to achieve high performance. In this study, we custom-design optimized schemas for three Apache big data platforms, Hadoop (MapReduce), HBase, and Spark, to perform sorted merging of a large number of VCF files. These schemas all adopt the divide-and-conquer strategy to split the merging job into sequential phases/stages consisting of subtasks that are conquered in an ordered, parallel, and bottleneck-free way. In two illustrating examples, we test the performance of our schemas on merging multiple VCF files into either a single TPED or a single VCF file, which are benchmarked with the traditional single/parallel multiway-merge methods, message passing interface (MPI)-based high-performance computing (HPC) implementation, and the popular VCFTools. Our experiments suggest all three schemas either deliver a significant improvement in efficiency or render much better strong and weak scalabilities over traditional methods. Our findings provide generalized scalable schemas for performing sorted merging on genetics and genomics data using these Apache distributed systems.

On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C+67.13

Science.gov (United States)

Hagino, K.; Stawarz, Ł.; Siemiginowska, A.; Cheung, C. C.; Kozieł-Wierzbowska, D.; Szostek, A.; Madejski, G.; Harris, D. E.; Simionescu, A.; Takahashi, T.

2015-06-01

Here we analyze radio, optical, and X-ray data for the peculiar cluster Abell 578. This cluster is not fully relaxed and consists of two merging sub-systems. The brightest cluster galaxy (BCG), CGPG 0719.8+6704, is a pair of interacting ellipticals with projected separation ˜10 kpc, the brighter of which hosts the radio source 4C+67.13. The Fanaroff-Riley type-II radio morphology of 4C+67.13 is unusual for central radio galaxies in local Abell clusters. Our new optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are active, albeit at low accretion rates corresponding to the Eddington ratio ˜ {{10}-4} (for the estimated black hole masses of ˜ 3× {{10}8} {{M}⊙ } and ˜ {{10}9} {{M}⊙ }). The gathered X-ray (Chandra) data allowed us to confirm and to quantify robustly the previously noted elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a large spatial offset (˜60 kpc projected) between the position of the BCG and the cluster center inferred from the modeling of the X-ray surface brightness distribution. Detailed analysis of the brightness profiles and temperature revealed also that the cluster gas in the vicinity of 4C+67.13 is compressed (by a factor of about ˜1.4) and heated (from ≃ 2.0 keV up to 2.7 keV), consistent with the presence of a weak shock (Mach number ˜1.3) driven by the expanding jet cocoon. This would then require the jet kinetic power of the order of ˜ {{10}45} erg s-1, implying either a very high efficiency of the jet production for the current accretion rate, or a highly modulated jet/accretion activity in the system. Based on service observations made with the WHT operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Cold dark matter. 1: The formation of dark halos

Science.gov (United States)

Gelb, James M.; Bertschinger, Edmund

1994-01-01

We use numerical simulations of critically closed cold dark matter (CDM) models to study the effects of numerical resolution on observable quantities. We study simulations with up to 256(exp 3) particles using the particle-mesh (PM) method and with up to 144(exp 3) particles using the adaptive particle-particle-mesh (P3M) method. Comparisons of galaxy halo distributions are made among the various simulations. We also compare distributions with observations, and we explore methods for identifying halos, including a new algorithm that finds all particles within closed contours of the smoothed density field surrounding a peak. The simulated halos show more substructure than predicted by the Press-Schechter theory. We are able to rule out all omega = 1 CDM models for linear amplitude sigma(sub 8) greater than or approximately = 0.5 because the simulations produce too many massive halos compared with the observations. The simulations also produce too many low-mass halos. The distribution of halos characterized by their circular velocities for the P3M simulations is in reasonable agreement with the observations for 150 km/s less than or = V(sub circ) less than or = 350 km/s.

BINARY BLACK HOLES, GAS SLOSHING, AND COLD FRONTS IN THE X-RAY HALO HOSTING 4C+37.11

Energy Technology Data Exchange (ETDEWEB)

Andrade-Santos, Felipe; Bogdán, Ákos; Forman, William R.; Jones, Christine; Murray, Stephen S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Romani, Roger W. [Department of Physics, Stanford University, Stanford, CA 94305-4060 (United States); Taylor, Greg B. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States); Zavala, Robert T. [US Naval Observatory, Flagstaff Station, 10391 W. Naval Observatory Road, Flagstaff, AZ 86001 (United States)

2016-07-20

We analyzed deep Chandra ACIS-I exposures of the cluster-scale X-ray halo surrounding the radio source 4C+37.11. This remarkable system hosts the closest resolved pair of super-massive black holes and an exceptionally luminous elliptical galaxy, the likely product of a series of past mergers. We characterize the halo with r {sub 500} ∼ 0.95 Mpc, M {sub 500} = 2.5 ± 0.2 × 10{sup 14} M {sub ⊙}, kT = 4.6 ± 0.2 keV, and a gas mass of M {sub g,500} = 2.2 ± 0.1 × 10{sup 13} M {sub ⊙}. The gas mass fraction within r {sub 500} is f {sub g} = 0.09 ± 0.01. The entropy profile shows large non-gravitational heating in the central regions. We see several surface brightness jumps, associated with substantial temperature and density changes but approximate pressure equilibrium, implying that these are sloshing structures driven by a recent merger. A residual intensity image shows a core spiral structure closely matching that seen in the Perseus cluster, although at z = 0.055 the spiral pattern is less distinct. We infer that the most recent merger occurred 1–2 Gyr ago and that the event that brought the two observed super-massive black holes to the system core is even older. Under this interpretation, the black hole binary pair has, unusually, remained at a parsec-scale separation for more than 2 Gyr.

THE ROCKSTAR PHASE-SPACE TEMPORAL HALO FINDER AND THE VELOCITY OFFSETS OF CLUSTER CORES

International Nuclear Information System (INIS)

Behroozi, Peter S.; Wechsler, Risa H.; Wu, Hao-Yi

2013-01-01

We present a new algorithm for identifying dark matter halos, substructure, and tidal features. The approach is based on adaptive hierarchical refinement of friends-of-friends groups in six phase-space dimensions and one time dimension, which allows for robust (grid-independent, shape-independent, and noise-resilient) tracking of substructure; as such, it is named ROCKSTAR (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement). Our method is massively parallel (up to 10 5 CPUs) and runs on the largest current simulations (>10 10 particles) with high efficiency (10 CPU hours and 60 gigabytes of memory required per billion particles analyzed). A previous paper has shown ROCKSTAR to have excellent recovery of halo properties; we expand on these comparisons with more tests and higher-resolution simulations. We show a significant improvement in substructure recovery compared to several other halo finders and discuss the theoretical and practical limits of simulations in this regard. Finally, we present results that demonstrate conclusively that dark matter halo cores are not at rest relative to the halo bulk or substructure average velocities and have coherent velocity offsets across a wide range of halo masses and redshifts. For massive clusters, these offsets can be up to 350 km s –1 at z = 0 and even higher at high redshifts. Our implementation is publicly available at http://code.google.com/p/rockstar.

WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

Energy Technology Data Exchange (ETDEWEB)

Fiorentino, Giuliana [INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy); Bono, Giuseppe [Dipartimento di Fisica, Universitá di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy); Monelli, Matteo; Gallart, Carme; Martínez-Vásquez, Clara E. [Instituto de Astrofísica de Canarias, Calle Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Stetson, Peter B. [National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Tolstoy, Eline [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Salaris, Maurizio [Astrophysics Research Institute, Liverpool John Moores University IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L35RF (United Kingdom); Bernard, Edouard J., E-mail: giuliana.fiorentino@oabo.inaf.it [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)

2015-01-01

We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittarius are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.

The role of neutron star mergers in the chemical evolution of the Galactic halo

Science.gov (United States)

Cescutti, G.; Romano, D.; Matteucci, F.; Chiappini, C.; Hirschi, R.

2015-05-01

Context. The dominant astrophysical production site of the r-process elements has not yet been unambiguously identified. The suggested main r-process sites are core-collapse supernovae and merging neutron stars. Aims: We explore the problem of the production site of Eu. We also use the information present in the observed spread in the Eu abundances in the early Galaxy, and not only its average trend. Moreover, we extend our investigations to other heavy elements (Ba, Sr, Rb, Zr) to provide additional constraints on our results. Methods: We adopt a stochastic chemical evolution model that takes inhomogeneous mixing into account. The adopted yields of Eu from merging neutron stars and from core-collapse supernovae are those that are able to explain the average [Eu/Fe]-[Fe/H] trend observed for solar neighbourhood stars, the solar abundance of Eu, and the present-day abundance gradient of Eu along the Galactic disc in the framework of a well-tested homogeneous model for the chemical evolution of the Milky Way. Rb, Sr, Zr, and Ba are produced by both the s- and r-processes. The r-process yields were obtained by scaling the Eu yields described above according to the abundance ratios observed in r-process rich stars. The s-process contribution by spinstars is the same as in our previous papers. Results: Neutron star binaries that merge in less than 10 Myr or neutron star mergers combined with a source of r-process generated by massive stars can explain the spread of [Eu/Fe] in the Galactic halo. The combination of r-process production by neutron star mergers and s-process production by spinstars is able to reproduce the available observational data for Sr, Zr, and Ba. We also show the first predictions for Rb in the Galactic halo. Conclusions: We confirm previous results that either neutron star mergers on a very short timescale or both neutron star mergers and at least a fraction of Type II supernovae have contributed to the synthesis of Eu in the Galaxy. The r

HOT GAS HALOS AROUND DISK GALAXIES: CONFRONTING COSMOLOGICAL SIMULATIONS WITH OBSERVATIONS

International Nuclear Information System (INIS)

Rasmussen, Jesper; Sommer-Larsen, Jesper; Pedersen, Kristian; Toft, Sune; Grove, Lisbeth F.; Benson, Andrew; Bower, Richard G.

2009-01-01

Models of disk galaxy formation commonly predict the existence of an extended reservoir of accreted hot gas surrounding massive spirals at low redshift. As a test of these models, we use X-ray and Hα data of the two massive, quiescent edge-on spirals NGC 5746 and NGC 5170 to investigate the amount and origin of any hot gas in their halos. Contrary to our earlier claim, the Chandra analysis of NGC 5746, employing more recent calibration data, does not reveal any significant evidence for diffuse X-ray emission outside the optical disk, with a 3σ upper limit to the halo X-ray luminosity of 4 x 10 39 erg s -1 . An identical study of the less massive NGC 5170 also fails to detect any extraplanar X-ray emission. By extracting hot halo properties of disk galaxies formed in cosmological hydrodynamical simulations, we compare these results to expectations for cosmological accretion of hot gas by spirals. For Milky-Way-sized galaxies, these high-resolution simulations predict hot halo X-ray luminosities which are lower by a factor of ∼2 compared to our earlier results reported by Toft et al. We find the new simulation predictions to be consistent with our observational constraints for both NGC 5746 and NGC 5170, while also confirming that the hot gas detected so far around more actively star-forming spirals is in general probably associated with stellar activity in the disk. Observational results on quiescent disk galaxies at the high-mass end are nevertheless providing powerful constraints on theoretical predictions, and hence on the assumed input physics in numerical studies of disk galaxy formation and evolution.

FPGA-based RF spectrum merging and adaptive hopset selection

Science.gov (United States)

McLean, R. K.; Flatley, B. N.; Silvius, M. D.; Hopkinson, K. M.

The radio frequency (RF) spectrum is a limited resource. Spectrum allotment disputes stem from this scarcity as many radio devices are confined to a fixed frequency or frequency sequence. One alternative is to incorporate cognition within a reconfigurable radio platform, therefore enabling the radio to adapt to dynamic RF spectrum environments. In this way, the radio is able to actively sense the RF spectrum, decide, and act accordingly, thereby sharing the spectrum and operating in more flexible manner. In this paper, we present a novel solution for merging many distributed RF spectrum maps into one map and for subsequently creating an adaptive hopset. We also provide an example of our system in operation, the result of which is a pseudorandom adaptive hopset. The paper then presents a novel hardware design for the frequency merger and adaptive hopset selector, both of which are written in VHDL and implemented as a custom IP core on an FPGA-based embedded system using the Xilinx Embedded Development Kit (EDK) software tool. The design of the custom IP core is optimized for area, and it can process a high-volume digital input via a low-latency circuit architecture. The complete embedded system includes the Xilinx PowerPC microprocessor, UART serial connection, and compact flash memory card IP cores, and our custom map merging/hopset selection IP core, all of which are targeted to the Virtex IV FPGA. This system is then incorporated into a cognitive radio prototype on a Rice University Wireless Open Access Research Platform (WARP) reconfigurable radio.

Major merging history in CANDELS. I. Evolution of the incidence of massive galaxy-galaxy pairs from z = 3 to z ˜ 0

Science.gov (United States)

Mantha, Kameswara Bharadwaj; McIntosh, Daniel H.; Brennan, Ryan; Ferguson, Henry C.; Kodra, Dritan; Newman, Jeffrey A.; Rafelski, Marc; Somerville, Rachel S.; Conselice, Christopher J.; Cook, Joshua S.; Hathi, Nimish P.; Koo, David C.; Lotz, Jennifer M.; Simmons, Brooke D.; Straughn, Amber N.; Snyder, Gregory F.; Wuyts, Stijn; Bell, Eric F.; Dekel, Avishai; Kartaltepe, Jeyhan; Kocevski, Dale D.; Koekemoer, Anton M.; Lee, Seong-Kook; Lucas, Ray A.; Pacifici, Camilla; Peth, Michael A.; Barro, Guillermo; Dahlen, Tomas; Finkelstein, Steven L.; Fontana, Adriano; Galametz, Audrey; Grogin, Norman A.; Guo, Yicheng; Mobasher, Bahram; Nayyeri, Hooshang; Pérez-González, Pablo G.; Pforr, Janine; Santini, Paola; Stefanon, Mauro; Wiklind, Tommy

2018-04-01

The rate of major galaxy-galaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development (1 ≤ z ≤ 3). We use close-pair statistics to objectively study the incidence of massive galaxies (stellar M1 > 2 × 1010 M⊙) hosting major companions (1 ≤ M1/M2 ≤ 4; i.e. 4:1) companions at z > 1. We show that these evolutionary trends are statistically robust to changes in companion proximity. We find disagreements between published results are resolved when selection criteria are closely matched. If we compute merger rates using constant fraction-to-rate conversion factors (Cmerg,pair = 0.6 and Tobs,pair = 0.65 Gyr), we find that MR rates disagree with theoretical predictions at z > 1.5. Instead, if we use an evolving Tobs,pair(z) ∝ (1 + z)-2 from Snyder et al., our MR-based rates agree with theory at 0 history.

MASSIVE+: The Growth Histories of MASSIVE Survey Galaxies from their Globular Cluster Colors

Science.gov (United States)

Blakeslee, John

2017-08-01

The MASSIVE survey is targeting the 100 most massive galaxies within 108 Mpc that are visible in the northern sky. These most massive galaxies in the present-day universe reside in a surprisingly wide variety of environments, from rich clusters to fossil groups to near isolation. We propose to use WFC3/UVIS and ACS to carry out a deep imaging study of the globular cluster populations around a selected subset of the MASSIVE targets. Though much is known about GC systems of bright galaxies in rich clusters, we know surprisingly little about the effects of environment on these systems. The MASSIVE sample provides a golden opportunity to learn about the systematics of GC systems and what they can tell us about environmental drivers on the evolution of the highest mass galaxies. The most pressing questions to be addressed include: (1) Do isolated giants have the same constant mass fraction of GCs to total halo mass as BCGs of similar luminosity? (2) Do their GC systems show the same color (metallicity) distribution, which is an outcome of the mass spectrum of gas-rich halos during hierarchical growth? (3) Do the GCs in isolated high-mass galaxies follow the same radial distribution versus metallicity as in rich environments (a test of the relative importance of growth by accretion)? (4) Do the GCs of galaxies in sparse environments follow the same mass function? Our proposed second-band imaging will enable us to secure answers to these questions and add enormously to the legacy value of existing HST imaging of the highest mass galaxies in the universe.

VizieR Online Data Catalog: Radio haloes in nearby galaxies (Heesen+, 2018)

Science.gov (United States)

Heesen, V.; Krause, M.; Beck, R.; Adebahr, B.; Bomans, D. J.; Carretti, E.; Dumke, M.; Heald, G.; Irwin, J.; Koribalski, B. S.; Mulcahy, D. D.; Westmeier, T.; Dettmar, R.-J.

2018-02-01

We present radio continuum observations of 12 nearby (D=2-27Mpc) edge-on galaxies at two different frequencies, namely at 1.4 and 5GHz (one galaxy at 8.5GHz instead of 5GHz). Our sample includes 11 late-type spiral (Sb or Sc) galaxies and one Magellanic-type barred galaxy (SBm), which are all highly inclined (i>=76°). As part of our study we have obtained several additional radio continuum maps. We make these maps publicly available (as well as all the other radio continuum maps in the paper). For 4 galaxies (NGC 55, 253, 891 and 4631) we have used single-dish maps, to correct for the missing zero-spacing flux where necessary. The Effelsberg maps of NGC 253 and 4631 were already presented in Heesen et al. (2009A&A...494..563H) and Mora & Krause (2013A&A...560A..42M), respectively, and the Effelsberg map of NGC 891 was already presented in Dumke (1997, PhD thesis, University of Bonn). We present these maps for completeness. The 4.80-GHz map of NGC 55 obtained with the 64-m Parkes telescope is so far unpublished. Furthermore, we show two maps of NGC 4631 at 1.35 and 1.65GHz observed with the VLA in D- configuration (R. Beck 2016, priv. comm.). The data were observed in August 1996, with 12 h on-source (ID: AG486) and reduced in standard fashion with AIPS. The maps have an angular resolution of 52 arcsec, so that we did not use them in the analysis, but they also show the halo of this galaxy very well. Lastly, we obtained maps of three further edge-on galaxies observed with the VLA (NGC 4157, 4217 and 4634). We reduced the data as described in Section 2, but since we had only one frequency available and no spectral index map, we did not use them in the analysis. The maps of NGC 4157 and 4217 were created by re-reducing archive data (IDs AI23, AF85, AH457 and AS392 for NGC 4157 and ID AM573 for NGC 4217). The map of NGC 4634 was created by using so far unpublished data from the VLA (ID: AD538). (3 data files).

EVOLUTION OF DARK MATTER PHASE-SPACE DENSITY DISTRIBUTIONS IN EQUAL-MASS HALO MERGERS

International Nuclear Information System (INIS)

Vass, Ileana M.; Kazanzidis, Stelios; Valluri, Monica; Kravtsov, Andrey V.

2009-01-01

We use dissipationless N-body simulations to investigate the evolution of the true coarse-grained phase-space density distribution f(x, v) in equal-mass mergers between dark matter (DM) halos. The halo models are constructed with various asymptotic power-law indices ρ ∝ r -γ ranging from steep cusps to core-like profiles and we employ the phase-space density estimator 'EnBid' developed by Sharma and Steinmetz to compute f(x, v). The adopted force resolution allows robust phase-space density profile estimates in the inner ∼1% of the virial radii of the simulated systems. We confirm that merger events result in a decrease of the coarse-grained phase-space density in accordance with expectations from Mixing Theorems for collisionless systems. We demonstrate that binary mergers between identical DM halos produce remnants that retain excellent memories of the inner slopes and overall shapes of the phase-space density distribution of their progenitors. The robustness of the phase-space density profiles holds for a range of orbital energies, and a variety of encounter configurations including sequences of several consecutive merger events, designed to mimic hierarchical merging, and collisions occurring at different cosmological epochs. If the progenitor halos are constructed with appreciably different asymptotic power-law indices, we find that the inner slope and overall shape of the phase-space density distribution of the remnant are substantially closer to that of the initial system with the steepest central density cusp. These results explicitly demonstrate that mixing is incomplete in equal-mass mergers between DM halos, as it does not erase memory of the progenitor properties. Our results also confirm the recent analytical predictions of Dehnen regarding the preservation of merging self-gravitating central density cusps.

The multi-messenger approach to particle acceleration by massive stars: a science case for optical, radio and X-ray observatories

Science.gov (United States)

De Becker, Michaël

2018-04-01

Massive stars are extreme stellar objects whose properties allow for the study of some interesting physical processes, including particle acceleration up to relativistic velocities. In particular, the collisions of massive star winds in binary systems lead notably to acceleration of electrons involved in synchrotron emission, hence their identification as non-thermal radio emitters. This has been demonstrated for about 40 objects so far. The relativistic electrons are also expected to produce non-thermal high-energy radiation through inverse Compton scattering. This class of objects permits thus to investigate non-thermal physics through observations in the radio and high energy spectral domains. However, the binary nature of these sources introduces some stringent requirements to adequately interpret their behavior and model non-thermal processes. In particular, these objects are well-established variable stellar sources on the orbital time-scale. The stellar and orbital parameters need to be determined, and this is notably achieved through studies in the optical domain. The combination of observations in the visible domain (including e.g. 3.6-m DOT) with radio measurements using notably GMRT and X-ray observations constitutes thus a promising strategy to investigate particle-accelerating colliding-wind binaries in the forthcoming decade.

Black holes with halos

Science.gov (United States)

Monten, Ruben; Toldo, Chiara

2018-02-01

We present new AdS4 black hole solutions in N =2 gauged supergravity coupled to vector and hypermultiplets. We focus on a particular consistent truncation of M-theory on the homogeneous Sasaki–Einstein seven-manifold M 111, characterized by the presence of one Betti vector multiplet. We numerically construct static and spherically symmetric black holes with electric and magnetic charges, corresponding to M2 and M5 branes wrapping non-contractible cycles of the internal manifold. The novel feature characterizing these nonzero temperature configurations is the presence of a massive vector field halo. Moreover, we verify the first law of black hole mechanics and we study the thermodynamics in the canonical ensemble. We analyze the behavior of the massive vector field condensate across the small-large black hole phase transition and we interpret the process in the dual field theory.

RHAPSODY. I. STRUCTURAL PROPERTIES AND FORMATION HISTORY FROM A STATISTICAL SAMPLE OF RE-SIMULATED CLUSTER-SIZE HALOS

International Nuclear Information System (INIS)

Wu, Hao-Yi; Hahn, Oliver; Wechsler, Risa H.; Mao, Yao-Yuan; Behroozi, Peter S.

2013-01-01

We present the first results from the RHAPSODY cluster re-simulation project: a sample of 96 'zoom-in' simulations of dark matter halos of 10 14.8±0.05 h –1 M ☉ , selected from a 1 h –3 Gpc 3 volume. This simulation suite is the first to resolve this many halos with ∼5 × 10 6 particles per halo in the cluster mass regime, allowing us to statistically characterize the distribution of and correlation between halo properties at fixed mass. We focus on the properties of the main halos and how they are affected by formation history, which we track back to z = 12, over five decades in mass. We give particular attention to the impact of the formation history on the density profiles of the halos. We find that the deviations from the Navarro-Frenk-White (NFW) model and the Einasto model depend on formation time. Late-forming halos tend to have considerable deviations from both models, partly due to the presence of massive subhalos, while early-forming halos deviate less but still significantly from the NFW model and are better described by the Einasto model. We find that the halo shapes depend only moderately on formation time. Departure from spherical symmetry impacts the density profiles through the anisotropic distribution of massive subhalos. Further evidence of the impact of subhalos is provided by analyzing the phase-space structure. A detailed analysis of the properties of the subhalo population in RHAPSODY is presented in a companion paper.

THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0-8

International Nuclear Information System (INIS)

Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

2013-01-01

We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 10 12 M ☉ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ∼ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ∼ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

The Average Star Formation Histories of Galaxies in Dark Matter Halos from z = 0-8

Science.gov (United States)

Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

2013-06-01

We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ⊙ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

Milliarcsecond Imaging of the Radio Emission from the Quasar with the Most Massive Black Hole at Reionization

Energy Technology Data Exchange (ETDEWEB)

Wang, Ran; Wu, Xue-Bing; Jiang, Linhua [Kavli Institute of Astronomy and Astrophysics at Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871 (China); Momjian, Emmanuel; Carilli, Chris L. [National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801 (United States); Fan, Xiaohui [Steward Observatory, University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721 (United States); Walter, Fabian [Max-Planck-Institute for Astronomy, Königsstuhl 17, D-69117 Heidelberg (Germany); Strauss, Michael A. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Wang, Feige [Department of Astronomy, School of Physics, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871 (China)

2017-02-01

We report Very Long Baseline Array (VLBA) observations of the 1.5 GHz radio continuum emission of the z = 6.326 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802). J0100+2802 is by far the most optically luminous and is a radio-quiet quasar with the most massive black hole known at z > 6. The VLBA observations have a synthesized beam size of 12.10 mas ×5.36 mas (FWHM), and detected the radio continuum emission from this object with a peak surface brightness of 64.6 ± 9.0 μ Jy beam{sup −1} and a total flux density of 88 ± 19 μ Jy. The position of the radio peak is consistent with that from SDSS in the optical and Chandra in the X-ray. The radio source is marginally resolved by the VLBA observations. A 2D Gaussian fit to the image constrains the source size to (7.1 ± 3.5) mas × (3.1 ± 1.7) mas. This corresponds to a physical scale of (40 ± 20) pc × (18 ± 10) pc. We estimate the intrinsic brightness temperature of the VLBA source to be T {sub B} = (1.6 ± 1.2) × 10{sup 7} K. This is significantly higher than the maximum value in normal star-forming galaxies, indicating an active galactic nucleus (AGN) origin for the radio continuum emission. However, it is also significantly lower than the brightness temperatures found in highest-redshift radio-loud quasars. J0100+2802 provides a unique example for studying the radio activity in optically luminous and radio-quiet AGNs in the early universe. Further observations at multiple radio frequencies will accurately measure the spectral index and address the dominant radiation mechanism of the radio emission.

Optical Variability Signatures from Massive Black Hole Binaries

Science.gov (United States)

Kasliwal, Vishal P.; Frank, Koby Alexander; Lidz, Adam

2017-01-01

The hierarchical merging of dark matter halos and their associated galaxies should lead to a population of supermassive black hole binaries (MBHBs). We consider plausible optical variability signatures from MBHBs at sub-parsec separations and search for these using data from the Catalina Real-Time Transient Survey (CRTS). Specifically, we model the impact of relativistic Doppler beaming on the accretion disk emission from the less massive, secondary black hole. We explore whether this Doppler modulation may be separated from other sources of stochastic variability in the accretion flow around the MBHBs, which we describe as a damped random walk (DRW). In the simple case of a circular orbit, relativistic beaming leads to a series of broad peaks — located at multiples of the orbital frequency — in the fluctuation power spectrum. We extend our analysis to the case of elliptical orbits and discuss the effect of beaming on the flux power spectrum and auto-correlation function using simulations. We present a code to model an observed light curve as a stochastic DRW-type time series modulated by relativistic beaming and apply the code to CRTS data.

Mining CANDELS for Tidal Features to Constrain Major Merging During Cosmic Noon

Science.gov (United States)

McIntosh, Daniel H.; Mantha, Kameswara; Ciaschi, Cody; Evan, Rubyet A.; Fries, Logan B.; Landry, Luther; Thompson, Scott E.; Snyder, Gregory; Guo, Yicheng; Ceverino, Daniel; Häuβler, Boris; Primack, Joel; Simons, Raymond C.; Zheng, Xianzhong; Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) Team

2018-01-01

The role of major merging in the rapid buildup and development of massive galaxies at z>1 remains an open question. New theories and observations suggest that non-merging processes like violent disk instabilities may be more vital than previously thought at assembling bulges, producing clumps, and inducing morphological disturbances that may be misinterpreted as the product of major merging. We will present initial results on a systematic search for hallmark tidal indicators of major merging in a complete sample of nearly 6000 massive z>1 galaxies from CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey), the premiere HST/WFC3 Treasury program. We have visually inspected published GALFIT F160W residual (image-model) maps and produced a comprehensive new catalog of Sersic residual characteristics based on a variety of natural features and poor-fit artifacts. Using this catalog, we find the frequency of galaxies with tidal signatures is very small in CANDELS data. Accounting for the brief time scale associated with faint transient tidal features, our preliminary finding indicates that merger fractions derived from the CANDELS morphological classification efforts are substantially overestimated. We are using the database of residual classifications as a baseline to (1) produce improved multi-component residual maps using GALFIT_M, (2) automatically extract and quantify plausible tidal indicators and substructures (clumps vs. multiple nuclei), (3) develop a new deep-learning classification pipeline to robustly identify merger indicators in imaging data, and (4) inform the systematic analyses of synthetic mock (CANDELized) images from zoom-in hydrodynamic simulations to thoroughly quantify the impacts of cosmological dimming, and calibrate the observability timescale of tidal feature detections. Our study will ultimately yield novel constraints on merger rates at z>1 and a definitive census of massive high-noon galaxies with tidal and double

EVOLUTION OF THE GALAXY-DARK MATTER CONNECTION AND THE ASSEMBLY OF GALAXIES IN DARK MATTER HALOS

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Yang Xiaohu; Zhang Youcai; Han Jiaxin [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Mo, H. J. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Van den Bosch, Frank C., E-mail: xhyang@shao.ac.cn [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)

2012-06-10

We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z {approx} 4, the conditional SMF at z {approx} 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z {approx} 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z {approx} 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the {Lambda}CDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M{sup 0.3} and M{sup {approx}>4.0} at the massive and low-mass ends, respectively. The ratio M{sub *,c}/M reveals a maximum of {approx}0.03 at a halo mass M {approx} 10{sup 11.8} h{sup -1} M{sub Sun }, much lower than the universal baryon fraction ({approx}0.17). At higher redshifts the maximum in M{sub *,c}/M remains close to {approx}0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host

Recoiling black holes in static and evolving dark matter halo potential

Directory of Open Access Journals (Sweden)

Smole M.

2015-01-01

Full Text Available We follow trajectories of kicked black holes in static and evolving dark matter halo potential. We explore both NFW and Einasto dark matter density distributions. Considered dark matter halos represent hosts of massive spiral and elliptical field galaxies. We study critical amplitude of kick velocity necessary for complete black hole ejection at various redshifts and find that ~40% lower kick velocities can remove black holes from their host haloes at z = 7 compared to z = 1. The greatest difference between static and evolving potential occurs near the critical velocity for black hole ejection and at high redshifts. When NFW and Einasto density distributions are compared ~30% higher kick velocities are needed for complete removal of BHs from dark matter halo described by NFW profile. [Projekat Ministarstva nauke Republike Srbije, br. 176021: Visible and invisible matter in nearby galaxies: Theory and observations

The gamma-ray-flux PDF from galactic halo substructure

International Nuclear Information System (INIS)

Lee, Samuel K.; Ando, Shin'ichiro; Kamionkowski, Marc

2009-01-01

One of the targets of the recently launched Fermi Gamma-ray Space Telescope is a diffuse gamma-ray background from dark-matter annihilation or decay in the Galactic halo. N-body simulations and theoretical arguments suggest that the dark matter in the Galactic halo may be clumped into substructure, rather than smoothly distributed. Here we propose the gamma-ray-flux probability distribution function (PDF) as a probe of substructure in the Galactic halo. We calculate this PDF for a phenomenological model of halo substructure and determine the regions of the substructure parameter space in which the PDF may be distinguished from the PDF for a smooth distribution of dark matter. In principle, the PDF allows a statistical detection of substructure, even if individual halos cannot be detected. It may also allow detection of substructure on the smallest microhalo mass scales, ∼ M ⊕ , for weakly-interacting massive particles (WIMPs). Furthermore, it may also provide a method to measure the substructure mass function. However, an analysis that assumes a typical halo substructure model and a conservative estimate of the diffuse background suggests that the substructure PDF may not be detectable in the lifespan of Fermi in the specific case that the WIMP is a neutralino. Nevertheless, for a large range of substructure, WIMP annihilation, and diffuse background models, PDF analysis may provide a clear signature of substructure

THE FORNAX DWARF GALAXY AS A REMNANT OF RECENT DWARF-DWARF MERGING IN THE LOCAL GROUP

International Nuclear Information System (INIS)

Yozin, C.; Bekki, K.

2012-01-01

We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al., that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on model parameters of dwarf-dwarf merging, and how the intermediate-age subpopulations found in the vicinity of these substructures may be formed from gas accretion in past merger events. We also suggest that one of Fornax's globular clusters originates from a merged dwarf companion, and demonstrate where as yet undetected tidal streams or H I gas formed from the dwarf merging may be found in the outer halo of the Galaxy.

The fate of high redshift massive compact galaxies in dense environments

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Kaufmann, Tobias; /Zurich, ETH; Mayer, Lucio; /Zurich U.; Carollo, Marcella; /Zurich, ETH; Feldmann, Robert; /Fermilab /Chicago U., KICP

2012-01-01

Massive compact galaxies seem to be more common at high redshift than in the local universe, especially in denser environments. To investigate the fate of such massive galaxies identified at z {approx} 2 we analyse the evolution of their properties in three cosmological hydrodynamical simulations that form virialized galaxy groups of mass {approx} 10{sup 13} M{sub {circle_dot}} hosting a central massive elliptical/S0 galaxy by redshift zero. We find that at redshift {approx} 2 the population of galaxies with M{sub *} > 2 x 10{sup 10} M{sub {circle_dot}} is diverse in terms of mass, velocity dispersion, star formation and effective radius, containing both very compact and relatively extended objects. In each simulation all the compact satellite galaxies have merged into the central galaxy by redshift 0 (with the exception of one simulation where one of such satellite galaxy survives). Satellites of similar mass at z = 0 are all less compact than their high redshift counterparts. They form later than the galaxies in the z = 2 sample and enter the group potential at z < 1, when dynamical friction times are longer than the Hubble time. Also, by z = 0 the central galaxies have increased substantially their characteristic radius via a combination of in situ star formation and mergers. Hence in a group environment descendants of compact galaxies either evolve towards larger sizes or they disappear before the present time as a result of the environment in which they evolve. Since the group-sized halos that we consider are representative of dense environments in the {Lambda}CDM cosmology, we conclude that the majority of high redshift compact massive galaxies do not survive until today as a result of the environment.

Stellar Velocity Dispersion: Linking Quiescent Galaxies to Their Dark Matter Halos

Science.gov (United States)

Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

2018-06-01

We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This proportionality holds even when a line-of-sight aperture dispersion is calculated in analogy to observations. In contrast, at a given stellar velocity dispersion, the dark matter halo mass of satellite galaxies is smaller than virial equilibrium expectations. This deviation from virial equilibrium probably results from tidal stripping of the outer dark matter halo. Stellar velocity dispersion appears insensitive to tidal effects and thus reflects the correlation between stellar velocity dispersion and dark matter halo mass prior to infall. There is a tight relation (≲0.2 dex scatter) between line-of-sight aperture stellar velocity dispersion and dark matter halo mass suggesting that the dark matter halo mass may be estimated from the measured stellar velocity dispersion for both central and satellite galaxies. We evaluate the impact of treating all objects as central galaxies if the relation we derive is applied to a statistical ensemble. A large fraction (≳2/3) of massive quiescent galaxies are central galaxies and systematic uncertainty in the inferred dark matter halo mass is ≲0.1 dex thus simplifying application of the simulation results to currently available observations.

XMM-Newton and Chandra Observations of the Remarkable Dynamics of the Intracluster Medium and Radio Sources in the Clusters Abell 2061 and 3667

Science.gov (United States)

Sarazin, C.; Hogge, T.; Chatzikos, M.; Wik, D.; Giacintucci, S.; Clarke, T.; Wong, K.; Gitti, M.; Finoguenov, A.

2014-07-01

XMM-Newton and Chandra observations of remarkable dynamic structures in the X-ray gas and connected radio sources in three clusters are presented. Abell 2061 is a highly irregular, merging cluster in the Corona Borealis supercluster. X-ray observations show that there is a plume of very cool gas (˜1 keV) to the NE of the cluster, and a hot (7.6 keV) shock region just NE of the center. There is a very bright radio relic to the far SW of the cluster, and a central radio halo/relic with an extension to the NE. Comparison to SLAM simulations show that this is an offset merger of a ˜5 × 10^{13} M⊙ subcluster with a ˜2.5 × 10^{14} M⊙ cluster seen after first core passage. The plume is the cool-core gas from the subcluster, which has been ``slingshot'' to the NE of the cluster. The plume gas is now falling back into the cluster center, and shocks when it hits the central gas. The model predicts a strong shock to the SW at the location of the bright radio relic, and another shock at the NE radio extension. Time permitting, the observations of Abell 2626 and Abell 3667 will also be presented.

A population of relic intermediate-mass black holes in the halo of the Milky Way

International Nuclear Information System (INIS)

Rashkov, Valery; Madau, Piero

2014-01-01

If 'seed' central black holes were common in the subgalactic building blocks that merged to form present-day massive galaxies, then relic intermediate-mass black holes (IMBHs) should be present in the Galactic bulge and halo. We use a particle tagging technique to dynamically populate the N-body Via Lactea II high-resolution simulation with black holes, and assess the size, properties, and detectability of the leftover population. The method assigns a black hole to the most tightly bound central particle of each subhalo at infall according to an extrapolation of the M BH -σ * relation, and self-consistently follows the accretion and disruption of Milky Way progenitor dwarfs and their holes in a cosmological 'live' host from high redshift to today. We show that, depending on the minimum stellar velocity dispersion, σ m , below which central black holes are assumed to be increasingly rare, as many as ∼2000 (σ m = 3 km s –1 ) or as few as ∼70 (σ m = 12 km s –1 ) IMBHs may be left wandering in the halo of the Milky Way today. The fraction of IMBHs forced from their hosts by gravitational recoil is ≲ 20%. We identify two main Galactic subpopulations, 'naked' IMBHs, whose host subhalos were totally destroyed after infall, and 'clothed' IMBHs residing in dark matter satellites that survived tidal stripping. Naked IMBHs typically constitute 40%-50% of the total and are more centrally concentrated. We show that, in the σ m = 12 km s –1 scenario, the clusters of tightly bound stars that should accompany naked IMBHs would be fainter than m V = 16 mag, spatially resolvable, and have proper motions of 0.1-10 mas yr –1 . Their detection may provide an observational tool to constrain the formation history of massive black holes in the early universe.

New halo formation mechanism at the KEK compact energy recovery linac

Science.gov (United States)

Tanaka, Olga; Nakamura, Norio; Shimada, Miho; Miyajima, Tsukasa; Ueda, Akira; Obina, Takashi; Takai, Ryota

2018-02-01

The beam halo mitigation is a very important challenge for reliable and safe operation of a high-energy machine. A systematic beam halo study was conducted at the KEK compact energy recovery linac (cERL) since non-negligible beam loss was observed in the recirculation loop during a common operation. We found that the beam loss can be avoided by making use of the collimation system. Beam halo measurements have demonstrated the presence of vertical beam halos at multiple locations in the beam line (except the region near the electron gun). Based on these observations, we made a conjecture that the transverse beam halo is attributed to the longitudinal bunch tail arising at the photocathode. The transfer of particles from the longitudinal space to a transverse halo may have been observed and studied in other machines, considering nonlinear effects as their causes. However, our study demonstrates a new unique halo formation mechanism, in which a transverse beam halo can be generated by a longitudinal bunch tail due to transverse rf kicks from the accelerating (monopole) fields of the radio-frequency cavities. This halo formation occurs when nonrelativistic particles enter the cavities with a transverse offset, even if neither nonlinear optics nor nonlinear beam effects are present. A careful realignment of the injector system will mitigate the present halo. Another possible cure is to reduce the bunch tails by changing the photocathode material from the present GaAs to a multi-alkali that is known to have a shorter longitudinal tail.

Remarks on search methods for stable, massive, elementary particles

International Nuclear Information System (INIS)

Perl, Martin L.

2001-01-01

This paper was presented at the 69th birthday celebration of Professor Eugene Commins, honoring his research achievements. These remarks are about the experimental techniques used in the search for new stable, massive particles, particles at least as massive as the electron. A variety of experimental methods such as accelerator experiments, cosmic ray studies, searches for halo particles in the galaxy and searches for exotic particles in bulk matter are described. A summary is presented of the measured limits on the existence of new stable, massive particle

BROKEN AND UNBROKEN: THE MILKY WAY AND M31 STELLAR HALOS

International Nuclear Information System (INIS)

Deason, A. J.; Belokurov, V.; Evans, N. W.; Johnston, K. V.

2013-01-01

We use the Bullock and Johnston suite of simulations to study the density profiles of L*-type galaxy stellar halos. Observations of the Milky Way and M31 stellar halos show contrasting results: the Milky Way has a 'broken' profile, where the density falls off more rapidly beyond ∼25 kpc, while M31 has a smooth profile out to 100 kpc with no obvious break. Simulated stellar halos, built solely by the accretion of dwarf galaxies, also exhibit this behavior: some halos have breaks, while others do not. The presence or absence of a break in the stellar halo profile can be related to the accretion history of the galaxy. We find that a break radius is strongly related to the buildup of stars at apocenters. We relate these findings to observations, and find that the 'break' in the Milky Way density profile is likely associated with a relatively early (∼6-9 Gyr ago) and massive accretion event. In contrast, the absence of a break in the M31 stellar halo profile suggests that its accreted satellites have a wide range of apocenters. Hence, it is likely that M31 has had a much more prolonged accretion history than the Milky Way.

THE SL2S GALAXY-SCALE LENS SAMPLE. V. DARK MATTER HALOS AND STELLAR IMF OF MASSIVE EARLY-TYPE GALAXIES OUT TO REDSHIFT 0.8

Energy Technology Data Exchange (ETDEWEB)

Sonnenfeld, Alessandro; Treu, Tommaso [Physics Department, University of California, Santa Barbara, CA 93106 (United States); Marshall, Philip J. [Kavli Institute for Particle Astrophysics and Cosmology, P.O. Box 20450, MS29, Stanford, CA 94309 (United States); Suyu, Sherry H. [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Gavazzi, Raphaël [Institut d' Astrophysique de Paris, UMR7095 CNRS-Université Pierre et Marie Curie, 98bis bd Arago, F-75014 Paris (France); Auger, Matthew W. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Nipoti, Carlo, E-mail: sonnen@physics.ucsb.edu [Department of Physics and Astronomy, Bologna University, viale Berti-Pichat 6/2, I-40127 Bologna (Italy)

2015-02-20

We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M {sub *} = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.

THE DISCOVERY OF BINARY WHITE DWARFS THAT WILL MERGE WITHIN 500 Myr

International Nuclear Information System (INIS)

Kilic, Mukremin; Brown, Warren R.; Kenyon, S. J.; Allende Prieto, Carlos; Panei, J. A.

2010-01-01

We present radial velocity observations of four extremely low-mass (0.2 M sun ) white dwarfs (WDs). All four stars show peak-to-peak radial velocity variations of 540-710 km s -1 with 1.0-5.9 hr periods. The optical photometry rules out main-sequence companions. In addition, no millisecond pulsar companions are detected in radio observations. Thus, the invisible companions are most likely WDs. Two of the systems are the shortest period binary WDs yet discovered. Due to the loss of angular momentum through gravitational radiation, three of the systems will merge within 500 Myr. The remaining system will merge within a Hubble time. The mass functions for three of the systems imply companions more massive than 0.46 M sun ; thus, those are carbon/oxygen core WDs. The unknown inclination angles prohibit a definitive conclusion about the future of these systems. However, the chance of a supernova Ia event is only 1%-5%. These systems are likely to form single R Coronae Borealis stars, providing evidence for a WD + WD merger mechanism for these unusual objects. One of the systems, SDSS J105353.89+520031.0, has a 70% chance of having a low-mass WD companion. This system will probably form a single helium-enriched subdwarf O star. All four WD systems have unusual mass ratios of ≤0.2-0.8 that may also lead to the formation of AM CVn systems.

DARK MATTER HALO MERGERS: DEPENDENCE ON ENVIRONMENT

International Nuclear Information System (INIS)

Hester, J. A.; Tasitsiomi, A.

2010-01-01

This paper presents a study of the specific major merger rate as a function of group membership, local environment, and redshift in a very large, 500 h -1 Mpc, cosmological N-body simulation, the Millennium Simulation. The goal is to provide environmental diagnostics of major merger populations in order to test simulations against observations and provide further constraints on major merger driven galaxy evolution scenarios. A halo sample is defined using the maximum circular velocity, which is both well defined for subhalos and closely correlated with galaxy luminosity. Subhalos, including the precursors of major mergers, are severely tidally stripped. Major mergers between subhalos are therefore rare compared to mergers between subhalos and their host halos. Tidal stripping also suppresses dynamical friction, resulting in long major merger timescales when the more massive merger progenitor does not host other subhalos. When other subhalos are present, however, major merger timescales are several times shorter. This enhancement may be due to inelastic unbound collisions between subhalos, which deplete their orbital angular momentum and lead to faster orbital decay. Following these results, we predict that major mergers in group environments are dominated by mergers involving the central galaxy, that the specific major merger rate is suppressed in groups when all group members are considered together, and that the frequency of fainter companions is enhanced for major mergers and their remnants. We also measure an 'assembly bias' in the specific major merger rate in that major mergers of galaxy-like halos are slightly suppressed in overdense environments while major mergers of group-like halos are slightly enhanced. A dynamical explanation for this trend is advanced which calls on both tidal effects and interactions between bound halos beyond the virial radii of locally dynamically dominant halos.

Baryon Budget of the Hot Circumgalactic Medium of Massive Spiral Galaxies

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Li, Jiang-Tao; Bregman, Joel N.; Wang, Q. Daniel; Crain, Robert A.; Anderson, Michael E.

2018-03-01

The baryon content around local galaxies is observed to be much less than is needed in Big Bang nucleosynthesis. Simulations indicate that a significant fraction of these “missing baryons” may be stored in a hot tenuous circumgalactic medium (CGM) around massive galaxies extending to or even beyond the virial radius of their dark matter halos. Previous observations in X-ray and Sunyaev–Zel’dovich (SZ) signals claimed that ∼(1–50)% of the expected baryons are stored in a hot CGM within the virial radius. The large scatter is mainly caused by the very uncertain extrapolation of the hot gas density profile based on the detection in a small radial range (typically within 10%–20% of the virial radius). Here, we report stacking X-ray observations of six local isolated massive spiral galaxies from the CGM-MASS sample. We find that the mean density profile can be characterized by a single power law out to a galactocentric radius of ≈200 kpc (or ≈130 kpc above the 1σ background uncertainty), about half the virial radius of the dark matter halo. We can now estimate that the hot CGM within the virial radius accounts for (8 ± 4)% of the baryonic mass expected for the halos. Including the stars, the baryon fraction is (27 ± 16)%, or (39 ± 20)% by assuming a flattened density profile at r ≳ 130 kpc. We conclude that the hot baryons within the virial radius of massive galaxy halos are insufficient to explain the “missing baryons.”

Cluster Physics with Merging Galaxy Clusters

Directory of Open Access Journals (Sweden)

Sandor M. Molnar

2016-02-01

Full Text Available Collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth. In the standard LCDM model, where the total density is dominated by the cosmological constant ($Lambda$ and the matter density by cold dark matter (CDM, structure formation is hierarchical, and clusters grow mostly by merging.Mergers of two massive clusters are the most energetic events in the universe after the Big Bang,hence they provide a unique laboratory to study cluster physics.The two main mass components in clusters behave differently during collisions:the dark matter is nearly collisionless, responding only to gravity, while the gas is subject to pressure forces and dissipation, and shocks and turbulenceare developed during collisions. In the present contribution we review the different methods used to derive the physical properties of merging clusters. Different physical processes leave their signatures on different wavelengths, thusour review is based on a multifrequency analysis. In principle, the best way to analyze multifrequency observations of merging clustersis to model them using N-body/HYDRO numerical simulations. We discuss the results of such detailed analyses.New high spatial and spectral resolution ground and space based telescopeswill come online in the near future. Motivated by these new opportunities,we briefly discuss methods which will be feasible in the near future in studying merging clusters.

HOT GAS HALOS IN EARLY-TYPE FIELD GALAXIES

International Nuclear Information System (INIS)

Mulchaey, John S.; Jeltema, Tesla E.

2010-01-01

We use Chandra and XMM-Newton to study the hot gas content in a sample of field early-type galaxies. We find that the L X -L K relationship is steeper for field galaxies than for comparable galaxies in groups and clusters. The low hot gas content of field galaxies with L K ∼ * suggests that internal processes such as supernovae-driven winds or active galactic nucleus feedback expel hot gas from low-mass galaxies. Such mechanisms may be less effective in groups and clusters where the presence of an intragroup or intracluster medium can confine outflowing material. In addition, galaxies in groups and clusters may be able to accrete gas from the ambient medium. While there is a population of L K ∼ * galaxies in groups and clusters that retain hot gas halos, some galaxies in these rich environments, including brighter galaxies, are largely devoid of hot gas. In these cases, the hot gas halos have likely been removed via ram pressure stripping. This suggests a very complex interplay between the intragroup/intracluster medium and hot gas halos of galaxies in rich environments, with the ambient medium helping to confine or even enhance the halos in some cases and acting to remove gas in others. In contrast, the hot gas content of more isolated galaxies is largely a function of the mass of the galaxy, with more massive galaxies able to maintain their halos, while in lower mass systems the hot gas escapes in outflowing winds.

The Eating Habits of Giants and Dwarfs: Chemo-dynamics of Halo Assembly in Nearby Galaxies

Science.gov (United States)

Romanowsky, Aaron J.; SAGES Team

2012-01-01

I will present novel results on the halo assembly of nearby galaxies, from dwarfs to the most massive ellipticals, using Subaru imaging and Keck spectroscopy. Field stars, globular clusters, and planetary nebulae are used as wide-field chemo-dynamical tracers, mapping out halo substructures that were previously known and unknown. Comparisons are made with simulations of galaxy formation. Supported by the National Science Foundation Grants AST-0808099, AST-0909237, and AST-1109878.

OPTICAL-NEAR-INFRARED COLOR GRADIENTS AND MERGING HISTORY OF ELLIPTICAL GALAXIES

International Nuclear Information System (INIS)

Kim, Duho; Im, Myungshin

2013-01-01

It has been suggested that merging plays an important role in the formation and the evolution of elliptical galaxies. While gas dissipation by star formation is believed to steepen metallicity and color gradients of the merger products, mixing of stars through dissipation-less merging (dry merging) is believed to flatten them. In order to understand the past merging history of elliptical galaxies, we studied the optical-near-infrared (NIR) color gradients of 204 elliptical galaxies. These galaxies are selected from the overlap region of the Sloan Digital Sky Survey (SDSS) Stripe 82 and the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The use of optical and NIR data (g, r, and K) provides large wavelength baselines, and breaks the age-metallicity degeneracy, allowing us to derive age and metallicity gradients. The use of the deep SDSS Stripe 82 images makes it possible for us to examine how the color/age/metallicity gradients are related to merging features. We find that the optical-NIR color and the age/metallicity gradients of elliptical galaxies with tidal features are consistent with those of relaxed ellipticals, suggesting that the two populations underwent a similar merging history on average and that mixing of stars was more or less completed before the tidal features disappeared. Elliptical galaxies with dust features have steeper color gradients than the other two types, even after masking out dust features during the analysis, which can be due to a process involving wet merging. More importantly, we find that the scatter in the color/age/metallicity gradients of the relaxed and merging feature types decreases as their luminosities (or masses) increase at M > 10 11.4 M ☉ but stays large at lower luminosities. Mean metallicity gradients appear nearly constant over the explored mass range, but a possible flattening is observed at the massive end. According to our toy model that predicts how the distribution of metallicity gradients

The Most Massive Galaxies and Black Holes Allowed by ΛCDM

Science.gov (United States)

Behroozi, Peter; Silk, Joseph

2018-04-01

Given a galaxy's stellar mass, its host halo mass has a lower limit from the cosmic baryon fraction and known baryonic physics. At z > 4, galaxy stellar mass functions place lower limits on halo number densities that approach expected ΛCDM halo mass functions. High-redshift galaxy stellar mass functions can thus place interesting limits on number densities of massive haloes, which are otherwise very difficult to measure. Although halo mass functions at z function of redshift given expected halo number densities from ΛCDM. We apply similar arguments to black holes. If their virial mass estimates are accurate, number density constraints alone suggest that the quasars SDSS J1044-0125 and SDSS J010013.02+280225.8 likely have black hole mass — stellar mass ratios higher than the median z = 0 relation, confirming the expectation from Lauer bias. Finally, we present a public code to evaluate the probability of an apparently ΛCDM-inconsistent high-mass halo being detected given the combined effects of multiple surveys and observational errors.

La abundancia de galaxias y halos de materia oscura en el universo CDM

Science.gov (United States)

Abadi, M. G.; Benítez-Llambay, A.; Ferrero, I.

A long-standing puzzle of CDM cosmological model concerns to the different shape of the galaxy stellar mass function and the halo mass function on dwarf galaxy scales. Dwarf galaxies are much less numerous than halos massive enough to host them; suggesting a complex non-linear relation between the mass of a galaxy and the mass of its surrounding halo. Usually; this is reconciled by appealing to baryonic processes that can reduce the efficiency of galaxy formation in low-mass halos. Recent work applying the abundance matching technique require that virtually no dwarf galaxies form in halos with virial mass below . We use rotation curves of dwarf galaxies compiled from the literature to explore whether their total enclosed mass is consistent with these constraints. Almost one-half of the dwarfs in our sample are at odds with this restriction; they are in halos with masses substantially below . Using a cosmological simulation of the formation of the Local Group of galaxies we found that ram-pressure stripping against the cosmic web removes baryons from low-mass halos without appealing to feedback or reionization. This mechanism may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. FULL TEXT IN SPANISH

The Ongoing Growth of the M87 Halo through Accretion Events

Directory of Open Access Journals (Sweden)

Alessia Longobardi

2015-12-01

Full Text Available Planetary nebulas (PNs offer a unique tool to investigate the outer regions of massive galaxies because their strong [OIII]λ5007Å emission line makes them detectable out to several effective radii from the galaxy’s centre. We use a deep and extended spectroscopic survey of PNs (∼300 objects to study the spatial distribution, the kinematics and the stellar populations in the extended outer halo of the bright elliptical galaxy M87 (NGC 4486 in the Virgo cluster. We show that in the Virgo core, M87 stellar halo and the intracluster light are two distinct dynamical components, with different velocity distributions. Moreover the synergy of the PN kinematical information and the deep V/B-band photometry revealed an ongoing accretion event in the outer regions of M87. This satellite accretion represents a non-negligible perturbation of the halo properties: beyond 60 kpc the M87 halo is still growing with 60% of its light being added by the accretion event at the distance where it is detected.

THE HALO MERGER RATE IN THE MILLENNIUM SIMULATION AND IMPLICATIONS FOR OBSERVED GALAXY MERGER FRACTIONS

International Nuclear Information System (INIS)

Genel, Shy; Genzel, Reinhard; Bouche, Nicolas; Naab, Thorsten; Sternberg, Amiel

2009-01-01

We have developed a new method to extract halo merger rates from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the standard friends-of-friends (FOF) halo identification algorithm, we find a lower merger rate compared to previous work. The reductions are more significant at lower redshifts and lower halo masses, and especially for minor mergers. Our new approach results in a better agreement with predictions from the extended Press-Schechter model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ∼20% overestimate of the merger rate. Therefore, we define halo masses by including only particles that are gravitationally bound to their FOF groups. We provide new best-fitting parameters for a global formula to account for these improvements. In addition, we extract the merger rate per progenitor halo, as well as per descendant halo. The merger rate per progenitor halo is the quantity that should be related to observed galaxy merger fractions when they are measured via pair counting. At low-mass/redshift, the merger rate increases moderately with mass and steeply with redshift. At high enough mass/redshift (for the rarest halos with masses a few times the 'knee' of the mass function), these trends break down, and the merger rate per progenitor halo decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos, in addition to the minor and major merger rates. We provide an analytic formula that converts any given merger rate per descendant halo into a merger rate per progenitor halo. Finally, we perform a direct comparison between observed merger fractions and the fraction of halos in the Millennium Simulation that have undergone a major merger during the recent dynamical friction time, and find a

Radio outburst from a massive (proto)star. When accretion turns into ejection

Science.gov (United States)

Cesaroni, R.; Moscadelli, L.; Neri, R.; Sanna, A.; Caratti o Garatti, A.; Eisloffel, J.; Stecklum, B.; Ray, T.; Walmsley, C. M.

2018-05-01

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims: As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods: We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results: We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely 13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free-free emission from the radio jet. Conclusions: Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (memory of MalcolmWalmsley, who passed away before the present study could be completed. Without his insights and enlightened advice this work would have been impossible

The Excursion Set Theory of Halo Mass Functions, Halo Clustering, and Halo Growth

Science.gov (United States)

Zentner, Andrew R.

I review the excursion set theory with particular attention toward applications to cold dark matter halo formation and growth, halo abundance, and halo clustering. After a brief introduction to notation and conventions, I begin by recounting the heuristic argument leading to the mass function of bound objects given by Press and Schechter. I then review the more formal derivation of the Press-Schechter halo mass function that makes use of excursion sets of the density field. The excursion set formalism is powerful and can be applied to numerous other problems. I review the excursion set formalism for describing both halo clustering and bias and the properties of void regions. As one of the most enduring legacies of the excursion set approach and one of its most common applications, I spend considerable time reviewing the excursion set theory of halo growth. This section of the review culminates with the description of two Monte Carlo methods for generating ensembles of halo mass accretion histories. In the last section, I emphasize that the standard excursion set approach is the result of several simplifying assumptions. Dropping these assumptions can lead to more faithful predictions and open excursion set theory to new applications. One such assumption is that the height of the barriers that define collapsed objects is a constant function of scale. I illustrate the implementation of the excursion set approach for barriers of arbitrary shape. One such application is the now well-known improvement of the excursion set mass function derived from the "moving" barrier for ellipsoidal collapse. I also emphasize that the statement that halo accretion histories are independent of halo environment in the excursion set approach is not a general prediction of the theory. It is a simplifying assumption. I review the method for constructing correlated random walks of the density field in the more general case. I construct a simple toy model to illustrate that excursion set

Merged Search Algorithms for Radio Frequency Identification Anticollision

Directory of Open Access Journals (Sweden)

Bih-Yaw Shih

2012-01-01

The arbitration algorithm for RFID system is used to arbitrate all the tags to avoid the collision problem with the existence of multiple tags in the interrogation field of a transponder. A splitting algorithm which is called Binary Search Tree (BST is well known for multitags arbitration. In the current study, a splitting-based schema called Merged Search Tree is proposed to capture identification codes correctly for anticollision. Performance of the proposed algorithm is compared with the original BST according to time and power consumed during the arbitration process. The results show that the proposed model can reduce searching time and power consumed to achieve a better performance arbitration.

A COMPACT GROUP OF GALAXIES AT Z = 2.48 HOSTING AN AGN-DRIVEN OUTFLOW

Energy Technology Data Exchange (ETDEWEB)

Shih, Hsin-Yi [Gemini Observatory, 670 N Aohoku Place, Hilo, HI 96720 (United States); Stockton, Alan, E-mail: jshih@gemini.edu, E-mail: stockton@ifa.hawaii.edu [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2015-12-10

We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 10{sup 11}M{sub ⊙} and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass–metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow.

THE SPIN AND ORIENTATION OF DARK MATTER HALOS WITHIN COSMIC FILAMENTS

International Nuclear Information System (INIS)

Zhang Youcai; Yang Xiaohu; Lin Weipeng; Faltenbacher, Andreas; Springel, Volker; Wang Huiyuan

2009-01-01

Clusters, filaments, sheets, and voids are the building blocks of the cosmic web. Forming dark matter halos respond to these different large-scale environments, and this in turn affects the properties of galaxies hosted by the halos. It is therefore important to understand the systematic correlations of halo properties with the morphology of the cosmic web, as this informs both about galaxy formation physics and possible systematics of weak lensing studies. In this study, we present and compare two distinct algorithms for finding cosmic filaments and sheets, a task which is far less well established than the identification of dark matter halos or voids. One method is based on the smoothed dark matter density field and the other uses the halo distributions directly. We apply both techniques to one high-resolution N-body simulation and reconstruct the filamentary/sheet like network of the dark matter density field. We focus on investigating the properties of the dark matter halos inside these structures, in particular, on the directions of their spins and the orientation of their shapes with respect to the directions of the filaments and sheets. We find that both the spin and the major axes of filament halos with masses ∼ 13 h -1 M sun are preferentially aligned with the direction of the filaments. The spins and major axes of halos in sheets tend to lie parallel to the sheets. There is an opposite mass dependence of the alignment strength for the spin (negative) and major (positive) axes, i.e. with increasing halo mass the major axis tends to be more strongly aligned with the direction of the filament, whereas the alignment between halo spin and filament becomes weaker with increasing halo mass. The alignment strength as a function of the distance to the most massive node halo indicates that there is a transit large-scale environment impact: from the two-dimensional collapse phase of the filament to the three-dimensional collapse phase of the cluster/node halo at

The Spin and Orientation of Dark Matter Halos Within Cosmic Filaments

Science.gov (United States)

Zhang, Youcai; Yang, Xiaohu; Faltenbacher, Andreas; Springel, Volker; Lin, Weipeng; Wang, Huiyuan

2009-11-01

Clusters, filaments, sheets, and voids are the building blocks of the cosmic web. Forming dark matter halos respond to these different large-scale environments, and this in turn affects the properties of galaxies hosted by the halos. It is therefore important to understand the systematic correlations of halo properties with the morphology of the cosmic web, as this informs both about galaxy formation physics and possible systematics of weak lensing studies. In this study, we present and compare two distinct algorithms for finding cosmic filaments and sheets, a task which is far less well established than the identification of dark matter halos or voids. One method is based on the smoothed dark matter density field and the other uses the halo distributions directly. We apply both techniques to one high-resolution N-body simulation and reconstruct the filamentary/sheet like network of the dark matter density field. We focus on investigating the properties of the dark matter halos inside these structures, in particular, on the directions of their spins and the orientation of their shapes with respect to the directions of the filaments and sheets. We find that both the spin and the major axes of filament halos with masses lsim1013 h -1 M sun are preferentially aligned with the direction of the filaments. The spins and major axes of halos in sheets tend to lie parallel to the sheets. There is an opposite mass dependence of the alignment strength for the spin (negative) and major (positive) axes, i.e. with increasing halo mass the major axis tends to be more strongly aligned with the direction of the filament, whereas the alignment between halo spin and filament becomes weaker with increasing halo mass. The alignment strength as a function of the distance to the most massive node halo indicates that there is a transit large-scale environment impact: from the two-dimensional collapse phase of the filament to the three-dimensional collapse phase of the cluster/node halo at

CONSTRAINTS ON THE RELATIONSHIP BETWEEN STELLAR MASS AND HALO MASS AT LOW AND HIGH REDSHIFT

International Nuclear Information System (INIS)

Moster, Benjamin P.; Somerville, Rachel S.; Maulbetsch, Christian; Van den Bosch, Frank C.; Maccio, Andrea V.; Naab, Thorsten; Oser, Ludwig

2010-01-01

We use a statistical approach to determine the relationship between the stellar masses of galaxies and the masses of the dark matter halos in which they reside. We obtain a parameterized stellar-to-halo mass (SHM) relation by populating halos and subhalos in an N-body simulation with galaxies and requiring that the observed stellar mass function be reproduced. We find good agreement with constraints from galaxy-galaxy lensing and predictions of semi-analytic models. Using this mapping, and the positions of the halos and subhalos obtained from the simulation, we find that our model predictions for the galaxy two-point correlation function (CF) as a function of stellar mass are in excellent agreement with the observed clustering properties in the Sloan Digital Sky Survey at z = 0. We show that the clustering data do not provide additional strong constraints on the SHM function and conclude that our model can therefore predict clustering as a function of stellar mass. We compute the conditional mass function, which yields the average number of galaxies with stellar masses in the range m ± dm/2 that reside in a halo of mass M. We study the redshift dependence of the SHM relation and show that, for low-mass halos, the SHM ratio is lower at higher redshift. The derived SHM relation is used to predict the stellar mass dependent galaxy CF and bias at high redshift. Our model predicts that not only are massive galaxies more biased than low-mass galaxies at all redshifts, but also the bias increases more rapidly with increasing redshift for massive galaxies than for low-mass ones. We present convenient fitting functions for the SHM relation as a function of redshift, the conditional mass function, and the bias as a function of stellar mass and redshift.

Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess

Energy Technology Data Exchange (ETDEWEB)

Hooper, Dan [Fermilab; Linden, Tim [UC, Santa Cruz, Inst. Part. Phys.

2018-03-21

Observations by HAWC indicate that many young pulsars (including Geminga and Monogem) are surrounded by spatially extended, multi-TeV emitting regions. It is not currently known, however, whether TeV emission is also produced by recycled, millisecond pulsars (MSPs). In this study, we perform a stacked analysis of 24 MSPs within HAWC's field-of-view, finding between 2.6-3.2 sigma evidence that these sources are, in fact, surrounded by TeV halos. The efficiency with which these MSPs produce TeV halos is similar to that exhibited by young pulsars. This result suggests that several dozen MSPs will ultimately be detectable by HAWC, including many "invisible" pulsars without radio beams oriented in our direction. The TeV halos of unresolved MSPs could also dominate the TeV-scale diffuse emission observed at high galactic latitudes. We also discuss the possibility that TeV and radio observations could be used to constrain the population of MSPs that is present in the inner Milky Way, thereby providing us with a new way to test the hypothesis that MSPs are responsible for the Galactic Center GeV excess.

FASHIONABLY LATE? BUILDING UP THE MILKY WAY'S INNER HALO

International Nuclear Information System (INIS)

Morrison, Heather L.; Harding, Paul; Helmi, Amina

2009-01-01

Using a sample of 246 metal-poor stars (RR Lyraes, red giants, and red horizontal branch stars) which is remarkable for the accuracy of its six-dimensional kinematical data, we find, by examining the distribution of stellar orbital angular momenta, a new component for the local halo which has an axial ratio c/a ∼ 0.2, a similar flattening to the thick disk. It has a small prograde rotation but is supported by velocity anisotropy, and contains more intermediate-metallicity stars (with -1.5 < [Fe/H] < -1.0) than the rest of our sample. We suggest that this component was formed quite late, during or after the formation of the disk. It formed either from the gas that was accreted by the last major mergers experienced by the Galaxy, or by dynamical friction of massive infalling satellite(s) with the halo and possibly the stellar disk or thick disk. The remainder of the halo stars in our sample, which are less closely confined to the disk plane, exhibit a clumpy distribution in energy and angular momentum, suggesting that the early, chaotic conditions under which the inner halo formed were not violent enough to erase the record of their origins. The clumpy structure suggests that a relatively small number of progenitors were responsible for building up the inner halo, in line with theoretical expectations. We find a difference in mean binding energy between the RR Lyrae variables and the red giants in our sample, suggesting that more of the RR Lyraes in the sample belong to the outer halo, and that the outer halo may be somewhat younger, as first suggested by Searle and Zinn. We also find that the RR Lyrae mean rotation is more negative than the red giants, which is consistent with the recent result of Carollo et al. that the outer halo has a retrograde rotation and with the difference in kinematics seen between RR Lyraes and blue horizontal branch stars by Kinman et al. (2007).

Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

Science.gov (United States)

Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

2018-03-01

Secondary halo bias, commonly known as `assembly bias', is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalo properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. This results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.

On the evolution of globular clusters and the origin of galactic halo stars

International Nuclear Information System (INIS)

Surdin, V.G.

1978-01-01

Evolution of globular clusters of galactic halo is considered. It is shown that evolution of massive globular clusters with a greater degree of probability takes place under the effect of dynamic friction, which brings about the cluster fall on the center of galactic and their destruction by tidal forces. Evolution of small massive cluster takes place under the effect of dissipation. All the other reasons, causing the destruction of globular clusters (gravitational tidal forces, mutual cluster collision, outflow of gas from red gigant atmospheres, the change of the radius of the cluster orbit at the expense of the change of the galaxy mass inside the cluster orbit) play a secondary role. The whole mass of the stars lost by globular clusters does not exceed 10 7 M sun. It is concluded that the origin of the star population of galactic halo field can not be explained by destruction of already formed only astral globular clusters

FIRST Bent-Double Radio Sources: Tracers of High-Redshift Clusters

International Nuclear Information System (INIS)

Blanton, E. L.; Gregg, M. D.; Helfand, D. J.; Becker, R. H.; White, R. L.

2000-01-01

Bent-double radio sources can act as tracers for clusters of galaxies. We present imaging and spectroscopic observations of the environments surrounding 10 of these sources (most of them wide-angle tails [WATs]) selected from the VLA FIRST survey. Our results reveal a previously unknown cluster associated with eight of the radio sources with redshifts in the range 0.33< z<0.85; furthermore, we cannot rule out that the other two bent doubles may be associated with clusters at higher redshift. Richness measurements indicate that these clusters are typical of the majority of those found in the Abell catalog, with a range of Abell richness classes from 0 to 2. The line-of-sight velocity dispersions are very different from cluster to cluster, ranging from approximately 300 to 1100 km s-1. At the upper end of these intervals, we may be sampling some of the highest redshift massive clusters known. Alternatively, the large velocity dispersions measured in some of the clusters may indicate that they are merging systems with significant substructure, consistent with recent ideas concerning WAT formation (Burns et al.). (c) 2000 The American Astronomical Society

Probing the non-thermal emission in Abell 2146 and the Perseus cluster with the JVLA

Science.gov (United States)

Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie; van Weeren, Reinout; Clarke, Tracy; Intema, Huib; Russell, Helen; Edge, Alastair; Fabian, Andy; Olamaie, Malak; Rumsey, Clare; King, Lindsay; McNamara, Brian; Fecteau-Beaucage, David; Hogan, Michael; Mezcua, Mar; Taylor, Gregory; Blundell, Katherine; Sanders, Jeremy

2018-01-01

Jets created from accretion onto supermassive black holes release relativistic particles on large distances. These strongly affect the intracluster medium when located in the center of a brightest cluster galaxy. The hierarchical merging of subclusters and groups, from which cluster originate, also generates perturbations into the intracluster medium through shocks and turbulence, constituting a potential source of reacceleration for these particles. I will present deep multi-configuration low radio frequency observations from the Karl G. Jansky Very Large Array of two unique clusters, probing the non-thermal emission from the old particle population of the AGN outflows.Recently awarded of 550 hours of Chandra observations, Abell 2146 is one of the rare clusters undergoing a spectacular merger in the plane of the sky. Our recent deep multi-configuration JVLA 1.4 GHz observations have revealed the presence of a structure extending to 850 kpc in size, consisting of one component associated with the upstream shock and classified as a radio relic, and one associated with the subcluster core, consistent with a radio halo bounded by the bow shock. Theses structures have some of the lowest radio powers detected thus far in any cluster. The flux measurements of the halo, its morphology and measurements of the dynamical state of the cluster suggest that the halo was recently created (~ 0.3 Gyr after core passage). This makes A2146 extremely interesting to study, allowing us to probe the complete evolutionary stages of halos.I will also present results on 230-470 MHz JVLA observations of the Perseus cluster. Our observations of this nearby relaxed cool core cluster have revealed a multitude of new structures associated with the mini-halo, extending to hundreds of kpc in size. Its irregular morphology seems to be have been influenced both by the AGN activity and by the sloshing motion of the cluster’ gas. In addition, it has a filamentary structure similar to that seen in

THE MASSIVE SATELLITE POPULATION OF MILKY-WAY-SIZED GALAXIES

International Nuclear Information System (INIS)

Rodríguez-Puebla, Aldo; Avila-Reese, Vladimir; Drory, Niv

2013-01-01

Several occupational distributions for satellite galaxies more massive than m * ≈ 4 × 10 7 M ☉ around Milky-Way (MW)-sized hosts are presented and used to predict the internal dynamics of these satellites as a function of m * . For the analysis, a large galaxy group mock catalog is constructed on the basis of (sub)halo-to-stellar mass relations fully constrained with currently available observations, namely the galaxy stellar mass function decomposed into centrals and satellites, and the two-point correlation functions at different masses. We find that 6.6% of MW-sized galaxies host two satellites in the mass range of the Small and Large Magellanic Clouds (SMC and LMC, respectively). The probabilities of the MW-sized galaxies having one satellite equal to or larger than the LMC, two satellites equal to or larger than the SMC, or three satellites equal to or larger than Sagittarius (Sgr) are ≈0.26, 0.14, and 0.14, respectively. The cumulative satellite mass function of the MW, N s (≥m * ) , down to the mass of the Fornax dwarf is within the 1σ distribution of all the MW-sized galaxies. We find that MW-sized hosts with three satellites more massive than Sgr (as the MW) are among the most common cases. However, the most and second most massive satellites in these systems are smaller than the LMC and SMC by roughly 0.7 and 0.8 dex, respectively. We conclude that the distribution N s (≥m * ) for MW-sized galaxies is quite broad, the particular case of the MW being of low frequency but not an outlier. The halo mass of MW-sized galaxies correlates only weakly with N s (≥m * ). Then, it is not possible to accurately determine the MW halo mass by means of its N s (≥m * ); from our catalog, we constrain a lower limit of 1.38 × 10 12 M ☉ at the 1σ level. Our analysis strongly suggests that the abundance of massive subhalos should agree with the abundance of massive satellites in all MW-sized hosts, i.e., there is not a missing (massive) satellite problem

Growing massive black holes in a Local Group environment: the central supermassive, slowly sinking and ejected populations

Science.gov (United States)

Micic, Miroslav; Holley-Bockelmann, Kelly; Sigurdsson, Steinn

2011-06-01

We explore the growth of ≤107 M⊙ black holes that reside at the centres of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea 2 (VL-2) as a framework to test two merger-driven semi-analytic recipes for black hole growth that include dynamical friction, tidal stripping and gravitational wave recoil in over 20 000 merger tree realizations. First, we apply a Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the central black hole to a maximum mass limited by the black hole Fundamental Plane after every merger. Next, we present a new model that allows for low-level prolonged gas accretion (PGA) during the merger. We find that both models can generate an Sgr A* mass black hole. We predict a population of massive black holes in local field dwarf galaxies - if the VL-2 simulation is representative of the growth of the Local Group, we predict up to 35 massive black holes (≤106 M⊙) in Local Group field dwarfs. We also predict that hundreds of ≤105 M⊙ black holes fail to merge, and instead populate the Milky Way halo, with the most massive of them at roughly the virial radius. In addition, we find that there may be hundreds of massive black holes ejected from their hosts into the nearby intergalactic medium due to gravitational wave recoil. We discuss how the black hole population in the Local Group field dwarfs may help to constrain the growth mechanism for Sgr A*.

GALAXY ENVIRONMENTS OVER COSMIC TIME: THE NON-EVOLVING RADIAL GALAXY DISTRIBUTIONS AROUND MASSIVE GALAXIES SINCE z = 1.6

International Nuclear Information System (INIS)

Tal, Tomer; Van Dokkum, Pieter G.; Leja, Joel; Franx, Marijn; Wake, David A.; Whitaker, Katherine E.

2013-01-01

We present a statistical study of the environments of massive galaxies in four redshift bins between z = 0.04 and z = 1.6, using data from the Sloan Digital Sky Survey and the NEWFIRM Medium Band Survey. We measure the projected radial distribution of galaxies in cylinders around a constant number density selected sample of massive galaxies and utilize a statistical subtraction of contaminating sources. Our analysis shows that massive primary galaxies typically live in group halos and are surrounded by 2-3 satellites with masses more than one-tenth of the primary galaxy mass. The cumulative stellar mass in these satellites roughly equals the mass of the primary galaxy itself. We further find that the radial number density profile of galaxies around massive primaries has not evolved significantly in either slope or overall normalization in the past 9.5 Gyr. A simplistic interpretation of this result can be taken as evidence for a lack of mergers in the studied groups and as support for a static evolution model of halos containing massive primaries. Alternatively, there exists a tight balance between mergers and accretion of new satellites such that the overall distribution of galaxies in and around the halo is preserved. The latter interpretation is supported by a comparison to a semi-analytic model, which shows a similar constant average satellite distribution over the same redshift range.

FIRST RESULTS FROM THE DRAGONFLY TELEPHOTO ARRAY: THE APPARENT LACK OF A STELLAR HALO IN THE MASSIVE SPIRAL GALAXY M101

Energy Technology Data Exchange (ETDEWEB)

Van Dokkum, Pieter G.; Merritt, Allison [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Abraham, Roberto [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H8 (Canada)

2014-02-20

We use a new telescope concept, the Dragonfly Telephoto Array, to study the low surface brightness outskirts of the spiral galaxy M101. The radial surface brightness profile is measured down to μ {sub g} ∼ 32 mag arcsec{sup –2}, a depth that approaches the sensitivity of star count studies in the Local Group. We convert surface brightness to surface mass density using the radial g – r color profile. The mass density profile shows no significant upturn at large radius and is well-approximated by a simple bulge + disk model out to R = 70 kpc, corresponding to 18 disk scale lengths. Fitting a bulge + disk + halo model we find that the best-fitting halo mass M{sub halo}=1.7{sub −1.7}{sup +3.4}×10{sup 8} M {sub ☉}. The total stellar mass of M101 is M{sub tot,∗}=5.3{sub −1.3}{sup +1.7}×10{sup 10} M {sub ☉}, and we infer that the halo mass fraction f{sub halo}=M{sub halo}/M{sub tot,∗}=0.003{sub −0.003}{sup +0.006}. This mass fraction is lower than that of the Milky Way (f {sub halo} ∼ 0.02) and M31 (f {sub halo} ∼ 0.04). All three galaxies fall below the f {sub halo}-M {sub tot,} {sub *} relation predicted by recent cosmological simulations that trace the light of disrupted satellites, with M101's halo mass a factor of ∼10 below the median expectation. However, the predicted scatter in this relation is large, and more galaxies are needed to better quantify this possible tension with galaxy formation models. Dragonfly is well suited for this project: as integrated-light surface brightness is independent of distance, large numbers of galaxies can be studied in a uniform way.

MassiveNuS: cosmological massive neutrino simulations

Science.gov (United States)

Liu, Jia; Bird, Simeon; Zorrilla Matilla, José Manuel; Hill, J. Colin; Haiman, Zoltán; Madhavacheril, Mathew S.; Petri, Andrea; Spergel, David N.

2018-03-01

The non-zero mass of neutrinos suppresses the growth of cosmic structure on small scales. Since the level of suppression depends on the sum of the masses of the three active neutrino species, the evolution of large-scale structure is a promising tool to constrain the total mass of neutrinos and possibly shed light on the mass hierarchy. In this work, we investigate these effects via a large suite of N-body simulations that include massive neutrinos using an analytic linear-response approximation: the Cosmological Massive Neutrino Simulations (MassiveNuS). The simulations include the effects of radiation on the background expansion, as well as the clustering of neutrinos in response to the nonlinear dark matter evolution. We allow three cosmological parameters to vary: the neutrino mass sum Mν in the range of 0–0.6 eV, the total matter density Ωm, and the primordial power spectrum amplitude As. The rms density fluctuation in spheres of 8 comoving Mpc/h (σ8) is a derived parameter as a result. Our data products include N-body snapshots, halo catalogues, merger trees, ray-traced galaxy lensing convergence maps for four source redshift planes between zs=1–2.5, and ray-traced cosmic microwave background lensing convergence maps. We describe the simulation procedures and code validation in this paper. The data are publicly available at http://columbialensing.org.

The MASSIVE survey. I. A volume-limited integral-field spectroscopic study of the most massive early-type galaxies within 108 Mpc

Energy Technology Data Exchange (ETDEWEB)

Ma, Chung-Pei [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Greene, Jenny E.; Murphy, Jeremy D. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); McConnell, Nicholas [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Janish, Ryan [Department of Physics, University of California, Berkeley, CA 94720 (United States); Blakeslee, John P. [Dominion Astrophysical Observatory, NRC Herzberg Institute of Astrophysics, Victoria, BC V9E 2E7 (Canada); Thomas, Jens, E-mail: cpma@berkeley.edu [Max Planck-Institute for Extraterrestrial Physics, Giessenbachstr. 1, D-85741 Garching (Germany)

2014-11-10

Massive early-type galaxies represent the modern day remnants of the earliest major star formation episodes in the history of the universe. These galaxies are central to our understanding of the evolution of cosmic structure, stellar populations, and supermassive black holes, but the details of their complex formation histories remain uncertain. To address this situation, we have initiated the MASSIVE Survey, a volume-limited, multi-wavelength, integral-field spectroscopic (IFS) and photometric survey of the structure and dynamics of the ∼100 most massive early-type galaxies within a distance of 108 Mpc. This survey probes a stellar mass range M* ≳ 10{sup 11.5} M {sub ☉} and diverse galaxy environments that have not been systematically studied to date. Our wide-field IFS data cover about two effective radii of individual galaxies, and for a subset of them, we are acquiring additional IFS observations on sub-arcsecond scales with adaptive optics. We are also acquiring deep K-band imaging to trace the extended halos of the galaxies and measure accurate total magnitudes. Dynamical orbit modeling of the combined data will allow us to simultaneously determine the stellar, black hole, and dark matter halo masses. The primary goals of the project are to constrain the black hole scaling relations at high masses, investigate systematically the stellar initial mass function and dark matter distribution in massive galaxies, and probe the late-time assembly of ellipticals through stellar population and kinematical gradients. In this paper, we describe the MASSIVE sample selection, discuss the distinct demographics and structural and environmental properties of the selected galaxies, and provide an overview of our basic observational program, science goals and early survey results.

The Fate of Massive Black Holes in Gas-Rich Galaxy Mergers

Science.gov (United States)

Escala, A.; Larson, R. B.; Coppi, P. S.; Mardones, D.

2006-06-01

Using SPH numerical simulations, we investigate the effects of gas on the inspiral and merger of a massive black hole binary. This study is motivated by the very massive nuclear gas disks observed in the central regions of merging galaxies. Here we present results that expand on the treatment in previous works (Escala et al. 2004, 2005), by studying the evolution of a binary with different black holes masses in a massive gas disk.

The Mass and Absorption Columns of Galactic Gaseous Halos

Science.gov (United States)

Qu, Zhijie; Bregman, Joel N.

2018-01-01

The gaseous halo surrounding the galaxy is a reservoir for the gas on the galaxy disk, supplying materials for the star formation. We developed a gaseous halo model connecting the galactic disk and the gaseous halo by assuming the star formation rate is equal to the radiative cooling rate. Besides the single-phase collisional gaseous halo, we also consider the photoionization effect and a time-independent cooling model that assumes the mass cooling rate is constant over all temperatures. The photoionization dominates the low mass galaxy and the outskirts of the massive galaxy due to the low-temperature or low-density nature. The multi-phase cooling model dominates the denser region within the cooling radius, where the efficient radiative cooling must be included. Applying these two improvements, our model can reproduce the most of observed high ionization state ions (i.e., O VI, O VII, Ne VIII and Mg X). Our models show that the O VI column density is almost a constant of around 10^14 cm^-2 over a wide stellar mass from M_\\star ~10^8 M_Sun to 10^11 M_Sun, which is constant with current observations. This model also implies the O VI is photoionized for the galaxy with a halo mass fraction function of the EAGLE simulation. Finally, our model predicts plateaus of the Ne VIII and the Mg X column densities above the sub-L^* galaxy, and the possibly detectable O VII and O VIII column densities for low-mass galaxies, which help to determine the required detection limit for the future observations and missions.

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources

Science.gov (United States)

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard;

THE PECULIAR CHEMICAL INVENTORY OF NGC 2419: AN EXTREME OUTER HALO 'GLOBULAR CLUSTER'

International Nuclear Information System (INIS)

Cohen, Judith G.; Kirby, Evan N.; Huang Wenjin

2011-01-01

NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs.

Painting galaxies into dark matter halos using machine learning

Science.gov (United States)

Agarwal, Shankar; Davé, Romeel; Bassett, Bruce A.

2018-05-01

We develop a machine learning (ML) framework to populate large dark matter-only simulations with baryonic galaxies. Our ML framework takes input halo properties including halo mass, environment, spin, and recent growth history, and outputs central galaxy and halo baryonic properties including stellar mass (M*), star formation rate (SFR), metallicity (Z), neutral (H I) and molecular (H_2) hydrogen mass. We apply this to the MUFASA cosmological hydrodynamic simulation, and show that it recovers the mean trends of output quantities with halo mass highly accurately, including following the sharp drop in SFR and gas in quenched massive galaxies. However, the scatter around the mean relations is under-predicted. Examining galaxies individually, at z = 0 the stellar mass and metallicity are accurately recovered (σ ≲ 0.2 dex), but SFR and H I show larger scatter (σ ≳ 0.3 dex); these values improve somewhat at z = 1, 2. Remarkably, ML quantitatively recovers second parameter trends in galaxy properties, e.g. that galaxies with higher gas content and lower metallicity have higher SFR at a given M*. Testing various ML algorithms, we find that none perform significantly better than the others, nor does ensembling improve performance, likely because none of the algorithms reproduce the large observed scatter around the mean properties. For the random forest algorithm, we find that halo mass and nearby (˜200 kpc) environment are the most important predictive variables followed by growth history, while halo spin and ˜Mpc scale environment are not important. Finally we study the impact of additionally inputting key baryonic properties M*, SFR, and Z, as would be available e.g. from an equilibrium model, and show that particularly providing the SFR enables H I to be recovered substantially more accurately.

Cumulative Neutrino and Gamma-Ray Backgrounds from Halo and Galaxy Mergers

Science.gov (United States)

Yuan, Chengchao; Mészáros, Peter; Murase, Kohta; Jeong, Donghui

2018-04-01

The merger of dark matter halos and the gaseous structures embedded in them, such as protogalaxies, galaxies, and groups and clusters of galaxies, results in strong shocks that are capable of accelerating cosmic rays (CRs) to ≳10 PeV. These shocks will produce high-energy neutrinos and γ-rays through inelastic pp collisions. In this work, we study the contributions of these halo mergers to the diffuse neutrino flux and to the nonblazar portion of the extragalactic γ-ray background. We formulate the redshift dependence of the shock velocity, galactic radius, halo gas content, and galactic/intergalactic magnetic fields over the dark matter halo distribution up to a redshift z = 10. We find that high-redshift mergers contribute a significant amount of the CR luminosity density, and the resulting neutrino spectra could explain a large part of the observed diffuse neutrino flux above 0.1 PeV up to several PeV. We also show that our model can somewhat alleviate tensions with the extragalactic γ-ray background. First, since a larger fraction of the CR luminosity density comes from high redshifts, the accompanying γ-rays are more strongly suppressed through γγ annihilations with the cosmic microwave background and the extragalactic background light. Second, mildly radiative-cooled shocks may lead to a harder CR spectrum with spectral indices of 1.5 ≲ s ≲ 2.0. Our study suggests that halo mergers, a fraction of which may also induce starbursts in the merged galaxies, can be promising neutrino emitters without violating the existing Fermi γ-ray constraints on the nonblazar component of the extragalactic γ-ray background.

The CGM of Massive Galaxies: Where Cold Gas Goes to Die?

Science.gov (United States)

Howk, Jay

2017-08-01

We propose to survey the cold HI content and metallicity of the circumgalactic medium (CGM) around 50 (45 new, 5 archival) z 0.5 Luminous Red Galaxies (LRGs) to directly test a fundamental prediction of galaxy assembly models: that cold, metal-poor accretion does not survive to the inner halos of very massive galaxies. Accretion and feedback through the CGM play key roles in our models of the star formation dichotomy in galaxies. Low mass galaxies are thought to accrete gas in cold streams, while high mass galaxies host hot, dense halos that heat incoming gas and prevent its cooling, thereby quenching star formation. HST/COS has provided evidence for cold, metal-poor streams in the halos of star-forming galaxies (consistent with cold accretion). Observations have also demonstrated the presence of cool gas in the halos of passive galaxies, a potential challenge to the cold/hot accretion model. Our proposed observations will target the most massive galaxies and address the origin of the cool CGM gas by measuring the metallicity. This experiment is enabled by our novel approach to deriving metallicities, allowing the use of much fainter QSOs. It cannot be done with archival data, as these rare systems are not often probed along random sight lines. The H I column density (and metallicity) measurements require access to the UV. The large size of our survey is crucial to robustly assess whether the CGM in these galaxies is unique from that of star-forming systems, a comparison that provides the most stringent test of cold-mode accretion/quenching models to date. Conversely, widespread detections of metal-poor gas in these halos will seriously challenge the prevailing theory.

Metal flows of the circumgalactic medium, and the metal budget in galactic haloes

Science.gov (United States)

Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Ma, Xiangcheng; Anglés-Alcázar, Daniel; Chan, T. K.; Torrey, Paul; Hafen, Zachary H.; Quataert, Eliot; Murray, Norman

2017-07-01

We present an analysis of the flow of metals through the circumgalactic medium (CGM) in the Feedback in Realistic Environments (FIRE) simulations of galaxy formation, ranging from isolated dwarfs to L* galaxies. We find that nearly all metals produced in high-redshift galaxies are carried out in winds that reach 0.25Rvir. When measured at 0.25Rvir the metallicity of outflows is slightly higher than the interstellar medium (ISM) metallicity. Many metals thus reside in the CGM. Cooling and recycling from this reservoir determine the metal budget in the ISM. The outflowing metal flux decreases by a factor of ˜2-5 between 0.25Rvir and Rvir. Furthermore, outflow metallicity is typically lower at Rvir owing to dilution of the remaining outflow by metal-poor material swept up from the CGM. The inflow metallicity at Rvir is generally low, but outflow and inflow metallicities are similar in the inner halo. At low redshift, massive galaxies no longer generate outflows that reach the CGM, causing a divergence in CGM and ISM metallicity. Dwarf galaxies continue to generate outflows, although they preferentially retain metal ejecta. In all but the least massive galaxy considered, a majority of the metals are within the halo at z = 0. We measure the fraction of metals in CGM, ISM and stars, and quantify the thermal state of CGM metals in each halo. The total amount of metals in the low-redshift CGM of two simulated L* galaxies is consistent with estimates from the Cosmic Origin Spectrograph haloes survey, while for the other two it appears to be lower.

The LAMOST stellar spectroscopic survey and the Galactic halo

International Nuclear Information System (INIS)

Liu Chao; Deng Licai

2015-01-01

The formation and evolution of galaxies is an extremely important and fundamental question in modern astrophysics. Among the galaxies, the Milky Way is a very special sample not only because we live in it, but also because it is the only one in which we can carefully and individually observe its member stars. It has been confirmed that the Galactic halo, including both the stellar spheroid and the dark matter halo, contains fairly complicated structures, from which the overall shape, formation, and evolutionary history of our Galaxy can be unveiled. Moreover, some very rare and special stars in the Milky Way can be used as tracers to indirectly detect the core region of the Galaxy around the central super-massive black hole, which is also a hot topic of astrophysics. The LAMOST survey of the Milky Way will collect millions of stellar spectra at low wavelength resolution, making it the largest of such projects throughout the world. Its data base is very suitable for the study of the structure and evolution of the Milky Way. In this article, we report our on-going studies on the Galactic halo with LAMOST data, and present some early scientific results. (authors)

Null Environmental Effects of the Cosmic Web on Dark Matter Halo Properties

Science.gov (United States)

Goh, Tze; Primack, Joel; Aragon-Calvo, Miguel; Hellinger, Doug; Rodriguez-Puebla, Aldo; Lee, Christoph; Eckleholm, Elliot; Johnston, Kathryn

2018-01-01

We study the effects of the cosmic web environment (filaments, voids and walls) and environmental density on key properties of dark matter halos at redshift z = 0 using the Bolshoi-Planck ΛCDM. The z=0 Bolshoi-Planck simulation is analysed into filaments, voids and walls using the SpineWeb method, as well as VIDE method, both of which use Voronoi tessellation and the watershed transform. The key halo properties that we study are the mass accretion rate, spin parameter, concentration, prolateness, scale factor of the last major merger, and scale factor when the halo had half of its z=0 mass. For all these properties, we find that there is no discernible difference between the halo properties in filaments, walls or voids when compared at the same environmental density. As a result, we conclude that environmental density is the core attribute that affects these properties. This conclusion is in line with recent findings that properties of galaxies in redshift surveys are independent of their cosmic web environment at the same environmental density. We also find that the local web environment of the Milky Way and the Andromeda galaxy near the centre of a cosmic wall does not appear to have any effect on the key properties of these galaxies' dark matter halos, although we find that it is rather rare to have such massive halos near the centre of a relatively small cosmic wall.

ON THE AVERAGE DENSITY PROFILE OF DARK-MATTER HALOS IN THE INNER REGIONS OF MASSIVE EARLY-TYPE GALAXIES

International Nuclear Information System (INIS)

Grillo, C.

2012-01-01

We study a sample of 39 massive early-type lens galaxies at redshift z ∼< 0.3 to determine the slope of the average dark-matter density profile in the innermost regions. We keep the strong-lensing and stellar population synthesis modeling as simple as possible to measure the galaxy total and luminous masses. By rescaling the values of the Einstein radius and dark-matter projected mass with the values of the luminous effective radius and mass, we combine all the data of the galaxies in the sample. We find that between 0.3 and 0.9 times the value of the effective radius the average logarithmic slope of the dark-matter projected density profile is –1.0 ± 0.2 (i.e., approximately isothermal) or –0.7 ± 0.5 (i.e., shallower than isothermal), if, respectively, a constant Chabrier or heavier, Salpeter-like stellar initial mass function is adopted. These results provide positive evidence of the influence of the baryonic component on the contraction of the galaxy dark-matter halos, compared to the predictions of dark-matter-only cosmological simulations, and open a new way to test models of structure formation and evolution within the standard ΛCDM cosmological scenario.

Multi-wavelength study of young and massive galaxy clusters

International Nuclear Information System (INIS)

Lemonon, Ludovic

1999-01-01

Clusters of galaxies are the most massive objects gravitationally bound observed. They are the consequence of the evolution of most important perturbations in the cosmological microwave background. Their formation depends strongly of the cosmology, so they represent key objects to understand the Universe. The aim of this thesis is to study the processes of formation in clusters of galaxies well far away than previous studies clone, by high-resolution observations obtained by using most powerful telescope in each studied wavelength: X-ray, visible, infrared and radio. After data reductions of 12 clusters located at 0.1; z; 0.3, I was able to classified them in three categories: dynamically perturbed clusters, with substructures in their X-ray/optical image or velocity distribution of galaxies; cooling flows clusters, more relaxed than previous, with huge amount of gas cooling in their center; AGN contaminated, where the central dominant galaxy is an AGN which contaminate considerably the X-ray emission. I have obtained a measurement of the baryonic fraction of the Universe mass, and an estimation of the Universe matter density parameter at the mega-parsec scale, claiming for a low density universe. The ISOCAM data showed the effect of the ICM interactions on the star formation in cluster galaxies, and demonstrated that optical and mid-IR deduced star-formation are not basically compatible. They also showed how IR-emitting galaxies distribute in clusters, most noticeably how 15 um galaxies are located preferably on the edge of clusters. X-ray and radio data showed that clusters at z 0.25 could be find in several dynamical state, similarly with nearby ones, from relaxed to severely perturbed. All clusters present signs of past or present merging, in agreement with hierarchical structure formation scenario. This clusters database is an excellent starting point to study process of merging in clusters since they showed different aspect of this evolution. (author) [fr

The dependence of halo mass on galaxy size at fixed stellar mass using weak lensing

Science.gov (United States)

Charlton, Paul J. L.; Hudson, Michael J.; Balogh, Michael L.; Khatri, Sumeet

2017-12-01

Stellar mass has been shown to correlate with halo mass, with non-negligible scatter. The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy size at fixed stellar mass. It is possible that, at fixed stellar mass and galaxy colour, the halo mass is correlated with galaxy size. Galaxy-galaxy lensing allows us to measure the mean masses of dark matter haloes for stacked samples of galaxies. We extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single Sérsic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing us to determine halo masses for lenses according to their size. Comparing our halo masses and sizes to baselines for that stellar mass yields a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as Mh(M_{*}) ∝ r_{eff}^{η }(M_{*}). We find that, on average, our lens galaxies have an η = 0.42 ± 0.12, i.e. larger galaxies live in more massive dark matter haloes. The η is strongest for high-mass luminous red galaxies. Investigation of this relationship in hydrodynamical simulations suggests that, at a fixed M*, satellite galaxies have a larger η and greater scatter in the Mh and reff relationship compared to central galaxies.

The Structure and Dark Halo Core Properties of Dwarf Spheroidal Galaxies

Science.gov (United States)

Burkert, A.

2015-08-01

The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal (DIS) model of an isothermal, non-self-gravitating stellar system embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar core scale length a* is sensitive to the central dark matter density ρ0,d. The maximum stellar radius traces the dark halo core radius {r}c,d. The concentration c* of the stellar system, determined by a King profile fit, depends on the ratio of the stellar-to-dark-matter velocity dispersion {σ }*/{σ }d. Simple empirical relationships are derived that allow us to calculate the dark halo core parameters ρ0,d, {r}c,d, and σd given the observable stellar quantities σ*, a*, and c*. The DIS model is applied to the Milky Way’s dSphs. All dSphs closely follow the same universal dark halo scaling relations {ρ }0,d× {r}c,d={75}-45+85 M⊙ pc-2 that characterize the cores of more massive galaxies over a large range in masses. The dark halo core mass is a strong function of core radius, {M}c,d˜ {r}c,d2. Inside a fixed radius of ˜400 pc the total dark matter mass is, however, roughly constant with {M}d=2.6+/- 1.4× {10}7 M⊙, although outliers are expected. The dark halo core densities of the Galaxy’s dSphs are very high, with {ρ }0,d ≈ 0.2 M⊙ pc-3. dSphs should therefore be tidally undisturbed. Evidence for tidal effects might then provide a serious challenge for the CDM scenario.

Merger Activity and Radio Emission Within A2061

Science.gov (United States)

Bailey, Avery; Sarazin, Craig L.; Clarke, Tracy E.; Chatzikos, Marios; Hogge, Taylor; Wik, Daniel R.; Rudnick, Lawrence; Farnsworth, Damon; Van Weeren, Reinout J.; Brown, Shea

2015-01-01

Abell 2061 is a galaxy cluster located in the Corona Borealis Supercluster that boasts radio and X-ray structures indicative of a merger. A2061 is located at a redshift z = .0784, contains two brightest cluster galaxies, and has another cluster (A2067) about 2.5 Mpc to the NE, falling towards it. Within A2061, there exists an elongated structure of soft X-ray emission extending to the NE of cluster's center (referred to as the 'Plume') along with a hard X-ray shock region (the 'Shock') located just NE of the cluster's center. Previous observations in the radio have indicated the presence of a extended, central radio halo/relic accompanying the cluster's main X-ray emission but with slight NE displacement and further NE extension. Also emitting in the radio, to the SW of A2061, is a radio relic. The X-ray structures of A2061 were previously examined in 2009 by a Chandra observation. Here we present the results of an August 2013 XMM-Newton observation of the cluster. This XMM-Newton observation, imaged by three detectors, covers a greater field of view with a longer exposure (48.6 ks) than the previous Chandra observation. We will present images and spectra of various regions of the cluster. In addition, we will discuss the dynamics of the cluster, the nature of the Plume, Shock and other features, and origin of the central diffuse radio halo/relic and SW radio relic. These X-ray observations will also be compared to a numerical simulation from the Simulation Library of Astrophysics cluster Mergers (SLAM).

An Excursion Set Model of the Cosmic Web: the Abundance of Sheets, Filaments And Halos

Energy Technology Data Exchange (ETDEWEB)

Shen, Jiajian; /Penn State U., Astron. Astrophys.; Abel, Tom; /KIPAC, Menlo Park; Mo, Houjun; /Massachusetts U., Amherst; Sheth, Ravi; /Pennsylvania U.

2006-01-11

We discuss an analytic approach for modeling structure formation in sheets, filaments and knots. This is accomplished by combining models of triaxial collapse with the excursion set approach: sheets are defined as objects which have collapsed along only one axis, filaments have collapsed along two axes, and halos are objects in which triaxial collapse is complete. In the simplest version of this approach, which we develop here, large scale structure shows a clear hierarchy of morphologies: the mass in large-scale sheets is partitioned up among lower mass filaments, which themselves are made-up of still lower mass halos. Our approach provides analytic estimates of the mass fraction in sheets, filaments and halos, and its evolution, for any background cosmological model and any initial fluctuation spectrum. In the currently popular {Lambda}CDM model, our analysis suggests that more than 99% of the mass in sheets, and 72% of the mass in filaments, is stored in objects more massive than 10{sup 10}M{sub {circle_dot}} at the present time. For halos, this number is only 46%. Our approach also provides analytic estimates of how halo abundances at any given time correlate with the morphology of the surrounding large-scale structure, and how halo evolution correlates with the morphology of large scale structure.

Exotic nuclei: Halos

Energy Technology Data Exchange (ETDEWEB)

Orr, Nigel [Lab. de Physique Corpusculaire, Caen Univ., 14 (France); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)

1998-12-31

A brief overview of the nuclear halo is presented. Following some historical remarks the general characteristics of the halo systems are discussed with reference to a simple model. The conditions governing the formation of halos are also explored, as are two subjects of current interest - low-lying resonances of halo nucleon correlations. (author) 54 refs., 16 figs., 1 tabs.

DEMNUni: massive neutrinos and the bispectrum of large scale structures

Science.gov (United States)

Ruggeri, Rossana; Castorina, Emanuele; Carbone, Carmelita; Sefusatti, Emiliano

2018-03-01

The main effect of massive neutrinos on the large-scale structure consists in a few percent suppression of matter perturbations on all scales below their free-streaming scale. Such effect is of particular importance as it allows to constraint the value of the sum of neutrino masses from measurements of the galaxy power spectrum. In this work, we present the first measurements of the next higher-order correlation function, the bispectrum, from N-body simulations that include massive neutrinos as particles. This is the simplest statistics characterising the non-Gaussian properties of the matter and dark matter halos distributions. We investigate, in the first place, the suppression due to massive neutrinos on the matter bispectrum, comparing our measurements with the simplest perturbation theory predictions, finding the approximation of neutrinos contributing at quadratic order in perturbation theory to provide a good fit to the measurements in the simulations. On the other hand, as expected, a linear approximation for neutrino perturbations would lead to Script O(fν) errors on the total matter bispectrum at large scales. We then attempt an extension of previous results on the universality of linear halo bias in neutrino cosmologies, to non-linear and non-local corrections finding consistent results with the power spectrum analysis.

CHANG-ES. IX. Radio scale heights and scale lengths of a consistent sample of 13 spiral galaxies seen edge-on and their correlations

Science.gov (United States)

Krause, Marita; Irwin, Judith; Wiegert, Theresa; Miskolczi, Arpad; Damas-Segovia, Ancor; Beck, Rainer; Li, Jiang-Tao; Heald, George; Müller, Peter; Stein, Yelena; Rand, Richard J.; Heesen, Volker; Walterbos, Rene A. M.; Dettmar, Ralf-Jürgen; Vargas, Carlos J.; English, Jayanne; Murphy, Eric J.

2018-03-01

Aim. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution. Methods: We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands. Results: The sample average values for the radio scale heights of the halo are 1.1 ± 0.3 kpc in C-band and 1.4 ± 0.7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h˜ which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h˜ shows a tight anticorrelation with the mass surface density. Conclusions: The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk.

THE MATRYOSHKA RUN. II. TIME-DEPENDENT TURBULENCE STATISTICS, STOCHASTIC PARTICLE ACCELERATION, AND MICROPHYSICS IMPACT IN A MASSIVE GALAXY CLUSTER

International Nuclear Information System (INIS)

Miniati, Francesco

2015-01-01

We use the Matryoshka run to study the time-dependent statistics of structure-formation-driven turbulence in the intracluster medium of a 10 15 M ☉ galaxy cluster. We investigate the turbulent cascade in the inner megaparsec for both compressional and incompressible velocity components. The flow maintains approximate conditions of fully developed turbulence, with departures thereof settling in about an eddy-turnover time. Turbulent velocity dispersion remains above 700 km s –1 even at low mass accretion rate, with the fraction of compressional energy between 10% and 40%. The normalization and the slope of the compressional turbulence are susceptible to large variations on short timescales, unlike the incompressible counterpart. A major merger occurs around redshift z ≅ 0 and is accompanied by a long period of enhanced turbulence, ascribed to temporal clustering of mass accretion related to spatial clustering of matter. We test models of stochastic acceleration by compressional modes for the origin of diffuse radio emission in galaxy clusters. The turbulence simulation model constrains an important unknown of this complex problem and brings forth its dependence on the elusive microphysics of the intracluster plasma. In particular, the specifics of the plasma collisionality and the dissipation physics of weak shocks affect the cascade of compressional modes with strong impact on the acceleration rates. In this context radio halos emerge as complex phenomena in which a hierarchy of processes acting on progressively smaller scales are at work. Stochastic acceleration by compressional modes implies statistical correlation of radio power and spectral index with merging cores distance, both testable in principle with radio surveys

Projection Of The Stellar To Halo Mass Relation Into The Scaling Relations Of A Disc Galaxy Population

Science.gov (United States)

Mancillas, Brisa; Ávila-Reese, Vladimir; Rodríguez-Puebla, Aldo; Valls-Gabaud, David

2017-06-01

Several pieces of evidence suggest that disk formation is the generic process of assembly of galaxies, while the spheroidal component arises from the merging/interactions of disks as well as from their secular evolution. To understand galaxy formation and evolution, a cosmological framework is required. The current cosmological paradigm is summarized in the so-called Λ-cold dark matter model (ΛCDM). The statistical connection between the masses of the observed galaxies and those of the simulated CDM halos in large volumes leads us to the galaxy-halo mass relation, which summarizes the main astrophysical processes of galaxy formation and evolution (gas heating and cooling, SF, SN- and AGN-driven feedback, etc.). An important question is how this relation constrained by semi-empirical methods (e.g., Rodriguez-Puebla et al. 2014) is "projected" into the disk galaxy scaling relations and other galaxy correlations. To explore this question, we generate a synthetic catalog of thousands of disk/halo systems by means of an extended Mo, Mao & White (1998) model, and by using as input the baryonic-to-halo mass relation, fbar(Mh), of local disk galaxy as recently constrained by Calette et al. (2015).

Halo assembly bias and the tidal anisotropy of the local halo environment

Science.gov (United States)

Paranjape, Aseem; Hahn, Oliver; Sheth, Ravi K.

2018-05-01

We study the role of the local tidal environment in determining the assembly bias of dark matter haloes. Previous results suggest that the anisotropy of a halo's environment (i.e. whether it lies in a filament or in a more isotropic region) can play a significant role in determining the eventual mass and age of the halo. We statistically isolate this effect, using correlations between the large-scale and small-scale environments of simulated haloes at z = 0 with masses between 1011.6 ≲ (m/h-1 M⊙) ≲ 1014.9. We probe the large-scale environment, using a novel halo-by-halo estimator of linear bias. For the small-scale environment, we identify a variable αR that captures the tidal anisotropy in a region of radius R = 4R200b around the halo and correlates strongly with halo bias at fixed mass. Segregating haloes by αR reveals two distinct populations. Haloes in highly isotropic local environments (αR ≲ 0.2) behave as expected from the simplest, spherically averaged analytical models of structure formation, showing a negative correlation between their concentration and large-scale bias at all masses. In contrast, haloes in anisotropic, filament-like environments (αR ≳ 0.5) tend to show a positive correlation between bias and concentration at any mass. Our multiscale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias. We also discuss potential implications for the nature and detectability of galaxy assembly bias.

The mass dependence of satellite quenching in Milky Way-like haloes

Science.gov (United States)

Phillips, John I.; Wheeler, Coral; Cooper, Michael C.; Boylan-Kolchin, Michael; Bullock, James S.; Tollerud, Erik

2015-02-01

Using the Sloan Digital Sky Survey, we examine the quenching of satellite galaxies around isolated Milky Way-like hosts in the local Universe. We find that the efficiency of satellite quenching around isolated galaxies is low and roughly constant over two orders of magnitude in satellite stellar mass (M⋆ = 108.5-1010.5 M⊙), with only ˜20 per cent of systems quenched as a result of environmental processes. While largely independent of satellite stellar mass, satellite quenching does exhibit clear dependence on the properties of the host. We show that satellites of passive hosts are substantially more likely to be quenched than those of star-forming hosts, and we present evidence that more massive haloes quench their satellites more efficiently. These results extend trends seen previously in more massive host haloes and for higher satellite masses. Taken together, it appears that galaxies with stellar masses larger than about 108 M⊙ are uniformly resistant to environmental quenching, with the relative harshness of the host environment likely serving as the primary driver of satellite quenching. At lower stellar masses (<108 M⊙), however, observations of the Local Group suggest that the vast majority of satellite galaxies are quenched, potentially pointing towards a characteristic satellite mass scale below which quenching efficiency increases dramatically.

Mismatch and misalignment: dark haloes and satellites of disc galaxies

Science.gov (United States)

Deason, A. J.; McCarthy, I. G.; Font, A. S.; Evans, N. W.; Frenk, C. S.; Belokurov, V.; Libeskind, N. I.; Crain, R. A.; Theuns, T.

2011-08-01

We study the phase-space distribution of satellite galaxies associated with late-type galaxies in the GIMIC suite of simulations. GIMIC consists of resimulations of five cosmologically representative regions from the Millennium Simulation, which have higher resolution and incorporate baryonic physics. Whilst the disc of the galaxy is well aligned with the inner regions (r˜ 0.1r200) of the dark matter halo, both in shape and angular momentum, there can be substantial misalignments at larger radii (r˜r200). Misalignments of >45° are seen in ˜30 per cent of our sample. We find that the satellite population aligns with the shape (and angular momentum) of the outer dark matter halo. However, the alignment with the galaxy is weak owing to the mismatch between the disc and dark matter halo. Roughly 20 per cent of the satellite systems with 10 bright galaxies within r200 exhibit a polar spatial alignment with respect to the galaxy - an orientation reminiscent of the classical satellites of the Milky Way. We find that a small fraction (˜10 per cent) of satellite systems show evidence for rotational support which we attribute to group infall. There is a bias towards satellites on prograde orbits relative to the spin of the dark matter halo (and to a lesser extent with the angular momentum of the disc). This preference towards co-rotation is stronger in the inner regions of the halo where the most massive satellites accreted at relatively early times are located. We attribute the anisotropic spatial distribution and angular momentum bias of the satellites at z= 0 to their directional accretion along the major axes of the dark matter halo. The satellite galaxies have been accreted relatively recently compared to the dark matter mass and have experienced less phase-mixing and relaxation - the memory of their accretion history can remain intact to z= 0. Understanding the phase-space distribution of the z= 0 satellite population is key for studies that estimate the host halo

The European Large-Area ISO Survey (ELAIS): the final band-merged catalogue

DEFF Research Database (Denmark)

Rowan-Robinson, M.; Lari, C.; Perez-Fournon, I.

2004-01-01

We present the final band-merged European Large-Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 mum, and the associated data at U, g', r', i', Z, J, H, K and 20 cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed...

BOW TIES IN THE SKY. I. THE ANGULAR STRUCTURE OF INVERSE COMPTON GAMMA-RAY HALOS IN THE FERMI SKY

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E.; Shalaby, Mohamad [Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada); Tiede, Paul [Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON, N2L 2Y5 (Canada); Pfrommer, Christoph [Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Puchwein, Ewald [Institute of Astronomy and Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Chang, Philip [Department of Physics, University of Wisconsin-Milwaukee, 1900 E. Kenwood Boulevard, Milwaukee, WI 53211 (United States); Lamberts, Astrid [Theoretical Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)

2016-12-01

Extended inverse Compton halos are generally anticipated around extragalactic sources of gamma rays with energies above 100 GeV. These result from inverse Compton scattered cosmic microwave background photons by a population of high-energy electron/positron pairs produced by the annihilation of the high-energy gamma rays on the infrared background. Despite the observed attenuation of the high-energy gamma rays, the halo emission has yet to be directly detected. Here, we demonstrate that in most cases these halos are expected to be highly anisotropic, distributing the upscattered gamma rays along axes defined either by the radio jets of the sources or oriented perpendicular to a global magnetic field. We present a pedagogical derivation of the angular structure in the inverse Compton halo and provide an analytic formalism that facilitates the generation of mock images. We discuss exploiting this fact for the purpose of detecting gamma-ray halos in a set of companion papers.

DARK MATTER HALOS IN GALAXIES AND GLOBULAR CLUSTER POPULATIONS

Energy Technology Data Exchange (ETDEWEB)

Hudson, Michael J.; Harris, Gretchen L. [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1 (Canada); Harris, William E., E-mail: mjhudson@uwaterloo.ca [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)

2014-05-20

We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio η ≡ M {sub GCS}/M {sub h} (total mass in globular clusters, divided by halo mass) is essentially constant at (η) ∼ 4 × 10{sup –5}, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in η appears to be at most 0.2 dex; we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of η also suggests that about one-fourth of the initial gas mass present in protogalaxies collected into giant molecular clouds large enough to form massive, dense star clusters. Finally, our calibration of (η) indicates that the halo masses of the Milky Way and M31 are (1.2 ± 0.5) × 10{sup 12} M {sub ☉} and (3.9 ± 1.8) × 10{sup 12} M {sub ☉}, respectively.

Winds of Massive Magnetic Stars: Interacting Fields and Flow

Science.gov (United States)

Daley-Yates, S.; Stevens, I. R.

2018-01-01

We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

The Atacama Cosmology Telescope: ACT-CL J0102-4215 "El Gordo," a Massive Merging Cluster at Redshift 0.87

Science.gov (United States)

Menanteau, Felipe; Hughes, John Pl; Baker, Andrew J.; Sifon, Cristobal; Gonzalez, Jorge; Infante, Leopoldo; Barrientos, L. Felipe; Hilton, Matt; Das, Sudeep; Spergel, David N.;

The formation of massive primordial stars in the presence of moderate UV backgrounds

Energy Technology Data Exchange (ETDEWEB)

Latif, M. A.; Schleicher, D. R. G.; Bovino, S. [Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany); Grassi, T. [Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5-7, DK-1350 Copenhagen (Denmark); Spaans, M., E-mail: mlatif@astro.physik.uni-goettingen.de [Kapteyn Astronomical Institute, University of Groningen, 9700-AV Groningen (Netherlands)

2014-09-01

Radiative feedback produced by stellar populations played a vital role in early structure formation. In particular, photons below the Lyman limit can escape the star-forming regions and produce a background ultraviolet (UV) flux, which consequently may influence the pristine halos far away from the radiation sources. These photons can quench the formation of molecular hydrogen by photodetachment of H{sup –}. In this study, we explore the impact of such UV radiation on fragmentation in massive primordial halos of a few times 10{sup 7} M {sub ☉}. To accomplish this goal, we perform high resolution cosmological simulations for two distinct halos and vary the strength of the impinging background UV field in units of J {sub 21} assuming a blackbody radiation spectrum with a characteristic temperature of T {sub rad} = 10{sup 4} K. We further make use of sink particles to follow the evolution for 10,000 yr after reaching the maximum refinement level. No vigorous fragmentation is observed in UV-illuminated halos while the accretion rate changes according to the thermal properties. Our findings show that a few 10{sup 2}-10{sup 4} solar mass protostars are formed when halos are irradiated by J {sub 21} = 10-500 at z > 10 and suggest a strong relation between the strength of the UV flux and mass of a protostar. This mode of star formation is quite different from minihalos, as higher accretion rates of about 0.01-0.1 M {sub ☉} yr{sup –1} are observed by the end of our simulations. The resulting massive stars are potential cradles for the formation of intermediate-mass black holes at earlier cosmic times and contribute to the formation of a global X-ray background.

Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters

Science.gov (United States)

Gaspari, M.; McDonald, M.; Hamer, S. L.; Brighenti, F.; Temi, P.; Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; Edge, A. C.; Werner, N.; Tozzi, P.; Sun, M.; Stone, J. M.; Tremblay, G. R.; Hogan, M. T.; Eckert, D.; Ettori, S.; Yu, H.; Biffi, V.; Planelles, S.

2018-02-01

We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations. As emerged in the recent picture of top-down multiphase condensation, hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (∼107 K) are perturbed by subsonic turbulence, warm (∼104 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in the Perseus cluster. The ensemble multiphase gas distributions (from the UV to the radio band) are characterized by substantial spectral line broadening (σ v,los ≈ 100–200 {km} {{{s}}}-1) with a mild line shift. On the other hand, pencil-beam detections (as H I absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shifts of up to several 100 {km} {{{s}}}-1 (for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,los of the warm Hα+[N II] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show that the physically motivated criterion C ≡ t cool/t eddy ≈ 1 best traces the condensation extent region and the presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic data sets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

STELLAR MASSES OF LYMAN BREAK GALAXIES, Lyα EMITTERS, AND RADIO GALAXIES IN OVERDENSE REGIONS AT z = 4-6

International Nuclear Information System (INIS)

Overzier, Roderik A.; Shu Xinwen; Zheng Wei; Rettura, Alessandro; Zirm, Andrew; Ford, Holland; Bouwens, Rychard J.; Illingworth, Garth D.; Miley, George K.; Venemans, Bram; White, Richard L.

2009-01-01

We present new information on galaxies in the vicinity of luminous radio galaxies (RGs) and quasars at z≅4, 5, and 6. These fields were previously found to contain overdensities of Lyman Break Galaxies (LBGs) or spectroscopic Lyα emitters, which were interpreted as evidence for clusters-in-formation ('protoclusters'). We use Hubble Space Telescope and Spitzer data to infer stellar masses from stellar synthesis models calibrated against the Millennium Run simulations, and contrast our results with large samples of LBGs in more average environments as probed by the Great Observatories Origins Deep Survey (GOODS). The following results were obtained. First, LBGs in both overdense regions and in the field at z = 4-5 lie on a very similar sequence in a z'-[3.6] versus 3.6 μm color-magnitude diagram. This is interpreted as a sequence in stellar mass (M * ∼ 10 9 -10 11 M sun ) in which galaxies become increasingly red due to dust and age as their star formation rate (SFR) increases, while their specific SFR stays constant. Second, the two RGs are among the most massive objects (M * ∼ 10 11 M sun ) known to exist at z ≅ 4-5, and are extremely rare based on the low number density of such objects as estimated from the ∼25x larger area GOODS survey. We suggest that the presence of the massive (radio) galaxies and associated supermassive black holes has been boosted through rapid accretion of gas or merging inside overdense regions. Third, the total stellar mass found in the z = 4 protocluster TN1338 accounts for 4, based on a comparison with the massive X-ray cluster Cl1252 at z = 1.2. Although future near-infrared observations should determine whether any massive galaxies are currently being missed by our UV/Lyα selections, one possible explanation for this mass difference is that TN1338 evolves into a smaller cluster than Cl1252. This raises the interesting question of whether the most massive protocluster regions at z > 4 remain yet to be discovered.

The difference between radio-loud and radio-quiet active galaxies

Science.gov (United States)

Wilson, A. S.; Colbert, E. J. M.

1995-01-01

The recent development of unified theories of active galactic nuclei (AGNs) has indicated that there are two physically distinct classes of these objects--radio-loud and radio-quiet. Despite differences, the (probable) thermal emissions from the AGNs (continua and lines from X-ray to infrared wavelengths) are quite similar to the two classes of object. We argue that this last result suggests that the black hole masses and mass accretion rates in the two classes are not greatly different, and that the difference between the classes is associated with the spin of the black hole. We assume that the normal process of accretion through a disk does not lead to rapidly spinning holes and propose that galaxies (e.g., spirals) which have not suffered a recent major merger event contain nonrotating or only slowly rotating black holes. When two such galaxies merge, the two black holes are known to form a binary and we assume that they eventually coalesce. The ratio of the number of radio-loud to radio-quiet AGNs at a given thermal (e.g., optical) luminosity is determined by the galaxy merger rate. Comparisons between the predicted and observed radio luminosity functions constrain the efficiencies with which jet power is extracted from the spinning hole and radio emission is produced by the jet.

The Peculiar Chemical Inventory of NGC 2419: An Extreme Outer Halo "Globular Cluster"

Science.gov (United States)

Cohen, Judith G.; Huang, Wenjin; Kirby, Evan N.

2011-10-01

NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

Particle content, radio-galaxy morphology, and jet power: all radio-loud AGN are not equal

Science.gov (United States)

Croston, J. H.; Ineson, J.; Hardcastle, M. J.

2018-05-01

Ongoing and future radio surveys aim to trace the evolution of black hole growth and feedback from active galactic nuclei (AGNs) throughout cosmic time; however, there remain major uncertainties in translating radio luminosity functions into a reliable assessment of the energy input as a function of galaxy and/or dark matter halo mass. A crucial and long-standing problem is the composition of the radio-lobe plasma that traces AGN jet activity. In this paper, we carry out a systematic comparison of the plasma conditions in Fanaroff & Riley class I and II radio galaxies to demonstrate conclusively that their internal composition is systematically different. This difference is best explained by the presence of an energetically dominant proton population in the FRI, but not the FRII radio galaxies. We show that, as expected from this systematic difference in particle content, radio morphology also affects the jet-power/radio-luminosity relationship, with FRII radio galaxies having a significantly lower ratio of jet power to radio luminosity than the FRI cluster radio sources used to derive jet-power scaling relations via X-ray cavity measurements. Finally, we also demonstrate conclusively that lobe composition is unconnected to accretion mode (optical excitation class): the internal conditions of low- and high-excitation FRII radio lobes are indistinguishable. We conclude that inferences of population-wide AGN impact require careful assessment of the contribution of different jet subclasses, particularly given the increased diversity of jet evolutionary states expected to be present in deep, low-frequency radio surveys such as the LOFAR Two-Metre Sky Survey.

Non-Gaussian halo assembly bias

International Nuclear Information System (INIS)

Reid, Beth A.; Verde, Licia; Dolag, Klaus; Matarrese, Sabino; Moscardini, Lauro

2010-01-01

The strong dependence of the large-scale dark matter halo bias on the (local) non-Gaussianity parameter, f NL , offers a promising avenue towards constraining primordial non-Gaussianity with large-scale structure surveys. In this paper, we present the first detection of the dependence of the non-Gaussian halo bias on halo formation history using N-body simulations. We also present an analytic derivation of the expected signal based on the extended Press-Schechter formalism. In excellent agreement with our analytic prediction, we find that the halo formation history-dependent contribution to the non-Gaussian halo bias (which we call non-Gaussian halo assembly bias) can be factorized in a form approximately independent of redshift and halo mass. The correction to the non-Gaussian halo bias due to the halo formation history can be as large as 100%, with a suppression of the signal for recently formed halos and enhancement for old halos. This could in principle be a problem for realistic galaxy surveys if observational selection effects were to pick galaxies occupying only recently formed halos. Current semi-analytic galaxy formation models, for example, imply an enhancement in the expected signal of ∼ 23% and ∼ 48% for galaxies at z = 1 selected by stellar mass and star formation rate, respectively

Halo histories versus galaxy properties at z = 0 II: large-scale galactic conformity

Science.gov (United States)

Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.; Conroy, Charlie

2018-06-01

Using group catalogues from the Sloan Digital Sky Survey (SDSS) Data Release 7, we measure galactic conformity in the local universe. We measure the quenched fraction of neighbour galaxies around isolated primary galaxies, dividing the isolated sample into star-forming and quiescent objects. We restrict our measurements to scales >1 Mpc to probe the correlations between halo formation histories. Over the stellar mass range 109.7 ≤ M*/M⊙ ≤ 1010.9, we find minimal evidence for conformity. We further compare these data to predictions of the halo age-matching model, in which the oldest galaxies are associated with the oldest haloes. For models with strong correlations between halo and stellar age, the conformity is too large to be consistent with the data. Weaker implementations of the age-matching model would not produce a detectable signal in SDSS data. We reproduce the results of Kauffmann et al., in which the star formation rates of neighbour galaxies are reduced around primary galaxies when the primaries are low star formers. However, we find this result is mainly driven by contamination in the isolation criterion; when removing the small fraction of satellite galaxies in the sample, the conformity signal largely goes away. Lastly, we show that small conformity signals, i.e. 2-5 per cent differences in the quenched fractions of neighbour galaxies, can be produced by mechanisms other than halo assembly bias. For example, if passive galaxies occupy more massive haloes than star-forming galaxies of the same stellar mass, a conformity signal that is consistent with recent measurements from PRIMUS (Berti et al.) can be produced.

Ultra Light Axionic Dark Matter: Galactic Halos and Implications for Observations with Pulsar Timing Arrays

Science.gov (United States)

de Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Shive, Hsi-Yu; Lazkoz, Ruth

2018-01-01

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃ 150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃ 400 ns/(m_B/10^{-22} eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.

Understanding the fate of merging supermassive black holes

International Nuclear Information System (INIS)

Campanelli, Manuela

2005-01-01

Understanding the fate of merging supermassive black holes in galactic mergers, and the gravitational wave emission from this process, are important LISA science goals. To this end, we present results from numerical relativity simulations of binary black hole mergers using the so-called Lazarus approach to model gravitational radiation from these events. In particular, we focus here on some recent calculations of the final spin and recoil velocity of the remnant hole formed at the end of a binary black hole merger process, which may constrain the growth history of massive black holes at the core of galaxies and globular clusters

Tune-Based Halo Diagnostics

International Nuclear Information System (INIS)

Cameron, Peter

2003-01-01

Tune-based halo diagnostics can be divided into two categories -- diagnostics for halo prevention, and diagnostics for halo measurement. Diagnostics for halo prevention are standard fare in accumulators, synchrotrons, and storage rings, and again can be divided into two categories -- diagnostics to measure the tune distribution (primarily to avoid resonances), and diagnostics to identify instabilities (which will not be discussed here). These diagnostic systems include kicked (coherent) tune measurement, phase-locked loop (PLL) tune measurement, Schottky tune measurement, beam transfer function (BTF) measurements, and measurement of transverse quadrupole mode envelope oscillations. We refer briefly to tune diagnostics used at RHIC and intended for the SNS, and then present experimental results. Tune-based diagnostics for halo measurement (as opposed to prevention) are considerably more difficult. We present one brief example of tune-based halo measurement

Conference: Seeing two black holes merge (with gravitational waves!) | 14 September | Uni Dufour

CERN Multimedia

2016-01-01

GW150914: the first direct observation of gravitational waves from the inspiral and merger of two black holes - Conference by Prof. Bruce Allen, Albert Einstein Institute Hannover.   "Seeing two black holes merge (with gravitational waves!)" Uni Dufour - Auditorium U300 Wednesday, 14 September at 7 p.m.   Bruce Allen. (Photo: ©F. Vinken/MPG) Abstract: On 14 September 2015, the advanced LIGO gravitational wave instruments detected the gravitational wave signal emitted as two black holes, about one billion light years away from Earth, made a final few orbits around each other then merged together. This was big news around the world, because scientists have tried to make such observations for more than half a century. Before they merged, the two black holes were about 29 and 36 times as massive as the sun; after the merger was complete, a single black hole about 62 times the sun's mass was left behind. I'll describe what black holes are, how they (...

The Eating Habits of Milky Way-mass Halos: Destroyed Dwarf Satellites and the Metallicity Distribution of Accreted Stars

Science.gov (United States)

Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H.

2016-04-01

We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (Mvir ˜ 1012.1 M⊙) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with Mstar ˜ 108-1010M⊙. Halos with more quiescent accretion histories tend to have lower mass progenitors (108-109 M⊙), and lower overall accreted stellar masses. Ultra-faint mass (Mstar 108 M⊙ can contribute a considerable fraction (˜20%-60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil” a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.

Fermionic halos at finite temperature in AdS/CFT

Science.gov (United States)

Argüelles, Carlos R.; Grandi, Nicolás E.

2018-05-01

We explore the gravitational backreaction of a system consisting in a very large number of elementary fermions at finite temperature, in asymptotically AdS space. We work in the hydrodynamic approximation, and solve the Tolman-Oppenheimer-Volkoff equations with a perfect fluid whose equation of state takes into account both the relativistic effects of the fermionic constituents, as well as its finite temperature effects. We find a novel dense core-diluted halo structure for the density profiles in the AdS bulk, similarly as recently reported in flat space, for the case of astrophysical dark matter halos in galaxies. We further study the critical equilibrium configurations above which the core undergoes gravitational collapse towards a massive black hole, and calculate the corresponding critical central temperatures, for two qualitatively different central regimes of the fermions: the diluted-Fermi case, and the degenerate case. As a probe for the dual CFT, we construct the holographic two-point correlator of a scalar operator with large conformal dimension in the worldline limit, and briefly discuss on the boundary CFT effects at the critical points.

Massive Black Hole Mergers: Can we see what LISA will hear?

Science.gov (United States)

Centrella, Joan

2009-01-01

Coalescing massive black hole binaries are formed when galaxies merge. The final stages of this coalescence produce strong gravitational wave signals that can be detected by the space-borne LISA. When the black holes merge in the presence of gas and magnetic fields, various types of electromagnetic signals may also be produced. Modeling such electromagnetic counterparts requires evolving the behavior of both gas and fields in the strong-field regions around the black holes. We have taken a first step towards this problem by mapping the flow of pressureless matter in the dynamic, 3-D general relativistic spacetime around the merging black holes. We report on the results of these initial simulations and discuss their likely importance for future hydrodynamical simulations.

The distribution of satellites around massive galaxies at 1 < z < 3 in ZFOURGE/CANDELS: Dependence on star formation activity

Energy Technology Data Exchange (ETDEWEB)

Kawinwanichakij, Lalitwadee; Papovich, Casey; Quadri, Ryan F.; Tran, Kim-Vy H.; Mehrtens, Nicola [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Spitler, Lee R.; Cowley, Michael [Department of Physics and Astronomy, Faculty of Sciences, Macquarie University, Sydney, NSW 2109 (Australia); Kacprzak, Glenn G.; Glazebrook, Karl; Nanayakkara, Themiya [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Labbé, Ivo; Straatman, Caroline M. S. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Allen, Rebecca [Australian Astronomical Observatories, P.O. Box 915, North Ryde, NSW 1670 (Australia); Davé, Romeel [University of the Western Cape, Bellville, Cape Town 7535 (South Africa); Dekel, Avishai [Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hartley, W. G. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Koo, David C. [University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Lu, Yu, E-mail: kawinwanichakij@physics.tamu.edu [Kavli Institute for Particle Astrophysics and Cosmology, 452 Lomita Mall, Stanford, CA 94305 (United States); and others

2014-09-10

We study the statistical distribution of satellites around star-forming and quiescent central galaxies at 1 < z < 3 using imaging from the FourStar Galaxy Evolution Survey and the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey. The deep near-IR data select satellites down to log (M/M {sub ☉}) > 9 at z < 3. The radial satellite distribution around centrals is consistent with a projected Navarro-Frenk-White profile. Massive quiescent centrals, log (M/M {sub ☉}) > 10.78, have ∼2 times the number of satellites compared to star-forming centrals with a significance of 2.7σ even after accounting for differences in the centrals' stellar-mass distributions. We find no statistical difference in the satellite distributions of intermediate-mass quiescent and star-forming centrals, 10.48 < log (M/M {sub ☉}) < 10.78. Compared to the Guo et al. semi-analytic model, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than star-forming centrals, even when the stellar-mass distributions are fixed. We use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between star-forming and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from ∼0 for log (M{sub h} /M {sub ☉}) ∼ 11 to ∼1 for log (M{sub h} /M {sub ☉}) ∼ 13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive halos.

Search for macroscopic dark matter in the halo of the milky way through microlensing. A feasibility study

International Nuclear Information System (INIS)

Moniez, M.

1990-05-01

The possibility of searching for non-visible massive compact objects in the galactic halo is discussed here. The discovery of such objects would solve the problem of the missing mass in the galaxies, and the experiments which investigate for weakly interacting particles assuming a diffuse cloud of dark matter would have to revise their limits. The non-discovery of these objects would exclude the last possibility left for baryonic dark matter, providing good evidence that the galactic halo has to be made of new particles. The description of the general-relativistic microlensing effect and its application to the search of massive compact objects are given here. A feasibility study shows that it is possible to monitor the luminosity of several million stars in the Large Magellanic Cloud with the required precision, in order to detect a possible microlensing phenomenon induced by heavy compact objects (10 -4 - 10 -1 solar mass units). A CCD-based experimental setup is described, which would make it possible to search for compact objects in the 10 -6 - 10 -4 solar mass unit domain

A massive, dead disk galaxy in the early Universe.

Science.gov (United States)

Toft, Sune; Zabl, Johannes; Richard, Johan; Gallazzi, Anna; Zibetti, Stefano; Prescott, Moire; Grillo, Claudio; Man, Allison W S; Lee, Nicholas Y; Gómez-Guijarro, Carlos; Stockmann, Mikkel; Magdis, Georgios; Steinhardt, Charles L

2017-06-21

At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies. Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which-surprisingly-turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo. This result confirms previous indirect indications that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

Relativistic N-body simulations with massive neutrinos

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Adamek, Julian; Durrer, Ruth; Kunz, Martin

2017-11-01

Some of the dark matter in the Universe is made up of massive neutrinos. Their impact on the formation of large scale structure can be used to determine their absolute mass scale from cosmology, but to this end accurate numerical simulations have to be developed. Due to their relativistic nature, neutrinos pose additional challenges when one tries to include them in N-body simulations that are traditionally based on Newtonian physics. Here we present the first numerical study of massive neutrinos that uses a fully relativistic approach. Our N-body code, gevolution, is based on a weak-field formulation of general relativity that naturally provides a self-consistent framework for relativistic particle species. This allows us to model neutrinos from first principles, without invoking any ad-hoc recipes. Our simulation suite comprises some of the largest neutrino simulations performed to date. We study the effect of massive neutrinos on the nonlinear power spectra and the halo mass function, focusing on the interesting mass range between 0.06 eV and 0.3 eV and including a case for an inverted mass hierarchy.

Radio transients from newborn black holes

Science.gov (United States)

Kashiyama, Kazumi; Hotokezaka, Kenta; Murase, Kohta

2018-05-01

We consider radio emission from a newborn black hole (BH), which is accompanied by a mini-disk with a mass of ≲ M⊙. Such a disk can be formed from an outer edge of the progenitor's envelope, especially for metal-poor massive stars and/or massive stars in close binaries. The disk accretion rate is typically super-Eddington and an ultrafast outflow with a velocity of ˜0.1-0.3 c will be launched into the circumstellar medium. The outflow forms a collisionless shock, and electrons are accelerated and emit synchrotron emission in radio bands with a flux of ˜ 10^{26-30} erg s^{-1} Hz^{-1} days to decades after the BH formation. The model predicts not only a fast UV/optical transient but also quasi-simultaneous inverse-Compton X-ray emission ˜ a few days after the BH formation, and the discovery of the radio counterpart with coordinated searches will enable us to identify this type of transients. The occurrence rate can be 0.1 - 10 % of the core-collapse supernova rate, which makes them a promising target of dedicated radio observations such as the Jansky VLA Sky Survey.

Quest of halo in 31Ne using Glauber model formalism with deformed relativistic mean field density

International Nuclear Information System (INIS)

Sharma, Mahesh K.; Patra, S.K.

2012-01-01

The advancement of radio active ion beam (RIB) explored the structure of exotic nuclei, which are away from the β stability line. Such nuclei with weak binding lie at the limit of stability and exhibit some fascinating phenomena. One of them is the formation of one or more nucleon halo structure. It is well established that the interaction cross section of halo nuclei like 11 Li, 11 Be and 19 C show anomalously large interaction cross sections and matter radius than that of their neighboring nuclei. Some recent investigations for 31 Ne predict that has a halo nature. The first experimental evidence also suggests 31 Ne as a halo candidate. The isotope 31 Ne having N=21, which breaks the shell closer structure as a consequence of deformation associated with the strong intruder configuration and having special interest, because it lie at island of inversion. Here we apply the well known Glauber approach with conjunction of deformed relativistic mean field densities of projectile and target nuclei. It is to be noted that Panda et al has done the similar calculation using a spherical density

Halo-independent analysis of direct detection data for light WIMPs

International Nuclear Information System (INIS)

Nobile, Eugenio Del; Gelmini, Graciela B.; Huh, Ji-Haeng; Gondolo, Paolo

2013-01-01

We present a halo-independent analysis of direct detection data on ''light WIMPs'', i.e. weakly interacting massive particles with mass close to or below 10 GeV/c 2 . We include new results from silicon CDMS detectors (bounds and excess events), the latest CoGeNT acceptances, and recent measurements of low sodium quenching factors in NaI crystals. We focus on light WIMPs with spin-independent isospin-conserving and isospin-violating interactions with nucleons. For these dark matter candidates we find that a low quenching factor would make the DAMA modulation incompatible with a reasonable escape velocity for the dark matter halo, and that the tension among experimental data tightens in both the isospin-conserving and isospin-violating scenarios. We also find that a new although milder tension appears between the CoGeNT and DAMA annual modulations on one side and the silicon excess events on the other, in that it seems difficult to interpret them as the modulated and unmodulated aspects of the same WIMP dark matter signal

THE ELM SURVEY. III. A SUCCESSFUL TARGETED SURVEY FOR EXTREMELY LOW MASS WHITE DWARFS

International Nuclear Information System (INIS)

Brown, Warren R.; Kenyon, Scott J.; Kilic, Mukremin; Allende Prieto, Carlos

2012-01-01

Extremely low mass (ELM) white dwarfs (WDs) with masses ☉ are rare objects that result from compact binary evolution. Here, we present a targeted spectroscopic survey of ELM WD candidates selected by color. The survey is 71% complete and has uncovered 18 new ELM WDs. Of the seven ELM WDs with follow-up observations, six are short-period binaries and four have merger times less than 5 Gyr. The most intriguing object, J1741+6526, likely has either a pulsar companion or a massive WD companion making the system a possible supernova Type Ia or an Ia progenitor. The overall ELM survey has now identified 19 double degenerate binaries with <10 Gyr merger times. The significant absence of short orbital period ELM WDs at cool temperatures suggests that common envelope evolution creates ELM WDs directly in short period systems. At least one-third of the merging systems are halo objects, thus ELM WD binaries continue to form and merge in both the disk and the halo.

Isospin quantum number and structure of the excited states in halo nuclei. Halo-isomers

International Nuclear Information System (INIS)

Izosimov, I.N.

2015-01-01

It has been shown that isobar-analog (IAS), double isobar-analog (DIAS), configuration (CS), and double configuration states (DCS) can simultaneously have n-n, n-p, and p-p halo components in their wave functions. Differences in halo structure of the excited and ground states can result in the formation of isomers (halo-isomers). Both the Borromean and tango halo types can be observed for n-p configurations of atomic nuclei. The structure of the ground and excited states with different isospin quantum number in halo-like nuclei is discussed. B(Mλ) and B(Eλ) for γ-transitions in 6-8 Li, 8-10 Be, 8,10,11 B, 10-14 C, 13-17 N, 15-17,19 O, and 17 F are analyzed. Special attention is given to nuclei whose ground state does not exhibit halo structure, but the excited state may have one.

Time-varying mixed logit model for vehicle merging behavior in work zone merging areas.

Science.gov (United States)

Weng, Jinxian; Du, Gang; Li, Dan; Yu, Yao

2018-08-01

This study aims to develop a time-varying mixed logit model for the vehicle merging behavior in work zone merging areas during the merging implementation period from the time of starting a merging maneuver to that of completing the maneuver. From the safety perspective, vehicle crash probability and severity between the merging vehicle and its surrounding vehicles are regarded as major factors influencing vehicle merging decisions. Model results show that the model with the use of vehicle crash risk probability and severity could provide higher prediction accuracy than previous models with the use of vehicle speeds and gap sizes. It is found that lead vehicle type, through lead vehicle type, through lag vehicle type, crash probability of the merging vehicle with respect to the through lag vehicle, crash severities of the merging vehicle with respect to the through lead and lag vehicles could exhibit time-varying effects on the merging behavior. One important finding is that the merging vehicle could become more and more aggressive in order to complete the merging maneuver as quickly as possible over the elapsed time, even if it has high vehicle crash risk with respect to the through lead and lag vehicles. Copyright © 2018 Elsevier Ltd. All rights reserved.

ATCA observations of the MACS-Planck Radio Halo Cluster Project. II. Radio observations of an intermediate redshift cluster sample

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Martinez Aviles, G.; Johnston-Hollitt, M.; Ferrari, C.; Venturi, T.; Democles, J.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Arnaud, M.; Aghanim, N.; Brown, S.; Douspis, M.; Hurier, J.; Intema, H. T.; Langer, M.; Macario, G.; Pointecouteau, E.

2018-04-01

Aim. A fraction of galaxy clusters host diffuse radio sources whose origins are investigated through multi-wavelength studies of cluster samples. We investigate the presence of diffuse radio emission in a sample of seven galaxy clusters in the largely unexplored intermediate redshift range (0.3 http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A94

The combined effect of AGN and supernovae feedback in launching massive molecular outflows in high-redshift galaxies

Science.gov (United States)

Biernacki, Pawel; Teyssier, Romain

2018-04-01

We have recently improved our model of active galactic nucleus (AGN) by attaching the supermassive black hole (SMBH) to a massive nuclear star cluster (NSC). Here, we study the effects of this new model in massive, gas-rich galaxies with several simulations of different feedback recipes with the hydrodynamics code RAMSES. These simulations are compared to a reference simulation without any feedback, in which the cooling halo gas is quickly consumed in a burst of star formation. In the presence of strong supernovae (SN) feedback, we observe the formation of a galactic fountain that regulates star formation over a longer period, but without halting it. If only AGN feedback is considered, as soon as the SMBH reaches a critical mass, strong outflows of hot gas are launched and prevent the cooling halo gas from reaching the disc, thus efficiently halting star formation, leading to the so-called `quenching'. If both feedback mechanisms act in tandem, we observe a non-linear coupling, in the sense that the dense gas in the supernovae-powered galactic fountain is propelled by the hot outflow powered by the AGN at much larger radii than without AGN. We argue that these particular outflows are able to unbind dense gas from the galactic halo, thanks to the combined effect of SN and AGN feedback. We speculate that this mechanism occurs at the end of the fast growing phase of SMBH, and is at the origin of the dense molecular outflows observed in many massive high-redshift galaxies.

Revealing the Cosmic Web-dependent Halo Bias

Science.gov (United States)

Yang, Xiaohu; Zhang, Youcai; Lu, Tianhuan; Wang, Huiyuan; Shi, Feng; Tweed, Dylan; Li, Shijie; Luo, Wentao; Lu, Yi; Yang, Lei

2017-10-01

Halo bias is the one of the key ingredients of the halo models. It was shown at a given redshift to be only dependent, to the first order, on the halo mass. In this study, four types of cosmic web environments—clusters, filaments, sheets, and voids—are defined within a state-of-the-art high-resolution N-body simulation. Within these environments, we use both halo-dark matter cross correlation and halo-halo autocorrelation functions to probe the clustering properties of halos. The nature of the halo bias differs strongly between the four different cosmic web environments described here. With respect to the overall population, halos in clusters have significantly lower biases in the {10}11.0˜ {10}13.5 {h}-1 {M}⊙ mass range. In other environments, however, halos show extremely enhanced biases up to a factor 10 in voids for halos of mass ˜ {10}12.0 {h}-1 {M}⊙ . Such a strong cosmic web environment dependence in the halo bias may play an important role in future cosmological and galaxy formation studies. Within this cosmic web framework, the age dependency of halo bias is found to be only significant in clusters and filaments for relatively small halos ≲ {10}12.5 {h}-1 {M}⊙ .

Radio emission of Abell galaxy clusters with red shifts from 0.02 to 0.075 at 102.5 MHz. Observations of clusters southward from the galactic plane

International Nuclear Information System (INIS)

Gubanov, A.G.

1983-01-01

The sample of 121 Abell clusters of galaxies with measured red shifts from 0.02 to 0.075, delta= 10 deg - +80 deg and within the completeness galactic-latitude region is presented. The completeness. with respect to the Abell's catalog is 80%. The completeness of the sample in function of distance (the completeness function) was constructed and the mean cluster density of 1.5x10 -6 Mpc -3 was derived. Observations at 102.5 MHz of 39 clusters southward from the galactic plane were carried out with BSA radio telescope. Flux density measurements for radio sources in the directions of the clusters have been made, integrated fluxes of clusters and luminosity estimations for their radio halos are presented. Radio emission of 11 clusters was detected , and for two of these and for other clust rs radio sources detected in the directions to the outskirts of clusters. Radio halos having the luminosity comparable to that of the A1656 (Coma) cluster are not typical for clusters

Brown dwarfs as dark galactic halos

International Nuclear Information System (INIS)

Adams, F.C.; Walker, T.P.

1990-01-01

The possibility that the dark matter in galactic halos can consist of brown dwarf stars is considered. The radiative signature for such halos consisting solely of brown dwarfs is calculated, and the allowed range of brown dwarf masses, the initial mass function (IMF), the stellar properties, and the density distribution of the galactic halo are discussed. The prediction emission from the halo is compared with existing observations. It is found that, for any IMF of brown dwarfs below the deuterium burning limit, brown dwarf halos are consistent with observations. Brown dwarf halos cannot, however, explain the recently observed near-IR background. It is shown that future satellite missions will either detect brown dwarf halos or place tight constraints on the allowed range of the IMF. 30 refs

Distributed Merge Trees

Energy Technology Data Exchange (ETDEWEB)

Morozov, Dmitriy; Weber, Gunther

2013-01-08

Improved simulations and sensors are producing datasets whose increasing complexity exhausts our ability to visualize and comprehend them directly. To cope with this problem, we can detect and extract significant features in the data and use them as the basis for subsequent analysis. Topological methods are valuable in this context because they provide robust and general feature definitions. As the growth of serial computational power has stalled, data analysis is becoming increasingly dependent on massively parallel machines. To satisfy the computational demand created by complex datasets, algorithms need to effectively utilize these computer architectures. The main strength of topological methods, their emphasis on global information, turns into an obstacle during parallelization. We present two approaches to alleviate this problem. We develop a distributed representation of the merge tree that avoids computing the global tree on a single processor and lets us parallelize subsequent queries. To account for the increasing number of cores per processor, we develop a new data structure that lets us take advantage of multiple shared-memory cores to parallelize the work on a single node. Finally, we present experiments that illustrate the strengths of our approach as well as help identify future challenges.

Detection of Hot Halo Gets Theory Out of Hot Water

Science.gov (United States)

2006-02-01

Scientists using NASA's Chandra X-ray Observatory have detected an extensive halo of hot gas around a quiescent spiral galaxy. This discovery is evidence that galaxies like our Milky Way are still accumulating matter from the gradual inflow of intergalactic gas. "What we are likely witnessing here is the ongoing galaxy formation process," said Kristian Pedersen of the University of Copenhagen, Denmark, and lead author of a report on the discovery. Chandra observations show that the hot halo extends more than 60,000 light years on either side of the disk of the galaxy known as NGC 5746. The detection of such a large halo alleviates a long-standing problem for the theory of galaxy formation. Spiral galaxies are thought to form from enormous clouds of intergalactic gas that collapse to form giant, spinning disks of stars and gas. Chandra X-ray Image of NGC 5746 Chandra X-ray Image of NGC 5746 One prediction of this theory is that large spiral galaxies should be immersed in halos of hot gas left over from the galaxy formation process. Hot gas has been detected around spiral galaxies in which vigorous star formation is ejecting matter from the galaxy, but until now hot halos due to infall of intergalactic matter have not been detected. "Our observations solve the mystery of the missing hot halos around spiral galaxies," said Pedersen. "The halos exist, but are so faint that an extremely sensitive telescope such as Chandra is needed to detect them." DSS Optical Image of NGC 5746 DSS Optical Image of NGC 5746 NGC 5746 is a massive spiral galaxy about a 100 million light years from Earth. Its disk of stars and gas is viewed almost edge-on. The galaxy shows no signs of unusual star formation, or energetic activity from its nuclear region, making it unlikely that the hot halo is produced by gas flowing out of the galaxy. "We targeted NGC 5746 because we thought its distance and orientation would give us the best chance to detect a hot halo caused by the infall of

Dark-ages reionization and galaxy formation simulation-XI. Clustering and halo masses of high redshift galaxies

Science.gov (United States)

Park, Jaehong; Kim, Han-Seek; Liu, Chuanwu; Trenti, Michele; Duffy, Alan R.; Geil, Paul M.; Mutch, Simon J.; Poole, Gregory B.; Mesinger, Andrei; Wyithe, J. Stuart B.

2017-12-01

We investigate the clustering properties of Lyman-break galaxies (LBGs) at z ∼ 6 - 8. Using the semi-analytical model MERAXES constructed as part of the dark-ages reionization and galaxy-formation observables from numerical simulation (DRAGONS) project, we predict the angular correlation function (ACF) of LBGs at z ∼ 6 - 8. Overall, we find that the predicted ACFs are in good agreement with recent measurements at z ∼ 6 and z ∼ 7.2 from observations consisting of the Hubble eXtreme Deep Field, the Hubble Ultra Deep Field and cosmic sssembly near-infrared deep extragalactic legacy survey field. We confirm the dependence of clustering on luminosity, with more massive dark matter haloes hosting brighter galaxies, remains valid at high redshift. The predicted galaxy bias at fixed luminosity is found to increase with redshift, in agreement with observations. We find that LBGs of magnitude MAB(1600) < -19.4 at 6 ≲ z ≲ 8 reside in dark matter haloes of mean mass ∼1011.0-1011.5 M⊙, and this dark matter halo mass does not evolve significantly during reionisation.

Feedback Limits to Maximum Seed Masses of Black Holes

International Nuclear Information System (INIS)

Pacucci, Fabio; Natarajan, Priyamvada; Ferrara, Andrea

2017-01-01

The most massive black holes observed in the universe weigh up to ∼10 10 M ⊙ , nearly independent of redshift. Reaching these final masses likely required copious accretion and several major mergers. Employing a dynamical approach that rests on the role played by a new, relevant physical scale—the transition radius—we provide a theoretical calculation of the maximum mass achievable by a black hole seed that forms in an isolated halo, one that scarcely merged. Incorporating effects at the transition radius and their impact on the evolution of accretion in isolated halos, we are able to obtain new limits for permitted growth. We find that large black hole seeds ( M • ≳ 10 4 M ⊙ ) hosted in small isolated halos ( M h ≲ 10 9 M ⊙ ) accreting with relatively small radiative efficiencies ( ϵ ≲ 0.1) grow optimally in these circumstances. Moreover, we show that the standard M • – σ relation observed at z ∼ 0 cannot be established in isolated halos at high- z , but requires the occurrence of mergers. Since the average limiting mass of black holes formed at z ≳ 10 is in the range 10 4–6 M ⊙ , we expect to observe them in local galaxies as intermediate-mass black holes, when hosted in the rare halos that experienced only minor or no merging events. Such ancient black holes, formed in isolation with subsequent scant growth, could survive, almost unchanged, until present.

Beam characterization of a new continuous wave radio frequency quadrupole accelerator

Energy Technology Data Exchange (ETDEWEB)

Perry, A., E-mail: aperry4@hawk.iit.edu [Argonne National Laboratory, Argonne, IL 60439 (United States); Illinois Institute of Technology, Chicago, IL 60616 (United States); Dickerson, C.; Ostroumov, P.N.; Zinkann, G. [Argonne National Laboratory, Argonne, IL 60439 (United States)

2014-01-21

A new Continuous Wave (CW) Radio Frequency Quadrupole (RFQ) for the ATLAS (Argonne Tandem Linac Accelerator System) Intensity Upgrade was developed, built and tested at Argonne National Laboratory. We present here a characterization of the RFQ output beam in the longitudinal phase space, as well as a measurement of the transverse beam halo. Measurement results are compared to simulations performed using the beam dynamics code TRACK. -- Highlights: • Beam commissioning of a new CW RFQ has been performed at Argonne National Laboratory. • Energy spread and bunch shape measurements were conducted. • The formation of a beam halo in the transverse phase space was studied.

Lensing of Fast Radio Bursts as a Probe of Compact Dark Matter.

Science.gov (United States)

Muñoz, Julian B; Kovetz, Ely D; Dai, Liang; Kamionkowski, Marc

2016-08-26

The possibility that part of the dark matter is made of massive compact halo objects (MACHOs) remains poorly constrained over a wide range of masses, and especially in the 20-100  M_{⊙} window. We show that strong gravitational lensing of extragalactic fast radio bursts (FRBs) by MACHOs of masses larger than ∼20  M_{⊙} would result in repeated FRBs with an observable time delay. Strong lensing of a FRB by a lens of mass M_{L} induces two images, separated by a typical time delay ∼few×(M_{L}/30  M_{⊙})  msec. Considering the expected FRB detection rate by upcoming experiments, such as canadian hydrogen intensity mapping experiment (CHIME), of 10^{4} FRBs per year, we should observe from tens to hundreds of repeated bursts yearly, if MACHOs in this window make up all the dark matter. A null search for echoes with just 10^{4} FRBs would constrain the fraction f_{DM} of dark matter in MACHOs to f_{DM}≲0.08 for M_{L}≳20  M_{⊙}.

Groups and clusters of galaxies

International Nuclear Information System (INIS)

Bijleveld, W.

1984-01-01

In this thesis, a correlative study is performed with respect to the radio and X-ray parameters of galaxy clusters and groups of galaxies (Msub(v)-Psub(1.4); Msub(v)-Lsub(x); Lsub(x)-Psub(1.4); R-Msub(v) correlations). Special attention is paid to correlations with cD and elliptical galaxies. It is concluded that in rich clusters massive cD galaxies form; massive galaxies are able to bind a large X-ray halo; strong X-ray emitters fuel their central radio sources at a high rate; the total gas content of groups is low, which implies that the contribution of groups to the total matter density in the universe is small. (Auth.)

The halo current in ASDEX Upgrade

International Nuclear Information System (INIS)

Pautasso, G.; Giannone, L.; Gruber, O.; Herrmann, A.; Maraschek, M.; Schuhbeck, K.H.

2011-01-01

Due to the complexity of the phenomena involved, a self-consistent physical model for the prediction of the halo current is not available. Therefore the ITER specifications of the spatial distribution and evolution of the halo current rely on empirical assumptions. This paper presents the results of an extensive analysis of the halo current measured in ASDEX Upgrade with particular emphasis on the evolution of the halo region, on the magnitude and time history of the halo current, and on the structure and duration of its toroidal and poloidal asymmetries. The effective length of the poloidal path of the halo current in the vessel is found to be rather insensitive to plasma parameters. Large values of the toroidally averaged halo current are observed in both vertical displacement events and centred disruptions but last a small fraction of the current quench; they coincide typically with a large but short-lived MHD event.

The halo current in ASDEX Upgrade

Science.gov (United States)

Pautasso, G.; Giannone, L.; Gruber, O.; Herrmann, A.; Maraschek, M.; Schuhbeck, K. H.; ASDEX Upgrade Team

2011-04-01

Due to the complexity of the phenomena involved, a self-consistent physical model for the prediction of the halo current is not available. Therefore the ITER specifications of the spatial distribution and evolution of the halo current rely on empirical assumptions. This paper presents the results of an extensive analysis of the halo current measured in ASDEX Upgrade with particular emphasis on the evolution of the halo region, on the magnitude and time history of the halo current, and on the structure and duration of its toroidal and poloidal asymmetries. The effective length of the poloidal path of the halo current in the vessel is found to be rather insensitive to plasma parameters. Large values of the toroidally averaged halo current are observed in both vertical displacement events and centred disruptions but last a small fraction of the current quench; they coincide typically with a large but short-lived MHD event.

In-depth analysis of drivers' merging behavior and rear-end crash risks in work zone merging areas.

Science.gov (United States)

Weng, Jinxian; Xue, Shan; Yang, Ying; Yan, Xuedong; Qu, Xiaobo

2015-04-01

This study investigates the drivers' merging behavior and the rear-end crash risk in work zone merging areas during the entire merging implementation period from the time of starting a merging maneuver to that of completing the maneuver. With the merging traffic data from a work zone site in Singapore, a mixed probit model is developed to describe the merging behavior, and two surrogate safety measures including the time to collision (TTC) and deceleration rate to avoid the crash (DRAC) are adopted to compute the rear-end crash risk between the merging vehicle and its neighboring vehicles. Results show that the merging vehicle has a bigger probability of completing a merging maneuver quickly under one of the following situations: (i) the merging vehicle moves relatively fast; (ii) the merging lead vehicle is a heavy vehicle; and (iii) there is a sizable gap in the adjacent through lane. Results indicate that the rear-end crash risk does not monotonically increase as the merging vehicle speed increases. The merging vehicle's rear-end crash risk is also affected by the vehicle type. There is a biggest increment of rear-end crash risk if the merging lead vehicle belongs to a heavy vehicle. Although the reduced remaining distance to work zone could urge the merging vehicle to complete a merging maneuver quickly, it might lead to an increased rear-end crash risk. Interestingly, it is found that the rear-end crash risk could be generally increased over the elapsed time after the merging maneuver being triggered. Copyright © 2015 Elsevier Ltd. All rights reserved.

High resolution radio observations of nuclear and circumnuclear regions of luminous infrared galaxies (LIRGs)

Energy Technology Data Exchange (ETDEWEB)

Alberdi, A; Perez-Torres, M A [Instituto de Astrofisica de Andalucia (IAA, CSIC), PO Box 3004, 18080-Granada (Spain); Colina, L [Instituto de Estructura de la Materia - IEM, CSIC, C, Serrano 115, 28005 Madrid (Spain); Torrelles, J M [Instituto de Ciencias del Espacio (ICE, CSIC) and IEEC, Gran Capita 2-4, 08034 Barcelona (Spain)], E-mail: antxon@iaa.es, E-mail: torres@iaa.es, E-mail: colina@damir.iem.csic.es, E-mail: torrelle@ieec.fcr.es

2008-10-15

High-resolution radio observations of the nuclear region of Luminous and Ultraluminous Infrared Galaxies (ULIRGs) have shown that its radio structure consists of a compact high surface-brightness central radio source immersed in a diffuse low brightness circumnuclear halo. While the central component could be associated with an AGN or compact star-forming regions where radio supernovae are exploding, it is well known that the circumnuclear regions host bursts of star-formation. The studies of radio supernovae can provide essential information about stellar evolution and CSM/ISM properties in regions hidden by dust at optical and IR wavelengths. In this contribution, we show results from radio interferometric observations from NGC 7469, IRAS 18293-3413 and IRAS 17138-1017 where three extremely bright radio supernovae have been found. High-resolution radio observations of these and other LIRGs would allow us to determine the core-collapse supernova rate in them as well as their star-formation rate.

Merging {DBMs} Efficiently

DEFF Research Database (Denmark)

David, Alexandre

2005-01-01

In this paper we present different algorithms to reduce the number of DBMs in federations by merging them. Federations are unions of DBMs and are used to represent non-convex zones. Inclusion checking between DBMs is a limited technique to reduce the size of federations and how to choose some DBMs...... to merge them into a larger one is a combi-natorial problem. We present a number of simple but efficient techniques to avoid searching the combinations while still being able to merge any number of DBMs...

The Splashback Radius of Halos from Particle Dynamics. II. Dependence on Mass, Accretion Rate, Redshift, and Cosmology

Science.gov (United States)

Diemer, Benedikt; Mansfield, Philip; Kravtsov, Andrey V.; More, Surhud

2017-07-01

The splashback radius R sp, the apocentric radius of particles on their first orbit after falling into a dark matter halo, has recently been suggested to be a physically motivated halo boundary that separates accreting from orbiting material. Using the Sparta code presented in Paper I, we analyze the orbits of billions of particles in cosmological simulations of structure formation and measure R sp for a large sample of halos that span a mass range from dwarf galaxy to massive cluster halos, reach redshift 8, and include WMAP, Planck, and self-similar cosmologies. We analyze the dependence of R sp/R 200m and M sp/M 200m on the mass accretion rate Γ, halo mass, redshift, and cosmology. The scatter in these relations varies between 0.02 and 0.1 dex. While we confirm the known trend that R sp/R 200m decreases with Γ, the relationships turn out to be more complex than previously thought, demonstrating that R sp is an independent definition of the halo boundary that cannot trivially be reconstructed from spherical overdensity definitions. We present fitting functions for R sp/R 200m and M sp/M 200m as a function of accretion rate, peak height, and redshift, achieving an accuracy of 5% or better everywhere in the parameter space explored. We discuss the physical meaning of the distribution of particle apocenters and show that the previously proposed definition of R sp as the radius of the steepest logarithmic density slope encloses roughly three-quarters of the apocenters. Finally, we conclude that no analytical model presented thus far can fully explain our results.

THE PSEUDO-EVOLUTION OF HALO MASS

International Nuclear Information System (INIS)

Diemer, Benedikt; Kravtsov, Andrey V.; More, Surhud

2013-01-01

A dark matter halo is commonly defined as a spherical overdensity of matter with respect to a reference density, such as the critical density or the mean matter density of the universe. Such definitions can lead to a spurious pseudo-evolution of halo mass simply due to redshift evolution of the reference density, even if its physical density profile remains constant over time. We estimate the amount of such pseudo-evolution of mass between z = 1 and 0 for halos identified in a large N-body simulation, and show that it accounts for almost the entire mass evolution of the majority of halos with M 200ρ-bar ≲ 10 12 h -1 M ☉ and can be a significant fraction of the apparent mass growth even for cluster-sized halos. We estimate the magnitude of the pseudo-evolution assuming that halo density profiles remain static in physical coordinates, and show that this simple model predicts the pseudo-evolution of halos identified in numerical simulations to good accuracy, albeit with significant scatter. We discuss the impact of pseudo-evolution on the evolution of the halo mass function and show that the non-evolution of the low-mass end of the halo mass function is the result of a fortuitous cancellation between pseudo-evolution and the absorption of small halos into larger hosts. We also show that the evolution of the low-mass end of the concentration-mass relation observed in simulations is almost entirely due to the pseudo-evolution of mass. Finally, we discuss the implications of our results for the interpretation of the evolution of various scaling relations between the observable properties of galaxies and galaxy clusters and their halo masses.

Reionization histories of Milky Way mass halos

International Nuclear Information System (INIS)

Li, Tony Y.; Wechsler, Risa H.; Abel, Tom; Alvarez, Marcelo A.

2014-01-01

We investigate the connection between the reionization era and the present-day universe by examining the mass reionization histories of z = 0 dark matter halos. In a 600 3 Mpc 3 volume, we combine a dark matter N-body simulation with a three-dimensional seminumerical reionization model. This tags each particle with a reionization redshift, so that individual present-day halos can be connected to their reionization histories and environments. We find that the vast majority of present-day halos with masses larger than ∼ few × 10 11 M ☉ reionize earlier than the rest of the universe. We also find significant halo-to-halo diversity in mass reionization histories, and find that in realistic inhomogeneous models, the material within a given halo is not expected to reionize at the same time. In particular, the scatter in reionization times within individual halos is typically larger than the scatter among halos. From our fiducial reionization model, we find that the typical 68% scatter in reionization times within halos is ∼115 Myr for 10 12±0.25 M ☉ halos, decreasing slightly to ∼95 Myr for 10 15±0.25 M ☉ halos. We find a mild correlation between reionization history and environment: halos with shorter reionization histories are typically in more clustered environments, with the strongest trend on a scale of ∼20 Mpc. Material in Milky Way mass halos with short reionization histories is preferentially reionized in relatively large H II regions, implying reionization mostly by sources external to the progenitors of the present-day halo. We investigate the impact on our results of varying the reionization model parameters, which span a range of reionization scenarios with varying timing and morphology.

THE OVERDENSITY AND MASSES OF THE FRIENDS-OF-FRIENDS HALOS AND UNIVERSALITY OF HALO MASS FUNCTION

International Nuclear Information System (INIS)

More, Surhud; Kravtsov, Andrey V.; Dalal, Neal; Gottloeber, Stefan

2011-01-01

The friends-of-friends algorithm (hereafter FOF) is a percolation algorithm which is routinely used to identify dark matter halos from N-body simulations. We use results from percolation theory to show that the boundary of FOF halos does not correspond to a single density threshold but to a range of densities close to a critical value that depends upon the linking length parameter, b. We show that for the commonly used choice of b = 0.2, this critical density is equal to 81.62 times the mean matter density. Consequently, halos identified by the FOF algorithm enclose an average overdensity which depends on their density profile (concentration) and therefore changes with halo mass, contrary to the popular belief that the average overdensity is ∼180. We derive an analytical expression for the overdensity as a function of the linking length parameter b and the concentration of the halo. Results of tests carried out using simulated and actual FOF halos identified in cosmological simulations show excellent agreement with our analytical prediction. We also find that the mass of the halo that the FOF algorithm selects crucially depends upon mass resolution. We find a percolation-theory-motivated formula that is able to accurately correct for the dependence on number of particles for the mock realizations of spherical and triaxial Navarro-Frenk-White halos. However, we show that this correction breaks down when applied to the real cosmological FOF halos due to the presence of substructures. Given that abundance of substructure depends on redshift and cosmology, we expect that the resolution effects due to substructure on the FOF mass and halo mass function will also depend on redshift and cosmology and will be difficult to correct for in general. Finally, we discuss the implications of our results for the universality of the mass function.

THE 5 GHz ARECIBO SEARCH FOR RADIO FLARES FROM ULTRACOOL DWARFS

Energy Technology Data Exchange (ETDEWEB)

Route, Matthew; Wolszczan, Alexander, E-mail: mroute@astro.psu.edu, E-mail: alex@astro.psu.edu [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States)

2013-08-10

We present the results of a 4.75 GHz survey of 33 brown dwarfs and one young exoplanetary system for flaring radio emission, conducted with the 305 m Arecibo radio telescope. The goal of this program was to detect and characterize the magnetic fields of objects cooler than spectral type L3.5, the coolest brown dwarf detected prior to our survey. We have also attempted to detect flaring radio emission from the HR 8799 planetary system, guided by theoretical work indicating that hot, massive exoplanets may have strong magnetic fields capable of generating radio emission at GHz frequencies. We have detected and confirmed radio flares from the T6.5 dwarf 2MASS J10475385+2124234. This detection dramatically extends the temperature range over which brown dwarfs appear to be at least sporadic radio-emitters, from 1900 K (L3.5) down to 900 K (T6.5). It also demonstrates that the utility of radio detection as a unique tool to study the magnetic fields of substellar objects extends to the coolest dwarfs, and, plausibly to hot, massive exoplanets. We have also identified a single, 3.6{sigma} flare from the L1 dwarf, 2MASS J1439284+192915. This detection is tentative and requires confirmation by additional monitoring observations.

Merge of terminological resources

DEFF Research Database (Denmark)

Henriksen, Lina; Braasch, Anna

2012-01-01

In our globalized world, the amount of cross-national communication increases rapidly, which also calls for easy access to multi-lingual high quality terminological resources. Sharing of terminology resources is currently becoming common practice, and efficient strategies for integration...... – or merging – of terminology resources are strongly needed. This paper discusses prerequisites for successful merging with the focus on identification of candidate duplicates of a subject domain found in the resources to be merged, and it describes automatic merging strategies to be applied to such duplicates...... in electronic terminology resources. Further, some perspectives of manual, supplementary assessment methods supporting the automatic procedures are sketched. Our considerations are primarily based on experience gained in the IATE and EuroTermBank projects, as merging was a much discussed issue in both projects....

Formation of the First Star Clusters and Massive Star Binaries by Fragmentation of Filamentary Primordial Gas Clouds

Science.gov (United States)

Hirano, Shingo; Yoshida, Naoki; Sakurai, Yuya; Fujii, Michiko S.

2018-03-01

We perform a set of cosmological simulations of early structure formation incorporating baryonic streaming motions. We present a case where a significantly elongated gas cloud with ∼104 solar mass (M ⊙) is formed in a pre-galactic (∼107 M ⊙) dark halo. The gas streaming into the halo compresses and heats the massive filamentary cloud to a temperature of ∼10,000 Kelvin. The gas cloud cools rapidly by atomic hydrogen cooling, and then by molecular hydrogen cooling down to ∼400 Kelvin. The rapid decrease of the temperature and hence of the Jeans mass triggers fragmentation of the filament to yield multiple gas clumps with a few hundred solar masses. We estimate the mass of the primordial star formed in each fragment by adopting an analytic model based on a large set of radiation hydrodynamics simulations of protostellar evolution. The resulting stellar masses are in the range of ∼50–120 M ⊙. The massive stars gravitationally attract each other and form a compact star cluster. We follow the dynamics of the star cluster using a hybrid N-body simulation. We show that massive star binaries are formed in a few million years through multi-body interactions at the cluster center. The eventual formation of the remnant black holes will leave a massive black hole binary, which can be a progenitor of strong gravitational wave sources similar to those recently detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

Baryonic distributions in galaxy dark matter haloes - II. Final results

Science.gov (United States)

Richards, Emily E.; van Zee, L.; Barnes, K. L.; Staudaher, S.; Dale, D. A.; Braun, T. T.; Wavle, D. C.; Dalcanton, J. J.; Bullock, J. S.; Chandar, R.

2018-06-01

Re-creating the observed diversity in the organization of baryonic mass within dark matter haloes represents a key challenge for galaxy formation models. To address the growth of galaxy discs in dark matter haloes, we have constrained the distribution of baryonic and non-baryonic matter in a statistically representative sample of 44 nearby galaxies defined from the Extended Disk Galaxy Exploration Science (EDGES) Survey. The gravitational potentials of each galaxy are traced using rotation curves derived from new and archival radio synthesis observations of neutral hydrogen (H I). The measured rotation curves are decomposed into baryonic and dark matter halo components using 3.6 μm images for the stellar content, the H I observations for the atomic gas component, and, when available, CO data from the literature for the molecular gas component. The H I kinematics are supplemented with optical integral field spectroscopic (IFS) observations to measure the central ionized gas kinematics in 26 galaxies, including 13 galaxies that are presented for the first time in this paper. Distributions of baryonic-to-total mass ratios are determined from the rotation curve decompositions under different assumptions about the contribution of the stellar component and are compared to global and radial properties of the dominant stellar populations extracted from optical and near-infrared photometry. Galaxies are grouped into clusters of similar baryonic-to-total mass distributions to examine whether they also exhibit similar star and gas properties. The radial distribution of baryonic-to-total mass in a galaxy does not appear to correlate with any characteristics of its star formation history.

Sparse Reconstruction of the Merging A520 Cluster System

Energy Technology Data Exchange (ETDEWEB)

Peel, Austin [Département d’Astrophysique, IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette (France); Lanusse, François [McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 (United States); Starck, Jean-Luc, E-mail: austin.peel@cea.fr [Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS, F-91191 Gif-sur-Yvette (France)

2017-09-20

Merging galaxy clusters present a unique opportunity to study the properties of dark matter in an astrophysical context. These are rare and extreme cosmic events in which the bulk of the baryonic matter becomes displaced from the dark matter halos of the colliding subclusters. Since all mass bends light, weak gravitational lensing is a primary tool to study the total mass distribution in such systems. Combined with X-ray and optical analyses, mass maps of cluster mergers reconstructed from weak-lensing observations have been used to constrain the self-interaction cross-section of dark matter. The dynamically complex Abell 520 (A520) cluster is an exceptional case, even among merging systems: multi-wavelength observations have revealed a surprising high mass-to-light concentration of dark mass, the interpretation of which is difficult under the standard assumption of effectively collisionless dark matter. We revisit A520 using a new sparsity-based mass-mapping algorithm to independently assess the presence of the puzzling dark core. We obtain high-resolution mass reconstructions from two separate galaxy shape catalogs derived from Hubble Space Telescope observations of the system. Our mass maps agree well overall with the results of previous studies, but we find important differences. In particular, although we are able to identify the dark core at a certain level in both data sets, it is at much lower significance than has been reported before using the same data. As we cannot confirm the detection in our analysis, we do not consider A520 as posing a significant challenge to the collisionless dark matter scenario.

Neutron halo in deformed nuclei

International Nuclear Information System (INIS)

Zhou Shangui; Meng Jie; Ring, P.; Zhao Enguang

2010-01-01

Halo phenomena in deformed nuclei are investigated within a deformed relativistic Hartree Bogoliubov (DRHB) theory. These weakly bound quantum systems present interesting examples for the study of the interdependence between the deformation of the core and the particles in the halo. Contributions of the halo, deformation effects, and large spatial extensions of these systems are described in a fully self-consistent way by the DRHB equations in a spherical Woods-Saxon basis with the proper asymptotic behavior at a large distance from the nuclear center. Magnesium and neon isotopes are studied and detailed results are presented for the deformed neutron-rich and weakly bound nucleus 44 Mg. The core of this nucleus is prolate, but the halo has a slightly oblate shape. This indicates a decoupling of the halo orbitals from the deformation of the core. The generic conditions for the occurrence of this decoupling effects are discussed.

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

International Nuclear Information System (INIS)

Van Weeren, R. J.; Jones, C.; Forman, W. R.; Andrade-Santos, F.; Pearce, Connor J. J.; David, L.; Kraft, R. P.; Nulsen, P. E. J.; Ogrean, G. A.; Bonafede, A.; Brüggen, M.; Bulbul, E.; Clarke, T. E.; Churazov, E.; Dawson, W. A.; Donahue, M.; Goulding, A.; Mason, B.; Merten, J.; Mroczkowski, T.

2017-01-01

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ∼0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. We detect a density discontinuity north-northeast of this core, which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100–300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

Energy Technology Data Exchange (ETDEWEB)

Van Weeren, R. J.; Jones, C.; Forman, W. R.; Andrade-Santos, F.; Pearce, Connor J. J.; David, L.; Kraft, R. P.; Nulsen, P. E. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ogrean, G. A. [Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305-4060 (United States); Bonafede, A.; Brüggen, M. [Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg (Germany); Bulbul, E. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Clarke, T. E. [U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, D.C. 20375 (United States); Churazov, E. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741, Garching (Germany); Dawson, W. A. [Lawrence Livermore National Lab, 7000 East Avenue, Livermore, CA 94550 (United States); Donahue, M. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Goulding, A. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Mason, B. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Merten, J. [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Mroczkowski, T., E-mail: rvanweeren@cfa.harvard.edu [ESO—European Organization for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Str. 2, D-85748 Garching b. München (Germany); and others

2017-02-01

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ∼0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. We detect a density discontinuity north-northeast of this core, which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100–300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.

Halo modelling in chameleon theories

Energy Technology Data Exchange (ETDEWEB)

Lombriser, Lucas; Koyama, Kazuya [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth, PO1 3FX (United Kingdom); Li, Baojiu, E-mail: lucas.lombriser@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk, E-mail: baojiu.li@durham.ac.uk [Institute for Computational Cosmology, Ogden Centre for Fundamental Physics, Department of Physics, University of Durham, Science Laboratories, South Road, Durham, DH1 3LE (United Kingdom)

2014-03-01

We analyse modelling techniques for the large-scale structure formed in scalar-tensor theories of constant Brans-Dicke parameter which match the concordance model background expansion history and produce a chameleon suppression of the gravitational modification in high-density regions. Thereby, we use a mass and environment dependent chameleon spherical collapse model, the Sheth-Tormen halo mass function and linear halo bias, the Navarro-Frenk-White halo density profile, and the halo model. Furthermore, using the spherical collapse model, we extrapolate a chameleon mass-concentration scaling relation from a ΛCDM prescription calibrated to N-body simulations. We also provide constraints on the model parameters to ensure viability on local scales. We test our description of the halo mass function and nonlinear matter power spectrum against the respective observables extracted from large-volume and high-resolution N-body simulations in the limiting case of f(R) gravity, corresponding to a vanishing Brans-Dicke parameter. We find good agreement between the two; the halo model provides a good qualitative description of the shape of the relative enhancement of the f(R) matter power spectrum with respect to ΛCDM caused by the extra attractive gravitational force but fails to recover the correct amplitude. Introducing an effective linear power spectrum in the computation of the two-halo term to account for an underestimation of the chameleon suppression at intermediate scales in our approach, we accurately reproduce the measurements from the N-body simulations.

Halo modelling in chameleon theories

International Nuclear Information System (INIS)

Lombriser, Lucas; Koyama, Kazuya; Li, Baojiu

2014-01-01

We analyse modelling techniques for the large-scale structure formed in scalar-tensor theories of constant Brans-Dicke parameter which match the concordance model background expansion history and produce a chameleon suppression of the gravitational modification in high-density regions. Thereby, we use a mass and environment dependent chameleon spherical collapse model, the Sheth-Tormen halo mass function and linear halo bias, the Navarro-Frenk-White halo density profile, and the halo model. Furthermore, using the spherical collapse model, we extrapolate a chameleon mass-concentration scaling relation from a ΛCDM prescription calibrated to N-body simulations. We also provide constraints on the model parameters to ensure viability on local scales. We test our description of the halo mass function and nonlinear matter power spectrum against the respective observables extracted from large-volume and high-resolution N-body simulations in the limiting case of f(R) gravity, corresponding to a vanishing Brans-Dicke parameter. We find good agreement between the two; the halo model provides a good qualitative description of the shape of the relative enhancement of the f(R) matter power spectrum with respect to ΛCDM caused by the extra attractive gravitational force but fails to recover the correct amplitude. Introducing an effective linear power spectrum in the computation of the two-halo term to account for an underestimation of the chameleon suppression at intermediate scales in our approach, we accurately reproduce the measurements from the N-body simulations

Updating the MACHO fraction of the Milky Way dark halo with improved mass models

Science.gov (United States)

Calcino, Josh; García-Bellido, Juan; Davis, Tamara M.

2018-05-01

Recent interest in primordial black holes as a possible dark matter candidate has motivated the reanalysis of previous methods for constraining massive astrophysical compact objects in the Milky Way halo and beyond. In order to derive these constraints, a model for the dark matter distribution around the Milky Way must be used. Previous microlensing searches have assumed a semi-isothermal density sphere for this task. We show this model is no longer consistent with data from the Milky Way rotation curve, and test two replacement models, namely NFW and power-law. The power-law model is the most flexible as it can break spherical symmetry, and best fits the data. Thus, we recommend the power-law model as a replacement, although it still lacks the flexibility to fully encapsulate all possible shapes of the Milky Way halo. We then use the power-law model to rederive some previous microlensing constraints in the literature, while propagating the primary halo-shape uncertainties through to our final constraints. Our analysis reveals that the microlensing constraints towards the Large Magellanic Cloud weaken somewhat for MACHO masses around 10 M⊙ when this uncertainty is taken into account, but the constraints tighten at lower masses. Exploring some of the simplifying assumptions of previous constraints we also study the effect of wide mass distributions of compact halo objects, as well as the effect of spatial clustering on microlensing constraints. We find that both effects induce a shift in the constraints towards smaller masses, and can effectively remove the microlensing constraints from M ˜ 1 - 10M⊙ for certain MACHO populations.

Self-consistent beam halo studies ampersand halo diagnostic development in a continuous linear focusing channel

International Nuclear Information System (INIS)

Jameson, R.A.

1994-01-01

Beam halos are formed via self-consistent motion of the beam particles. Interactions of single particles with time-varying density distributions of other particles are a major source of halo. Aspects of these interactions are studied for an initially equilibrium distribution in a radial, linear, continuous focusing system. When there is a mismatch, it is shown that in the self-consistent system, there is a threshold in space-charge and mismatch, above which a halo is formed that extends to ∼1.5 times the initial maximum mismatch radius. Tools are sought for characterizing the halo dynamics. Testing the particles against the width of the mismatch driving resonance is useful for finding a conservative estimate of the threshold. The exit, entering and transition times, and the time evolution of the halo, are also explored using this technique. Extension to higher dimensions is briefly discussed

A new direction for dark matter research: intermediate-mass compact halo objects

Energy Technology Data Exchange (ETDEWEB)

Chapline, George F. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA (United States); Frampton, Paul H., E-mail: george.chapline@gmail.com, E-mail: paul.h.frampton@gmail.com [15 Summerheights, 29 Water Eaton Road, Oxford OX2 7PG (United Kingdom)

2016-11-01

The failure to find evidence for elementary particles that could serve as the constituents of dark matter brings to mind suggestions that dark matter might consist of massive compact objects (MACHOs). In particular, it has recently been argued that MACHOs with masses > 15 M {sub ⊙} may have been prolifically produced at the onset of the big bang. Although a variety of astrophysical signatures for primordial MACHOs with masses in this range have been discussed in the literature, we favor a strategy that uses the potential for magnification of stars outside our galaxy due to gravitational microlensing of these stars by MACHOs in the halo of our galaxy. We point out that the effect of the motion of the Earth on the shape of the micro-lensing brightening curves provides a promising approach to testing over the course of next several years the hypothesis that dark matter consists of massive compact objects.

DEMNUni: the clustering of large-scale structures in the presence of massive neutrinos

International Nuclear Information System (INIS)

Castorina, Emanuele; Carbone, Carmelita; Bel, Julien; Sefusatti, Emiliano; Dolag, Klaus

2015-01-01

We analyse the clustering features of Large Scale Structures (LSS) in the presence of massive neutrinos, employing a set of large-volume, high-resolution cosmological N-body simulations, where neutrinos are treated as separate collisionless particles. The volume of 8 h -3 Gpc 3 , combined with a resolution of about 8×10 10 h -1 M ⊚ for the cold dark matter (CDM) component, represents a significant improvement over previous N-body simulations in massive neutrino cosmologies. In this work we focus, in the first place, on the analysis of nonlinear effects in CDM and neutrinos perturbations contributing to the total matter power spectrum. We show that most of the nonlinear evolution is generated exclusively by the CDM component. We therefore compare mildly nonlinear predictions from Eulerian Perturbation Theory (PT), and fully nonlinear prescriptions (HALOFIT) with the measurements obtained from the simulations. We find that accounting only for the nonlinear evolution of the CDM power spectrum allows to recover the total matter power spectrum with the same accuracy as the massless case. Indeed, we show that, the most recent version of the (HALOFIT) formula calibrated on ΛCDM simulations can be applied directly to the linear CDM power spectrum without requiring additional fitting parameters in the massive case. As a second step, we study the abundance and clustering properties of CDM halos, confirming that, in massive neutrino cosmologies, the proper definition of the halo bias should be made with respect to the cold rather than the total matter distribution, as recently shown in the literature. Here we extend these results to the redshift space, finding that, when accounting for massive neutrinos, an improper definition of the linear bias can lead to a systematic error of about 1-2 % in the determination of the linear growth rate from anisotropic clustering. This result is quite important if we consider that future spectroscopic galaxy surveys, as e.g. Euclid, are

Feedback Limits to Maximum Seed Masses of Black Holes

Energy Technology Data Exchange (ETDEWEB)

Pacucci, Fabio; Natarajan, Priyamvada [Department of Physics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Ferrara, Andrea [Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy)

2017-02-01

The most massive black holes observed in the universe weigh up to ∼10{sup 10} M {sub ⊙}, nearly independent of redshift. Reaching these final masses likely required copious accretion and several major mergers. Employing a dynamical approach that rests on the role played by a new, relevant physical scale—the transition radius—we provide a theoretical calculation of the maximum mass achievable by a black hole seed that forms in an isolated halo, one that scarcely merged. Incorporating effects at the transition radius and their impact on the evolution of accretion in isolated halos, we are able to obtain new limits for permitted growth. We find that large black hole seeds ( M {sub •} ≳ 10{sup 4} M {sub ⊙}) hosted in small isolated halos ( M {sub h} ≲ 10{sup 9} M {sub ⊙}) accreting with relatively small radiative efficiencies ( ϵ ≲ 0.1) grow optimally in these circumstances. Moreover, we show that the standard M {sub •}– σ relation observed at z ∼ 0 cannot be established in isolated halos at high- z , but requires the occurrence of mergers. Since the average limiting mass of black holes formed at z ≳ 10 is in the range 10{sup 4–6} M {sub ⊙}, we expect to observe them in local galaxies as intermediate-mass black holes, when hosted in the rare halos that experienced only minor or no merging events. Such ancient black holes, formed in isolation with subsequent scant growth, could survive, almost unchanged, until present.

Spectro-polarimetric study of the early evolutionary phases of the most massive galaxies

International Nuclear Information System (INIS)

Vernet, Joel

2001-01-01

This research thesis addresses the study of the early phases of evolution of the most massive galaxies (giant elliptic), a fundamental process which is a matter of study for various reasons exposed by the author in his introduction. While presented results are based on spectro-polarimetric observations, the author first presents specific instruments and methods used by spectropolarimetry which provides access to variations of all vectorial properties of light, without loss of information. Then, he reports the study of a near powerful radio-galaxy, Cygnus A, the study of nine radio-galaxies with a high redshift, and the study of a far ultra-luminous infrared galaxy (SMM J02399-0136). Results are then discussed and perspectives of research are proposed. Appendices present the theoretical study of the contribution of massive stars to the diffuse extragalactic ionizing background, and observations made on a near radio-galaxy (NGC 6251)

Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements

Science.gov (United States)

Prantzos, N.; Abia, C.; Limongi, M.; Chieffi, A.; Cristallo, S.

2018-05-01

We present a comprehensive study of the abundance evolution of the elements from H to U in the Milky Way halo and local disc. We use a consistent chemical evolution model, metallicity-dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss, and rotation for a large grid of stellar masses and for all stages of stellar evolution. The yields of massive stars are weighted by a metallicity-dependent function of the rotational velocities, constrained by observations as to obtain a primary-like 14N behaviour at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. We show that the Solar system isotopic composition can be reproduced to better than a factor of 2 for isotopes up to the Fe-peak, and at the 10 per cent level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). We conclude that the light element primary process (LEPP), invoked to explain the apparent abundance deficiency of the s-elements with A values of ^{12}C/^{13}C in halo red giants, which is rather due to internal processes in those stars.

THE PREVALENCE AND IMPACT OF WOLF–RAYET STARS IN EMERGING MASSIVE STAR CLUSTERS

Energy Technology Data Exchange (ETDEWEB)

Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States); Massey, Philip, E-mail: krs9tb@virginia.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

2016-08-01

We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.{sup 4} We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

ORIGAMI: DELINEATING HALOS USING PHASE-SPACE FOLDS

Energy Technology Data Exchange (ETDEWEB)

Falck, Bridget L.; Neyrinck, Mark C.; Szalay, Alexander S. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)

2012-08-01

We present the ORIGAMI method of identifying structures, particularly halos, in cosmological N-body simulations. Structure formation can be thought of as the folding of an initially flat three-dimensional manifold in six-dimensional phase space. ORIGAMI finds the outer folds that delineate these structures. Halo particles are identified as those that have undergone shell-crossing along three orthogonal axes, providing a dynamical definition of halo regions that is independent of density. ORIGAMI also identifies other morphological structures: particles that have undergone shell-crossing along 2, 1, or 0 orthogonal axes correspond to filaments, walls, and voids, respectively. We compare this method to a standard friends-of-friends halo-finding algorithm and find that ORIGAMI halos are somewhat larger, more diffuse, and less spherical, though the global properties of ORIGAMI halos are in good agreement with other modern halo-finding algorithms.

ORIGAMI: DELINEATING HALOS USING PHASE-SPACE FOLDS

International Nuclear Information System (INIS)

Falck, Bridget L.; Neyrinck, Mark C.; Szalay, Alexander S.

2012-01-01

We present the ORIGAMI method of identifying structures, particularly halos, in cosmological N-body simulations. Structure formation can be thought of as the folding of an initially flat three-dimensional manifold in six-dimensional phase space. ORIGAMI finds the outer folds that delineate these structures. Halo particles are identified as those that have undergone shell-crossing along three orthogonal axes, providing a dynamical definition of halo regions that is independent of density. ORIGAMI also identifies other morphological structures: particles that have undergone shell-crossing along 2, 1, or 0 orthogonal axes correspond to filaments, walls, and voids, respectively. We compare this method to a standard friends-of-friends halo-finding algorithm and find that ORIGAMI halos are somewhat larger, more diffuse, and less spherical, though the global properties of ORIGAMI halos are in good agreement with other modern halo-finding algorithms.

Preparation for electron ring - plasma ring merging experiments in RECE-MERGE

International Nuclear Information System (INIS)

Taggart, D.; Sekiguchi, A.; Fleischmann, H.H.

1986-01-01

The formation of a mixed-CT using relativistic electron rings and gun-produced plasma rings by MERGE-ing them axially is simulated. This process is similar to the axial stacking of relativistic electron rings in RECE-Christa. The results of their first plasm production experiment are reported here. After study of the gun-produced plasma's properties is completed, the gun will be mounted at the downstream end of the vacuum tank and the source of relativistic electron rings will be at the upstream end. The two rings, formed at opposite ends of the tank, will be translated axially and merged

ANGULAR MOMENTUM ACQUISITION IN GALAXY HALOS

International Nuclear Information System (INIS)

Stewart, Kyle R.; Brooks, Alyson M.; Bullock, James S.; Maller, Ariyeh H.; Diemand, Jürg; Wadsley, James; Moustakas, Leonidas A.

2013-01-01

We use high-resolution cosmological hydrodynamic simulations to study the angular momentum acquisition of gaseous halos around Milky-Way-sized galaxies. We find that cold mode accreted gas enters a galaxy halo with ∼70% more specific angular momentum than dark matter averaged over cosmic time (though with a very large dispersion). In fact, we find that all matter has a higher spin parameter when measured at accretion than when averaged over the entire halo lifetime, and is well characterized by λ ∼ 0.1, at accretion. Combined with the fact that cold flow gas spends a relatively short time (1-2 dynamical times) in the halo before sinking to the center, this naturally explains why cold flow halo gas has a specific angular momentum much higher than that of the halo and often forms ''cold flow disks.'' We demonstrate that the higher angular momentum of cold flow gas is related to the fact that it tends to be accreted along filaments.

NEW CONSTRAINTS ON THE GALACTIC HALO MAGNETIC FIELD USING ROTATION MEASURES OF EXTRAGALACTIC SOURCES TOWARD THE OUTER GALAXY

International Nuclear Information System (INIS)

Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown, J. C.; Van Eck, C. L.; Stil, J. M.; Taylor, A. R.; Haverkorn, M.; Kronberg, P. P.; Shukurov, A.

2012-01-01

We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100°-117°, within 30° of the Galactic plane. For |b| –2 and –62 ± 5 rad m –2 in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2 μG (7 μG) at a height 0.8-2 kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.

THE ELM SURVEY. III. A SUCCESSFUL TARGETED SURVEY FOR EXTREMELY LOW MASS WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Brown, Warren R.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138 (United States); Kilic, Mukremin [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States); Allende Prieto, Carlos, E-mail: wbrown@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: kilic@ou.edu, E-mail: callende@iac.es [Instituto de Astrofisica de Canarias, E-38205, La Laguna, Tenerife (Spain)

2012-01-10

Extremely low mass (ELM) white dwarfs (WDs) with masses < 0.25 M{sub Sun} are rare objects that result from compact binary evolution. Here, we present a targeted spectroscopic survey of ELM WD candidates selected by color. The survey is 71% complete and has uncovered 18 new ELM WDs. Of the seven ELM WDs with follow-up observations, six are short-period binaries and four have merger times less than 5 Gyr. The most intriguing object, J1741+6526, likely has either a pulsar companion or a massive WD companion making the system a possible supernova Type Ia or an Ia progenitor. The overall ELM survey has now identified 19 double degenerate binaries with <10 Gyr merger times. The significant absence of short orbital period ELM WDs at cool temperatures suggests that common envelope evolution creates ELM WDs directly in short period systems. At least one-third of the merging systems are halo objects, thus ELM WD binaries continue to form and merge in both the disk and the halo.

HBT+: an improved code for finding subhaloes and building merger trees in cosmological simulations

Science.gov (United States)

Han, Jiaxin; Cole, Shaun; Frenk, Carlos S.; Benitez-Llambay, Alejandro; Helly, John

2018-02-01

Dark matter subhalos are the remnants of (incomplete) halo mergers. Identifying them and establishing their evolutionary links in the form of merger trees is one of the most important applications of cosmological simulations. The HBT (Hierachical Bound-Tracing) code identifies haloes as they form and tracks their evolution as they merge, simultaneously detecting subhaloes and building their merger trees. Here we present a new implementation of this approach, HBT+ , that is much faster, more user friendly, and more physically complete than the original code. Applying HBT+ to cosmological simulations, we show that both the subhalo mass function and the peak-mass function are well fitted by similar double-Schechter functions. The ratio between the two is highest at the high-mass end, reflecting the resilience of massive subhaloes that experience substantial dynamical friction but limited tidal stripping. The radial distribution of the most-massive subhaloes is more concentrated than the universal radial distribution of lower mass subhaloes. Subhalo finders that work in configuration space tend to underestimate the masses of massive subhaloes, an effect that is stronger in the host centre. This may explain, at least in part, the excess of massive subhaloes in galaxy cluster centres inferred from recent lensing observations. We demonstrate that the peak-mass function is a powerful diagnostic of merger tree defects, and the merger trees constructed using HBT+ do not suffer from the missing or switched links that tend to afflict merger trees constructed from more conventional halo finders. We make the HBT+ code publicly available.

How do stars affect ψDM halos?

Science.gov (United States)

Chan, James H. H.; Schive, Hsi-Yu; Woo, Tak-Pong; Chiueh, Tzihong

2018-04-01

Wave dark matter (ψDM) predicts a compact soliton core and a granular halo in every galaxy. This work presents the first simulation study of an elliptical galaxy by including both stars and ψDM, focusing on the systematic changes of the central soliton and halo granules. With the addition of stars in the inner halo, we find the soliton core consistently becomes more prominent by absorbing mass from the host halo than that without stars, and the halo granules become "non-isothermal", "hotter" in the inner halo and "cooler" in the outer halo, as opposed to the isothermal halo in pure ψDM cosmological simulations. Moreover, the composite (star+ψDM) mass density is found to follow a r-2 isothermal profile near the half-light radius in most cases. Most striking is the velocity dispersion of halo stars that increases rapidly toward the galactic center by a factor of at least 2 inside the half-light radius caused by the deepened soliton gravitational potential, a result that compares favorably with observations of elliptical galaxies and bulges in spiral galaxies. However in some rare situations we find a phase segregation turning a compact distribution of stars into two distinct populations with high and very low velocity dispersions; while the high-velocity component mostly resides in the halo, the very low-velocity component is bound to the interior of the soliton core, resembling stars in faint dwarf spheroidal galaxies.

Triadic split-merge sampler

Science.gov (United States)

van Rossum, Anne C.; Lin, Hai Xiang; Dubbeldam, Johan; van der Herik, H. Jaap

2018-04-01

In machine vision typical heuristic methods to extract parameterized objects out of raw data points are the Hough transform and RANSAC. Bayesian models carry the promise to optimally extract such parameterized objects given a correct definition of the model and the type of noise at hand. A category of solvers for Bayesian models are Markov chain Monte Carlo methods. Naive implementations of MCMC methods suffer from slow convergence in machine vision due to the complexity of the parameter space. Towards this blocked Gibbs and split-merge samplers have been developed that assign multiple data points to clusters at once. In this paper we introduce a new split-merge sampler, the triadic split-merge sampler, that perform steps between two and three randomly chosen clusters. This has two advantages. First, it reduces the asymmetry between the split and merge steps. Second, it is able to propose a new cluster that is composed out of data points from two different clusters. Both advantages speed up convergence which we demonstrate on a line extraction problem. We show that the triadic split-merge sampler outperforms the conventional split-merge sampler. Although this new MCMC sampler is demonstrated in this machine vision context, its application extend to the very general domain of statistical inference.

Mass and environment as drivers of galaxy evolution. III. The constancy of the faint-end slope and the merging of galaxies

Energy Technology Data Exchange (ETDEWEB)

Peng, Ying-jie; Lilly, Simon J.; Carollo, Marcella [Institute of Astronomy, ETH Zurich, 8093 Zurich (Switzerland); Renzini, Alvio [INAF-Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy)

2014-08-01

Using our continuity approach, we explore the underlying connections between the evolution of the faint-end slope α{sub s} of the stellar mass function of star-forming galaxies, the logarithmic slope β of the specific star formation rate (sSFR)-mass relation, and the merging of galaxies. We derive analytically the consequences of the observed constancy of α{sub s} since redshifts of at least z ∼ 2. If the logarithmic slope β of the sSFR-mass relation is negative, then the faint-end slope α{sub s} should quickly diverge due to the differential mass increase of galaxies on the star-forming main sequence, and this will also quickly destroy the Schechter form of the mass function. This problem can be solved by removing low-mass galaxies by merging them into more massive galaxies. We quantify this process by introducing the specific merger mass rate (sMMR) as the specific rate of mass added to a given galaxy through mergers. For a modest negative value of β ∼ –0.1, an average sMMR ∼ 0.1 sSFR across the population is required to keep α{sub s} constant with epoch, as observed. This in turn implies a merger rate of ∼0.2 sSFR for major mergers, which is consistent with the available observational estimates. More negative values of β require higher sMMR and higher merger rates, and the steepening of the mass function becomes impossible to control for β < –(α{sub s} + 2). The close link that is required between the in situ sSFR and the sMMR probably arises because both are closely linked to the buildup of dark matter halos. These new findings further develop the formalism for the evolving galaxy population that we introduced earlier and show how striking symmetries in the galaxy population can emerge as the result of deep links between the physical processes involved.

Characteristic time for halo current growth and rotation

Energy Technology Data Exchange (ETDEWEB)

Boozer, Allen H., E-mail: ahb17@columbia.edu [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2015-10-15

A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channel in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141 687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halo currents and are discussed as a summary of the theory.

LoCuSS: The infall of X-ray groups onto massive clusters

Science.gov (United States)

Haines, C. P.; Finoguenov, A.; Smith, G. P.; Babul, A.; Egami, E.; Mazzotta, P.; Okabe, N.; Pereira, M. J.; Bianconi, M.; McGee, S. L.; Ziparo, F.; Campusano, L. E.; Loyola, C.

2018-03-01

Galaxy clusters are expected to form hierarchically in a ΛCDM universe, growing primarily through mergers with lower mass clusters and the continual accretion of group-mass halos. Galaxy clusters assemble late, doubling their masses since z ˜ 0.5, and so the outer regions of clusters should be replete with accreting group-mass systems. We present an XMM-Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters ( ˜ 1015 M⊙) at z ˜ 0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2 × 1013 - 7 × 1014 M⊙, and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is ˜25 × higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2 × 1014 M⊙, or 19 ± 5% of the mass within the primary cluster itself. We estimate that ˜1015 M⊙ clusters increase their masses by 16 ± 4% between z = 0.223 and the present day due to the accretion of groups with M200 ≥ 1013.2 M⊙. This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound within halos. The mass function of the infalling X-ray groups appears significantly top heavy with respect to that of "field" X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter halos being biased tracers of the underlying large-scale density distribution.

ULTRAVIOLET HALOS AROUND SPIRAL GALAXIES. I. MORPHOLOGY

Energy Technology Data Exchange (ETDEWEB)

Hodges-Kluck, Edmund; Cafmeyer, Julian; Bregman, Joel N., E-mail: hodgeskl@umich.edu [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)

2016-12-10

We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that ultraviolet (UV) halos occur around each galaxy in our sample. Around most galaxies the halos form a thick, diffuse disk-like structure, but starburst galaxies with galactic superwinds have qualitatively different halos that are more extensive and have filamentary structure. The spatial coincidence of the UV halos above star-forming regions, the lack of consistent association with outflows or extraplanar ionized gas, and the strong correlation between the halo and galaxy UV luminosity suggest that the UV light is an extragalactic reflection nebula. UV halos may thus represent 10{sup 6}–10{sup 7} M {sub ⊙} of dust within 2–10 kpc of the disk, whose properties may change with height in starburst galaxies.

MODIFIED GRAVITY SPINS UP GALACTIC HALOS

Energy Technology Data Exchange (ETDEWEB)

Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of); Zhao, Gong-Bo [National Astronomy Observatories, Chinese Academy of Science, Beijing 100012 (China); Li, Baojiu [Institute of Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Koyama, Kazuya, E-mail: jounghun@astro.snu.ac.kr [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom)

2013-01-20

We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

Energy Technology Data Exchange (ETDEWEB)

Yan, Peng-Fei; Yuan, Qi-Rong [Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023 (China); Zhang, Li [QuFu Education Bureau, QuFu 273100 (China); Zhou, Xu, E-mail: pfyan0822@sina.com, E-mail: yuanqirong@njnu.edu.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2014-05-01

Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have

Testing the dark matter origin of the WMAP-Planck haze with radio observations of spiral galaxies

Energy Technology Data Exchange (ETDEWEB)

Carlson, Eric; Linden, Tim; Profumo, Stefano [Department of Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064 (United States); Hooper, Dan, E-mail: erccarls@ucsc.edu, E-mail: dhooper@fnal.gov, E-mail: tlinden@ucsc.edu, E-mail: profumo@ucsc.edu [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States)

2013-07-01

If the Galactic WMAP radio haze, as recently confirmed by Planck, is produced by dark matter annihilation or decay, similar diffuse radio halos should exist around other galaxies with physical properties comparable to the Milky Way. If instead the haze is due to an astrophysical mechanism peculiar to the Milky Way or to a transient event, a similar halo need not exist around all Milky Way ''twins''. We use radio observations of 66 spiral galaxies to test the dark matter origin of the haze. We select galaxies based on morphological type and maximal rotational velocity, and obtain their luminosities from a 1.49 GHz catalog and additional radio observations at other frequencies. We find many instances of galaxies with radio emission that is less than 5% as bright as naively expected from dark matter models that could produce the Milky Way haze, and at least 3 galaxies that are less than 1% as bright as expected, assuming dark matter distributions, magnetic fields, and cosmic ray propagation parameters equal to those of the Milky Way. For reasonable ranges for the variation of these parameters, we estimate the fraction of galaxies that should be expected to be significantly less bright in radio, and argue that this is marginally compatible with the observed distribution. While our findings therefore cannot rule out a dark matter origin for the radio haze at this time, we find numerous examples (including the Andromeda Galaxy) where, if dark matter is indeed the origin of the Milky Way haze, some mechanism must be in place to suppress the corresponding haze of the external galaxy. We point out that Planck data will offer opportunities to improve this type of constraint in a highly relevant frequency range and for a potentially larger set of candidate galaxies.

Unbound particles in dark matter halos

Energy Technology Data Exchange (ETDEWEB)

Behroozi, Peter S.; Loeb, Abraham; Wechsler, Risa H.

2013-06-13

We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches for intergalactic supernovae.

Molecular line study of massive star-forming regions from the Red MSX Source survey

Science.gov (United States)

Yu, Naiping; Wang, Jun-Jie

2014-05-01

In this paper, we have selected a sample of massive star-forming regions from the Red MSX Source survey, in order to study star formation activities (mainly outflow and inflow signatures). We have focused on three molecular lines from the Millimeter Astronomy Legacy Team Survey at 90 GHz: HCO+(1-0), H13CO+(1-0) and SiO(2-1). According to previous observations, our sources can be divided into two groups: nine massive young stellar object candidates (radio-quiet) and 10 H II regions (which have spherical or unresolved radio emissions). Outflow activities have been found in 11 sources, while only three show inflow signatures in all. The high outflow detection rate means that outflows are common in massive star-forming regions. The inflow detection rate was relatively low. We suggest that this was because of the beam dilution of the telescope. All three inflow candidates have outflow(s). The outward radiation and thermal pressure from the central massive star(s) do not seem to be strong enough to halt accretion in G345.0034-00.2240. Our simple model of G318.9480-00.1969 shows that it has an infall velocity of about 1.8 km s-1. The spectral energy distribution analysis agrees our sources are massive and intermediate-massive star formation regions.

Halos and related structures

DEFF Research Database (Denmark)

Riisager, Karsten

2013-01-01

The halo structure originated from nuclear physics but is now encountered more widely. It appears in loosely bound, clustered systems where the spatial extension of the system is significantly larger than that of the binding potentials. A review is given on our current understanding of these stru......The halo structure originated from nuclear physics but is now encountered more widely. It appears in loosely bound, clustered systems where the spatial extension of the system is significantly larger than that of the binding potentials. A review is given on our current understanding...... of these structures, with an emphasis on how the structures evolve as more cluster components are added and on the experimental situation concerning halo states in light nuclei....

Halo formation in three-dimensional bunches

International Nuclear Information System (INIS)

Gluckstern, R.L.; Fedotov, A.V.; Kurennoy, S.; Ryne, R.

1998-01-01

We have constructed, analytically and numerically, a class of self-consistent six-dimensional (6D) phase space stationary distributions. Stationary distributions allow us to study the halo development mechanism without it being obscured by beam redistribution and its effect on halo formation. The beam is then mismatched longitudinally and/or transversely, and we explore the formation of longitudinal and transverse halos in 3D axisymmetric beam bunches. We find that the longitudinal halo forms first for comparable longitudinal and transverse mismatches because the longitudinal tune depression is more severe than the transverse one for elongated bunches. Of particular importance is the result that, due to the coupling between longitudinal and transverse motion, a longitudinal or transverse halo is observed for a mismatch less than 10% if the mismatch in the other plane is large. copyright 1998 The American Physical Society

Galactic synchrotron emission from WIMPs at radio frequencies

International Nuclear Information System (INIS)

Fornengo, Nicolao; Regis, Marco; Lineros, Roberto A.; Taoso, Marco

2012-01-01

Dark matter annihilations in the Galactic halo inject relativistic electrons and positrons which in turn generate a synchrotron radiation when interacting with the galactic magnetic field. We calculate the synchrotron flux for various dark matter annihilation channels, masses, and astrophysical assumptions in the low-frequency range and compare our results with radio surveys from 22 MHz to 1420 MHz. We find that current observations are able to constrain particle dark matter with ''thermal'' annihilation cross-sections, i.e. (σv) = 3 × 10 −26 cm 3 s −1 , and masses M DM ∼<10 GeV. We discuss the dependence of these bounds on the astrophysical assumptions, namely galactic dark matter distribution, cosmic rays propagation parameters, and structure of the galactic magnetic field. Prospects for detection in future radio surveys are outlined

The cosmic evolution of massive black holes in the Horizon-AGN simulation

Science.gov (United States)

Volonteri, M.; Dubois, Y.; Pichon, C.; Devriendt, J.

2016-08-01

We analyse the demographics of black holes (BHs) in the large-volume cosmological hydrodynamical simulation Horizon-AGN. This simulation statistically models how much gas is accreted on to BHs, traces the energy deposited into their environment and, consequently, the back-reaction of the ambient medium on BH growth. The synthetic BHs reproduce a variety of observational constraints such as the redshift evolution of the BH mass density and the mass function. Strong self-regulation via AGN feedback, weak supernova feedback, and unresolved internal processes result in a tight BH-galaxy mass correlation. Starting at z ˜ 2, tidal stripping creates a small population of BHs over-massive with respect to the halo. The fraction of galaxies hosting a central BH or an AGN increases with stellar mass. The AGN fraction agrees better with multi-wavelength studies, than single-wavelength ones, unless obscuration is taken into account. The most massive haloes present BH multiplicity, with additional BHs gained by ongoing or past mergers. In some cases, both a central and an off-centre AGN shine concurrently, producing a dual AGN. This dual AGN population dwindles with decreasing redshift, as found in observations. Specific accretion rate and Eddington ratio distributions are in good agreement with observational estimates. The BH population is dominated in turn by fast, slow, and very slow accretors, with transitions occurring at z = 3 and z = 2, respectively.

A tangent subsolar merging line

International Nuclear Information System (INIS)

Crooker, N.U.; Siscoe, G.L.; Toffoletto, F.R.

1990-01-01

The authors describe a global magnetospheric model with a single subsolar merging line whose position is determined neither locally by the relative orientations and strengths of the merging fields nor globally by the orientation of a separator line--the governing parameters of most previous models--but by the condition of tangential contact between the external field and the magnetopause. As in previous models, the tilt of the merging line varies with IMF orientation, but here it also depends upon the ratio of Earth's magnetic flux that leaks out of the magnetopause to IMF flux that penetrates in. In the limiting case treated by Alekseyev and Belen'kaya, with no leakage of Earth's field and total IMF penetration, the merging line forms a great circle around a spherical magnetosphere where undeviated IMF lines lie tangent to its surface. This tangent merging line lies perpendicular to the IMF. They extend their work to the case of finite leakage and partial penetration, which distort the IMF into a draped pattern, thus changing the locus of tangency to the sphere. In the special case where the penetrating IMF flux is balanced by an equal amount of Earth flux leakage, the tangent merging line bisects the angle between the IMF and Earth's northward subsolar field. This result is identical to the local merging line model result for merging fields with equal magnitude. Here a global flux balance condition replaces the local equal magnitude condition

Magnetized environs of a repeating radio burst

Science.gov (United States)

Metzger, Brian D.

2018-03-01

One of the astrophysical sources that gives rise to the mysterious transients known as fast radio bursts is embedded in a highly magnetized environment, such as the vicinity of an accreting massive black hole or the birth nebula of a highly magnetized neutron star.

Radio continuum processes in clusters of galaxies; Proceedings of the Workshop, Green Bank, WV, Aug. 4-8, 1986

International Nuclear Information System (INIS)

O'dea, C.P.; Uson, J.M.

1986-01-01

Recent observational and theoretical investigations of clusters of galaxies are examined in reviews and reports. Topics addressed include radio surveys of clusters, accretion flows, wide-angle-tail radio sources, the interaction of radio sources with the intracluster medium, diffuse emission in clusters, cluster dynamics, and the environment of powerful radio sources. Particular attention is given to a local perspective on galaxies in rich clusters, X-ray observations of clusters, VLA observations of distant clusters, the halo of Vir A at 327 MHz, Exosat observations of the Vir Cluster, accretion flows in elliptical galaxies, jet disruption in wide-angle-tail radio galaxies, beam trajectories in the intracluster medium, the Suniaev-Zel'dovich effect, dark matter in clusters, and the H I environment of high-redshift quasars

Properties of Radio Sources in the FRB 121102 Field

Science.gov (United States)

Bower, Geoffrey C.; Chatterjee, Shami; Wharton, Robert; Law, Casey J.; Hessels, Jason; Spolaor, Sarah; Abruzzo, Matthew W.; Bassa, Cees; Butler, Bryan J.; Cordes, James M.; Demorest, Paul; Kaspi, Victoria M.; McLaughlin, Maura; Ransom, Scott M.; Scholz, Paul; Seymour, Andrew; Spitler, Laura; Tendulkar, Shriharsh P.; PALFA Survey; VLA+AO FRB121102 Simultaneous Campaign Team; EVN FRB121102 Campaign Team; Realfast Team

2017-01-01

Fast radio bursts are millisecond duration radio pulses of unknown origin. With dispersion measures substantially in excess of expected Galactic contributions, FRBs are inferred to originate extragalactically, implying very high luminosities. Models include a wide range of high energy systems such as magnetars, merging neutron star binaries, black holes, and strong stellar magnetic fields driving coherent radio emission. Central to the mystery of FRB origins are the absence of confirmed host objects at any wavelength. This is primarily the result of the poor localization from single dish detection of FRBs. Of the approximately 20 known examples, only one, FRB 121102, has been observed to repeat. This repetition presents an opportunity for detailed follow-up if interferometric localization to arcsecond accuracy can be obtained. The Very Large Array has previously been used to localize individual pulses from pulsars and rotating radio transients to arcsecond localizaiton. We present here the results of radio observations of the field of FRB 121102 that permit us to constrain models of possible progenitors of this bursting source. These observations can characterize active galactic nuclei, stars, and other progenitor objects.

Weighing halo nuclides

International Nuclear Information System (INIS)

Lunney, D.

2009-01-01

Weak binding energy is one of the fundamental criteria characterizing the unique properties of nuclear halos. As such, it must be known with great accuracy and is best obtained through direct mass measurements. The global mass market is now a competitive one. Of the many investment vehicles, the Penning trap has emerged as providing the best rate of return and reliability. We examine mass-market trends, highlighting the recent cases of interest. We also hazard a prediction for the halo futures market. (author)

Merging By Decentralized Eventual Consistency Algorithms

Directory of Open Access Journals (Sweden)

Ahmed-Nacer Mehdi

2015-12-01

Full Text Available Merging mechanism is an essential operation for version control systems. When each member of collaborative development works on an individual copy of the project, software merging allows to reconcile modifications made concurrently as well as managing software change through branching. The collaborative system is in charge to propose a merge result that includes user’s modifications. Theusers now have to check and adapt this result. The adaptation should be as effort-less as possible, otherwise, the users may get frustrated and will quit the collaboration. This paper aims to reduce the conflicts during the collaboration and im prove the productivity. It has three objectives: study the users’ behavior during the collaboration, evaluate the quality of textual merging results produced by specific algorithms and propose a solution to improve the r esult quality produced by the default merge tool of distributed version control systems. Through a study of eight open-source repositories totaling more than 3 million lines of code, we observe the behavior of the concurrent modifications during t he merge p rocedure. We i dentified when th e ex isting merge techniques under-perform, and we propose solutions to improve the quality of the merge. We finally compare with the traditional merge tool through a large corpus of collaborative editing.

The phase-space structure of a dark-matter halo: Implications for dark-matter direct detection experiments

International Nuclear Information System (INIS)

Helmi, Amina; White, Simon D.M.; Springel, Volker

2002-01-01

We study the phase-space structure of a dark-matter halo formed in a high resolution simulation of a ΛCDM cosmology. Our goal is to quantify how much substructure is left over from the inhomogeneous growth of the halo, and how it may affect the signal in experiments aimed at detecting the dark matter particles directly. If we focus on the equivalent of 'solar vicinity', we find that the dark matter is smoothly distributed in space. The probability of detecting particles bound within dense lumps of individual mass less than 10 7 M · h -1 is small, less than 10 -2 . The velocity ellipsoid in the solar neighborhood deviates only slightly from a multivariate Gaussian, and can be thought of as a superposition of thousands of kinematically cold streams. The motions of the most energetic particles are, however, strongly clumped and highly anisotropic. We conclude that experiments may safely assume a smooth multivariate Gaussian distribution to represent the kinematics of dark-matter particles in the solar neighborhood. Experiments sensitive to the direction of motion of the incident particles could exploit the expected anisotropy to learn about the recent merging history of our Galaxy

Supersonic gas streams enhance the formation of massive black holes in the early universe.

Science.gov (United States)

Hirano, Shingo; Hosokawa, Takashi; Yoshida, Naoki; Kuiper, Rolf

2017-09-29

The origin of super-massive black holes in the early universe remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We report numerical simulations of early black hole formation starting from realistic cosmological conditions. Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a protogalactic halo. A protostar is formed in the dense, turbulent gas cloud, and it grows by sporadic mass accretion until it acquires 34,000 solar masses. The massive star ends its life with a catastrophic collapse to leave a black hole-a promising seed for the formation of a monstrous black hole. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Analytic modeling of axisymmetric disruption halo currents

International Nuclear Information System (INIS)

Humphreys, D.A.; Kellman, A.G.

1999-01-01

Currents which can flow in plasma facing components during disruptions pose a challenge to the design of next generation tokamaks. Induced toroidal eddy currents and both induced and conducted poloidal ''halo'' currents can produce design-limiting electromagnetic loads. While induction of toroidal and poloidal currents in passive structures is a well-understood phenomenon, the driving terms and scalings for poloidal currents flowing on open field lines during disruptions are less well established. A model of halo current evolution is presented in which the current is induced in the halo by decay of the plasma current and change in enclosed toroidal flux while being convected into the halo from the core by plasma motion. Fundamental physical processes and scalings are described in a simplified analytic version of the model. The peak axisymmetric halo current is found to depend on halo and core plasma characteristics during the current quench, including machine and plasma dimensions, resistivities, safety factor, and vertical stability growth rate. Two extreme regimes in poloidal halo current amplitude are identified depending on the minimum halo safety factor reached during the disruption. A 'type I' disruption is characterized by a minimum safety factor that remains relatively high (typically 2 - 3, comparable to the predisruption safety factor), and a relatively low poloidal halo current. A 'type II' disruption is characterized by a minimum safety factor comparable to unity and a relatively high poloidal halo current. Model predictions for these two regimes are found to agree well with halo current measurements from vertical displacement event disruptions in DIII-D [T. S. Taylor, K. H. Burrell, D. R. Baker, G. L. Jackson, R. J. La Haye, M. A. Mahdavi, R. Prater, T. C. Simonen, and A. D. Turnbull, open-quotes Results from the DIII-D Scientific Research Program,close quotes in Proceedings of the 17th IAEA Fusion Energy Conference, Yokohama, 1998, to be published in

HALO | Arts at CERN

CERN Multimedia

Caraban Gonzalez, Noemi

2018-01-01

In 2015, the artists participated in a research residency at CERN and began to work with data captured by ATLAS, one of the four detectors at the Large Hadron Collider (LHC) that sits in a cavern 100 metres below ground near the main site of CERN, in Meyrin (Switzerland). For Art Basel, they created HALO, an installation that surrounds visitors with data collected by the ATLAS experiment at the LHC. HALO consists of a 10 m wide cylinder defined by vertical piano wires, within which a 4-m tall screen displays particle collisions. The data also triggers hammers that strike the vertical wires and set up vibrations to create a truly multisensory experience. More info: https://arts.cern/event/unveiling-halo-art-basel

Effective field theory description of halo nuclei

Science.gov (United States)

Hammer, H.-W.; Ji, C.; Phillips, D. R.

2017-10-01

Nuclear halos emerge as new degrees of freedom near the neutron and proton driplines. They consist of a core and one or a few nucleons which spend most of their time in the classically-forbidden region outside the range of the interaction. Individual nucleons inside the core are thus unresolved in the halo configuration, and the low-energy effective interactions are short-range forces between the core and the valence nucleons. Similar phenomena occur in clusters of 4He atoms, cold atomic gases near a Feshbach resonance, and some exotic hadrons. In these weakly-bound quantum systems universal scaling laws for s-wave binding emerge that are independent of the details of the interaction. Effective field theory (EFT) exposes these correlations and permits the calculation of non-universal corrections to them due to short-distance effects, as well as the extension of these ideas to systems involving the Coulomb interaction and/or binding in higher angular-momentum channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo nuclei, has been used to compute the properties of single-neutron, two-neutron, and single-proton halos of s-wave and p-wave type. This review summarizes these results for halo binding energies, radii, Coulomb dissociation, and radiative capture, as well as the connection of these properties to scattering parameters, thereby elucidating the universal correlations between all these observables. We also discuss how Halo EFT's encoding of the long-distance physics of halo nuclei can be used to check and extend ab initio calculations that include detailed modeling of their short-distance dynamics.

Dark matter haloes: a multistream view

Science.gov (United States)

Ramachandra, Nesar S.; Shandarin, Sergei F.

2017-09-01

Mysterious dark matter constitutes about 85 per cent of all masses in the Universe. Clustering of dark matter plays a dominant role in the formation of all observed structures on scales from a fraction to a few hundreds of Mega-parsecs. Galaxies play a role of lights illuminating these structures so they can be observed. The observations in the last several decades have unveiled opulent geometry of these structures currently known as the cosmic web. Haloes are the highest concentrations of dark matter and host luminous galaxies. Currently the most accurate modelling of dark matter haloes is achieved in cosmological N-body simulations. Identifying the haloes from the distribution of particles in N-body simulations is one of the problems attracting both considerable interest and efforts. We propose a novel framework for detecting potential dark matter haloes using the field unique for dark matter-multistream field. The multistream field emerges at the non-linear stage of the growth of perturbations because the dark matter is collisionless. Counting the number of velocity streams in gravitational collapses supplements our knowledge of spatial clustering. We assume that the virialized haloes have convex boundaries. Closed and convex regions of the multistream field are hence isolated by imposing a positivity condition on all three eigenvalues of the Hessian estimated on the smoothed multistream field. In a single-scale analysis of high multistream field resolution and low softening length, the halo substructures with local multistream maxima are isolated as individual halo sites.

The growth of galaxies and their gaseous haloes

NARCIS (Netherlands)

Voort, Frederieke van de

2012-01-01

Galaxies grow by accreting gas, which they need to form stars, from their surrounding haloes. These haloes, in turn, accrete gas from the diffuse intergalactic medium. Feedback from stars and black holes returns gas from the galaxy to the halo and can even expel it from the halo. This cycle of gas

Smooth halos in the cosmic web

Energy Technology Data Exchange (ETDEWEB)

Gaite, José, E-mail: jose.gaite@upm.es [Physics Dept., ETSIAE, IDR, Universidad Politécnica de Madrid, Pza. Cardenal Cisneros 3, E-28040 Madrid (Spain)

2015-04-01

Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ''smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.

Smooth halos in the cosmic web

International Nuclear Information System (INIS)

Gaite, José

2015-01-01

Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ''smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness

Imbalance in the Local Galactic halo?

International Nuclear Information System (INIS)

Croswell, K.; Latham, D.W.; Carney, B.W.; North Carolina Univ., Chapel Hill)

1987-01-01

In a kinematically biased sample of 119 single halo stars, 65 percent of the stars are traveling away from the plane of the Galaxy. Halo spectroscopic binaries do not show this imbalance. Other kinematically biased halo surveys exhibit the same effect. Combining these samples with those of the authors' results in 223 halo stars, 63 percent of which are heading away from the plane of the Galaxy. The probability that the first result could be obtained from a symmetric w velocity distribution is 0.2 percent; the probability that the second result could be so obtained is 0.02 percent. Single halo stars traveling away from the disk appear to have a larger w velocity dispersion than those traveling toward it. Selection effects are analyzed and rejected as the cause of the observed asymmetry. Possible mechanisms for producing the imbalance are discussed, but each has serious difficulties accounting for the observations. 28 references

GRAVITATIONALLY CONSISTENT HALO CATALOGS AND MERGER TREES FOR PRECISION COSMOLOGY

International Nuclear Information System (INIS)

Behroozi, Peter S.; Wechsler, Risa H.; Wu, Hao-Yi; Busha, Michael T.; Klypin, Anatoly A.; Primack, Joel R.

2013-01-01

We present a new algorithm for generating merger trees and halo catalogs which explicitly ensures consistency of halo properties (mass, position, and velocity) across time steps. Our algorithm has demonstrated the ability to improve both the completeness (through detecting and inserting otherwise missing halos) and purity (through detecting and removing spurious objects) of both merger trees and halo catalogs. In addition, our method is able to robustly measure the self-consistency of halo finders; it is the first to directly measure the uncertainties in halo positions, halo velocities, and the halo mass function for a given halo finder based on consistency between snapshots in cosmological simulations. We use this algorithm to generate merger trees for two large simulations (Bolshoi and Consuelo) and evaluate two halo finders (ROCKSTAR and BDM). We find that both the ROCKSTAR and BDM halo finders track halos extremely well; in both, the number of halos which do not have physically consistent progenitors is at the 1%-2% level across all halo masses. Our code is publicly available at http://code.google.com/p/consistent-trees. Our trees and catalogs are publicly available at http://hipacc.ucsc.edu/Bolshoi/.

Characteristics of halo current in JT-60U

International Nuclear Information System (INIS)

Neyatani, Y.; Nakamura, Y.; Yoshino, R.; Hatae, T.

1999-01-01

Halo currents and their toroidal peaking factor (TPF) have been measured in JT-60U by Rogowski coil type halo current sensors. The electron temperature in the halo region was around 10 eV at 1 ms before the timing of the maximum halo current. The maximum TPF*I h /I p0 was 0.52 in the operational range of I p = 0.7 ∼ 1.8 MA, B T = 2.2 ∼ 3.5 T, including ITER design parameters of κ > 1.6 and q 95 = 3, which was lower than that of the maximum value of ITER data base (0.75). The magnitude of halo currents tended to decrease with the increase in stored energy just before the energy quench and with the line integrated electron density at the time of the maximum halo current. A termination technique in which the current channel remains stationary was useful to avoid halo current generation. Intense neon gas puffing during the VDE was effective for reducing the halo currents. (author)

Characteristics of halo current in JT-60U

International Nuclear Information System (INIS)

Neyatani, Y.; Nakamura, Y.; Yoshino, R.; Hatae, T.

2001-01-01

Halo currents and their toroidal peaking factor (TPF) have been measured in JT-60U by Rogowski coil type halo current sensors. The electron temperature in the halo region was around 10 eV at 1 ms before the timing of the maximum halo current. The maximum TPF *I h /I p0 was 0.52 in the operational range of I p =0.7∼1.8MA, B T =2.2∼3.5T, including ITER design parameters of κ>1.6 and q 95 =3, which was lower than that of the maximum value of ITER data base (0.75). The magnitude of halo currents tended to decrease with the increase in stored energy just before the energy quench and with the line integrated electron density at the time of the maximum halo current. A termination technique in which the current channel remains stationary was useful to avoid halo current generation. Intense neon gas puffing during the VDE was effective for reducing the halo currents. (author)

A faint galaxy redshift survey behind massive clusters

Energy Technology Data Exchange (ETDEWEB)

Frye, Brenda Louise [Univ. of California, Berkeley, CA (United States)

1999-05-01

This thesis is concerned with the gravitational lensing effect by massive galaxy clusters. We have explored a new technique for measuring galaxy masses and for detecting high-z galaxies by their optical colors. A redshift survey has been obtained at the Keck for a magnitude limited sample of objects (I<23) behind three clusters, A1689, A2390, and A2218 within a radius of 0.5M pc. For each cluster we see both a clear trend of increasing flux and redshift towards the center. This behavior is the result of image magnifications, such that at fixed redshift one sees further down the luminosity function. The gradient of this magnification is, unlike measurements of image distortion, sensitive to the mass profile, and found to depart strongly from a pure isothermal halo. We have found that V RI color selection can be used effectively as a discriminant for finding high-z galaxies behind clusters and present five 4.1 < z < 5.1 spectra which are of very high quality due to their high mean magnification of ~20, showing strong, visibly-saturated interstellar metal lines in some cases. We have also investigated the radio ring lens PKS 1830-211, locating the source and multiple images and detected molecular absorption at mm wavelengths. Broad molecular absorption of width 1/40kms is found toward the southwest component only, where surprisingly it does not reach the base of the continuum, which implies incomplete coverage of the SW component by molecular gas, despite the small projected size of the source, less than 1/8h pc at the absorption redshift.

Dayside merging and cusp geometry

International Nuclear Information System (INIS)

Crooker, N.U.

1979-01-01

Geometrical considerations are presented to show that dayside magnetic merging when constrained to act only where the fields are antiparallel results in lines of merging that converge at the polar cusps. An important consequence of this geometry is that no accelerated flows are predicted across the dayside magnetopause. Acceleration owing to merging acts in opposition to the magnetosheath flow at the merging point and produces the variably directed, slower-than-magnetosheath flows observed in the entry layer. Another consequence of the merging geometry is that much of the time closed field lines constitute the subsolar region of the magnetopause. The manner in which the polar cap convection patterns predicted by the proposed geometry change as the interplanetary field is rotated through 360 0 provides a unifying description of how the observed single circular vortex and the crescent-shaped double vortex patterns mutually evolve under the influence of a single operating principle

The TESIS Project: Revealing Massive Early-Type Galaxies at z > 1

Science.gov (United States)

Saracco, P.; Longhetti, M.; Severgnini, P.; Della Ceca, R.; Braito, V.; Bender, R.; Drory, N.; Feulner, G.; Hopp, U.; Mannucci, F.; Maraston, C.

How and when present-day massive early-type galaxies built up and what type of evolution has characterized their growth (star formation and/or merging) still remain open issues. The different competing scenarios of galaxy formation predict much different properties of early-type galaxies at z > 1. The "monolithic" collapse predicts that massive spheroids formed at high redshift (z > 2.5-3) and that their comoving density is constant at z 1, their comoving density decreases from z = 0 to z ~ 1.5 and they should experience their last burst of star formation at z 1 can be probed observationally once a well defined sample of massive early-types at z > 1 is available. We are constructing such a sample through a dedicated near-IR very low resolution (λ/Δλ≃50) spectroscopic survey (TNG EROs Spectroscopic Identification Survey, TESIS, [6]) of a complete sample of 30 bright (K < 18.5) Extremely Red Objects (EROs).

A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34.

Science.gov (United States)

Riechers, Dominik A; Bradford, C M; Clements, D L; Dowell, C D; Pérez-Fournon, I; Ivison, R J; Bridge, C; Conley, A; Fu, Hai; Vieira, J D; Wardlow, J; Calanog, J; Cooray, A; Hurley, P; Neri, R; Kamenetzky, J; Aguirre, J E; Altieri, B; Arumugam, V; Benford, D J; Béthermin, M; Bock, J; Burgarella, D; Cabrera-Lavers, A; Chapman, S C; Cox, P; Dunlop, J S; Earle, L; Farrah, D; Ferrero, P; Franceschini, A; Gavazzi, R; Glenn, J; Solares, E A Gonzalez; Gurwell, M A; Halpern, M; Hatziminaoglou, E; Hyde, A; Ibar, E; Kovács, A; Krips, M; Lupu, R E; Maloney, P R; Martinez-Navajas, P; Matsuhara, H; Murphy, E J; Naylor, B J; Nguyen, H T; Oliver, S J; Omont, A; Page, M J; Petitpas, G; Rangwala, N; Roseboom, I G; Scott, D; Smith, A J; Staguhn, J G; Streblyanska, A; Thomson, A P; Valtchanov, I; Viero, M; Wang, L; Zemcov, M; Zmuidzinas, J

2013-04-18

Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts--that is, increased rates of star formation--in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ~5 (refs 2-4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.

Expanding radio astronomy in Africa

International Nuclear Information System (INIS)

Gaylard, M J

2013-01-01

The Square Kilometre Array (SKA) Organisation announced in May 2012 that its members had agreed on a dual site solution for the SKA [1]. South Africa's bid for hosting the SKA has caused a ramp up of radio astronomy in Africa. To develop technology towards the SKA, the South African SKA Project (SKA SA) built a protoype radio telescope in 2007, followed in 2010 the seven antenna Karoo Array Telescope (KAT-7). Next is the 64 antenna MeerKAT, which will merge into SKA Phase 1 in Africa. As SKA Phase 2 is intended to add a high resolution capability with baselines out to 3000 km, the SKA SA brought in partner countries in Africa to host outstations. South Africa has been working with the partners to build capacity to operate the SKA and to benefit from it. The SA Department of Science and Technology (DST) developed a proposal to establish radio telescopes in the partner countries to provide hands-on learning and a capability for Very Long Baseline Interferometry (VLBI) research. Redundant 30 m class satellite antennas are being incorporated in this project.

MINIMARS interim report appendix halo model and computer code

International Nuclear Information System (INIS)

Santarius, J.F.; Barr, W.L.; Deng, B.Q.; Emmert, G.A.

1985-01-01

A tenuous, cool plasma called the halo shields the core plasma in a tandem mirror from neutral gas and impurities. The neutral particles are ionized and then pumped by the halo to the end tanks of the device, since flow of plasma along field lines is much faster than radial flow. Plasma reaching the end tank walls recombines, and the resulting neutral gas is vacuum pumped. The basic geometry of the MINIMARS halo is shown. For halo modeling purposes, the core plasma and cold gas regions may be treated as single radial zones leading to halo source and sink terms. The halo itself is differential into two major radial zones: halo scraper and halo dump. The halo scraper zone is defined by the radial distance required for the ion end plugging potential to drop to the central cell value, and thus have no effect on axial confinement; this distance is typically a sloshing plug ion Larmor diameter. The outer edge of the halo dump zone is defined by the last central cell flux tube to pass through the choke coil. This appendix will summarize the halo model that has been developed for MINIMARS and the methodology used in implementing that model as a computer code

THE TILT OF THE HALO VELOCITY ELLIPSOID AND THE SHAPE OF THE MILKY WAY HALO

International Nuclear Information System (INIS)

Smith, Martin C.; Wyn Evans, N.; An, Jin H.

2009-01-01

A sample of ∼1800 halo subdwarf stars with radial velocities and proper motions is assembled from Bramich et al.'s light-motion catalog of 2008. This is based on the repeated multiband Sloan Digital Sky Survey photometric measurements in Stripe 82. Our sample of halo subdwarfs is extracted via a reduced proper motion diagram and distances are obtained using photometric parallaxes, thus giving full phase-space information. The tilt of the velocity ellipsoid with respect to the spherical polar coordinate system is computed and found to be consistent with zero for two of the three tilt angles, and very small for the third. We prove that if the inner halo is in a steady state and the triaxial velocity ellipsoid is everywhere aligned in spherical polar coordinates, then the potential must be spherically symmetric. The detectable, but very mild, misalignment with spherical polars is consistent with the perturbative effects of the Galactic disk on a spherical dark halo. Banana orbits are generated at the 1:1 resonance (in horizontal and vertical frequencies) by the disk. They populate Galactic potentials at the typical radii of our subdwarf sample, along with the much more dominant short-axis tubes. However, on geometric grounds alone, the tilt cannot vanish for the banana orbits and this leads to a slight, but detectable, misalignment. We argue that the tilt of the stellar halo velocity ellipsoid therefore provides a hitherto largely neglected but important line of argument that the Milky Way's dark halo, which dominates the potential, must be nearly spherical.

Fragmentation inside atomic cooling haloes exposed to Lyman-Werner radiation

Science.gov (United States)

Regan, John A.; Downes, Turlough P.

2018-04-01

Supermassive stars born in pristine environments in the early Universe hold the promise of being the seeds for the supermassive black holes observed as high redshift quasars shortly after the epoch of reionisation. H2 suppression is thought to be crucial in order to negate normal Population III star formation and allow high accretion rates to drive the formation of supermassive stars. Only in the cases where vigorous fragmentation is avoided will a monolithic collapse be successful, giving rise to a single massive central object. We investigate the number of fragmentation sites formed in collapsing atomic cooling haloes subject to various levels of background Lyman-Werner flux. The background Lyman-Werner flux manipulates the chemical properties of the gas in the collapsing halo by destroying H2. We find that only when the collapsing gas cloud shifts from the molecular to the atomic cooling regime is the degree of fragmentation suppressed. In our particular case, we find that this occurs above a critical Lyman-Werner background of J ˜ 10 J21. The important criterion being the transition to the atomic cooling regime rather than the actual value of J, which will vary locally. Once the temperature of the gas exceeds T ≳ 104 K and the gas transitions to atomic line cooling, then vigorous fragmentation is strongly suppressed.

Halo Mitigation Using Nonlinear Lattices

CERN Document Server

Sonnad, Kiran G

2005-01-01

This work shows that halos in beams with space charge effects can be controlled by combining nonlinear focusing and collimation. The study relies on Particle-in-Cell (PIC) simulations for a one dimensional, continuous focusing model. The PIC simulation results show that nonlinear focusing leads to damping of the beam oscillations thereby reducing the mismatch. It is well established that reduced mismatch leads to reduced halo formation. However, the nonlinear damping is accompanied by emittance growth causing the beam to spread in phase space. As a result, inducing nonlinear damping alone cannot help mitigate the halo. To compensate for this expansion in phase space, the beam is collimated in the simulation and further evolution of the beam shows that the halo is not regenerated. The focusing model used in the PIC is analysed using the Lie Transform perturbation theory showing that by averaging over a lattice period, one can reuduce the focusing force to a form that is identical to that used in the PIC simula...

Galactic synchrotron emission from WIMPs at radio frequencies

Energy Technology Data Exchange (ETDEWEB)

Fornengo, Nicolao; Regis, Marco [Dipartimento di Fisica Teorica, Università di Torino, Istituto Nazionale di Fisica Nucleare, via P. Giuria 1, I-10125 Torino (Italy); Lineros, Roberto A.; Taoso, Marco, E-mail: fornengo@to.infn.it, E-mail: rlineros@ific.uv.es, E-mail: regis@to.infn.it, E-mail: taoso@ific.uv.es [IFIC, CSIC-Universidad de Valencia, Ed. Institutos, Apdo. Correos 22085, E-46071 Valencia (Spain)

2012-01-01

Dark matter annihilations in the Galactic halo inject relativistic electrons and positrons which in turn generate a synchrotron radiation when interacting with the galactic magnetic field. We calculate the synchrotron flux for various dark matter annihilation channels, masses, and astrophysical assumptions in the low-frequency range and compare our results with radio surveys from 22 MHz to 1420 MHz. We find that current observations are able to constrain particle dark matter with ''thermal'' annihilation cross-sections, i.e. (σv) = 3 × 10{sup −26} cm{sup 3} s{sup −1}, and masses M{sub DM}∼<10 GeV. We discuss the dependence of these bounds on the astrophysical assumptions, namely galactic dark matter distribution, cosmic rays propagation parameters, and structure of the galactic magnetic field. Prospects for detection in future radio surveys are outlined.

FORMATION RATES OF POPULATION III STARS AND CHEMICAL ENRICHMENT OF HALOS DURING THE REIONIZATION ERA

International Nuclear Information System (INIS)

Trenti, Michele; Stiavelli, Massimo

2009-01-01

The first stars in the universe formed out of pristine primordial gas clouds that were radiatively cooled to a few hundreds of degrees kelvin either via molecular or atomic (Lyman-α) hydrogen lines. This primordial mode of star formation was eventually quenched once radiative and/or chemical (metal enrichment) feedbacks marked the transition to Population II stars. In this paper, we present a model for the formation rate of Population III stars based on Press-Schechter modeling coupled with analytical recipes for gas cooling and radiative feedback. Our model also includes a novel treatment for metal pollution based on self-enrichment due to a previous episode of Population III star formation in progenitor halos. With this model, we derive the star formation history of Population III stars, their contribution to the reionization of the universe and the time of the transition from Population III star formation in minihalos (M ∼ 10 6 M sun , cooled via molecular hydrogen) to that in more massive halos (M ∼> 2 x 10 7 M sun , where atomic hydrogen cooling is also possible). We consider a grid of models highlighting the impact of varying the values for the free parameters used, such as star formation and feedback efficiency. The most critical factor is the assumption that only one Population III star is formed in a halo. In this scenario, metal-free stars contribute only to a minor fraction of the total number of photons required to reionize the universe. In addition, metal-free star formation is primarily located in minihalos, and chemically enriched halos become the dominant locus of star formation very early in the life of the universe-at redshift z ∼ 25-even assuming a modest fraction (0.5%) of enriched gas converted in stars. If instead multiple metal-free stars are allowed to form out of a single halo, then there is an overall boost of Population III star formation, with a consequent significant contribution to the reionizing radiation budget. In addition

Mass-invariance of the iron enrichment in the hot haloes of massive ellipticals, groups, and clusters of galaxies

Science.gov (United States)

Mernier, F.; de Plaa, J.; Werner, N.; Kaastra, J. S.; Raassen, A. J. J.; Gu, L.; Mao, J.; Urdampilleta, I.; Truong, N.; Simionescu, A.

2018-05-01

X-ray measurements find systematically lower Fe abundances in the X-ray emitting haloes pervading groups (kT ≲ 1.7 keV) than in clusters of galaxies. These results have been difficult to reconcile with theoretical predictions. However, models using incomplete atomic data or the assumption of isothermal plasmas may have biased the best fit Fe abundance in groups and giant elliptical galaxies low. In this work, we take advantage of a major update of the atomic code in the spectral fitting package SPEX to re-evaluate the Fe abundance in 43 clusters, groups, and elliptical galaxies (the CHEERS sample) in a self-consistent analysis and within a common radius of 0.1r500. For the first time, we report a remarkably similar average Fe enrichment in all these systems. Unlike previous results, this strongly suggests that metals are synthesised and transported in these haloes with the same average efficiency across two orders of magnitude in total mass. We show that the previous metallicity measurements in low temperature systems were biased low due to incomplete atomic data in the spectral fitting codes. The reasons for such a code-related Fe bias, also implying previously unconsidered biases in the emission measure and temperature structure, are discussed.

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

Energy Technology Data Exchange (ETDEWEB)

Gondolo, Paolo [Department of Physics, University of Utah, 115 South 1400 East #201, Salt Lake City, Utah 84112-0830 (United States); Scopel, Stefano, E-mail: paolo.gondolo@utah.edu, E-mail: scopel@sogang.ac.kr [Department of Physics, Sogang University, Seoul 121-742 (Korea, Republic of)

2017-09-01

We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame from which the unmodulated signal descends. Then we describe a mathematically-sound profile likelihood analysis in which the likelihood is profiled over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysis to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.

The Origin of Powerful Radio Sources

Science.gov (United States)

Wilson, A. S.; Colbert, E. J. M.

1995-05-01

Radio-loud active galaxies are associated with elliptical or elliptical-like galaxies, many of which appear to be the result of a recent merger. In contrast, radio-quiet active galaxies prefer spiral hosts. Despite the very large difference in radio luminosities between the two classes, their continua and line spectra from infrared through X-ray frequencies are very similar. In this paper, we describe recent developments of our model (Ap. J. 438, 62 1995) in which the radio-loud phenomenon is the result of a merger of two galaxies, with each galaxy nucleus containing a slowly (or non-) rotating supermassive black hole. It is envisaged that the two black holes eventually coalesce. For the small fraction of mergers in which the two holes are both massive and of comparable mass, a rapidly-spinning, high-mass hole results. The spin energy of a rapidly rotating 10(8-9) solar mass hole suffices to provide the ~ 10(60) ergs in relativistic particles and magnetic fields in the most energetic radio sources. Luminous radio-quiet active galaxies contain high-mass, slowly-rotating holes, with the infrared through X-ray emission of both classes being fuelled by accretion as commonly assumed. We discuss constraints on the model from the luminosity functions of radio-loud and radio-quiet galaxies and from the known cosmological evolution of the radio source population; this evolution is assumed to reflect higher galaxy merger rates in the past.

Extended radio emission and the nature of blazars

International Nuclear Information System (INIS)

Antonucci, R.R.J.; Ulvestad, J.S.

1985-01-01

The VLA has been used at 20 cm to map all 23 of the 54 confirmed blazars listed in the Angel and Stockman review paper that had not been mapped before at high resolution. (Blazars include BL Lac objects and optically violently variable quasars.) In addition, data on most of the previously mapped blazars have been reprocessed in order to achieve higher dynamic range. Extended emission has been detected associated with 49 of the 54 objects. The extended radio emission has been used to test the hypothesis that blazars are normal radio galaxies and radio quasars viewed along the jet axes. We find that blazars have substantial extended power, consistent with this hypothesis. Many have extended powers as high as the luminous Fanaroff-Riley class 2 radio doubles. The projected linear sizes are small, as expected from foreshortening of the extended sources, and many blazars have the expected core-halo morphology. There are also several small doubles, a head-tail source, and some one-sided sources, and these could be in cases where the line of sight is slightly off the jet axis, or projections of asymmetrical radio galaxies and quasars. The ratio of core to extended radio emission has been studied as a possible indicator of viewing aspect or beaming intensity. It is found to correlate with optical polarization, optical and radio core variability, and one-sided radio morphology. We can go beyond these consistency checks and work toward a proof of the hypothesis under discussion. The flux from the extended emission alone is sufficient in some blazars to qualify them for inclusion in the 3C and 4C catalogs. Suppose that the radio core emission is anisotropic, but the extended emission is predominantly isotropic. The isotropy of the extended emission implies that these blazars would be in the catalogs even if viewed from the side

Simulation of halo particles with Simpsons

International Nuclear Information System (INIS)

Machida, Shinji

2003-01-01

Recent code improvements and some simulation results of halo particles with Simpsons will be presented. We tried to identify resonance behavior of halo particles by looking at tune evolution of individual macro particle

Simulation of halo particles with Simpsons

Science.gov (United States)

Machida, Shinji

2003-12-01

Recent code improvements and some simulation results of halo particles with Simpsons will be presented. We tried to identify resonance behavior of halo particles by looking at tune evolution of individual macro particle.

Binaries discovered by the SPY project V. GD 687 - a massive double degenerate binary progenitor that will merge within a Hubble time

OpenAIRE

Geier, S.; Heber, U.; Kupfer, T.; Napiwotzki, R.

2010-01-01

Aims. The ESO SN Ia Progenitor Survey (SPY) aims at finding merging double degenerate binaries as candidates for supernova type Ia (SN Ia) explosions. A white dwarf merger has also been suggested to explain the formation of rare types of stars like R CrB, extreme helium or He sdO stars. Here we present the hot subdwarf B binary GD 687, which will merge in less than a Hubble time. Methods. The orbital parameters of the close binary have been determined from time resolved spectroscopy. Since GD...

Morphology of magnetic merging at the magnetopause

International Nuclear Information System (INIS)

Crooker, N.U.

1990-01-01

To illustrate the basic features of magnetospheric topology, the development of a global model is traced from the superposition of dipole and uniform fields to the effects of adding, in turn, diffusion regions, surface currents, and a magnetic field component normal to the magnetopause. The subsolar, antiparallel, tearing, and patchy merging geometries proposed in the past all emerge under various conditions, but models tht deduce merging geometry from global boundary conditions are lacking. An exception is a model in which the external field merges wherever it falls tangent to the magnetopause. The result is a subsolar merging line that has all the characteristics of early sketches based on local arguments. Magnetosheath plasma beta affects magnetospheric topology and, consequently, merging geometry. Low, high, and variable beta favor subsolar, tearing, and patchy merging, respectively. Proposed flux transfer event models of burst reconnection from a single merging line, flux ropes from multiple merging lines, and flux tube elbows from patches can also be categorized by plasma beta in the same respective order. The topological modeling reviewed here may prove to be most useful for interpreting merging results from MHD simulations. (author)

THE CIRCUMGALACTIC MEDIUM OF SUBMILLIMETER GALAXIES. I. FIRST RESULTS FROM A RADIO-IDENTIFIED SAMPLE

Energy Technology Data Exchange (ETDEWEB)

Fu, Hai; Mutel, R.; Isbell, J.; Lang, C.; McGinnis, D. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); Hennawi, J. F. [Max-Planck-Institut fur Astronomie, Heidelberg (Germany); Prochaska, J. X. [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Casey, C. [Department of Astronomy, the University of Texas at Austin, 2515 Speedway Blvd, Stop C1400, Austin, TX 78712 (United States); Cooray, A. [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Kereš, D. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States); Zhang, Z.-Y.; Michałowski, M. J. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Clements, D. [Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom); Mooley, K. [Oxford Centre For Astrophysical Surveys, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United States); Perley, D. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 København Ø (Denmark); Stockton, A. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Thompson, D. [Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 (United States)

2016-11-20

We present the first results from an ongoing survey to characterize the circumgalactic medium (CGM) of massive high-redshift galaxies detected as submillimeter galaxies (SMGs). We constructed a parent sample of 163 SMG–QSO pairs with separations less than ∼36″ by cross-matching far-infrared-selected galaxies from Herschel with spectroscopically confirmed QSOs. The Herschel sources were selected to match the properties of the SMGs. We determined the sub-arcsecond positions of six Herschel sources with the Very Large Array and obtained secure redshift identification for three of those with near-infrared spectroscopy. The QSO sightlines probe transverse proper distances of 112, 157, and 198 kpc at foreground redshifts of 2.043, 2.515, and 2.184, respectively, which are comparable to the virial radius of the ∼10{sup 13} M {sub ⊙} halos expected to host SMGs. High-quality absorption-line spectroscopy of the QSOs reveals systematically strong H i Ly α absorption around all three SMGs, with rest-frame equivalent widths of ∼2–3 Å. However, none of the three absorbers exhibit compelling evidence for optically thick H i gas or metal absorption, in contrast to the dominance of strong neutral absorbers in the CGM of luminous z ∼ 2 QSOs. The low covering factor of optically thick H i gas around SMGs tentatively indicates that SMGs may not have as prominent cool gas reservoirs in their halos as the coeval QSOs and that they may inhabit less massive halos than previously thought.

60-GHz Millimeter-Wave Radio: Principle, Technology, and New Results

Directory of Open Access Journals (Sweden)

Nan Guo

2006-12-01

Full Text Available The worldwide opening of a massive amount of unlicensed spectra around 60 GHz has triggered great interest in developing affordable 60-GHz radios. This interest has been catalyzed by recent advance of 60-GHz front-end technologies. This paper briefly reports recent work in the 60-GHz radio. Aspects addressed in this paper include global regulatory and standardization, justification of using the 60-GHz bands, 60-GHz consumer electronics applications, radio system concept, 60-GHz propagation and antennas, and key issues in system design. Some new simulation results are also given. Potentials and problems are explained in detail.

Local Group dSph radio survey with ATCA (III): constraints on particle dark matter

International Nuclear Information System (INIS)

Regis, Marco; Colafrancesco, Sergio; Profumo, Stefano; De Blok, W.J.G.; Massardi, Marcella; Richter, Laura

2014-01-01

We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors

Local Group dSph radio survey with ATCA (III): constraints on particle dark matter

Energy Technology Data Exchange (ETDEWEB)

Regis, Marco [Dipartimento di Fisica, Università di Torino, via P. Giuria 1, I-10125 Torino (Italy); Colafrancesco, Sergio [School of Physics, University of the Witwatersrand, Johannesburg (South Africa); Profumo, Stefano [Department of Physics, University of California, 1156 High St., Santa Cruz, CA 95064 (United States); De Blok, W.J.G. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo (Netherlands); Massardi, Marcella [INAF—Istituto di Radioastronomia, Via Gobetti 101, I-40129, Bologna (Italy); Richter, Laura, E-mail: regis@to.infn.it, E-mail: sergio.colafrancesco@wits.ac.za, E-mail: profumo@ucsc.edu, E-mail: blok@astron.nl, E-mail: massardi@ira.inaf.it, E-mail: laura@ska.ac.za [SKA South Africa, 3rd Floor, The Park, Park Road, Pinelands, 7405 (South Africa)

2014-10-01

We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors.

[Halos and multifocal intraocular lenses: origin and interpretation].

Science.gov (United States)

Alba-Bueno, F; Vega, F; Millán, M S

2014-10-01

To present the theoretical and experimental characterization of the halo in multifocal intraocular lenses (MIOL). The origin of the halo in a MIOL is the overlaying of 2 or more images. Using geometrical optics, it can be demonstrated that the diameter of each halo depends on the addition of the lens (ΔP), the base power (P(d)), and the diameter of the IOL that contributes to the «non-focused» focus. In the image plane that corresponds to the distance focus, the halo diameter (δH(d)) is given by: δH(d)=d(pn) ΔP/P(d), where d(pn) is the diameter of the IOL that contributes to the near focus. Analogously, in the near image plane the halo diameter (δH(n)) is: δH(n)=d(pd) ΔP/P(d), where d(pd) is the diameter of the IOL that contributes to the distance focus. Patients perceive halos when they see bright objects over a relatively dark background. In vitro, the halo can be characterized by analyzing the intensity profile of the image of a pinhole that is focused by each of the foci of a MIOL. A comparison has been made between the halos induced by different MIOL of the same base power (20D) in an optical bench. As predicted by theory, the larger the addition of the MIOL, the larger the halo diameter. For large pupils and with MIOL with similar aspheric designs and addition (SN6AD3 vs ZMA00), the apodized MIOL has a smaller halo diameter than a non-apodized one in distance vision, while in near vision the size is very similar, but the relative intensity is higher in the apodized MIOL. When comparing lenses with the same diffractive design, but with different spherical-aspheric base design (SN60D3 vs SN6AD3), the halo in distance vision of the spherical MIOL is larger, while in near vision the spherical IOL induces a smaller halo, but with higher intensity due to the spherical aberration of the distance focus in the near image. In the case of a trifocal-diffractive IOL (AT LISA 839MP) the most noticeable characteristic is the double-halo formation due to the 2 non

HIERARCHICAL FORMATION OF THE GALACTIC HALO AND THE ORIGIN OF HYPER METAL-POOR STARS

International Nuclear Information System (INIS)

Komiya, Yutaka; Habe, Asao; Suda, Takuma; Fujimoto, Masayuki Y.

2009-01-01

Extremely metal-poor (EMP) stars in the Galactic halo are unique probes into the early universe and the first stars. We construct a new program to calculate the formation history of EMP stars in the early universe with the chemical evolution, based on the merging history of the Galaxy. We show that the hierarchical structure formation model reproduces the observed metallicity distribution function and also the total number of observed EMP stars, when we take into account the high-mass initial mass function and the contribution of binaries, as proposed by Komiya et al. The low-mass survivors divide into two groups of those born before and after the mini-halos are polluted by their own first supernovae. The former has observational counterparts in the hyper metal-poor (HMP) stars below [Fe/H] - 4. In this Letter, we focus on the origin of the extremely small iron abundances of HMP stars. We compute the change in the surface abundances of individual stars through the accretion of the metal-enriched interstellar gas along with the dynamical and chemical evolution of the Galaxy, to demonstrate that after-birth pollution of Population III stars is sufficiently effective to explain the observed abundances of HMP stars. Metal pre-enrichment by possible pair instability supernovae is also discussed, to derive constraints on their roles and on the formation of the first low-mass stars.

On physical scales of dark matter halos

International Nuclear Information System (INIS)

Zemp, Marcel

2014-01-01

It is common practice to describe formal size and mass scales of dark matter halos as spherical overdensities with respect to an evolving density threshold. Here, we critically investigate the evolutionary effects of several such commonly used definitions and compare them to the halo evolution within fixed physical scales as well as to the evolution of other intrinsic physical properties of dark matter halos. It is shown that, in general, the traditional way of characterizing sizes and masses of halos dramatically overpredicts the degree of evolution in the last 10 Gyr, especially for low-mass halos. This pseudo-evolution leads to the illusion of growth even though there are no major changes within fixed physical scales. Such formal size definitions also serve as proxies for the virialized region of a halo in the literature. In general, those spherical overdensity scales do not coincide with the virialized region. A physically more precise nomenclature would be to simply characterize them by their very definition instead of calling such formal size and mass definitions 'virial'. In general, we find a discrepancy between the evolution of the underlying physical structure of dark matter halos seen in cosmological structure formation simulations and pseudo-evolving formal virial quantities. We question the importance of the role of formal virial quantities currently ubiquitously used in descriptions, models, and relations that involve properties of dark matter structures. Concepts and relations based on pseudo-evolving formal virial quantities do not properly reflect the actual evolution of dark matter halos and lead to an inaccurate picture of the physical evolution of our universe.

Galactic Angular Momentum in Cosmological Zoom-in Simulations. I. Disk and Bulge Components and the Galaxy-Halo Connection

Science.gov (United States)

Sokołowska, Aleksandra; Capelo, Pedro R.; Fall, S. Michael; Mayer, Lucio; Shen, Sijing; Bonoli, Silvia

2017-02-01

We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way-sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *-M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation {j}* \\propto {M}* α past major mergers, with α ˜ 0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α ˜ 1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (I.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

Halo scale predictions of symmetron modified gravity

Energy Technology Data Exchange (ETDEWEB)

Clampitt, Joseph; Jain, Bhuvnesh; Khoury, Justin, E-mail: clampitt@sas.upenn.edu, E-mail: bjain@physics.upenn.edu, E-mail: jkhoury@sas.upenn.edu [Center for Particle Cosmology and Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, PA 19104 (United States)

2012-01-01

We offer predictions of symmetron modified gravity in the neighborhood of realistic dark matter halos. The predictions for the fifth force are obtained by solving the nonlinear symmetron equation of motion in the spherical NFW approximation. In addition, we compare the three major known screening mechanisms: Vainshtein, Chameleon, and Symmetron around such dark matter halos, emphasizing the significant differences between them and highlighting observational tests which exploit these differences. Finally, we demonstrate the host halo environmental screening effect (''blanket screening'') on smaller satellite halos by solving for the modified forces around a density profile which is the sum of satellite and approximate host components.

THE EATING HABITS OF MILKY WAY-MASS HALOS: DESTROYED DWARF SATELLITES AND THE METALLICITY DISTRIBUTION OF ACCRETED STARS

International Nuclear Information System (INIS)

Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H.

2016-01-01

We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M vir  ∼ 10 12.1 M ⊙ ) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M star  ∼ 10 8 –10 10 M ⊙ . Halos with more quiescent accretion histories tend to have lower mass progenitors (10 8 –10 9 M ⊙ ), and lower overall accreted stellar masses. Ultra-faint mass (M star  < 10 5 M ⊙ ) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10 5  < M star /M ⊙  < 10 8 provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M star  > 10 8 M ⊙ can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo

Research Progresses of Halo Streams in the Solar Neighborhood

Science.gov (United States)

Xi-long, Liang; Jing-kun, Zhao; Yu-qin, Chen; Gang, Zhao

2018-01-01

The stellar streams originated from the Galactic halo may be detected when they pass by the solar neighborhood, and they still keep some information at their birth times. Thus, the investigation of halo streams in the solar neighborhood is very important for understanding the formation and evolution of our Galaxy. In this paper, the researches of halo streams in the solar neighborhood are briefly reviewed. We have introduced the methods how to detect the halo streams and identify their member stars, summarized the progresses in the observation of member stars of halo streams and in the study of their origins, introduced in detail how to analyze the origins of halo streams in the solar neighborhood by means of numerical simulation and chemical abundance, and finally discussed the prospects of the LAMOST and GAIA in the research of halo streams in the solar neighborhood.

Analog of the Milky Way and the Magellanic Clouds

Science.gov (United States)

Kohler, Susanna

2017-11-01

A hunt for merging dwarf galaxies has yielded an intriguing result: 180 million light-years away, a galaxy very similar to the Milky Way with two dwarf-galaxy satellites just like our own Magellanic clouds.Unusual SatellitesThe Large and Small Magellanic clouds, as observed from Earth. [ESO/S. Brunier]The Large and Small Magellanic clouds (LMC and SMC), the only bright and star-forming satellite galaxies around the Milky Way, have proven unusual in the universe: satellite pairs of LMCSMC mass are neither common in observation nor typically produced in numerical simulations of galaxy formation and evolution.Since the probability of having such an interacting pair of satellites in a massive halo is so low, this raises questions about how our system came about. Did the Magellanic clouds form independently around the Milky Way and then interact? Were they more recently captured as an already-merging pair of dwarf galaxies? Or is there some other explanation?If we could find other systems that look like the LMCSMCMilky-Way system, we might be able to learn more about pairs of dwarf galaxies and how they interact near the halos of large galaxies like the Milky Way. Conveniently, two researchers from Yonsei University in South Korea, Sanjaya Paudel and Chandreyee Sengupta, have now identified exactly such a system.The UGC 4703 pair of dwarf galaxies show a stellar bridge connecting them a sign of their past interaction, when tidal forces stripped material from them as they passed each other. [Adapted from Paudel Sengupta 2017]An Interacting PairHunting for merging dwarf galaxies in various environments, Paudel and Sengupta found UGC 4703, an interacting pair of dwarf galaxies that are located near the isolated spiral galaxy NGC 2718. This pair of satellites around the massive spiral bear a striking resemblance to the LMCSMC system around the Milky-Way.The authors performed a multi-wavelength study of the system using archival images from the Sloan Digital Sky Survey, The

Numerical Investigation of Merged and Non-merged Flame of a Twin Cavity Annular Trapped Vortex Combustor

Directory of Open Access Journals (Sweden)

Pravendra Kumar

2016-09-01

Full Text Available : The present work is focused to characterize numerically the merged and non-merged flame emanating from the cavities in downstream of twin cavity Annular Trapped Vortex Combustor (ATVC.The isotherm corresponding to the auto-ignition temperature is used to locate the merging point of the flame in the mainstream region along the combustor length. In present study, the cavity flame is said to be merged only if this isotherm corresponding to self-ignition temperature of methane is located within 20 percentage of the combustor length from aft wall of cavities. It is interesting to note that on increasing the power loading parameter (PLP in mainstream for a constant power loading parameter ratio (outer to inner cavity, the merging point gets shifted towards the cavity aft-wall. This leads to the reduction of combustor length and subsequent reduction in overall weight of the gas turbine engine.

Dynamics of merging: post-merger mixing and relaxation of an Illustris galaxy

Science.gov (United States)

Young, Anthony M.; Williams, Liliya L. R.; Hjorth, Jens

2018-02-01

During the merger of two galaxies, the resulting system undergoes violent relaxation and seeks stable equilibrium. However, the details of this evolution are not fully understood. Using Illustris simulation, we probe two physically related processes, mixing and relaxation. Though the two are driven by the same dynamics—global time-varying potential for the energy, and torques caused by asymmetries for angular momentum—we measure them differently. We define mixing as the redistribution of energy and angular momentum between particles of the two merging galaxies. We assess the degree of mixing as the difference between the shapes of their energy distributions, N(E)s, and their angular momentum distributions, N(L2)s. We find that the difference is decreasing with time, indicating mixing. To measure relaxation, we compare N(E) of the newly merged system to N(E) of a theoretical prediction for relaxed collisionless systems, DARKexp, and witness the system becoming more relaxed, in the sense that N(E) approaches DARKexp N(E). Because the dynamics driving mixing and relaxation are the same, the timescale is similar for both. We measure two sequential timescales: a rapid, 1 Gyr phase after the initial merger, during which the difference in N(E) of the two merging halos decreases by ~ 80%, followed by a slow phase, when the difference decreases by ~ 50% over ~ 8.5 Gyrs. This is a direct measurement of the relaxation timescale. Our work also draws attention to the fact that when a galaxy has reached Jeans equilibrium it may not yet have reached a fully relaxed state given by DARKexp, in that it retains information about its past history. This manifests itself most strongly in stars being centrally concentrated. We argue that it is particularly difficult for stars, and other tightly bound particles, to mix because they have less time to be influenced by the fluctuating potential, even across multiple merger events.

Cosmological radio emission induced by WIMP Dark Matter

International Nuclear Information System (INIS)

Fornengo, N.; Regis, M.; Lineros, R.; Taoso, M.

2012-01-01

We present a detailed analysis of the radio synchrotron emission induced by WIMP dark matter annihilations and decays in extragalactic halos. We compute intensity, angular correlation, and source counts and discuss the impact on the expected signals of dark matter clustering, as well as of other astrophysical uncertainties as magnetic fields and spatial diffusion. Bounds on dark matter microscopic properties are then derived, and, depending on the specific set of assumptions, they are competitive with constraints from other indirect dark matter searches. At GHz frequencies, dark matter sources can become a significant fraction of the total number of sources with brightness below the microJansky level. We show that, at this level of fluxes (which are within the reach of the next-generation radio surveys), properties of the faint edge of differential source counts, as well as angular correlation data, can become an important probe for WIMPs

Cosmological radio emission induced by WIMP Dark Matter

Energy Technology Data Exchange (ETDEWEB)

Fornengo, N.; Regis, M. [Dipartimento di Fisica Teorica, Università di Torino, via P. Giuria 1, I-10125 Torino (Italy); Lineros, R.; Taoso, M., E-mail: fornengo@to.infn.it, E-mail: rlineros@ific.uv.es, E-mail: regis@to.infn.it, E-mail: mtaoso@phas.ubc.ca [IFIC, CSIC-Universidad de Valencia, Ed. Institutos, Apdo. Correos 22085, E-46071 Valencia (Spain)

2012-03-01

We present a detailed analysis of the radio synchrotron emission induced by WIMP dark matter annihilations and decays in extragalactic halos. We compute intensity, angular correlation, and source counts and discuss the impact on the expected signals of dark matter clustering, as well as of other astrophysical uncertainties as magnetic fields and spatial diffusion. Bounds on dark matter microscopic properties are then derived, and, depending on the specific set of assumptions, they are competitive with constraints from other indirect dark matter searches. At GHz frequencies, dark matter sources can become a significant fraction of the total number of sources with brightness below the microJansky level. We show that, at this level of fluxes (which are within the reach of the next-generation radio surveys), properties of the faint edge of differential source counts, as well as angular correlation data, can become an important probe for WIMPs.

HaloPlex Targeted Resequencing for Mutation Detection in Clinical Formalin-Fixed, Paraffin-Embedded Tumor Samples.

Science.gov (United States)

Moens, Lotte N J; Falk-Sörqvist, Elin; Ljungström, Viktor; Mattsson, Johanna; Sundström, Magnus; La Fleur, Linnéa; Mathot, Lucy; Micke, Patrick; Nilsson, Mats; Botling, Johan

2015-11-01

In recent years, the advent of massively parallel next-generation sequencing technologies has enabled substantial advances in the study of human diseases. Combined with targeted DNA enrichment methods, high sequence coverage can be obtained for different genes simultaneously at a reduced cost per sample, creating unique opportunities for clinical cancer diagnostics. However, the formalin-fixed, paraffin-embedded (FFPE) process of tissue samples, routinely used in pathology departments, results in DNA fragmentation and nucleotide modifications that introduce a number of technical challenges for downstream biomolecular analyses. We evaluated the HaloPlex target enrichment system for somatic mutation detection in 80 tissue fractions derived from 20 clinical cancer cases with paired tumor and normal tissue available in both FFPE and fresh-frozen format. Several modifications to the standard method were introduced, including a reduced target fragment length and two strand capturing. We found that FFPE material can be used for HaloPlex-based target enrichment and next-generation sequencing, even when starting from small amounts of DNA. By specifically capturing both strands for each target fragment, we were able to reduce the number of false-positive errors caused by FFPE-induced artifacts and lower the detection limit for somatic mutations. We believe that the HaloPlex method presented here will be broadly applicable as a tool for somatic mutation detection in clinical cancer settings. Copyright © 2015 American Society for Investigative Pathology and the Association for Molecular Pathology. Published by Elsevier Inc. All rights reserved.

Colliding and merging galaxies. II. S0 galaxies with polar rings

International Nuclear Information System (INIS)

Schweizer, F.; Whitmore, B.D.; Rubin, V.C.

1983-01-01

We first present a detailed optical study of A0136-0801, a 16 1/2 -mag ''spindle'' galaxy girdled by a ring of gas, dust, and young stars. The spindle is a normal S0 disk seen nearly edge-on, as shown by its photometric profile and fast rotation (v/sub rot//sigma/sub v/ = 2.2); a prolate structure seems to be ruled out. The surrounding ring runs over the poles of this S0 disk and serves as a probe of the vertical potential. The ring motions suggest that a massive halo extends far beyond the S0 disk (out to 3R 25 ) and that this halo is more nearly spherical than flat. We then list 22 related galaxies and derive that a few percent of all field S0's possess near-polar rings or disks. We suggest that these structures are due to a second event, most likely the transfer of mass from a companion galaxy during a close encounter and occasionally also the merger of a companion. Although accretion occurs presumably at random angles, polar rings are favored statistically because of their slow differential precession and consequent longevity. Alternate evolutionary schemes are also discussed. Finally, we suggest that M82 may be forming a polar ring from former M81 material, and predict that the ''tilted bulge'' of UGC 7576 is an S0 disk seen nearly edge-on

HALOE test and evaluation software

Science.gov (United States)

Edmonds, W.; Natarajan, S.

1987-01-01

Computer programming, system development and analysis efforts during this contract were carried out in support of the Halogen Occultation Experiment (HALOE) at NASA/Langley. Support in the major areas of data acquisition and monitoring, data reduction and system development are described along with a brief explanation of the HALOE project. Documented listings of major software are located in the appendix.

Tracking the LHC halo

CERN Multimedia

Antonella Del Rosso

2015-01-01

In the LHC, beams of 25-ns-spaced proton bunches travel at almost the speed of light and pass through many different devices installed along the ring that monitor their properties. During their whirling motion, beam particles might interact with the collimation instrumentation or with residual gas in the vacuum chambers and this creates the beam halo – an annoying source of background for the physics data. Newly installed CMS sub-detectors are now able to monitor it.   The Beam Halo Monitors (BHM) are installed around the CMS rotating shielding. The BHM are designed and built by University of Minnesota, CERN, Princeton University, INFN Bologna and the National Technical University of Athens. (Image: Andrea Manna). The Beam Halo Monitor (BHM) is a set of 20 Cherenkov radiators – 10-cm-long quartz crystals – installed at each end of the huge CMS detector. Their design goal is to measure the particles that can cause the so-called “machine-induced...

Ionised Jets Associated With Massive Young Stellar Objects

Science.gov (United States)

Purser, Simon John Derek

2017-09-01

This thesis focuses on the phenomena of ionised jets associated with massive young stellar objects. Firstly a study was conducted with the aim to establish a statistical sample of such objects. Radio observations towards a sample of 49 MYSOs resulted in the detection of 28 objects classified as ionised jets. The jets’ radio luminosities scaled with their MYSOs’ bolometric luminosities in the same way as for low-mass examples. This infers that the jet launching and collimation mechanisms of high-mass jets are very similar to that in their low-mass counterparts and they are ejected for the last ≤65000 yr of the MYSO phase. Interestingly non-thermal emission was regularly detected towards spatially distinct radio lobes (associated with ˜50% of the jets), suggesting the presence of synchrotron emission and therefore, magnetic fields. With an average spectral index of ¯α=‑0. 55 (indicative of the 1st order Fermi acceleration mechanism) it is concluded these lobes are the result of shocks in the jets’ stream. My second science chapter is a study of radio variability, precession and proper motions towards a subset of objects from the first chapter. Over a two year time period, no significant variability and only one example of proper motion (1800±600 km s‑1) was detected. Precession was found to be commonplace however and if it arises as the result of binary interactions, we infer orbital radii between 30 and 1800 au for the binary companions. Lastly, high-resolution, VLA observations at C and Q-bands were analysed to extend the known sample of MYSOs harbouring ionised jets into the northern hemisphere. Only 3 radio sources were detected possessing jet-like characteristics towards the work’s sub-sample of 8 IRDCs containing 44 mm-cores (in our field of view), highlighting the radio-quiet (≳30μJy) nature of this early phase in massive star formation. Towards the RMS survey derived sample of 48 MYSOs, a total of 38 radio sources with jet

Halo vest effect on balance.

Science.gov (United States)

Richardson, J K; Ross, A D; Riley, B; Rhodes, R L

2000-03-01

To determine the effect of a halo vest, a cervical orthosis, on clinically relevant balance parameters. Subjects performed unipedal stance (with eyes open and closed, on both firm and soft surfaces) and functional reach, with and without the application of a halo vest. A convenience sample of 12 healthy young subjects, with an equal number of men and women. Seconds for unipedal stance (maximum 45); inches for functional reach. Both unipedal stance times and functional reach (mean +/- standard deviation) were significantly decreased with the halo vest as compared to without it (29.1+/-5.8 vs. 32.8+/-6.4 seconds, p = .002; 12.9+/-1.4 vs. 15.1+/-2.1 inches, prisk for a fall, which could have devastating consequences.

Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection

International Nuclear Information System (INIS)

Sivertsson, Sofia; Edsjoe, Joakim

2010-01-01

Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so-called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.

Merged neutral beams

Energy Technology Data Exchange (ETDEWEB)

Osterwalder, Andreas [Ecole Polytechnique Federale de Lausanne (EPFL), Institute for Chemical Sciences and Engineering, Lausanne (Switzerland)

2015-12-15

A detailed description of a merged beam apparatus for the study of low energy molecular scattering is given. This review is intended to guide any scientist who plans to construct a similar experiment, and to provide some inspiration in describing the approach we chose to our goal. In our experiment a supersonic expansion of paramagnetic particles is merged with one of polar molecules. A magnetic and an electric multipole guide are used to bend the two beams onto the same axis. We here describe in detail how the apparatus is designed, characterised, and operated. (orig.)

Resolving the Polarized Dust Emission of the Disk around the Massive Star Powering the HH 80–81 Radio Jet

Science.gov (United States)

Girart, J. M.; Fernández-López, M.; Li, Z.-Y.; Yang, H.; Estalella, R.; Anglada, G.; Áñez-López, N.; Busquet, G.; Carrasco-González, C.; Curiel, S.; Galvan-Madrid, R.; Gómez, J. F.; de Gregorio-Monsalvo, I.; Jiménez-Serra, I.; Krasnopolsky, R.; Martí, J.; Osorio, M.; Padovani, M.; Rao, R.; Rodríguez, L. F.; Torrelles, J. M.

2018-04-01

Here we present deep (16 μJy beam‑1), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protostar driving the HH 80–81 radio jet. The observations clearly resolve the disk oriented perpendicularly to the radio jet, with a radius of ≃0.″171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R ≲ 170 au. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼0.″1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 μm. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with the self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.

Gamma-Ray Bursts: A Radio Perspective

Directory of Open Access Journals (Sweden)

Poonam Chandra

2016-01-01

Full Text Available Gamma-ray bursts (GRBs are extremely energetic events at cosmological distances. They provide unique laboratory to investigate fundamental physical processes under extreme conditions. Due to extreme luminosities, GRBs are detectable at very high redshifts and potential tracers of cosmic star formation rate at early epoch. While the launch of Swift and Fermi has increased our understanding of GRBs tremendously, many new questions have opened up. Radio observations of GRBs uniquely probe the energetics and environments of the explosion. However, currently only 30% of the bursts are detected in radio bands. Radio observations with upcoming sensitive telescopes will potentially increase the sample size significantly and allow one to follow the individual bursts for a much longer duration and be able to answer some of the important issues related to true calorimetry, reverse shock emission, and environments around the massive stars exploding as GRBs in the early Universe.

Disc-halo interactions in ΛCDM

Science.gov (United States)

Bauer, Jacob S.; Widrow, Lawrence M.; Erkal, Denis

2018-05-01

We present a new method for embedding a stellar disc in a cosmological dark matter halo and provide a worked example from a Λ cold dark matter zoom-in simulation. The disc is inserted into the halo at a redshift z = 3 as a zero-mass rigid body. Its mass and size are then increased adiabatically while its position, velocity, and orientation are determined from rigid-body dynamics. At z = 1, the rigid disc (RD) is replaced by an N-body disc whose particles sample a three-integral distribution function (DF). The simulation then proceeds to z = 0 with live disc (LD) and halo particles. By comparison, other methods assume one or more of the following: the centre of the RD during the growth phase is pinned to the minimum of the halo potential, the orientation of the RD is fixed, or the live N-body disc is constructed from a two rather than three-integral DF. In general, the presence of a disc makes the halo rounder, more centrally concentrated, and smoother, especially in the innermost regions. We find that methods in which the disc is pinned to the minimum of the halo potential tend to overestimate the amount of adiabatic contraction. Additionally, the effect of the disc on the subhalo distribution appears to be rather insensitive to the disc insertion method. The LD in our simulation develops a bar that is consistent with the bars seen in late-type spiral galaxies. In addition, particles from the disc are launched or `kicked up' to high galactic latitudes.

Environmental screening of dark matter haloes in f(R) gravity

Science.gov (United States)

Shi, Difu; Li, Baojiu; Han, Jiaxin

2017-07-01

In certain theories of modified gravity, Solar system constraints on deviations from general relativity (GR) are satisfied by virtue of a so-called screening mechanism, which enables the theory to revert to GR in regions where the matter density is high or the gravitational potential is deep. In the case of chameleon theories, the screening has two contributions - self-screening, which is due to the mass of an object itself, and environmental screening, which is caused by the surrounding matter - which are often entangled, with the second contribution being more crucial for less massive objects. A quantitative understanding of the effect of the environment on the screening can prove critical in observational tests of such theories using systems such as the Local Group and dwarf galaxies, for which the environment may be inferred in various ways. We use the high-resolution liminality simulation of Shi et al. to test the fidelity of different definitions of environment. We find that, although the different ways to define environment in practice do not agree with one another perfectly, they can provide useful guidance, and cross checks about how well a dark matter halo is screened. In addition, the screening of subhaloes in dark matter haloes is primarily determined by the environment, with the subhalo mass playing a minor role, which means that lower resolution simulations where subhaloes are not well resolved can still be useful for understanding the modification of gravity inside subhaloes.

Subhalo demographics in the Illustris simulation: effects of baryons and halo-to-halo variation

Science.gov (United States)

Chua, Kun Ting Eddie; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Vogelsberger, Mark; Bird, Simeon; Hernquist, Lars

2017-12-01

We study the abundance of subhaloes in the hydrodynamical cosmological simulation Illustris, which includes both baryons and dark matter in a cold dark matter volume 106.5 Mpc a side. We compare Illustris to its dark-matter only (DMO) analogue, Illustris-Dark and quantify the effects of baryonic processes on the demographics of subhaloes in the host mass range 1011-3 × 1014 M⊙. We focus on both the evolved (z = 0) subhalo cumulative mass functions (SHMF) and the statistics of subhaloes ever accreted, i.e. infall SHMF. We quantify the variance in subhalo abundance at fixed host mass and investigate the physical reasons responsible for such scatter. We find that in Illustris, baryonic physics impacts both the infall and z = 0 subhalo abundance by tilting the DMO function and suppressing the abundance of low-mass subhaloes. The breaking of self-similarity in the subhalo abundance at z = 0 is enhanced by the inclusion of baryonic physics. The non-monotonic alteration of the evolved subhalo abundances can be explained by the modification of the concentration-mass relation of Illustris hosts compared to Illustris-Dark. Interestingly, the baryonic implementation in Illustris does not lead to an increase in the halo-to-halo variation compared to Illustris-Dark. In both cases, the normalized intrinsic scatter today is larger for Milky Way-like haloes than for cluster-sized objects. For Milky Way-like haloes, it increases from about eight per cent at infall to about 25 per cent at the current epoch. In both runs, haloes of fixed mass formed later host more subhaloes than early formers.

The dynamical fingerprint of core scouring in massive elliptical galaxies

International Nuclear Information System (INIS)

Thomas, J.; Saglia, R. P.; Bender, R.; Erwin, P.; Fabricius, M.

2014-01-01

The most massive elliptical galaxies have low-density centers or cores that differ dramatically from the high-density centers of less massive ellipticals and bulges of disk galaxies. These cores have been interpreted as the result of mergers of supermassive black hole binaries, which depopulate galaxy centers by gravitationally slingshotting central stars toward large radii. Such binaries naturally form in mergers of luminous galaxies. Here, we analyze the population of central stellar orbits in 11 massive elliptical galaxies that we observed with the integral field spectrograph SINFONI at the European Southern Observatory Very Large Telescope. Our dynamical analysis is orbit-based and includes the effects of a central black hole, the mass distribution of the stars, and a dark matter halo. We show that the use of integral field kinematics and the inclusion of dark matter is important to conclude on the distribution of stellar orbits in galaxy centers. Six of our galaxies are core galaxies. In these six galaxies, but not in the galaxies without cores, we detect a coherent lack of stars on radial orbits in the core region and a uniform excess of radial orbits outside of it: when scaled by the core radius r b , the radial profiles of the classical anisotropy parameter β(r) are nearly identical in core galaxies. Moreover, they quantitatively match the predictions of black hole binary simulations, providing the first convincing dynamical evidence for core scouring in the most massive elliptical galaxies.

Vacuum pumping by the halo plasma

International Nuclear Information System (INIS)

Barr, W.L.

1985-01-01

An estimate is made of the effective vacuum pumping speed of the halo plasma in a tandem mirror fusion reactor, and it is shown that, if the electron temperature and line density are great enough, the halo can be a very good vacuum pump. One can probably obtain the required density by recycling the ions at the halo dumps. An array of small venting ports in the dump plates allows local variation of the recycle fraction and local removal of the gas at a conveniently high pressure. This vented-port concept could introduce more flexibility in the design of pumped limiters for tokamaks

The prolate dark matter halo of the Andromeda galaxy

Energy Technology Data Exchange (ETDEWEB)

Hayashi, Kohei; Chiba, Masashi, E-mail: k.hayasi@astr.tohoku.ac.jp, E-mail: chiba@astr.tohoku.ac.jp [Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan)

2014-07-01

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

Accurate mass and velocity functions of dark matter haloes

Science.gov (United States)

Comparat, Johan; Prada, Francisco; Yepes, Gustavo; Klypin, Anatoly

2017-08-01

N-body cosmological simulations are an essential tool to understand the observed distribution of galaxies. We use the MultiDark simulation suite, run with the Planck cosmological parameters, to revisit the mass and velocity functions. At redshift z = 0, the simulations cover four orders of magnitude in halo mass from ˜1011M⊙ with 8783 874 distinct haloes and 532 533 subhaloes. The total volume used is ˜515 Gpc3, more than eight times larger than in previous studies. We measure and model the halo mass function, its covariance matrix w.r.t halo mass and the large-scale halo bias. With the formalism of the excursion-set mass function, we explicit the tight interconnection between the covariance matrix, bias and halo mass function. We obtain a very accurate (function. We also model the subhalo mass function and its relation to the distinct halo mass function. The set of models obtained provides a complete and precise framework for the description of haloes in the concordance Planck cosmology. Finally, we provide precise analytical fits of the Vmax maximum velocity function up to redshift z publicly available in the Skies and Universes data base.

The prolate dark matter halo of the Andromeda galaxy

International Nuclear Information System (INIS)

Hayashi, Kohei; Chiba, Masashi

2014-01-01

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

Bouncing and Merging of Liquid Jets

Science.gov (United States)

Saha, Abhishek; Li, Minglei; Law, Chung K.

2014-11-01

Collision of two fluid jets is a technique that is utilized in many industrial applications, such as in rocket engines, to achieve controlled mixing, atomization and sometimes liquid phase reactions. Thus, the dynamics of colliding jets have direct impact on the performance, efficiency and reliability of such applications. In analogy with the dynamics of droplet-droplet collision, in this work we have experimentally demonstrated, for n-alkane hydrocarbons as well as water, that with increasing impact inertia obliquely colliding jets also exhibit the same nonmonotonic responses of merging, bouncing, merging again, and merging followed by disintegration; and that the continuous entrainment of the boundary layer air over the jet surface into the colliding interfacial region leads to two distinguishing features of jet collision, namely: there exists a maximum impact angle beyond which merging is always possible, and that merging is inhibited and then promoted with increasing pressure. These distinct response regimes were mapped and explained on the bases of impact inertia, deformation of the jet surface, viscous loss within the jet interior, and the thickness and pressure build-up within the interfacial region in order to activate the attractive surface van der Waals force to effect merging.

UARS Halogen Occultation Experiment (HALOE) Level 2 V001

Data.gov (United States)

National Aeronautics and Space Administration — The HALOE home page on the WWW is http://haloe.gats-inc.com/home/index.php The Halogen Occultation Experiment (HALOE) on NASA's Upper Atmosphere Research Satellite...

Reduction and processing of astrophysical data by visualization and creation of merger trees from dark matter particle simulations

International Nuclear Information System (INIS)

Riser, T.

2012-01-01

State of the art dark matter particle simulations of galaxy clusters produce vast amounts of raw data that need to be interpreted and scientifically understood. In this thesis two cornerstones involved in this process are presented. First, a unique and robust algorithm is shown, which extracts a so called ''merger tree'' from dark matter particle data. It represents the development and history of every galaxy that lives within the gravitational potential of the dark matter halos formed by the simulated structure formation process, with a special focus on the merging of smaller halos into bigger ones through the course of time. Second, a modern approach is discussed that facilitates the massively parallel calculative power of state of the art graphics cards to greatly improve the image quality of real-time particle visualizations without the requirement of additional geometric data. (author)

Automatic generation of data merging program codes.

OpenAIRE

Hyensook, Kim; Oussena, Samia; Zhang, Ying; Clark, Tony

2010-01-01

Data merging is an essential part of ETL (Extract-Transform-Load) processes to build a data warehouse system. To avoid rewheeling merging techniques, we propose a Data Merging Meta-model (DMM) and its transformation into executable program codes in the manner of model driven engineering. DMM allows defining relationships of different model entities and their merging types in conceptual level. Our formalized transformation described using ATL (ATLAS Transformation Language) enables automatic g...

Direct detection of WIMPs: implications of a self-consistent truncated isothermal model of the Milky Way's dark matter halo

Science.gov (United States)

Chaudhury, Soumini; Bhattacharjee, Pijushpani; Cowsik, Ramanath

2010-09-01

Direct detection of Weakly Interacting Massive Particle (WIMP) candidates of Dark Matter (DM) is studied within the context of a self-consistent truncated isothermal model of the finite-size dark halo of the Galaxy. The halo model, based on the ``King model'' of the phase space distribution function of collisionless DM particles, takes into account the modifications of the phase-space structure of the halo due to the gravitational influence of the observed visible matter in a self-consistent manner. The parameters of the halo model are determined by a fit to a recently determined circular rotation curve of the Galaxy that extends up to ~ 60 kpc. Unlike in the Standard Halo Model (SHM) customarily used in the analysis of the results of WIMP direct detection experiments, the velocity distribution of the WIMPs in our model is non-Maxwellian with a cut-off at a maximum velocity that is self-consistently determined by the model itself. For our halo model that provides the best fit to the rotation curve data, the 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section from the recent results of the CDMS-II experiment, for example, is ~ 5.3 × 10-8 pb at a WIMP mass of ~ 71 GeV. We also find, using the original 2-bin annual modulation amplitude data on the nuclear recoil event rate seen in the DAMA experiment, that there exists a range of small WIMP masses, typically ~ 2-16 GeV, within which DAMA collaboration's claimed annual modulation signal purportedly due to WIMPs is compatible with the null results of other experiments. These results, based as they are on a self-consistent model of the dark matter halo of the Galaxy, strengthen the possibility of low-mass (lsim10 GeV) WIMPs as a candidate for dark matter as indicated by several earlier studies performed within the context of the SHM. A more rigorous analysis using DAMA bins over smaller intervals should be able to better constrain the ``DAMA regions'' in the WIMP parameter space within the context of

Scale dependence of halo and galaxy bias: Effects in real space

International Nuclear Information System (INIS)

Smith, Robert E.; Scoccimarro, Roman; Sheth, Ravi K.

2007-01-01

We examine the scale dependence of dark matter halo and galaxy clustering on very large scales (0.01 -1 ] -1 ] -1 ], and only show amplification on smaller scales, whereas low mass haloes show strong, ∼5%-10%, suppression over the range 0.05 -1 ]<0.15. These results were primarily established through the use of the cross-power spectrum of dark matter and haloes, which circumvents the thorny issue of shot-noise correction. The halo-halo power spectrum, however, is highly sensitive to the shot-noise correction; we show that halo exclusion effects make this sub-Poissonian and a new correction is presented. Our results have special relevance for studies of the baryon acoustic oscillation features in the halo power spectra. Nonlinear mode-mode coupling: (i) damps these features on progressively larger scales as halo mass increases; (ii) produces small shifts in the positions of the peaks and troughs which depend on halo mass. We show that these effects on halo clustering are important over the redshift range relevant to such studies (0< z<2), and so will need to be accounted for when extracting information from precision measurements of galaxy clustering. Our analytic model is described in the language of the ''halo model.'' The halo-halo clustering term is propagated into the nonlinear regime using ''1-loop'' perturbation theory and a nonlinear halo bias model. Galaxies are then inserted into haloes through the halo occupation distribution. We show that, with nonlinear bias parameters derived from simulations, this model produces predictions that are qualitatively in agreement with our numerical results. We then use it to show that the power spectra of red and blue galaxies depend differently on scale, thus underscoring the fact that proper modeling of nonlinear bias parameters will be crucial to derive reliable cosmological constraints. In addition to showing that the bias on very large scales is not simply linear, the model also shows that the halo-halo and halo

The team behind HALO, a large-scale art installation conceived at CERN and inspired by ATLAS data, exhibited at 2018 Art Basel.

CERN Multimedia

Marcelloni, Claudia

2018-01-01

Merging particle physics and art, a CERN-inspired artwork is being featured for the first time at Art Basel, the international art fair in Basel, Switzerland from 13 to 17 June. A large-scale immersive art installation entitled HALO is the artistic interpretation of the Large Hadron Collider’s ATLAS experiment and celebrates the links between art, science and technology. Inspired by raw data generated by ATLAS, the artwork has been conceived and executed by CERN’s former artists-in-residence, the “Semiconductor” duo Ruth Jarman and Joe Gerhardt, in collaboration with Mónica Bello, curator and head of Arts at CERN. During their three-month Arts at CERN residency in 2015, Semiconductor had the chance to explore particle-collision data in collaboration with scientists from the University of Sussex ATLAS group and work with them on the data later used in the artwork. HALO is a cylindrical structure, measuring ten metres in diameter and surrounded by 4-metre-long vertical piano wires. On the inside, an en...

THE UNORTHODOX ORBITS OF SUBSTRUCTURE HALOS

NARCIS (Netherlands)

Ludlow, Aaron D.; Navarro, Julio F.; Springel, Volker; Jenkins, Adrian; Frenk, Carlos S.; Helmi, Amina

2009-01-01

We use a suite of cosmological N-body simulations to study the properties of substructure halos (subhalos) in galaxy-sized cold dark matter halos. We extend prior work on the subject by considering the whole population of subhalos physically associated with the main system. These are defined as

Changes in thunderstorm characteristics due to feeder cloud merging

Science.gov (United States)

Sinkevich, Andrei A.; Krauss, Terrence W.

2014-06-01

Cumulus cloud merging is a complex dynamical and microphysical process in which two convective cells merge into a single cell. Previous radar observations and numerical simulations have shown a substantial increase in the maximum area, maximum echo top and maximum reflectivity as a result of the merging process. Although the qualitative aspects of merging have been well documented, the quantitative effects on storm properties remain less defined. Therefore, a statistical assessment of changes in storm characteristics due to merging is of importance. Further investigation into the effects of cloud merging on precipitation flux (Pflux) in a statistical manner provided the motivation for this study in the Asir region of Saudi Arabia. It was confirmed that merging has a strong effect on storm development in this region. The data analysis shows that an increase in the median of the distribution of maximum reflectivity was observed just after merging and was equal to 3.9 dBZ. A detailed analysis of the individual merge cases compared the merged storm Pflux and mass to the sum of the individual Feeder and Storm portions just before merging for each case. The merged storm Pflux increased an average of 106% over the 20-min period after merging, and the mass increased on average 143%. The merged storm clearly became larger and more severe than the sum of the two parts prior to merging. One consequence of this study is that any attempts to evaluate the precipitation enhancement effects of cloud seeding must also include the issue of cloud mergers because merging can have a significant effect on the results.

Bimodal Formation Time Distribution for Infall Dark Matter Halos

Science.gov (United States)

Shi, Jingjing; Wang, Huiyuan; Mo, H. J.; Xie, Lizhi; Wang, Xiaoyu; Lapi, Andrea; Sheth, Ravi K.

2018-04-01

We use a 200 {h}-1 {Mpc} a-side N-body simulation to study the mass accretion history (MAH) of dark matter halos to be accreted by larger halos, which we call infall halos. We define a quantity {a}nf}\\equiv (1+{z}{{f}})/(1+{z}peak}) to characterize the MAH of infall halos, where {z}peak} and {z}{{f}} are the accretion and formation redshifts, respectively. We find that, at given {z}peak}, their MAH is bimodal. Infall halos are dominated by a young population at high redshift and by an old population at low redshift. For the young population, the {a}nf} distribution is narrow and peaks at about 1.2, independent of {z}peak}, while for the old population, the peak position and width of the {a}nf} distribution both increase with decreasing {z}peak} and are both larger than those of the young population. This bimodal distribution is found to be closely connected to the two phases in the MAHs of halos. While members of the young population are still in the fast accretion phase at z peak, those of the old population have already entered the slow accretion phase at {z}peak}. This bimodal distribution is not found for the whole halo population, nor is it seen in halo merger trees generated with the extended Press–Schechter formalism. The infall halo population at {z}peak} are, on average, younger than the whole halo population of similar masses identified at the same redshift. We discuss the implications of our findings in connection to the bimodal color distribution of observed galaxies and to the link between central and satellite galaxies.

What sets the central structure of dark matter haloes?

Science.gov (United States)

Ogiya, Go; Hahn, Oliver

2018-02-01

Dark matter (DM) haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers. While standard cold dark matter (CDM) simulations readily produce haloes that follow the universal Navarro-Frenk-White (NFW) density profile with an inner slope, ρ ∝ r-α, with α = 1, recent simulations have found that when the free-streaming cut-off expected for the CDM model is resolved, the resulting haloes follow nearly power-law density profiles of α ∼ 1.5. In this paper, we study the formation of density cusps in haloes using idealized N-body simulations of the collapse of proto-haloes. When the proto-halo profile is initially cored due to particle free-streaming at high redshift, we universally find ∼r-1.5 profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations. Quite in contrast, when the proto-halo has a power-law profile, then we obtain profiles compatible with the NFW shape when the density slope of the proto-halo patch is shallower than a critical value, αini ∼ 0.3, while the final slope can be steeper for αini ≳ 0.3. We further demonstrate that the r-1.5 profiles are sensitive to small-scale noise, which gradually drives them towards an inner slope of -1, where they become resilient to such perturbations. We demonstrate that the r-1.5 solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

Minimizing the stochasticity of halos in large-scale structure surveys

Science.gov (United States)

Hamaus, Nico; Seljak, Uroš; Desjacques, Vincent; Smith, Robert E.; Baldauf, Tobias

2010-08-01

In recent work (Seljak, Hamaus, and Desjacques 2009) it was found that weighting central halo galaxies by halo mass can significantly suppress their stochasticity relative to the dark matter, well below the Poisson model expectation. This is useful for constraining relations between galaxies and the dark matter, such as the galaxy bias, especially in situations where sampling variance errors can be eliminated. In this paper we extend this study with the goal of finding the optimal mass-dependent halo weighting. We use N-body simulations to perform a general analysis of halo stochasticity and its dependence on halo mass. We investigate the stochasticity matrix, defined as Cij≡⟨(δi-biδm)(δj-bjδm)⟩, where δm is the dark matter overdensity in Fourier space, δi the halo overdensity of the i-th halo mass bin, and bi the corresponding halo bias. In contrast to the Poisson model predictions we detect nonvanishing correlations between different mass bins. We also find the diagonal terms to be sub-Poissonian for the highest-mass halos. The diagonalization of this matrix results in one large and one low eigenvalue, with the remaining eigenvalues close to the Poisson prediction 1/n¯, where n¯ is the mean halo number density. The eigenmode with the lowest eigenvalue contains most of the information and the corresponding eigenvector provides an optimal weighting function to minimize the stochasticity between halos and dark matter. We find this optimal weighting function to match linear mass weighting at high masses, while at the low-mass end the weights approach a constant whose value depends on the low-mass cut in the halo mass function. This weighting further suppresses the stochasticity as compared to the previously explored mass weighting. Finally, we employ the halo model to derive the stochasticity matrix and the scale-dependent bias from an analytical perspective. It is remarkably successful in reproducing our numerical results and predicts that the

DETECTION OF FLUX EMERGENCE, SPLITTING, MERGING, AND CANCELLATION OF NETWORK FIELD. I. SPLITTING AND MERGING

Energy Technology Data Exchange (ETDEWEB)

Iida, Y.; Yokoyama, T. [Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Hagenaar, H. J. [Lockheed Martin Advanced Technology Center, Org. ADBS, Building 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)

2012-06-20

Frequencies of magnetic patch processes on the supergranule boundary, namely, flux emergence, splitting, merging, and cancellation, are investigated through automatic detection. We use a set of line-of-sight magnetograms taken by the Solar Optical Telescope (SOT) on board the Hinode satellite. We found 1636 positive patches and 1637 negative patches in the data set, whose time duration is 3.5 hr and field of view is 112'' Multiplication-Sign 112''. The total numbers of magnetic processes are as follows: 493 positive and 482 negative splittings, 536 positive and 535 negative mergings, 86 cancellations, and 3 emergences. The total numbers of emergence and cancellation are significantly smaller than those of splitting and merging. Further, the frequency dependence of the merging and splitting processes on the flux content are investigated. Merging has a weak dependence on the flux content with a power-law index of only 0.28. The timescale for splitting is found to be independent of the parent flux content before splitting, which corresponds to {approx}33 minutes. It is also found that patches split into any flux contents with the same probability. This splitting has a power-law distribution of the flux content with an index of -2 as a time-independent solution. These results support that the frequency distribution of the flux content in the analyzed flux range is rapidly maintained by merging and splitting, namely, surface processes. We suggest a model for frequency distributions of cancellation and emergence based on this idea.

Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history

Science.gov (United States)

Poole, Gregory B.; Mutch, Simon J.; Croton, Darren J.; Wyithe, Stuart

2017-12-01

We introduce GBPTREES: an algorithm for constructing merger trees from cosmological simulations, designed to identify and correct for pathological cases introduced by errors or ambiguities in the halo finding process. GBPTREES is built upon a halo matching method utilizing pseudo-radial moments constructed from radially sorted particle ID lists (no other information is required) and a scheme for classifying merger tree pathologies from networks of matches made to-and-from haloes across snapshots ranging forward-and-backward in time. Focusing on SUBFIND catalogues for this work, a sweep of parameters influencing our merger tree construction yields the optimal snapshot cadence and scanning range required for converged results. Pathologies proliferate when snapshots are spaced by ≲0.128 dynamical times; conveniently similar to that needed for convergence of semi-analytical modelling, as established by Benson et al. Total merger counts are converged at the level of ∼5 per cent for friends-of-friends (FoF) haloes of size np ≳ 75 across a factor of 512 in mass resolution, but substructure rates converge more slowly with mass resolution, reaching convergence of ∼10 per cent for np ≳ 100 and particle mass mp ≲ 109 M⊙. We present analytic fits to FoF and substructure merger rates across nearly all observed galactic history (z ≤ 8.5). While we find good agreement with the results presented by Fakhouri et al. for FoF haloes, a slightly flatter dependence on merger ratio and increased major merger rates are found, reducing previously reported discrepancies with extended Press-Schechter estimates. When appropriately defined, substructure merger rates show a similar mass ratio dependence as FoF rates, but with stronger mass and redshift dependencies for their normalization.

Dark Matter: Looking for WIMPs in the Galactic Halo

International Nuclear Information System (INIS)

Akerib, Daniel S.

2006-01-01

Overwhelming observational evidence indicates that most of the matter in the Universe consists of non-baryonic dark matter. One possibility is that the dark matter is Weakly-Interacting Massive Particles (WIMPs) that were produced in the early Universe. These relics could comprise the Milky Way's dark halo and provide evidence for new particle physics, such as Supersymmetry. After reviewing some of the evidence for dark matter and the WIMP hypothesis, I will describe the strategy for searching for WIMPs, along with a survey of the current status and outlook. In particular, dark matter searches have begun to explore the region of parameter space where SUSY particles could provide dark matter candidates. I will also mention some of the recent theoretical work on dark matter candidates which is being done in anticipation of the turn-on of the LHC and as part of the active R and D on the ILC. Finally, a vigorous detector development program promises significant advances in WIMP sensitivity in the coming years

QUENCHED COLD ACCRETION OF A LARGE-SCALE METAL-POOR FILAMENT DUE TO VIRIAL SHOCKING IN THE HALO OF A MASSIVE z = 0.7 GALAXY

Energy Technology Data Exchange (ETDEWEB)

Churchill, Christopher W.; Holtzman, Jon; Nielsen, Nikole M.; Trujillo-Gomez, Sebastian [Department of Astronomy, New Mexico State University, MSC 4500, Las Cruces, NM 88003 (United States); Kacprzak, Glenn G.; Spitler, Lee R. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia); Steidel, Charles C. [Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States)

2012-11-20

Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a remarkable H I absorbing complex at z = 0.672 toward the quasar Q1317+277. The H I absorption has a velocity spread of {Delta}v = 1600 km s{sup -1}, comprises 21 Voigt profile components, and resides at an impact parameter of D = 58 kpc from a bright, high-mass (log M {sub vir}/M {sub Sun} {approx_equal} 13.7) elliptical galaxy that is deduced to have a 6 Gyr old, solar metallicity stellar population. Ionization models suggest the majority of the structure is cold gas surrounding a shock-heated cloud that is kinematically adjacent to a multi-phase group of clouds with detected C III, C IV, and O VI absorption, suggestive of a conductive interface near the shock. The deduced metallicities are consistent with the moderate in situ enrichment relative to the levels observed in the z {approx} 3 Ly{alpha} forest. We interpret the H I complex as a metal-poor filamentary structure being shock heated as it accretes into the halo of the galaxy. The data support the scenario of an early formation period (z > 4) in which the galaxy was presumably fed by cold-mode gas accretion that was later quenched via virial shocking by the hot halo such that, by intermediate redshift, the cold filamentary accreting gas is continuing to be disrupted by shock heating. Thus, continued filamentary accretion is being mixed into the hot halo, indicating that the star formation of the galaxy will likely remain quenched. To date, the galaxy and the H I absorption complex provide some of the most compelling observational data supporting the theoretical picture in which accretion is virial shocked in the hot coronal halos of high-mass galaxies.

Radio emission from embryonic superluminous supernova remnants

Science.gov (United States)

Omand, Conor M. B.; Kashiyama, Kazumi; Murase, Kohta

2018-02-01

It has been widely argued that Type-I superluminous supernovae (SLSNe-I) are driven by powerful central engines with a long-lasting energy injection after the core-collapse of massive progenitors. One of the popular hypotheses is that the hidden engines are fast-rotating pulsars with a magnetic field of B ˜ 1013-1015 G. Murase, Kashiyama & Mészáros proposed that quasi-steady radio/submm emission from non-thermal electron-positron pairs in nascent pulsar wind nebulae can be used as a relevant counterpart of such pulsar-driven supernovae (SNe). In this work, focusing on the nascent SLSN-I remnants, we examine constraints that can be placed by radio emission. We show that the Atacama Large Millimeter/submillimetre Array can detect the radio nebula from SNe at DL ˜ 1 Gpc in a few years after the explosion, while the Jansky Very Large Array can also detect the counterpart in a few decades. The proposed radio follow-up observation could solve the parameter degeneracy in the pulsar-driven SN model for optical/UV light curves, and could also give us clues to young neutron star scenarios for SLSNe-I and fast radio bursts.

Occurrences of flares with type II and IV radio events in interacting sunspot groups in the course of revolutions

International Nuclear Information System (INIS)

Klimes, J.; Krivsky, L.

1984-01-01

Using data from 11-year solar cycle No. 20, it was found that flares with type II radio bursts are more than twice as frequent and flares with type IV bursts nearly twice as frequent in sunspot groups which developed close to each other or which merged in the course of revolutions than in isolated sunspot groups. With both types the occurrence of these flares is concentrated in the revolution of the so-called sunspot group interaction (their approximation, merging). (author)

The origin of the mass, disk-to-halo mass ratio, and L-V relation of spiral galaxies

International Nuclear Information System (INIS)

Ashman, K.M.

1990-01-01

A model is presented in which spiral galaxies only form when t(c) is roughly equal to t(f) in a hot component of the protogalactic gas. This assumption, along with a disk stability criterion, predicts a range of spiral galaxy masses roughly consistent with observation. The nature of the cooling function for a primordial plasma implies that in less massive galaxies, more gas must fragment in the halo to preserve t(c) roughly equal to t(f). Consequently, less gas survives to form the disk, so that the disk-to-halo mass ratio increases with disk mass and hence galaxy luminosity. The canonical L proportional to V exp 4 relation can be reproduced by the model, and the apparent change in the slope of this relation also arises naturally. In the hierarchical clustering scenario, the model requires that all spirals formed at about the same epoch. These results support earlier claims that much of the dark matter observed in the universe is baryonic and probably formed during protogalactic collapse. 38 refs

Are baryonic galactic halos possible

International Nuclear Information System (INIS)

Olive, K.A.; Hegyi, D.J.

1986-01-01

There is little doubt from the rotation curves of spiral galaxies that galactic halos must contain large amounts of dark matter. In this contribution, the authors review arguments which indicate that it is very unlikely that galactic halos contain substantial amounts of baryonic matter. While the authors would like to be able to present a single argument which would rule out baryonic matter, at the present time they are only able to present a collection of arguments each of which argues against one form of baryonic matter. These include: 1) snowballs; 2) gas; 3) low mass stars and Jupiters; 4) high mass stars; and 5) high metalicity objects such as rooks or dust. Black holes, which do not have a well defined baryon number, are also a possible candidate for halo matter. They briefly discuss black holes

Halo-independent direct detection analyses without mass assumptions

International Nuclear Information System (INIS)

Anderson, Adam J.; Fox, Patrick J.; Kahn, Yonatan; McCullough, Matthew

2015-01-01

Results from direct detection experiments are typically interpreted by employing an assumption about the dark matter velocity distribution, with results presented in the m χ −σ n plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the v min −g-tilde plane, but these in turn require an assumption on the dark matter mass. Here we present an extension of these halo-independent methods for dark matter direct detection which does not require a fiducial choice of the dark matter mass. With a change of variables from v min to nuclear recoil momentum (p R ), the full halo-independent content of an experimental result for any dark matter mass can be condensed into a single plot as a function of a new halo integral variable, which we call h-til-tilde(p R ). The entire family of conventional halo-independent g-tilde(v min ) plots for all DM masses are directly found from the single h-tilde(p R ) plot through a simple rescaling of axes. By considering results in h-tilde(p R ) space, one can determine if two experiments are inconsistent for all masses and all physically possible halos, or for what range of dark matter masses the results are inconsistent for all halos, without the necessity of multiple g-tilde(v min ) plots for different DM masses. We conduct a sample analysis comparing the CDMS II Si events to the null results from LUX, XENON10, and SuperCDMS using our method and discuss how the results can be strengthened by imposing the physically reasonable requirement of a finite halo escape velocity

Halo statistics analysis within medium volume cosmological N-body simulation

Directory of Open Access Journals (Sweden)

Martinović N.

2015-01-01

Full Text Available In this paper we present halo statistics analysis of a ΛCDM N body cosmological simulation (from first halo formation until z = 0. We study mean major merger rate as a function of time, where for time we consider both per redshift and per Gyr dependence. For latter we find that it scales as the well known power law (1 + zn for which we obtain n = 2.4. The halo mass function and halo growth function are derived and compared both with analytical and empirical fits. We analyse halo growth through out entire simulation, making it possible to continuously monitor evolution of halo number density within given mass ranges. The halo formation redshift is studied exploring possibility for a new simple preliminary analysis during the simulation run. Visualization of the simulation is portrayed as well. At redshifts z = 0−7 halos from simulation have good statistics for further analysis especially in mass range of 1011 − 1014 M./h. [176021 ’Visible and invisible matter in nearby galaxies: theory and observations

The f ( R ) halo mass function in the cosmic web

Energy Technology Data Exchange (ETDEWEB)

Braun-Bates, F. von; Winther, H.A.; Alonso, D.; Devriendt, J., E-mail: francesca.vonbraun-bates@physics.ox.ac.uk, E-mail: hans.a.winther@physics.ox.ac.uk, E-mail: david.alonso@physics.ox.ac.uk, E-mail: julien.devriendt@physics.ox.ac.uk [Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)

2017-03-01

An important indicator of modified gravity is the effect of the local environment on halo properties. This paper examines the influence of the local tidal structure on the halo mass function, the halo orientation, spin and the concentration-mass relation. We use the excursion set formalism to produce a halo mass function conditional on large-scale structure. Our simple model agrees well with simulations on large scales at which the density field is linear or weakly non-linear. Beyond this, our principal result is that f ( R ) does affect halo abundances, the halo spin parameter and the concentration-mass relationship in an environment-independent way, whereas we find no appreciable deviation from \\text(ΛCDM) for the mass function with fixed environment density, nor the alignment of the orientation and spin vectors of the halo to the eigenvectors of the local cosmic web. There is a general trend for greater deviation from \\text(ΛCDM) in underdense environments and for high-mass haloes, as expected from chameleon screening.

Observation and analysis of halo current in EAST

Science.gov (United States)

Chen, Da-Long; Shen, Biao; Qian, Jin-Ping; Sun, You-Wen; Liu, Guang-Jun; Shi, Tong-Hui; Zhuang, Hui-Dong; Xiao, Bing-Jia

2014-06-01

Plasma in a typically elongated cross-section tokamak (for example, EAST) is inherently unstable against vertical displacement. When plasma loses the vertical position control, it moves downward or upward, leading to disruption, and a large halo current is generated helically in EAST typically in the scrape-off layer. When flowing into the vacuum vessel through in-vessel components, the halo current will give rise to a large J × B force acting on the vessel and the in-vessel components. In EAST VDE experiment, part of the eddy current is measured in halo sensors, due to the large loop voltage. Primary experimental data demonstrate that the halo current first lands on the outer plate and then flows clockwise, and the analysis of the information indicates that the maximum halo current estimated in EAST is about 0.4 times the plasma current and the maximum value of TPF × Ih/IP0 is 0.65, furthermore Ih/Ip0 and TPF × Ih/Ip0 tend to increase with the increase of Ip0. The test of the strong gas injection system shows good success in increasing the radiated power, which may be effective in reducing the halo current.

Unmixing the Galactic halo with RR Lyrae tagging

Science.gov (United States)

Belokurov, V.; Deason, A. J.; Koposov, S. E.; Catelan, M.; Erkal, D.; Drake, A. J.; Evans, N. W.

2018-06-01

We show that tagging RR Lyrae stars according to their location in the period-amplitude diagram can be used to shed light on the genesis of the Galactic stellar halo. The mixture of RR Lyrae of ab type, separated into classes along the lines suggested by Oosterhoff, displays a strong and coherent evolution with Galactocentric radius. The change in the RR Lyrae composition appears to coincide with the break in the halo's radial density profile at ˜25 kpc. Using simple models of the stellar halo, we establish that at least three different types of accretion events are necessary to explain the observed RRab behaviour. Given that there exists a correlation between the RRab class fraction and the total stellar content of a dwarf satellite, we hypothesize that the field halo RRab composition is controlled by the mass of the progenitor contributing the bulk of the stellar debris at the given radius. This idea is tested against a suite of cosmological zoom-in simulations of Milky Way-like stellar halo formation. Finally, we study some of the most prominent stellar streams in the Milky Way halo and demonstrate that their RRab class fractions follow the trends established previously.

Remapping dark matter halo catalogues between cosmological simulations

Science.gov (United States)

Mead, A. J.; Peacock, J. A.

2014-05-01

We present and test a method for modifying the catalogue of dark matter haloes produced from a given cosmological simulation, so that it resembles the result of a simulation with an entirely different set of parameters. This extends the method of Angulo & White, which rescales the full particle distribution from a simulation. Working directly with the halo catalogue offers an advantage in speed, and also allows modifications of the internal structure of the haloes to account for non-linear differences between cosmologies. Our method can be used directly on a halo catalogue in a self-contained manner without any additional information about the overall density field; although the large-scale displacement field is required by the method, this can be inferred from the halo catalogue alone. We show proof of concept of our method by rescaling a matter-only simulation with no baryon acoustic oscillation (BAO) features to a more standard Λ cold dark matter model containing a cosmological constant and a BAO signal. In conjunction with the halo occupation approach, this method provides a basis for the rapid generation of mock galaxy samples spanning a wide range of cosmological parameters.

THE EFFECTS OF ANGULAR MOMENTUM ON HALO PROFILES

Energy Technology Data Exchange (ETDEWEB)

Lentz, Erik W; Rosenberg, Leslie J [Physics Department, University of Washington, Seattle, WA 98195-1580 (United States); Quinn, Thomas R, E-mail: lentze@phys.washington.edu, E-mail: ljrosenberg@phys.washington.edu, E-mail: trq@astro.washington.edu [Astronomy Department, University of Washington, Seattle, WA 98195-1580 (United States)

2016-05-10

The near universality of DM halo density profiles provided by N -body simulations proved to be robust against changes in total mass density, power spectrum, and some forms of initial velocity dispersion. Here we study the effects of coherently spinning up an isolated DM-only progenitor on halo structure. Halos with spins within several standard deviations of the simulated mean ( λ ≲ 0.20) produce profiles with negligible deviations from the universal form. Only when the spin becomes quite large ( λ ≳ 0.20) do departures become evident. The angular momentum distribution also exhibits a near universal form, which is also independent of halo spin up to λ ≲ 0.20. A correlation between these epidemic profiles and the presence of a strong bar in the virialized halo is also observed. These bar structures bear resemblance to the radial orbit instability in the rotationless limit.

Galaxy halo occupation at high redshift

Science.gov (United States)

Bullock, James S.; Wechsler, Risa H.; Somerville, Rachel S.

2002-01-01

We discuss how current and future data on the clustering and number density of z~3 Lyman-break galaxies (LBGs) can be used to constrain their relationship to dark matter haloes. We explore a three-parameter model in which the number of LBGs per dark halo scales like a power law in the halo mass: N(M)=(M/M1)S for M>Mmin. Here, Mmin is the minimum mass halo that can host an LBG, M1 is a normalization parameter, associated with the mass above which haloes host more than one observed LBG, and S determines the strength of the mass-dependence. We show how these three parameters are constrained by three observable properties of LBGs: the number density, the large-scale bias and the fraction of objects in close pairs. Given these three quantities, the three unknown model parameters may be estimated analytically, allowing a full exploration of parameter space. As an example, we assume a ΛCDM cosmology and consider the observed properties of a recent sample of spectroscopically confirmed LBGs. We find that the favoured range for our model parameters is Mmin~=(0.4-8)×1010h- 1Msolar, M1~=(6-10)×1012h- 1Msolar, and 0.9acceptable if the allowed range of bg is permitted to span all recent observational estimates. We also discuss how the observed clustering of LBGs as a function of luminosity can be used to constrain halo occupation, although because of current observational uncertainties we are unable to reach any strong conclusions. Our methods and results can be used to constrain more realistic models that aim to derive the occupation function N(M) from first principles, and offer insight into how basic physical properties affect the observed properties of LBGs.

An automatic system to discriminate malignant from benign massive lesions on mammograms

International Nuclear Information System (INIS)

Retico, A.; Delogu, P.; Fantacci, M.E.; Kasae, P.

2006-01-01

Mammography is widely recognized as the most reliable technique for early detection of breast cancers. Automated or semi-automated computerized classification schemes can be very useful in assisting radiologists with a second opinion about the visual diagnosis of breast lesions, thus leading to a reduction in the number of unnecessary biopsies. We present a computer-aided diagnosis (CADi) system for the characterization of massive lesions in mammograms, whose aim is to distinguish malignant from benign masses. The CADi system we realized is based on a three-stage algorithm: (a) a segmentation technique extracts the contours of the massive lesion from the image; (b) 16 features based on size and shape of the lesion are computed; (c) a neural classifier merges the features into an estimated likelihood of malignancy. A data set of 226 massive lesions (109 malignant and 117 benign) has been used in this study. The system performances have been evaluated in terms of the receiver-operating characteristic (ROC) analysis, obtaining A z =0.80+/-0.04 as the estimated area under the ROC curve

Historic halo displays as weather indicator: Criteria and examples

Science.gov (United States)

Neuhäuser, Dagmar L.; Neuhäuser, Ralph

2016-04-01

There are numerous celestial signs reported in historic records, many of them refer to atmospheric ("sub-lunar") phenomena, such as ice halos and aurorae. In an interdisciplinary collaboration between astrophysics and cultural astronomy, we noticed that celestial observations including meteorological phenomena are often misinterpreted, mostly due to missing genuine criteria: especially ice crystal halos were recorded frequently in past centuries for religious reasons, but are mistaken nowadays often for other phenomena like aurorae. Ice halo displays yield clear information on humidity and temperature in certain atmospheric layers, and thereby indicate certain weather patterns. Ancient so-called rain makers used halo observations for weather forecast; e.g., a connection between certain halo displays and rain a few day later is statistically significant. Ice halos exist around sun and moon and are reported for both (they can stay for several days): many near, middle, and far eastern records from day- and night-time include such observations with high frequency. (Partly based on publications on halos by D.L. Neuhäuser & R. Neuhäuser, available at http://www.astro.uni-jena.de/index.php/terra-astronomy.html)

Beam halo in high-intensity beams

International Nuclear Information System (INIS)

Wangler, T.P.

1993-01-01

In space-charge dominated beams the nonlinear space-charge forces produce a filamentation pattern, which in projection to the 2-D phase spaces results in a 2-component beam consisting of an inner core and a diffuse outer halo. The beam-halo is of concern for a next generation of cw, high-power proton linacs that could be applied to intense neutron generators for nuclear materials processing. The author describes what has been learned about beam halo and the evolution of space-charge dominated beams using numerical simulations of initial laminar beams in uniform linear focusing channels. Initial results are presented from a study of beam entropy for an intense space-charge dominated beam

Sensitivity of the halo nuclei-12C elastic scattering at incident nucleon energy 800 MeV to the halo density distribution

Science.gov (United States)

Hassan, M. A. M.; Nour El-Din, M. S. M.; Ellithi, A.; Hosny, H.; Salama, T. N. E.

2017-10-01

In the framework of Glauber optical limit approximation where Coulomb effect is taken into account, the elastic scattering differential cross section for halo nuclei with {}^{12}{C} at 800 MeV/N has been calculated. Its sensitivity to the halo densities and the root mean square of the core and halo is the main goal of the current study. The projectile nuclei are taken to be one-neutron and two-neutron halo. The calculations are carried out for Gaussian-Gaussian, Gaussian-Oscillator and Gaussian-2 s phenomenological densities for each considered projectile in the mass number range 6-29. Also included a comparison between the obtained results of phenomenological densities and the results within the microscopic densities LSSM of {}6{He} and {}^{11}{Li} and microscopic densities GCM of {}^{11}{Be} where the density of the target nucleus {}^{12}{C} obtained from electron-{}^{12}{C} scattering is used. The zero range approximation is considered in the calculations. We found that the sensitivity of elastic scattering differential cross section to the halo density is clear if the nucleus appears as two clear different clusters, core and halo.

THE X-RAY HALO OF CEN X-3

International Nuclear Information System (INIS)

Thompson, Thomas W. J.; Rothschild, Richard E.

2009-01-01

Using two Chandra observations, we have derived estimates of the dust distribution and distance to the eclipsing high-mass X-ray binary Cen X-3 using the energy-resolved dust-scattered X-ray halo. By comparing the observed X-ray halos in 200 eV bands from 2-5 keV to the halo profiles predicted by the Weingartner and Draine interstellar grain model, we find that the vast majority (∼ 70%) of the dust along the line of sight to the system is located within about 300 pc of the Sun, although the halo measurements are insensitive to dust very close to the source. One of the Chandra observations occurred during an egress from eclipse as the pulsar emerged from behind the mass-donating primary. By comparing model halo light curves during this transition to the halo measurements, a source distance of 5.7 ± 1.5 kpc (68% confidence level) is estimated, although we find this result depends on the distribution of dust on very small scales. Nevertheless, this value is marginally inconsistent with the commonly accepted distance to Cen X-3 of 8 kpc. We also find that the energy scaling of the scattering optical depth predicted by the Weingartner and Draine interstellar grain model does not accurately represent the results determined by X-ray halo studies of Cen X-3. Relative to the model, there appears to be less scattering at low energies or more scattering at high energies in Cen X-3.

ELUCID—Exploring the Local Universe with the reConstructed Initial Density Field. II. Reconstruction Diagnostics, Applied to Numerical Halo Catalogs

Energy Technology Data Exchange (ETDEWEB)

Tweed, Dylan; Yang, Xiaohu; Li, Shijie; Jing, Y. P. [Center for Astronomy and Astrophysics, Shanghai Jiao Tong University, Shanghai 200240 (China); Wang, Huiyuan [Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China); Cui, Weiguang [Departamento de Física Teórica, Módulo 15, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Zhang, Youcai [Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Mo, H. J., E-mail: dtweed@sjtu.edu.cn [Department of Astronomy, University of Massachusetts, Amherst MA, 01003-9305 (United States)

2017-05-20

The ELUCID project aims to build a series of realistic cosmological simulations that reproduce the spatial and mass distributions of the galaxies as observed in the Sloan Digital Sky Survey. This requires powerful reconstruction techniques to create constrained initial conditions (ICs). We test the reconstruction method by applying it to several N -body simulations. We use two medium-resolution simulations, which each produced three additional constrained N -body simulations. We compare the resulting friend-of-friend catalogs by using the particle indexes as tracers, and quantify the quality of the reconstruction by varying the main smoothing parameter. The cross-identification method we use proves to be efficient, and the results suggest that the most massive reconstructed halos are effectively traced from the same Lagrangian regions in the ICs. A preliminary time-dependence analysis indicates that high-mass-end halos converge only at a redshift close to the reconstruction redshift. This suggests that, for earlier snapshots, only collections of progenitors may be effectively cross-identified.

SDSS J1254+0846: A BINARY QUASAR CAUGHT IN THE ACT OF MERGING

International Nuclear Information System (INIS)

Green, Paul J.; Cox, Thomas J.; Aldcroft, Thomas L.; Myers, Adam D.; Barkhouse, Wayne A.; Mulchaey, John S.; Bennert, Vardha N.

2010-01-01

We present the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z = 0.44 radio-quiet quasars, with a radial velocity difference of just 215 km s -1 , separated on the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal tails. The pair was targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry. We present follow-up optical imaging which shows broad, symmetrical tidal arm features spanning some 75 kpc at the quasars' redshift. Previously, the triggering of two quasars during a merger had only been hypothesized but our observations provide strong evidence of such an event. SDSS J1254+0846, as a face-on, pre-coalescence merger hosting two luminous quasars separated by a few dozen kpc, provides a unique opportunity to probe quasar activity in an ongoing gas-rich merger. Numerical modeling suggests that the system consists of two massive disk galaxies prograde to their mutual orbit, caught during the first passage of an active merger. This demonstrates rapid black hole growth during the early stages of a merger between galaxies with pre-existing bulges. Neither of the two luminous nuclei show significant intrinsic absorption by gas or dust in our optical or X-ray observations, illustrating that not all merging quasars will be in an obscured, ultraluminous phase. We find that the Eddington ratio for the fainter component B is rather normal, while for the A component L/L Edd is quite (>3σ) high compared to quasars of similar luminosity and redshift, possibly evidence for strong merger-triggered accretion. More such mergers should be identifiable at higher redshifts using binary quasars as tracers.

Phase models of galaxies consisting of disk and halo

International Nuclear Information System (INIS)

Osipkov, L.P.; Kutuzov, S.A.

1987-01-01

A method of finding the phase density of a two-component model of mass distribution is developed. The equipotential surfaces and the potential law are given. The equipotentials are lenslike surfaces with a sharp edge in the equatorial plane, which provides the existence of an imbedded thin disk in halo. The equidensity surfaces of the halo coincide with the equipotentials. Phase models for the halo and the disk are constructed separately on the basis of spatial and surface mass densities by solving the corresponding integral equations. In particular the models for the halo with finite dimensions can be constructed. The even part of the phase density in respect to velocities is only found. For the halo it depends on the energy integral as a single argument

Global Infrared–Radio Spectral Energy Distributions of Galactic Massive Star-Forming Regions

Science.gov (United States)

Povich, Matthew Samuel; Binder, Breanna Arlene

2018-01-01

We present a multiwavelength study of 30 Galactic massive star-forming regions. We fit multicomponent dust, blackbody, and power-law continuum models to 3.6 µm through 10 mm spectral energy distributions obtained from Spitzer, MSX, IRAS, Herschel, and Planck archival survey data. Averaged across our sample, ~20% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ~50% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates NC ≥ 1050 s–1 and total infrared luminosity LTIR ≥ 106.8 L⊙) have higher percentages of absorbed Lyman continuum photons (~40%) and dust-reprocessed starlight (~80%). The monochromatic 70-µm luminosity L70 is linearly correlated with LTIR, and on average L70/LTIR = 50%, in good agreement with extragalactic studies. Calibrated against the known massive stellar content in our sampled H II regions, we find that star formation rates based on L70 are in reasonably good agreement with extragalactic calibrations, when corrected for the smaller physical sizes of the Galactic regions. We caution that absorption of Lyman continuum photons prior to contributing to the observed ionizing photon rate may reduce the attenuation-corrected Hα emission, systematically biasing extragalactic calibrations toward lower star formation rates when applied to spatially-resolved studies of obscured star formation.This work was supported by the National Science Foundation under award CAREER-1454333.

Abort Options for Human Missions to Earth-Moon Halo Orbits

Science.gov (United States)

Jesick, Mark C.

2013-01-01

Abort trajectories are optimized for human halo orbit missions about the translunar libration point (L2), with an emphasis on the use of free return trajectories. Optimal transfers from outbound free returns to L2 halo orbits are numerically optimized in the four-body ephemeris model. Circumlunar free returns are used for direct transfers, and cislunar free returns are used in combination with lunar gravity assists to reduce propulsive requirements. Trends in orbit insertion cost and flight time are documented across the southern L2 halo family as a function of halo orbit position and free return flight time. It is determined that the maximum amplitude southern halo incurs the lowest orbit insertion cost for direct transfers but the maximum cost for lunar gravity assist transfers. The minimum amplitude halo is the most expensive destination for direct transfers but the least expensive for lunar gravity assist transfers. The on-orbit abort costs for three halos are computed as a function of abort time and return time. Finally, an architecture analysis is performed to determine launch and on-orbit vehicle requirements for halo orbit missions.

Dynamical Constraints On The Galaxy-Halo Connection

Science.gov (United States)

Desmond, Harry

2017-07-01

Dark matter halos comprise the bulk of the universe's mass, yet must be probed by the luminous galaxies that form within them. A key goal of modern astrophysics, therefore, is to robustly relate the visible and dark mass, which to first order means relating the properties of galaxies and halos. This may be expected not only to improve our knowledge of galaxy formation, but also to enable high-precision cosmological tests using galaxies and hence maximise the utility of future galaxy surveys. As halos are inaccessible to observations - as galaxies are to N-body simulations - this relation requires an additional modelling step.The aim of this thesis is to develop and evaluate models of the galaxy-halo connection using observations of galaxy dynamics. In particular, I build empirical models based on the technique of halo abundance matching for five key dynamical scaling relations of galaxies - the Tully-Fisher, Faber-Jackson, mass-size and mass discrepancy-acceleration relations, and Fundamental Plane - which relate their baryon distributions and rotation or velocity dispersion profiles. I then develop a statistical scheme based on approximate Bayesian computation to compare the predicted and measured values of a number of summary statistics describing the relations' important features. This not only provides quantitative constraints on the free parameters of the models, but also allows absolute goodness-of-fit measures to be formulated. I find some features to be naturally accounted for by an abundance matching approach and others to impose new constraints on the galaxy-halo connection; the remainder are challenging to account for and may imply galaxy-halo correlations beyond the scope of basic abundance matching.Besides providing concrete statistical tests of specific galaxy formation theories, these results will be of use for guiding the inputs of empirical and semi-analytic galaxy formation models, which require galaxy-halo correlations to be imposed by hand. As

Dark energy and extended dark matter halos

Science.gov (United States)

Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

2012-03-01

The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

Structure study in the 19C halo

International Nuclear Information System (INIS)

Angelique, J.C.; Le Brun, C.; Liegard, E.; Marques, F.M.; Orr, N.A.

1997-01-01

The halo nuclei are nuclei which have one or more neutrons (or protons) with very weak binding energy what results in a spatial extension beyond the core containing the other nucleons. This important spatial extension is related via the Heisenberg principle to a narrow momentum distribution which signs the halo structure of the nucleus under consideration. To extend our understanding of this phenomenon an experiment has been carried out with the DEMON multidetector in the frame of the collaboration E133. The subject was the study of 19 C, a nucleus susceptible of having a neutron halo due to the low binding energy of its last neutron (S n = 240 ± 100 keV). The 19 C secondary beam was produced by fragmentation of a primary 40 Ar beam in a carbon target between the two solenoids of SISSI and than directed to a GANIL experimental room. A silicon detector telescope was used to detect the charged particles issued from the reaction of 19 C nuclei with the tantalum target while the DEMON detection modular assembly separated by four meters from the target allowed the neutron detection between 0 and 42 degrees. The first results of this analysis are favorable to a halo structure for this nucleus for the reaction channel in which the 18 C core is destroyed. We have compared the angular distribution of the neutrons of 19 C with those obtained from the breakup reactions of other exotic nuclei ( 21 N, 22 O and 24 F) but having no halo structure. A net different behavior of these nuclei indicate a clear difference in structure. Actually, the 19 C distribution corresponds to the superposition of a broad distribution and narrow distribution. The last one having width of 42 ± 12 MeV/c, compatible with an important spatial extension, corresponds to neutrons coming from the halo. It is argued that the model in which the halo neutron moves on a s orbital cannot described the structure of 19 C halo. A more adequate description would be a mixture of s and d orbitals which would also

THE EATING HABITS OF MILKY WAY-MASS HALOS: DESTROYED DWARF SATELLITES AND THE METALLICITY DISTRIBUTION OF ACCRETED STARS

Energy Technology Data Exchange (ETDEWEB)

Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H., E-mail: adeason@stanford.edu [Kavli Institute for Particle Astrophysics and Cosmology and Physics Department, Stanford University, Stanford, CA 94305 (United States)

2016-04-10

We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M{sub vir} ∼ 10{sup 12.1} M{sub ⊙}) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M{sub star} ∼ 10{sup 8}–10{sup 10}M{sub ⊙}. Halos with more quiescent accretion histories tend to have lower mass progenitors (10{sup 8}–10{sup 9} M{sub ⊙}), and lower overall accreted stellar masses. Ultra-faint mass (M{sub star} < 10{sup 5} M{sub ⊙}) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10{sup 5} < M{sub star}/M{sub ⊙} < 10{sup 8} provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M{sub star} > 10{sup 8} M{sub ⊙} can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.

New 20-cm radio-continuum study of the small Magellanic cloud - part III: Compact Hii regions

Directory of Open Access Journals (Sweden)

Wong G.F.

2012-01-01

Full Text Available We present and discuss a new catalogue of 48 compact Hii regions in the Small Magellanic Cloud (SMC and a newly created deep 1420 MHz (λ=20 cm radio-continuum image of the N19 region located in the southwestern part of the SMC. The new images were created by merging 1420 MHz radiocontinuum archival data from the Australian Telescope Compact Array. The majority of these detected radio compact Hii regions have rather flat spectral indices which indicates, as expected, that the dominant emission mechanism is of thermal nature.

El halo de la memoria

OpenAIRE

GAVINO ROSELLÓ, AARÓN

2017-01-01

The halo effect is one of the most classic cognitive biases of psychology, and one that we can observe frequently in everyday life. It consists in the realization of an erroneous generalization from a single characteristic or quality of an object or a person, that is, we make a previous judgment from which, we generalize the rest of characteristics. The halo effect manifests itself as continuous in our life. For example, if someone is very handsome or attractive we attribute another series...

Chataika Halo.pmd

African Journals Online (AJOL)

Prof. Adipala Ekwamu

INHERITANCE OF HALO BLIGHT RESISTANCE IN COMMON BEAN ... pv phaseolicola (Psp) is a serious seed-borne disease of common bean ... a toxin produced by the Psp bacterium when ... stakes or in association with maize for support.

DARK MATTER SUB-HALO COUNTS VIA STAR STREAM CROSSINGS

International Nuclear Information System (INIS)

Carlberg, R. G.

2012-01-01

Dark matter sub-halos create gaps in the stellar streams orbiting in the halos of galaxies. We evaluate the sub-halo stream crossing integral with the guidance of simulations to find that the linear rate of gap creation, R U , in a typical cold dark matter (CDM) galactic halo at 100 kpc is R U ≅0.0066 M-hat 8 -0.35 kpc -1 Gyr -1 , where M-hat 8 (≡ M-hat /10 8 M ☉ ) is the minimum mass halo that creates a visible gap. The relation can be recast entirely in terms of observables, as R U ≅0.059w -0.85 kpc -1 Gyr -1 , for w in kpc, normalized at 100 kpc. Using published data, the density of gaps is estimated for M31's NW stream and the Milky Way Pal 5 stream, Orphan stream, and Eastern Banded Structure. The estimated rates of gap creation all have errors of 50% or more due to uncertain dynamical ages and the relatively noisy stream density measurements. The gap-rate-width data are in good agreement with the CDM-predicted relation. The high density of gaps in the narrow streams requires a total halo population of 10 5 sub-halos above a minimum mass of 10 5 M ☉ .

Does the chemical signature of TYC 8442-1036-1 originate from a rotating massive star that died in a faint explosion?

Science.gov (United States)

Cescutti, G.; Valentini, M.; François, P.; Chiappini, C.; Depagne, E.; Christlieb, N.; Cortés, C.

2016-11-01

Context. We have recently investigated the origin of chemical signatures observed in Galactic halo stars by means of a stochastic chemical evolution model. We found that rotating massive stars are a promising way to explain several signatures observed in these fossil stars. Aims: We discuss how the extremely metal-poor halo star TYC 8442-1036-1, for which we have now obtained detailed abundances from VLT-UVES spectra, fits into the framework of our previous work. Methods: We applied a standard one-dimensional (1D) LTE analysis to the spectrum of this star. We measured the abundances of 14 chemical elements; we computed the abundances for Na, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, and Zn using equivalent widths; we obtained the abundances for C, Sr, and Ba by means of synthetic spectra generated by MOOG. Results: We find an abundance of [Fe/H] = -3.5 ±0.13 dex based on our high-resolution spectrum; this points to an iron content that is lower by a factor of three (0.5 dex) compared to that obtained by a low-resolution spectrum. The star has a [C/Fe] = 0.4 dex, and it is not carbon enhanced like most of the stars at this metallicity. Moreover, this star lies in the plane [Ba/Fe] versus [Fe/H] in a relatively unusual position, shared by a few other Galactic halo stars, which is only marginally explained by our past results. Conclusions: The comparison of the model results with the chemical abundance characteristics of this group of stars can be improved if we consider in our model the presence of faint supernovae coupled with rotating massive stars. These results seem to imply that rotating massive stars and faint supernovae scenarios are complementary to each other, and are both required in order to match the observed chemistry of the earliest phases of the chemical enrichment of the Universe. Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 094.B-0781(A); P.I. G. Cescutti).

Mechanical device for enhancing halo density in the TMX-U tandem mirror

International Nuclear Information System (INIS)

Hsu, W.L.; Barr, W.L.; Simonen, T.C.

1984-04-01

The halo recycler, a mechanical device similar to pumped limiters used in tokamaks, is studied as a means of enhancing the halo plasma density in the Tandem Mirror Experiment Upgrade (TMX-U). The recycler structure consists of an annular chamber at each end of the tandem mirror device where the halo plasma is collected. The halo plasma density is increased by recycling the halo ions as they are neutralized by the collector plate. With sufficient power fed into the halo electrons, the recycler can sustain an upstream electron temperature of 30 eV for effective halo shielding while maintaining a low temperature of 5 eV near the collector plate to reduce sputtering. A power flow model has shown that the required power for heating the halo is low enough to make the halo recycler a practical concept

The shape of the invisible halo: N-body simulations on parallel supercomputers

Energy Technology Data Exchange (ETDEWEB)

Warren, M.S.; Zurek, W.H. (Los Alamos National Lab., NM (USA)); Quinn, P.J. (Australian National Univ., Canberra (Australia). Mount Stromlo and Siding Spring Observatories); Salmon, J.K. (California Inst. of Tech., Pasadena, CA (USA))

1990-01-01

We study the shapes of halos and the relationship to their angular momentum content by means of N-body (N {approximately} 10{sup 6}) simulations. Results indicate that in relaxed halos with no apparent substructure: (i) the shape and orientation of the isodensity contours tends to persist throughout the virialised portion of the halo; (ii) most ({approx}70%) of the halos are prolate; (iii) the approximate direction of the angular momentum vector tends to persist throughout the halo; (iv) for spherical shells centered on the core of the halo the magnitude of the specific angular momentum is approximately proportional to their radius; (v) the shortest axis of the ellipsoid which approximates the shape of the halo tends to align with the rotation axis of the halo. This tendency is strongest in the fastest rotating halos. 13 refs., 4 figs.

A diffusive model for halo width growth during vertical displacement events

International Nuclear Information System (INIS)

Eidietis, N.W.; Humphreys, D.A.

2011-01-01

The electromagnetic loads produced by halo currents during vertical displacement events (VDEs) impose stringent requirements on the strength of ITER in-vessel components. A predictive understanding of halo current evolution is essential for ensuring the robust design of these components. A significant factor determining that evolution is the plasma resistance, which is a function of three quantities: the resistivities of the core and halo regions, and the halo region width. A diffusive model of halo width growth during VDEs has been developed, which provides one part of a physics basis for predictive halo current simulations. The diffusive model was motivated by DIII-D observations that VDEs with cold post-thermal quench plasma and a current decay time much faster than the vertical motion (type I VDE) possess much wider halo region widths than warmer plasma VDEs, where the current decay is much slower than the vertical motion (type II). A 2D finite element code is used to model the diffusion of toroidal halo current during selected type I and type II DIII-D VDEs. The model assumes a core plasma region within the last closed flux surface (LCFS) diffusing current into a halo plasma filling the vessel outside the LCFS. LCFS motion and plasma temperature are prescribed from experimental observations. The halo width evolution produced by this model compares favourably with experimental measurements of type I and type II toroidal halo current width evolution.

Controlling beam halo-chaos via backstepping design

International Nuclear Information System (INIS)

Gao Yuan; Kong Feng

2008-01-01

A backstepping control method is proposed for controlling beam halo-chaos in the periodic focusing channels (PFCs) of high-current ion accelerator. The analysis and numerical results show that the method, via adjusting an exterior magnetic field, is effective to control beam halo chaos with five types of initial distribution ion beams, all statistical quantities of the beam halo-chaos are largely reduced, and the uniformity of ion beam is improved. This control method has an important value of application, for the exterior magnetic field can be easily adjusted in the periodical magnetic focusing channels in experiment

Close entrainment of massive molecular gas flows by radio bubbles in the central galaxy of Abell 1795

Science.gov (United States)

Russell, H. R.; McNamara, B. R.; Fabian, A. C.; Nulsen, P. E. J.; Combes, F.; Edge, A. C.; Hogan, M. T.; McDonald, M.; Salomé, P.; Tremblay, G.; Vantyghem, A. N.

2017-12-01

We present new ALMA observations tracing the morphology and velocity structure of the molecular gas in the central galaxy of the cluster Abell 1795. The molecular gas lies in two filaments that extend 5-7 kpc to the N and S from the nucleus and project exclusively around the outer edges of two inner radio bubbles. Radio jets launched by the central active galactic nucleus have inflated bubbles filled with relativistic plasma into the hot atmosphere surrounding the central galaxy. The N filament has a smoothly increasing velocity gradient along its length from the central galaxy's systemic velocity at the nucleus to -370 km s^{-1}, the average velocity of the surrounding galaxies, at the furthest extent. The S filament has a similarly smooth but shallower velocity gradient and appears to have partially collapsed in a burst of star formation. The close spatial association with the radio lobes, together with the ordered velocity gradients and narrow velocity dispersions, shows that the molecular filaments are gas flows entrained by the expanding radio bubbles. Assuming a Galactic XCO factor, the total molecular gas mass is 3.2 ± 0.2 × 109 M⊙. More than half lies above the N radio bubble. Lifting the molecular clouds appears to require an infeasibly efficient coupling between the molecular gas and the radio bubble. The energy required also exceeds the mechanical power of the N radio bubble by a factor of 2. Stimulated feedback, where the radio bubbles lift low-entropy X-ray gas that becomes thermally unstable and rapidly cools in situ, provides a plausible model. Multiple generations of radio bubbles are required to lift this substantial gas mass. The close morphological association then indicates that the cold gas either moulds the newly expanding bubbles or is itself pushed aside and shaped as they inflate.

Merged ozone profiles from four MIPAS processors

Science.gov (United States)

Laeng, Alexandra; von Clarmann, Thomas; Stiller, Gabriele; Dinelli, Bianca Maria; Dudhia, Anu; Raspollini, Piera; Glatthor, Norbert; Grabowski, Udo; Sofieva, Viktoria; Froidevaux, Lucien; Walker, Kaley A.; Zehner, Claus

2017-04-01

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared (IR) limb emission spectrometer on the Envisat platform. Currently, there are four MIPAS ozone data products, including the operational Level-2 ozone product processed at ESA, with the scientific prototype processor being operated at IFAC Florence, and three independent research products developed by the Istituto di Fisica Applicata Nello Carrara (ISAC-CNR)/University of Bologna, Oxford University, and the Karlsruhe Institute of Technology-Institute of Meteorology and Climate Research/Instituto de Astrofísica de Andalucía (KIT-IMK/IAA). Here we present a dataset of ozone vertical profiles obtained by merging ozone retrievals from four independent Level-2 MIPAS processors. We also discuss the advantages and the shortcomings of this merged product. As the four processors retrieve ozone in different parts of the spectra (microwindows), the source measurements can be considered as nearly independent with respect to measurement noise. Hence, the information content of the merged product is greater and the precision is better than those of any parent (source) dataset. The merging is performed on a profile per profile basis. Parent ozone profiles are weighted based on the corresponding error covariance matrices; the error correlations between different profile levels are taken into account. The intercorrelations between the processors' errors are evaluated statistically and are used in the merging. The height range of the merged product is 20-55 km, and error covariance matrices are provided as diagnostics. Validation of the merged dataset is performed by comparison with ozone profiles from ACE-FTS (Atmospheric Chemistry Experiment-Fourier Transform Spectrometer) and MLS (Microwave Limb Sounder). Even though the merging is not supposed to remove the biases of the parent datasets, around the ozone volume mixing ratio peak the merged product is found to have a smaller (up to 0.1 ppmv

Chemical Cartography. I. A Carbonicity Map of the Galactic Halo

Energy Technology Data Exchange (ETDEWEB)

Lee, Young Sun; Kim, Young Kwang [Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134 (Korea, Republic of); Beers, Timothy C.; Placco, Vinicius; Yoon, Jinmi [Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556 (United States); Carollo, Daniela [Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 (Australia); Masseron, Thomas [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Jung, Jaehun, E-mail: youngsun@cnu.ac.kr [Department of Astronomy, Space Science, and Geology, Chungnam National University, Daejeon 34134 (Korea, Republic of)

2017-02-10

We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H] = −1.5 and −2.2, respectively. From consideration of the absolute carbon abundances for our sample, A (C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP- s stars (those with strong overabundances of elements associated with the s -process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP- s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP- s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.

LISA detection of massive black hole binaries: imprint of seed populations and extreme recoils

International Nuclear Information System (INIS)

Sesana, A; Volonteri, M; Haardt, F

2009-01-01

All the physical processes involved in the formation, merging and accretion history of massive black holes along the hierarchical build-up of cosmic structures are likely to leave an imprint on the gravitational waves detectable by future space-borne missions, such as LISA. We report here the results of recent studies, carried out by means of dedicated simulations of black hole build-up, aiming at understanding the impact on LISA observations of two ingredients that are crucial in every massive black hole formation scenario, namely: (i) the nature and abundance of the first black hole seeds and (ii) the large gravitational recoils following the merger of highly spinning black holes. We predict LISA detection rates spanning two orders of magnitude, in the range 3-300 events per year, depending on the detail of the assumed massive black hole seed model. On the other hand, large recoil velocities do not dramatically compromise the efficiency of LISA observations. The number of detections may drop substantially (by ∼60%), in scenarios characterized by abundant light seeds, but if seeds are already massive and/or relatively rare, the detection rate is basically unaffected.

Massive stars in advanced evolutionary stages, and the progenitor of GW150914

Science.gov (United States)

Hamann, Wolf-Rainer; Oskinova, Lidia; Todt, Helge; Sander, Andreas; Hainich, Rainer; Shenar, Tomer; Ramachandran, Varsha

2017-11-01

The recent discovery of a gravitational wave from the merging of two black holes of about 30 solar masses each challenges our incomplete understanding of massive stars and their evolution. Critical ingredients comprise mass-loss, rotation, magnetic fields, internal mixing, and mass transfer in close binary systems. The imperfect knowledge of these factors implies large uncertainties for models of stellar populations and their feedback. In this contribution we summarize our empirical studies of Wolf-Rayet populations at different metallicities by means of modern non-LTE stellar atmosphere models, and confront these results with the predictions of stellar evolution models. At the metallicity of our Galaxy, stellar winds are probably too strong to leave remnant masses as high as ~30 M⊙, but given the still poor agreement between evolutionary tracks and observation even this conclusion is debatable. At the low metallicity of the Small Magellanic Cloud, all WN stars which are (at least now) single are consistent with evolving quasi-homogeneously. O and B-type stars, in contrast, seem to comply with standard evolutionary models without strong internal mixing. Close binaries which avoided early merging could evolve quasi-homogeneously and lead to close compact remnants of relatively high masses that merge within a Hubble time.

Baryonic pinching of galactic dark matter halos

International Nuclear Information System (INIS)

Gustafsson, Michael; Fairbairn, Malcolm; Sommer-Larsen, Jesper

2006-01-01

High resolution cosmological N-body simulations of four galaxy-scale dark matter halos are compared to corresponding N-body/hydrodynamical simulations containing dark matter, stars and gas. The simulations without baryons share features with others described in the literature in that the dark matter density slope continuously decreases towards the center, with a density ρ DM ∝r -1.3±0.2 , at about 1% of the virial radius for our Milky Way sized galaxies. The central cusps in the simulations which also contain baryons steepen significantly, to ρ DM ∝r -1.9±0.2 , with an indication of the inner logarithmic slope converging. Models of adiabatic contraction of dark matter halos due to the central buildup of stellar/gaseous galaxies are examined. The simplest and most commonly used model, by Blumenthal et al., is shown to overestimate the central dark matter density considerably. A modified model proposed by Gnedin et al. is tested and it is shown that, while it is a considerable improvement, it is not perfect. Moreover, it is found that the contraction parameters in their model not only depend on the orbital structure of the dark-matter-only halos but also on the stellar feedback prescription which is most relevant for the baryonic distribution. Implications for dark matter annihilation at the galactic center are discussed and it is found that, although our simulations show a considerable reduced dark matter halo contraction as compared to the Blumenthal et al. model, the fluxes from dark matter annihilation are still expected to be enhanced by at least a factor of a hundred, as compared to dark-matter-only halos. Finally, it is shown that, while dark-matter-only halos are typically prolate, the dark matter halos containing baryons are mildly oblate with minor-to-major axis ratios of c/a=0.73±0.11, with their flattening aligned with the central baryonic disks

THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

International Nuclear Information System (INIS)

Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke; Zheng Zheng; Shen Yue

2012-01-01

We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02 h –1 Mpc p –1 Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing ∼48, 000 quasars in the redshift range 0.4 ∼ sat = (7.4 ± 1.4) × 10 –4 , be satellites in dark matter halos. At z ∼ 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M cen = 4.1 +0.3 –0.4 × 10 12 h –1 M ☉ and M sat = 3.6 +0.8 –1.0 × 10 14 h –1 M ☉ , respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos—the inferred median mass of halos hosting central quasars at z ∼ 3.2 is M cen = 14.1 +5.8 –6.9 × 10 12 h –1 M ☉ . The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f q = 7.3 +0.6 –1.5 × 10 –4 at z ∼ 1.4 and f q = 8.6 +20.4 –7.2 × 10 –2 at z ∼ 3.2. We discuss the implications of our results for quasar evolution and quasar-galaxy co-evolution.

Halo-Independent Direct Detection Analyses Without Mass Assumptions

CERN Document Server

Anderson, Adam J.; Kahn, Yonatan; McCullough, Matthew

2015-10-06

Results from direct detection experiments are typically interpreted by employing an assumption about the dark matter velocity distribution, with results presented in the $m_\\chi-\\sigma_n$ plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the $v_{min}-\\tilde{g}$ plane, but these in turn require an assumption on the dark matter mass. Here we present an extension of these halo-independent methods for dark matter direct detection which does not require a fiducial choice of the dark matter mass. With a change of variables from $v_{min}$ to nuclear recoil momentum ($p_R$), the full halo-independent content of an experimental result for any dark matter mass can be condensed into a single plot as a function of a new halo integral variable, which we call $\\tilde{h}(p_R)$. The entire family of conventional halo-independent $\\tilde{g}(v_{min})$ plots for all DM masses are directly found from the single $\\tilde{h}(p_R)$ plot through a simple re...

Merging history of three bimodal clusters

Science.gov (United States)

Maurogordato, S.; Sauvageot, J. L.; Bourdin, H.; Cappi, A.; Benoist, C.; Ferrari, C.; Mars, G.; Houairi, K.

2011-01-01

We present a combined X-ray and optical analysis of three bimodal galaxy clusters selected as merging candidates at z ~ 0.1. These targets are part of MUSIC (MUlti-Wavelength Sample of Interacting Clusters), which is a general project designed to study the physics of merging clusters by means of multi-wavelength observations. Observations include spectro-imaging with XMM-Newton EPIC camera, multi-object spectroscopy (260 new redshifts), and wide-field imaging at the ESO 3.6 m and 2.2 m telescopes. We build a global picture of these clusters using X-ray luminosity and temperature maps together with galaxy density and velocity distributions. Idealized numerical simulations were used to constrain the merging scenario for each system. We show that A2933 is very likely an equal-mass advanced pre-merger ~200 Myr before the core collapse, while A2440 and A2384 are post-merger systems (~450 Myr and ~1.5 Gyr after core collapse, respectively). In the case of A2384, we detect a spectacular filament of galaxies and gas spreading over more than 1 h-1 Mpc, which we infer to have been stripped during the previous collision. The analysis of the MUSIC sample allows us to outline some general properties of merging clusters: a strong luminosity segregation of galaxies in recent post-mergers; the existence of preferential axes - corresponding to the merging directions - along which the BCGs and structures on various scales are aligned; the concomitance, in most major merger cases, of secondary merging or accretion events, with groups infalling onto the main cluster, and in some cases the evidence of previous merging episodes in one of the main components. These results are in good agreement with the hierarchical scenario of structure formation, in which clusters are expected to form by successive merging events, and matter is accreted along large-scale filaments. Based on data obtained with the European Southern Observatory, Chile (programs 072.A-0595, 075.A-0264, and 079.A-0425

ZOMG - III. The effect of halo assembly on the satellite population

Science.gov (United States)

Garaldi, Enrico; Romano-Díaz, Emilio; Borzyszkowski, Mikolaj; Porciani, Cristiano

2018-01-01

We use zoom hydrodynamical simulations to investigate the properties of satellites within galaxy-sized dark-matter haloes with different assembly histories. We consider two classes of haloes at redshift z = 0: 'stalled' haloes that assembled at z > 1 and 'accreting' ones that are still forming nowadays. Previously, we showed that the stalled haloes are embedded within thick filaments of the cosmic web, while the accreting ones lie where multiple thin filaments converge. We find that satellites in the two classes have both similar and different properties. Their mass spectra, radial count profiles, baryonic and stellar content, and the amount of material they shed are indistinguishable. However, the mass fraction locked in satellites is substantially larger for the accreting haloes as they experience more mergers at late times. The largest difference is found in the satellite kinematics. Substructures fall towards the accreting haloes along quasi-radial trajectories whereas an important tangential velocity component is developed, before accretion, while orbiting the filament that surrounds the stalled haloes. Thus, the velocity anisotropy parameter of the satellites (β) is positive for the accreting haloes and negative for the stalled ones. This signature enables us to tentatively categorize the Milky Way halo as stalled based on a recent measurement of β. Half of our haloes contain clusters of satellites with aligned orbital angular momenta corresponding to flattened structures in space. These features are not driven by baryonic physics and are only found in haloes hosting grand-design spiral galaxies, independently of their assembly history.

Studying dark matter haloes with weak lensing

NARCIS (Netherlands)

Velander, Malin Barbro Margareta

2012-01-01

Our Universe is comprised not only of normal matter but also of unknown components: dark matter and dark energy. This Thesis recounts studies of dark matter haloes, using a technique known as weak gravitational lensing, in order to learn more about the nature of these dark components. The haloes

The globular cluster-dark matter halo connection

Science.gov (United States)

Boylan-Kolchin, Michael

2017-12-01

I present a simple phenomenological model for the observed linear scaling of the stellar mass in old globular clusters (GCs) with z = 0 halo mass in which the stellar mass in GCs scales linearly with progenitor halo mass at z = 6 above a minimum halo mass for GC formation. This model reproduces the observed MGCs-Mhalo relation at z = 0 and results in a prediction for the minimum halo mass at z = 6 required for hosting one GC: Mmin(z = 6) = 1.07 × 109 M⊙. Translated to z = 0, the mean threshold mass is Mhalo(z = 0) ≈ 2 × 1010 M⊙. I explore the observability of GCs in the reionization era and their contribution to cosmic reionization, both of which depend sensitively on the (unknown) ratio of GC birth mass to present-day stellar mass, ξ. Based on current detections of z ≳ 6 objects with M1500 10 are strongly disfavoured; this, in turn, has potentially important implications for GC formation scenarios. Even for low values of ξ, some observed high-z galaxies may actually be GCs, complicating estimates of reionization-era galaxy ultraviolet luminosity functions and constraints on dark matter models. GCs are likely important reionization sources if 5 ≲ ξ ≲ 10. I also explore predictions for the fraction of accreted versus in situ GCs in the local Universe and for descendants of systems at the halo mass threshold of GC formation (dwarf galaxies). An appealing feature of the model presented here is the ability to make predictions for GC properties based solely on dark matter halo merger trees.

The immitigable nature of assembly bias: the impact of halo definition on assembly bias

Science.gov (United States)

Villarreal, Antonio S.; Zentner, Andrew R.; Mao, Yao-Yuan; Purcell, Chris W.; van den Bosch, Frank C.; Diemer, Benedikt; Lange, Johannes U.; Wang, Kuan; Campbell, Duncan

2017-11-01

Dark matter halo clustering depends not only on halo mass, but also on other properties such as concentration and shape. This phenomenon is known broadly as assembly bias. We explore the dependence of assembly bias on halo definition, parametrized by spherical overdensity parameter, Δ. We summarize the strength of concentration-, shape-, and spin-dependent halo clustering as a function of halo mass and halo definition. Concentration-dependent clustering depends strongly on mass at all Δ. For conventional halo definitions (Δ ∼ 200 - 600 m), concentration-dependent clustering at low mass is driven by a population of haloes that is altered through interactions with neighbouring haloes. Concentration-dependent clustering can be greatly reduced through a mass-dependent halo definition with Δ ∼ 20 - 40 m for haloes with M200 m ≲ 1012 h-1M⊙. Smaller Δ implies larger radii and mitigates assembly bias at low mass by subsuming altered, so-called backsplash haloes into now larger host haloes. At higher masses (M200 m ≳ 1013 h-1M⊙) larger overdensities, Δ ≳ 600 m, are necessary. Shape- and spin-dependent clustering are significant for all halo definitions that we explore and exhibit a relatively weaker mass dependence. Generally, both the strength and the sense of assembly bias depend on halo definition, varying significantly even among common definitions. We identify no halo definition that mitigates all manifestations of assembly bias. A halo definition that mitigates assembly bias based on one halo property (e.g. concentration) must be mass dependent. The halo definitions that best mitigate concentration-dependent halo clustering do not coincide with the expected average splashback radii at fixed halo mass.

Testing approximate predictions of displacements of cosmological dark matter halos

Energy Technology Data Exchange (ETDEWEB)

Munari, Emiliano; Monaco, Pierluigi; Borgani, Stefano [Department of Physics, Astronomy Unit, University of Trieste, via Tiepolo 11, I-34143 Trieste (Italy); Koda, Jun [INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (Italy); Kitaura, Francisco-Shu [Instituto de Astrofísica de Canarias, 38205 San Cristóbal de La Laguna, Santa Cruz de Tenerife (Spain); Sefusatti, Emiliano, E-mail: munari@oats.inaf.it, E-mail: monaco@oats.inaf.it, E-mail: jun.koda@brera.inaf.it, E-mail: fkitaura@iac.es, E-mail: sefusatti@oats.inaf.it, E-mail: borgani@oats.inaf.it [INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, I-34143 Trieste (Italy)

2017-07-01

We present a test to quantify how well some approximate methods, designed to reproduce the mildly non-linear evolution of perturbations, are able to reproduce the clustering of DM halos once the grouping of particles into halos is defined and kept fixed. The following methods have been considered: Lagrangian Perturbation Theory (LPT) up to third order, Truncated LPT, Augmented LPT, MUSCLE and COLA. The test runs as follows: halos are defined by applying a friends-of-friends (FoF) halo finder to the output of an N-body simulation. The approximate methods are then applied to the same initial conditions of the simulation, producing for all particles displacements from their starting position and velocities. The position and velocity of each halo are computed by averaging over the particles that belong to that halo, according to the FoF halo finder. This procedure allows us to perform a well-posed test of how clustering of the matter density and halo density fields are recovered, without asking to the approximate method an accurate reconstruction of halos. We have considered the results at z =0,0.5,1, and we have analysed power spectrum in real and redshift space, object-by-object difference in position and velocity, density Probability Distribution Function (PDF) and its moments, phase difference of Fourier modes. We find that higher LPT orders are generally able to better reproduce the clustering of halos, while little or no improvement is found for the matter density field when going to 2LPT and 3LPT. Augmentation provides some improvement when coupled with 2LPT, while its effect is limited when coupled with 3LPT. Little improvement is brought by MUSCLE with respect to Augmentation. The more expensive particle-mesh code COLA outperforms all LPT methods, and this is true even for mesh sizes as large as the inter-particle distance. This test sets an upper limit on the ability of these methods to reproduce the clustering of halos, for the cases when these objects are