WorldWideScience

Sample records for 21cm angular power

  1. The CMBR ISW and HI 21-cm Cross-correlation Angular Power Spectrum

    CERN Document Server

    Sarkar, Tapomoy Guha; Bharadwaj, Somnath

    2008-01-01

    The late-time growth of large scale structures (LSS) is imprinted in the CMBR anisotropy through the Integrated Sachs Wolfe (ISW) effect. This is perceived to be a very important observational probe of dark energy. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the possibility of detecting the ISW through cross-correlations between the CMBR anisotropies and redshifted 21-cm observations. Assuming that the HI traces the dark matter, we find that the ISW-HI cross-correlation angular power spectrum at an angular multipole l is proportional to the dark matter power spectrum evaluated at the comoving wave number l/r, where r is the comoving distance to the redshift from which the HI signal originated. The amplitude of the cross-correlation signal depends on parameters related to the HI distribution and the growth of cosmological perturbations. However the cross-correla...

  2. CMBR Weak Lensing and HI 21-cm Cross-correlation Angular Power Spectrum

    CERN Document Server

    Sarkar, Tapomoy Guha

    2009-01-01

    Weak gravitational lensing of the CMBR manifests as a secondary anisotropy in the temperature maps. The effect, quantified through the shear and convergence fields imprint the underlying large scale structure (LSS), geometry and evolution history of the Universe. It is hence perceived to be an important observational probe of cosmology. De-lensing the CMBR temperature maps is also crucial for detecting the gravitational wave generated B-modes. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the correlation between post-reionization HI signal and weak lensing convergence field. Assuming that the HI follows the dark matter distribution, the cross-correlation angular power spectrum at a multipole \\ell is found to be proportional to the cold dark matter power spectrum evaluated at \\ell/r, where r denotes the comoving distance to the redshift where the HI is located. Th...

  3. Contribution of Cross-Correlations to the 21cm Angular Power Spectrum in the Epoch of Reionization

    CERN Document Server

    Zheng, Qian

    2009-01-01

    Measurement of the 21cm hyperfine transition of neutral hydrogen provides a unique probe of the epoch of reionization and the Dark Ages. Three major mechanisms are believed to dominate the radiation process: emission from neutral hydrogen surrounding the ionized bubbles of first galaxies and/or quasars, emission from neutral hydrogen inside minihalos, and absorption of diffuse neutral hydrogen against the cosmic microwave background. In the present work, by simply combining the existing analytic models for the three mechanisms, we investigate the contribution of cross-correlation between these three components to the total 21cm angular power spectrum, in the sense that neutral hydrogen associated with different radiation processes traces the large-scale structures of underlying density perturbations. While the overall 21cm power spectrum remains almost unchanged with the inclusion of the cross-correlations, the cross-correlation may play a key role in the determination of the 21cm power spectrum during the tr...

  4. Detecting the 21cm Forest in the 21 cm Power Spectrum

    CERN Document Server

    Ewall-Wice, Aaron; Mesinger, Andrei; Hewitt, Jacqueline

    2013-01-01

    Measurements of the 21 cm brightness temperature at high redshift are expected to yield tremendous insight into the nature of the first stars and black holes. A first generation of experiments is already underway, seeking a first detection. The brightness temperature fluctuations to be measured, also contain absorption features in the spectra of high redshift radio sources, the 21 cm forest. We describe a new technique for constraining the radio loud population of active galactic nuclei at high redshift by measuring the imprint of the 21 cm forest on the 21 cm power spectrum. We analytically relate the 21 cm forest power spectrum to the optical depth power spectrum and the radio loud luminosity function. Using semi-numeric simulations of the intergalactic medium and a semi-empirical source population, we show that the 21 cm forest dominates a distinctive region of k-space, $k \\gtrsim 0.5 \\Mpci$, allowing for the simultaneous determination of the intergalactic medium's thermal properties and the radio loud pop...

  5. Foregrounds in Wide-Field Redshifted 21 cm Power Spectra

    CERN Document Server

    Thyagarajan, Nithyanandan; Bowman, Judd D; Barry, N; Beardsley, A P; Bernardi, G; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Dillon, Joshua S; Emrich, D; Ewall-Wice, A; Feng, L; Goeke, R; Greenhill, L J; Hazelton, B J; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kim, Han-Seek; Kittiwisit, P; Kratzenberg, E; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Neben, A R; Oberoi, D; Offringa, A R; Ord, S M; Paul, Sourabh; Pindor, B; Pober, J C; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Sullivan, I S; Tegmark, M; Tingay, S J; Trott, C M; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B

    2015-01-01

    Detection of 21 cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffu...

  6. Violation of statistical isotropy and homogeneity in the 21-cm power spectrum

    CERN Document Server

    Shiraishi, Maresuke; Kamionkowski, Marc; Raccanelli, Alvise

    2016-01-01

    Most inflationary models predict primordial perturbations to be statistically isotropic and homogeneous. Cosmic-Microwave-Background (CMB) observations, however, indicate a possible departure from statistical isotropy in the form of a dipolar power modulation at large angular scales. Alternative models of inflation, beyond the simplest single-field slow-roll models, can generate a small power asymmetry, consistent with these observations. Observations of clustering of quasars show, however, agreement with statistical isotropy at much smaller angular scales. Here we propose to use off-diagonal components of the angular power spectrum of the 21-cm fluctuations during the dark ages to test this power asymmetry. We forecast results for the planned SKA radio array, a future radio array, and the cosmic-variance-limited case as a theoretical proof of principle. Our results show that the 21-cm-line power spectrum will enable access to information at very small scales and at different redshift slices, thus improving u...

  7. The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology

    Science.gov (United States)

    Jacobs, Daniel C.; Hazelton, B. J.; Trott, C. M.; Dillon, Joshua S.; Pindor, B.; Sullivan, I. S.; Pober, J. C.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; de Oliveira-Costa, A.; Emrich, D.; Ewall-Wice, A.; Feng, L.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hewitt, J. N.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.; Kim, HS; Kratzenberg, E.; Lenc, E.; Line, J.; Loeb, A.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Neben, A. R.; Thyagarajan, N.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Udaya Shankar, N.; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Tegmark, M.; Tingay, S. J.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S. B.

    2016-07-01

    We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple independent data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction, and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds.

  8. The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology

    CERN Document Server

    Jacobs, Daniel C; Trott, C M; Dillon, Joshua S; Pindor, B; Sullivan, I S; Pober, J C; Barry, N; Beardsley, A P; Bernardi, G; Bowman, Judd D; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Emrich, D; Ewall-Wice, A; Feng, L; Gaensler, B M; Goeke, R; Greenhill, L J; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kim, H S; Kratzenberg, E; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Neben, A R; Thyagarajan, N; Oberoi, D; Offringa, A R; Ord, S M; Paul, S; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Tegmark, M; Tingay, S J; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B

    2016-01-01

    We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregr...

  9. The visibility based Tapered Gridded Estimator (TGE) for the redshifted 21-cm power spectrum

    CERN Document Server

    Choudhuri, Samir; Chatterjee, Suman; Ali, Sk Saiyad; Roy, Nirupam; Ghosh, Abhik

    2016-01-01

    We present the improved visibility based Tapered Gridded Estimator (TGE) for the power spectrum of the diffuse sky signal. The visibilities are gridded to reduce the computation, and tapered through a convolution to suppress the contribution from the outer regions of the telescope's field of view. The TGE also internally estimates the noise bias, and subtracts this out to give an unbiased estimate of the power spectrum. An earlier version of the 2D TGE for the angular power spectrum $C_{\\ell}$ is improved and then extended to obtain the 3D TGE for the power spectrum $P({\\bf k})$ of the 21-cm brightness temperature fluctuations. Analytic formulas are also presented for predicting the variance of the binned power spectrum. The estimator and its variance predictions are validated using simulations of $150 \\, {\\rm MHz}$ GMRT observations. We find that the estimator accurately recovers the input model for the 1D Spherical Power Spectrum $P(k)$ and the 2D Cylindrical Power Spectrum $P(k_\\perp,k_\\parallel)$, and the...

  10. Constraining cosmology and ionization history with combined 21 cm power spectrum and global signal measurements

    CERN Document Server

    Liu, Adrian

    2015-01-01

    Improvements in current instruments and the advent of next-generation instruments will soon push observational 21 cm cosmology into a new era, with high significance measurements of both the power spectrum and the mean ("global") signal of the 21 cm brightness temperature. In this paper we use the recently commenced Hydrogen Epoch of Reionization Array as a worked example to provide forecasts on astrophysical and cosmological parameter constraints. In doing so we improve upon previous forecasts in a number of ways. First, we provide updated forecasts using the latest best-fit cosmological parameters from the Planck satellite, exploring the impact of different Planck datasets on 21 cm experiments. We also show that despite the exquisite constraints that other probes have placed on cosmological parameters, the remaining uncertainties are still large enough to have a non-negligible impact on upcoming 21 cm data analyses. While this complicates high-precision constraints on reionization models, it provides an ave...

  11. Predictions for the 21cm-galaxy cross-power spectrum observable with LOFAR and Subaru

    CERN Document Server

    Vrbanec, Dijana; Jelić, Vibor; Jensen, Hannes; Zaroubi, Saleem; Fernandez, Elizabeth R; Ghosh, Abhik; Iliev, Ilian T; Kakiichi, Koki; Koopmans, Léon V E; Mellema, Garrelt

    2016-01-01

    The 21cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21cm emission from the EoR with the Low Frequency Array (LOFAR), and of high redshift Lyalpha emitters (LAEs) with Subaru's Hyper Suprime Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z=6.6. In this paper we use N-body + radiative transfer (both for continuum and Lyalpha photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21cm-galaxy cross-power spectrum, as well as to predict the 2D 21cm-galaxy cross-power spectrum expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21cm-galaxy cross-power spectrum show clear anti-correlation on s...

  12. Primordial non-Gaussianity from the 21 cm power spectrum during the epoch of reionization.

    Science.gov (United States)

    Joudaki, Shahab; Doré, Olivier; Ferramacho, Luis; Kaplinghat, Manoj; Santos, Mario G

    2011-09-23

    Primordial non-Gaussianity is a crucial test of inflationary cosmology. We consider the impact of non-Gaussianity on the ionization power spectrum from 21 cm emission at the epoch of reionization. We focus on the power spectrum on large scales at redshifts of 7 to 8 and explore the expected constraint on the local non-Gaussianity parameter f(NL) for current and next-generation 21 cm experiments. We show that experiments such as SKA and MWA could measure f(NL) values of order 10. This can be improved by an order of magnitude with a fast-Fourier transform telescope like Omniscope.

  13. Primordial Non-Gaussianity from the 21 cm Power Spectrum during the Epoch of Reionization

    OpenAIRE

    Joudaki, Shahab; Dore, Olivier; Ferramacho, Luis; Kaplinghat, Manoj; Santos, Mario G.

    2011-01-01

    Primordial non-Gaussianity is a crucial test of inflationary cosmology. We consider the impact of non-Gaussianity on the ionization power spectrum from 21 cm emission during the epoch of reionization. We focus on the power spectrum on large scales at redshifts of 7 to 8 and explore the expected constraint on the local non-Gaussianity parameter f_NL for current and next-generation 21 cm experiments. We show that experiments such as SKA and MWA could measure f_NL values of order 10. This can be...

  14. Predictions for the 21 cm-galaxy cross-power spectrum observable with LOFAR and Subaru

    Science.gov (United States)

    Vrbanec, Dijana; Ciardi, Benedetta; Jelić, Vibor; Jensen, Hannes; Zaroubi, Saleem; Fernandez, Elizabeth R.; Ghosh, Abhik; Iliev, Ilian T.; Kakiichi, Koki; Koopmans, Léon V. E.; Mellema, Garrelt

    2016-03-01

    The 21 cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21 cm emission from the EoR with the Low Frequency Array (LOFAR), and of high-redshift Ly α emitters with Subaru's Hyper Suprime-Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z = 6.6. In this paper, we use N-body + radiative transfer (both for continuum and Ly α photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21 cm-galaxy cross-power spectrum and cross-correlation function, as well as to predict the 2D 21 cm-galaxy cross-power spectrum and cross-correlation function expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21 cm-galaxy cross-power spectrum show clear anti-correlation on scales larger than ˜60 h-1 Mpc (corresponding to k ˜ 0.1 h Mpc-1), with levels of significance p = 0.003 at z = 6.6 and p = 0.08 at z = 7.3. On smaller scales, instead, the signal is completely contaminated. On the other hand, our 21 cm-galaxy cross-correlation function is strongly contaminated by noise on all scales, since the noise is no longer being separated by its k modes.

  15. First limits on the 21 cm power spectrum during the Epoch of X-ray heating

    NARCIS (Netherlands)

    Ewall-Wice, A.; Dillon, Joshua S.; Hewitt, J. N.; Loeb, A.; Mesinger, A.; Neben, A. R.; Offringa, A. R.; Tegmark, M.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; de Oliveira-Costa, A.; Emrich, D.; Feng, L.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hazelton, B. J.; Hurley-Walker, N.; Johnston-Hollitt, M.; Jacobs, Daniel C.; Kaplan, D. L.; Kasper, J. C.; Kim, HS; Kratzenberg, E.; Lenc, E.; Line, J.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Thyagarajan, Nithyanandan; Oberoi, D.; Ord, S. M.; Paul, S.; Pindor, B.; Pober, J. C.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Sullivan, I. S.; Tingay, S. J.; Trott, C. M.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S. B.

    2016-01-01

    We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly diff

  16. The Impact of Modeling Errors on Interferometer Calibration for 21 cm Power Spectra

    CERN Document Server

    Ewall-Wice, Aaron; Liu, Adrian; Hewitt, Jacqueline

    2016-01-01

    We study the impact of sky-based calibration errors from source mismodeling on 21 cm power spectrum measurements with an interferometer and propose a method for suppressing their effects. While emission from faint sources that are not accounted for in calibration catalogs is believed to be spectrally smooth, deviations of true visibilities from model visibilities are not, due to the inherent chromaticity of the interferometer's sky-response (the "wedge"). Thus, unmodeled foregrounds at the $\\approx 1$ mJy level introduce frequency structure into gain solutions on the same line-of-sight scales on which we hope to observe the cosmological signal. We derive analytic expressions describing these errors using linearized approximations of the calibration equations and determine the impact of this bias on measurements of the 21 cm power spectrum during the Epoch of Reionization (EoR). Given our current precision in primary beam and foreground modeling, this noise will significantly impact the sensitivity of existing...

  17. THE EFFECTS OF POLARIZED FOREGROUNDS ON 21 cm EPOCH OF REIONIZATION POWER SPECTRUM MEASUREMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Moore, David F.; Aguirre, James E. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA (United States); Parsons, Aaron R.; Pober, Jonathan C. [Astronomy Department, University of California, Berkeley, Berkeley, CA (United States); Jacobs, Daniel C., E-mail: damo@sas.upenn.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA (United States)

    2013-06-01

    Experiments aimed at detecting highly-redshifted 21 cm emission from the epoch of reionization (EoR) are plagued by the contamination of foreground emission. A potentially important source of contaminating foregrounds may be Faraday-rotated, polarized emission, which leaks into the estimate of the intrinsically unpolarized EoR signal. While these foregrounds' intrinsic polarization may not be problematic, the spectral structure introduced by the Faraday rotation could be. To better understand and characterize these effects, we present a simulation of the polarized sky between 120 and 180 MHz. We compute a single visibility, and estimate the three-dimensional power spectrum from that visibility using the delay spectrum approach presented in Parsons et al. Using the Donald C. Backer Precision Array to Probe the Epoch of Reionization as an example instrument, we show the expected leakage into the unpolarized power spectrum to be several orders of magnitude above the expected 21 cm EoR signal.

  18. Warm dark matter signatures on the 21cm power spectrum: Intensity mapping forecasts for SKA

    CERN Document Server

    Carucci, Isabella P; Viel, Matteo; Lapi, Andrea

    2015-01-01

    We investigate the impact that warm dark matter (WDM) has in terms of 21cm intensity mapping in the post-reionization Universe at z = 3 - 5. We perform hydrodynamic simulations for 5 different models: cold dark matter and WDM with 1,2,3,4 keV (thermal relic) mass and assign the neutral hydrogen a-posteriori using two different methods that both reproduce observations in terms of column density distribution function of neutral hydrogen systems. Contrary to naive expectations, the suppression of power present in the linear and non-linear matter power spectra, results in an increase of power in terms of neutral hydrogen and 21cm power spectra. This is due to the fact that there is a lack of small mass halos in WDM models with respect to cold dark matter: in order to distribute a total amount of neutral hydrogen within the two cosmological models, a larger quantity has to be placed in the most massive halos, that are more biased compared to the cold dark matter cosmology. We quantify this effect and address signi...

  19. Power spectrum extraction for redshifted 21-cm epoch of reionization experiments: the LOFAR case

    CERN Document Server

    Harker, Geraint; Bernardi, Gianni; Brentjens, Michiel A; de Bruyn, A G; Ciardi, Benedetta; Jelic, Vibor; Koopmans, Leon V E; Labropoulos, Panagiotis; Mellema, Garrelt; Offringa, Andre; Pandey, V N; Pawlik, Andreas H; Schaye, Joop; Thomas, Rajat M; Yatawatta, Sarod

    2010-01-01

    One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization (EoR) project is to measure the power spectrum of variations in the intensity of redshifted 21-cm radiation from the EoR. The sensitivity with which this power spectrum can be estimated depends on the level of thermal noise and sample variance, and also on the systematic errors arising from the extraction process, in particular from the subtraction of foreground contamination. We model the extraction process using realistic simulations of the cosmological signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR EoR experiment to the redshifted 21-cm power spectrum. Detection of emission from the EoR should be possible within 360 hours of observation with a single station beam. Integrating for longer, and synthesizing multiple station beams within the primary (tile) beam, then enables us to extract progressively more accurate estimates of the power at a greater range of scales and redshifts. We discuss different obs...

  20. Probing reionization with the cross power spectrum of 21 cm and near-infrared radiation backgrounds

    CERN Document Server

    Mao, Xiao-Chun

    2014-01-01

    The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from the high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then the intensity of NIR background is estimated by collecting emission from stars in the first-light galaxies. On large scales, we find the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolut...

  1. The impact of modelling errors on interferometer calibration for 21 cm power spectra

    Science.gov (United States)

    Ewall-Wice, Aaron; Dillon, Joshua S.; Liu, Adrian; Hewitt, Jacqueline

    2017-09-01

    We study the impact of sky-based calibration errors from source mismodelling on 21 cm power spectrum measurements with an interferometer and propose a method for suppressing their effects. While emission from faint sources that are not accounted for in calibration catalogues is believed to be spectrally smooth, deviations of true visibilities from model visibilities are not, due to the inherent chromaticity of the interferometer's sky response (the 'wedge'). Thus, unmodelled foregrounds, below the confusion limit of many instruments, introduce frequency structure into gain solutions on the same line-of-sight scales on which we hope to observe the cosmological signal. We derive analytic expressions describing these errors using linearized approximations of the calibration equations and estimate the impact of this bias on measurements of the 21 cm power spectrum during the epoch of reionization. Given our current precision in primary beam and foreground modelling, this noise will significantly impact the sensitivity of existing experiments that rely on sky-based calibration. Our formalism describes the scaling of calibration with array and sky-model parameters and can be used to guide future instrument design and calibration strategy. We find that sky-based calibration that downweights long baselines can eliminate contamination in most of the region outside of the wedge with only a modest increase in instrumental noise.

  2. A Fast Method for Power Spectrum and Foreground Analysis for 21 cm Cosmology

    CERN Document Server

    Dillon, Joshua S; Tegmark, Max

    2012-01-01

    We develop and demonstrate an acceleration of the Liu & Tegmark quadratic estimator formalism for inverse variance foreground subtraction and power spectrum estimation in 21 cm tomography from O(N^3) to O(N log N), where N is the number of voxels of data. This technique makes feasible the megavoxel scale analysis necessary for current and upcoming radio interferometers by making only moderately restrictive assumptions about foreground models and survey geometry. We exploit iterative and Monte Carlo techniques and the symmetries of the foreground covariance matrices to quickly estimate the 21 cm brightness temperature power spectrum, P(k_parallel, k_perpendicular), the Fisher information matrix, the error bars, the window functions, and the bias. We also extend the Liu & Tegmark foreground model to include bright point sources with known positions in a way that scales as O[(N log N)(N point sources)] < O(N^5/3). As a first application of our method, we forecast error bars and window functions for th...

  3. PAPER-64 Constraints on Reionization: The 21cm Power Spectrum at z=8.4

    CERN Document Server

    Ali, Zaki S; Zheng, Haoxuan; Pober, Jonathan C; Liu, Adrian; Aguirre, James E; Bradley, Richard F; Bernardi, Gianni; Carilli, Chris L; Cheng, Carina; DeBoer, David R; Dexter, Matthew R; Grobbelaar, Jasper; Horrell, Jasper; Jacobs, Daniel C; Klima, Pat; MacMahon, David H E; Maree, Matthys; Moore, David F; Razavi, Nima; Stefan, Irina I; Walbrugh, William P; Walker, Andre

    2015-01-01

    In this paper, we report new limits on 21cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. This work extends the work presented in Parsons et al. (2014) with more collecting area, a longer observing period, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optimal quadratic estimators. The result is a new $2\\sigma$ upper limit on $\\Delta^{2}(k)$ of (22.4 mK)$^2$ in the range $0.15 < k < 0.5h\\ {\\rm Mpc}^{-1}$ at $z = 8.4$. This represents a three-fold improvement over the previous best upper limit. As we discuss in more depth in a forthcoming paper (Pober et al. 2015, in prep), this upper limit supports and extends previous evidence against extremely cold reionization scenarios. We conclude with a discussion of implications for future 21cm reionization experiments, including the newly fun...

  4. Confirmation of Wide-Field Signatures in Redshifted 21 cm Power Spectra

    CERN Document Server

    Thyagarajan, Nithyanandan; Bowman, Judd D; Barry, N; Beardsley, A P; Bernardi, G; Briggs, F; Cappallo, R J; Carroll, P; Deshpande, A A; de Oliveira-Costa, A; Dillon, Joshua S; Ewall-Wice, A; Feng, L; Greenhill, L J; Hazelton, B J; Hernquist, L; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Kaplan, D L; Kim, Han-Seek; Kittiwisit, P; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Neben, A R; Oberoi, D; Offringa, A R; Ord, S M; Paul, Sourabh; Pindor, B; Pober, J C; Prabu, T; Procopio, P; Riding, J; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Sullivan, I S; Tegmark, M; Tingay, S J; Trott, C M; Wayth, R B; Webster, R L; Williams, A; Williams, C L; Wyithe, J S B

    2015-01-01

    We confirm our recent prediction of the "pitchfork" foreground signature in power spectra of high-redshift 21 cm measurements, wherein the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be most sensitive to the cosmological HI signal. In our recent paper, many signatures from the simulation which predicted this feature were validated against Murchison Widefield Array (MWA) data but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through coherent averaging of 12 independent snapshots with identical instrument settings, and provide the first confirmation of the prediction with a signal-noise ratio > 10. This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures proposed ...

  5. First Limits on the 21 cm Power Spectrum during the Epoch of X-ray heating

    CERN Document Server

    Ewall-Wice, A; Hewitt, J N; Loeb, A; Mesinger, A; Neben, A R; Offringa, A R; Tegmark, M; Barry, N; Beardsley, A P; Bernardi, G; Bowman, Judd D; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Emrich, D; Feng, L; Gaensler, B M; Goeke, R; Greenhill, L J; Hazelton, B J; Hurley-Walker, N; Johnston-Hollit, M; Jacobs, Daniel C; Kaplan, D L; Kasper, J C; Kim, HS; Kratzenberg, E; Lenc, E; Line, J; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Thyagarajan, Nithyanandan; Oberoi, D; Ord, S M; Paul, S; Pindor, B; Pober, J C; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Sullivan, I S; Tingay, S J; Trott, C M; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B

    2016-01-01

    We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most se...

  6. Constraining high-redshift X-ray sources with next generation 21-cm power spectrum measurements

    Science.gov (United States)

    Ewall-Wice, Aaron; Hewitt, Jacqueline; Mesinger, Andrei; Dillon, Joshua S.; Liu, Adrian; Pober, Jonathan

    2016-05-01

    We use the Fisher matrix formalism and seminumerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA), will place on the characteristics of the X-ray sources that heated the high-redshift intergalactic medium. Incorporating observations between z = 5 and 25, we find that the proposed 331 element HERA and SKA phase 1 will be capable of placing ≲ 10 per cent constraints on the spectral properties of these first X-ray sources, even if one is unable to perform measurements within the foreground contaminated `wedge' or the FM band. When accounting for the enhancement in power spectrum amplitude from spin temperature fluctuations, we find that the observable signatures of reionization extend well beyond the peak in the power spectrum usually associated with it. We also find that lower redshift degeneracies between the signatures of heating and reionization physics lead to errors on reionization parameters that are significantly greater than previously predicted. Observations over the heating epoch are able to break these degeneracies and improve our constraints considerably. For these two reasons, 21-cm observations during the heating epoch significantly enhance our understanding of reionization as well.

  7. Line of sight anisotropies in the Cosmic Dawn and EoR 21-cm power spectrum

    CERN Document Server

    Majumdar, Suman; Ghara, Raghunath; Mondal, Rajesh; Choudhury, T Roy; Bharadwaj, Somnath; Ali, Sk Saiyad; Datta, Abhirup

    2016-01-01

    The line of sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc will imprint their signature along the line of sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for it's actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line of sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by ...

  8. Possibility of precise measurement of the cosmological power spectrum with a dedicated survey of 21 cm emission after reionization.

    Science.gov (United States)

    Loeb, Abraham; Wyithe, J Stuart B

    2008-04-25

    Measurements of the 21 cm line emission by residual cosmic hydrogen after reionization can be used to trace the power spectrum of density perturbations through a significant fraction of the observable volume of the Universe. We show that a dedicated 21 cm observatory could probe a number of independent modes that is 2 orders of magnitude larger than currently available, and enable a cosmic-variance limited detection of the signature of a neutrino mass approximately 0.05 eV. The evolution of the linear growth factor with redshift could also constrain exotic theories of gravity or dark energy to an unprecedented precision.

  9. LOFAR insights into the epoch of reionization from the cross-power spectrum of 21 cm emission and galaxies

    NARCIS (Netherlands)

    Wiersma, R. P. C.; Ciardi, B.; Thomas, R. M.; Harker, G. J. A.; Zaroubi, S.; Bernardi, G.; Brentjens, M.; de Bruyn, A. G.; Daiboo, S.; Jelic, V.; Kazemi, S.; Koopmans, L. V. E.; Labropoulos, P.; Martinez, O.; Offringa, A.; Pandey, V. N.; Schaye, J.; Veligatla, V.; Vedantham, H.; Yatawatta, S.; Mellema, G.

    2013-01-01

    Using a combination of N-body simulations, semi-analytic models and radiative transfer calculations, we have estimated the theoretical cross-power spectrum between galaxies and the 21 cm emission from neutral hydrogen during the epoch of reionization. In accordance with previous studies, we find tha

  10. Probing reionization with the cross-power spectrum of 21 cm and near-infrared radiation backgrounds

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Xiao-Chun, E-mail: xcmao@bao.ac.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2014-08-01

    The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross-power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then, the intensity of the NIR background is estimated by collecting emission from stars in first-light galaxies. On large scales, we find that the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolute value of the cross-power spectrum is |Δ{sub 21,NIR}{sup 2}|∼10{sup −4} mK nW m{sup –2} sr{sup –1}, reached at ℓ ∼ 1000 when the mean fraction of ionized hydrogen is x-bar{sub i}∼0.9. We find that Square Kilometer Array can measure the 21 cm-NIR cross-power spectrum in conjunction with mild extensions to the existing CIBER survey, provided that the integration time independently adds up to 1000 and 1 hr for 21 cm and NIR observations, and that the sky coverage fraction of the CIBER survey is extended from 4 × 10{sup –4} to 0.1. Measuring the cross-correlation signal as a function of redshift provides valuable information on reionization and helps confirm the origin of the 'missing' NIR background.

  11. Probing Reionization with the Cross-power Spectrum of 21 cm and Near-infrared Radiation Backgrounds

    Science.gov (United States)

    Mao, Xiao-Chun

    2014-08-01

    The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross-power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then, the intensity of the NIR background is estimated by collecting emission from stars in first-light galaxies. On large scales, we find that the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolute value of the cross-power spectrum is |\\Delta ^2_{21,NIR}|\\sim 10^{-4} mK nW m-2 sr-1, reached at l ~ 1000 when the mean fraction of ionized hydrogen is \\bar{x}_{i}\\sim 0.9. We find that Square Kilometer Array can measure the 21 cm-NIR cross-power spectrum in conjunction with mild extensions to the existing CIBER survey, provided that the integration time independently adds up to 1000 and 1 hr for 21 cm and NIR observations, and that the sky coverage fraction of the CIBER survey is extended from 4 × 10-4 to 0.1. Measuring the cross-correlation signal as a function of redshift provides valuable information on reionization and helps confirm the origin of the "missing" NIR background.

  12. Upper Limits on the 21 cm Power Spectrum at z = 5.9 from Quasar Absorption Line Spectroscopy

    CERN Document Server

    Pober, Jonathan C; Mesinger, Andrei

    2016-01-01

    We present upper limits on the 21 cm power spectrum at $z = 5.9$ calculated from the model-independent limit on the neutral fraction of the intergalactic medium of $x_{\\rm H{\\small I }} < 0.06 + 0.05\\ (1\\sigma)$ derived from dark pixel statistics of quasar absorption spectra. Using 21CMMC, a Markov chain Monte Carlo Epoch of Reionization analysis code, we explore the probability distribution of 21 cm power spectra consistent with this constraint on the neutral fraction. We present 99 per cent confidence upper limits of $\\Delta^2(k) < 10$ to $20\\ {\\rm mK}^2$ over a range of $k$ from 0.5 to $2.0\\ h{\\rm Mpc}^{-1}$, with the exact limit dependent on the sampled $k$ mode. This limit can be used as a null test for 21 cm experiments: a detection of power at $z=5.9$ in excess of this value is highly suggestive of residual foreground contamination or other systematic errors affecting the analysis.

  13. Constraining High Redshift X-ray Sources with Next Generation 21 cm Power Spectrum Measurements

    CERN Document Server

    Ewall-Wice, Aaron; Mesinger, Andrei; Dillon, Joshua S; Liu, Adrian; Pober, Jonathan

    2015-01-01

    We use the Fisher matrix formalism and semi-numerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA), will place on the characteristics of the X-ray sources that heated the high redshift intergalactic medium. Incorporating observations between $z=5$ and $z=25$, we find that the proposed 331 element HERA and SKA phase 1 will be capable of placing $\\lesssim 10\\%$ constraints on the spectral properties of these first X-ray sources, even if one is unable to perform measurements within the foreground contaminated "wedge" or the FM band. When accounting for the enhancement in power spectrum amplitude from spin temperature fluctuations, we find that the observable signatures of reionization extend well beyond the peak in the power spectrum usually associated with it. We also find that lower redshift degeneracies between the signatures of ...

  14. Multi-redshift limits on the 21cm power spectrum from PAPER

    CERN Document Server

    Pober, Daniel C Jacobs Jonathan C; Aguirre, James E; Ali, Zaki; Bowman, Judd; Bradley, Richard F; Carilli, Chris L; DeBoer, David R; Dexter, Matthew R; Gugliucci, Nicole E; Klima, Pat; Liu, Adrian; MacMahon, Dave H E; Manley, Jason R; Moore, David F; Stefan, Irina I; Walbrugh, William P

    2014-01-01

    The epoch of reionization power spectrum is expected to evolve strongly with redshift, and it is this variation with cosmic history that will allow us to begin to place constraints on the physics of reionization. The primary obstacle to the measurement of the EoR power spectrum is bright foreground emission. We present an analysis of observations from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) telescope which place new limits on the HI power spectrum over the redshift range of $7.5Power spectra at different points across the redshift range r...

  15. Calibration Requirements for Detecting the 21 cm Epoch of Reionization Power Spectrum and Implications for the SKA

    CERN Document Server

    Barry, N; Sullivan, I; Morales, M F; Pober, J C

    2016-01-01

    21 cm Epoch of Reionization observations promise to transform our understanding of galaxy formation, but these observations are impossible without unprecedented levels of instrument calibration. We present end-to-end simulations of a full EoR power spectrum analysis including all of the major components of a real data processing pipeline: models of astrophysical foregrounds and EoR signal, frequency-dependent instrument effects, sky-based antenna calibration, and the full PS analysis. This study reveals that traditional sky-based per-frequency antenna calibration can only be implemented in EoR measurement analyses if the calibration model is unrealistically accurate. For reasonable levels of catalog completeness, the calibration introduces contamination in otherwise foreground-free power spectrum modes, precluding a PS measurement. We explore the origin of this contamination and potential mitigation techniques. We show that there is a strong joint constraint on the precision of the calibration catalog and the...

  16. Effects of Antenna Beam Chromaticity on Redshifted 21~cm Power Spectrum and Implications for Hydrogen Epoch of Reionization Array

    CERN Document Server

    Thyagarajan, Nithyanandan; DeBoer, David; Bowman, Judd; Ewall-Wice, Aaron; Neben, Abraham; Patra, Nipanjana

    2016-01-01

    Unaccounted for systematics from foregrounds and instruments can severely limit the sensitivity of current experiments from detecting redshifted 21~cm signals from the Epoch of Reionization (EoR). Upcoming experiments are faced with a challenge to deliver more collecting area per antenna element without degrading the data with systematics. This paper and its companions show that dishes are viable for achieving this balance using the Hydrogen Epoch of Reionization Array (HERA) as an example. Here, we specifically identify spectral systematics associated with the antenna power pattern as a significant detriment to all EoR experiments which causes the already bright foreground power to leak well beyond ideal limits and contaminate the otherwise clean EoR signal modes. A primary source of this chromaticity is reflections in the antenna-feed assembly and between structures in neighboring antennas. Using precise foreground simulations taking wide-field effects into account, we provide a framework to set cosmologica...

  17. What next-generation 21 cm power spectrum measurements can teach us about the epoch of reionization

    Energy Technology Data Exchange (ETDEWEB)

    Pober, Jonathan C.; Morales, Miguel F. [Physics Department, University of Washington, Seattle, WA 98105 (United States); Liu, Adrian; McQuinn, Matthew; Parsons, Aaron R. [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720 (United States); Dillon, Joshua S.; Hewitt, Jacqueline N.; Tegmark, Max [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Aguirre, James E. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Bowman, Judd D.; Jacobs, Daniel C. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85004 (United States); Bradley, Richard F. [Astronomy Department, University of Virginia, Charlottesville, VA 22904 (United States); Carilli, Chris L. [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); DeBoer, David R. [Radio Astronomy Laboratory, University of California Berkeley, Berkeley, CA 94720 (United States); Werthimer, Dan J. [Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720 (United States)

    2014-02-20

    A number of experiments are currently working toward a measurement of the 21 cm signal from the epoch of reionization (EoR). Whether or not these experiments deliver a detection of cosmological emission, their limited sensitivity will prevent them from providing detailed information about the astrophysics of reionization. In this work, we consider what types of measurements will be enabled by the next generation of larger 21 cm EoR telescopes. To calculate the type of constraints that will be possible with such arrays, we use simple models for the instrument, foreground emission, and the reionization history. We focus primarily on an instrument modeled after the ∼0.1 km{sup 2} collecting area Hydrogen Epoch of Reionization Array concept design and parameterize the uncertainties with regard to foreground emission by considering different limits to the recently described 'wedge' footprint in k space. Uncertainties in the reionization history are accounted for using a series of simulations that vary the ionizing efficiency and minimum virial temperature of the galaxies responsible for reionization, as well as the mean free path of ionizing photons through the intergalactic medium. Given various combinations of models, we consider the significance of the possible power spectrum detections, the ability to trace the power spectrum evolution versus redshift, the detectability of salient power spectrum features, and the achievable level of quantitative constraints on astrophysical parameters. Ultimately, we find that 0.1 km{sup 2} of collecting area is enough to ensure a very high significance (≳ 30σ) detection of the reionization power spectrum in even the most pessimistic scenarios. This sensitivity should allow for meaningful constraints on the reionization history and astrophysical parameters, especially if foreground subtraction techniques can be improved and successfully implemented.

  18. Effects of Antenna Beam Chromaticity on Redshifted 21 cm Power Spectrum and Implications for Hydrogen Epoch of Reionization Array

    Science.gov (United States)

    Thyagarajan, Nithyanandan; Parsons, Aaron R.; DeBoer, David R.; Bowman, Judd D.; Ewall-Wice, Aaron M.; Neben, Abraham R.; Patra, Nipanjana

    2016-07-01

    Unaccounted for systematics from foregrounds and instruments can severely limit the sensitivity of current experiments from detecting redshifted 21 cm signals from the Epoch of Reionization (EoR). Upcoming experiments are faced with a challenge to deliver more collecting area per antenna element without degrading the data with systematics. This paper and its companions show that dishes are viable for achieving this balance using the Hydrogen Epoch of Reionization Array (HERA) as an example. Here, we specifically identify spectral systematics associated with the antenna power pattern as a significant detriment to all EoR experiments which causes the already bright foreground power to leak well beyond ideal limits and contaminate the otherwise clean EoR signal modes. A primary source of this chromaticity is reflections in the antenna-feed assembly and between structures in neighboring antennas. Using precise foreground simulations taking wide-field effects into account, we provide a generic framework to set cosmologically motivated design specifications on these reflections to prevent further EoR signal degradation. We show that HERA will not be impeded by such spectral systematics and demonstrate that even in a conservative scenario that does not perform removal of foregrounds, HERA will detect the EoR signal in line-of-sight k-modes, {k}\\parallel ≳ 0.2 h Mpc-1, with high significance. Under these conditions, all baselines in a 19-element HERA layout are capable of detecting EoR over a substantial observing window on the sky.

  19. Line-of-Sight Anisotropies in the Cosmic Dawn and Epoch of Reionization 21-cm Power Spectrum

    Indian Academy of Sciences (India)

    Suman Majumdar; Kanan K. Datta; Raghunath Ghara; Rajesh Mondal; T. Roy Choudhury; Somnath Bharadwaj; Sk. Saiyad Ali; Abhirup Datta

    2016-12-01

    The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW.

  20. Statistics of the epoch of reionization (EoR) 21-cm signal -- II. The evolution of the power spectrum error-covariance

    CERN Document Server

    Mondal, Rajesh; Majumdar, Suman

    2016-01-01

    The EoR 21-cm signal is expected to become highly non-Gaussian as reionization progresses. This severely affects the error-covariance of the EoR 21-cm power spectrum which is important for predicting the prospects of a detection with ongoing and future experiments. Most earlier works have assumed that the EoR 21-cm signal is a Gaussian random field where (1) the error variance depends only on the power spectrum and the number of Fourier modes in the particular $k$ bin, and (2) the errors in the different $k$ bins are uncorrelated. Here we use an ensemble of simulated 21-cm maps to analysis the error-covariance at various stages of reionization. We find that even at the very early stages of reionization ($\\bar{x}_{\\rm HI} \\sim 0.9 $) the error variance significantly exceeds the Gaussian predictions at small length-scales ($k > 0.5 \\,{\\rm Mpc}^{-1}$) while they are consistent at larger scales. The errors in most $k$ bins (both large and small scales), are however found to be correlated. Considering the later st...

  1. 21 cm Intensity Mapping

    CERN Document Server

    Peterson, Jeffrey B; Ansari, Reza; Bandura, Kevin; Bond, Dick; Bunton, John; Carlson, Kermit; Chang, Tzu-Ching; DeJongh, Fritz; Dobbs, Matt; Dodelson, Scott; Darhmaoui, Hassane; Gnedin, Nick; Halpern, Mark; Hogan, Craig; Goff, Jean-Marc Le; Liu, Tiehui Ted; Legrouri, Ahmed; Loeb, Avi; Loudiyi, Khalid; Magneville, Christophe; Marriner, John; McGinnis, David P; McWilliams, Bruce; Moniez, Marc; Palanque-Delabruille, Nathalie; Pasquinelli, Ralph J; Pen, Ue-Li; Rich, Jim; Scarpine, Vic; Seo, Hee-Jong; Sigurdson, Kris; Seljak, Uros; Stebbins, Albert; Steffen, Jason H; Stoughton, Chris; Timbie, Peter T; Vallinotto, Alberto; Wyithe, Stuart; Yeche, Christophe

    2009-01-01

    Using the 21 cm line, observed all-sky and across the redshift range from 0 to 5, the large scale structure of the Universe can be mapped in three dimensions. This can be accomplished by studying specific intensity with resolution ~ 10 Mpc, rather than via the usual galaxy redshift survey. The data set can be analyzed to determine Baryon Acoustic Oscillation wavelengths, in order to address the question: 'What is the nature of Dark Energy?' In addition, the study of Large Scale Structure across this range addresses the questions: 'How does Gravity effect very large objects?' and 'What is the composition our Universe?' The same data set can be used to search for and catalog time variable and transient radio sources.

  2. Fisher Matrix-based Predictions for Measuring the z = 3.35 Binned 21-cm Power Spectrum using the Ooty Wide Field Array (OWFA)

    Indian Academy of Sciences (India)

    Anjan Kumar Sarkar; Somnath Bharadwaj; Sk. Saiyad Ali

    2017-03-01

    We use the Fisher matrix formalism to predict the prospects of measuring the redshifted 21-cm power spectrum in different $k$-bins using observations with the upcoming Ooty Wide Field Array (OWFA) which will operate at $326.5 {\\rm MHZ}$. This corresponds to neutral hydrogen (HI) at $z=3.35$, and a measurement of the 21-cm power spectrum provides a unique method to probe the large-scale structures at this redshift. Our analysis indicates that a $5 \\sigma$ detection of the binned power spectrum is possible in the $k$ range $0.05 \\leq k \\leq 0.3 \\, {\\rm Mpc}^{-1}$ with $1000$ hours of observation. We find that the signal- to-noise ratio (${\\rm SNR}$) peaks in the $k$ range $0.1- 0.2\\, {\\rm Mpc}^{-1}$ where a $10 \\sigma$ detection is possible with $2000$ hours of observations. Our analysis also indicates that it is not very advantageous to observe beyond $1000$ h in a single field-of-view as the (${\\rm SNR}$) increases rather slowly beyond this in many of the small $k$-bins. The entire analysis reported here assumes that the foregrounds have been completely removed.

  3. Empirical Covariance Modeling for 21 cm Power Spectrum Estimation: A Method Demonstration and New Limits from Early Murchison Widefield Array 128-Tile Data

    CERN Document Server

    Dillon, Joshua S; Hewitt, Jacqueline N; Tegmark, Max; Barry, N; Beardsley, A P; Bowman, J D; Briggs, F; Carroll, P; de Oliveira-Costa, A; Ewall-Wice, A; Feng, L; Greenhill, L J; Hazelton, B J; Hernquist, L; Hurley-Walker, N; Jacobs, D C; Kim, H S; Kittiwisit, P; Lenc, E; Line, J; Loeb, A; McKinley, B; Mitchell, D A; Morales, M F; Offringa, A R; Paul, S; Pindor, B; Pober, J C; Procopio, P; Riding, J; Sethi, S; Shankar, N Udaya; Subrahmanyan, R; Sullivan, I; Thyagarajan, Nithyanandan; Tingay, S J; Trott, C; Wayth, R B; Webster, R L; Wyithe, S; Bernardi, G; Cappallo, R J; Deshpande, A A; Johnston-Hollitt, M; Kaplan, D L; Lonsdale, C J; McWhirter, S R; Morgan, E; Oberoi, D; Ord, S M; Prabu, T; Srivani, K S; Williams, A; Williams, C L

    2015-01-01

    The separation of the faint cosmological background signal from bright astrophysical foregrounds remains one of the most daunting challenges of mapping the high-redshift intergalactic medium with the redshifted 21 cm line of neutral hydrogen. Advances in mapping and modeling of diffuse and point source foregrounds have improved subtraction accuracy, but no subtraction scheme is perfect. Precisely quantifying the errors and error correlations due to missubtracted foregrounds allows for both the rigorous analysis of the 21 cm power spectrum and for the maximal isolation of the "EoR window" from foreground contamination. We present a method to infer the covariance of foreground residuals from the data itself in contrast to previous attempts at a priori modeling. We demonstrate our method by setting limits on the power spectrum using a 3 h integration from the 128-tile Murchison Widefield Array. Observing between 167 and 198 MHz, we find at 95% confidence a best limit of Delta^2(k) < 3.7 x 10^4 mK^2 at comovin...

  4. The effect of non-Gaussianity on error predictions for the Epoch of Reionization (EoR) 21-cm power spectrum

    CERN Document Server

    Mondal, Rajesh; Majumdar, Suman; Bera, Apurba; Acharyya, Ayan

    2014-01-01

    The EoR 21-cm signal is expected to become increasingly non-Gaussian as reionization proceeds. We have used semi-numerical simulations to study how this affects the error predictions for the EoR 21-cm power spectrum. We expect $SNR=\\sqrt{N_k}$ for a Gaussian random field where $N_k$ is the number of Fourier modes in each $k$ bin. We find that the effect of non-Gaussianity on the $SNR$ does not depend on $k$. Non-Gaussianity is important at high $SNR$ where it imposes an upper limit $[SNR]_l$. It is not possible to achieve $SNR > [SNR]_l$ even if $N_k$ is increased. The value of $[SNR]_l$ falls as reionization proceeds, dropping from $\\sim 500$ at $\\bar{x}_{{\\rm HI}} = 0.8-0.9$ to $\\sim 10$ at $\\bar{x}_{{\\rm HI}} = 0.15$. For $SNR \\ll [SNR]_l$ we find $SNR = \\sqrt{N_k}/A$ with $A \\sim 1.5 - 2.5$, roughly consistent with the Gaussian prediction. We present a fitting formula for the $SNR$ as a function of $N_k$, with two parameters $A$ and $[SNR]_l$ that have to be determined using simulations. Our results are r...

  5. Lensing Reconstruction using redshifted 21cm Fluctuations

    CERN Document Server

    Zahn, O; Zahn, Oliver; Zaldarriaga, Matias

    2005-01-01

    We investigate the potential of second generation measurements of redshifted 21 cm radiation from the epoch of reionization (EOR) to reconstruct the matter density fluctuations along the line of sight. To do so we generalize the quadratic methods developed for the Cosmic Microwave Background (CMB) to 21cm fluctuations. The three dimensional signal can be analyzed into a finite number of line of sight Fourier modes that contribute to the lensing reconstruction. In comparison with reconstruction using the CMB, 21cm fluctuations have a disadvantage of relative featurelessness, which can be compensated for by the fact that there are multiple uncorrelated backgrounds. The multiple redshift information allows to reconstruct relatively small scales even if one is limited by angular resolution. We estimate that a square kilometer of collecting area is needed with a maximal baseline of 3 km to achieve lensing reconstruction noise levels an order of magnitude below CMB quadratic estimator constraints at $l=1000$, and c...

  6. The future of primordial features with 21 cm tomography

    Science.gov (United States)

    Chen, Xingang; Meerburg, P. Daniel; Münchmeyer, Moritz

    2016-09-01

    Detecting a deviation from a featureless primordial power spectrum of fluctuations would give profound insight into the physics of the primordial Universe. Depending on their nature, primordial features can either provide direct evidence for the inflation scenario or pin down details of the inflation model. Thus far, using the cosmic microwave background (CMB) we have only been able to put stringent constraints on the amplitude of features, but no significant evidence has been found for such signals. Here we explore the limit of the experimental reach in constraining such features using 21 cm tomography at high redshift. A measurement of the 21 cm power spectrum from the Dark Ages is generally considered as the ideal experiment for early Universe physics, with potentially access to a large number of modes. We consider three different categories of theoretically motivated models: the sharp feature models, resonance models, and standard clock models. We study the improvements on bounds on features as a function of the total number of observed modes and identify parameter degeneracies. The detectability depends critically on the amplitude, frequency and scale-location of the features, as well as the angular and redshift resolution of the experiment. We quantify these effects by considering different fiducial models. Our forecast shows that a cosmic variance limited 21 cm experiment measuring fluctuations in the redshift range 30 <= z <= 100 with a 0.01-MHz bandwidth and sub-arcminute angular resolution could potentially improve bounds by several orders of magnitude for most features compared to current Planck bounds. At the same time, 21 cm tomography also opens up a unique window into features that are located on very small scales.

  7. Selection effects at 21cm

    NARCIS (Netherlands)

    Briggs, FH; Davies, JI; Impey, C; Phillipps, S

    1999-01-01

    Surveys in the 21cm line of neutral hydrogen are testing the completeness of the catalogs of nearby galaxies. The remarkable observational fact is that the potential wells that confine gas to sufficient density that it can remain neutral in the face of ionizing radiation also provide sites for star

  8. 21cmFAST: A Fast, Semi-Numerical Simulation of the High-Redshift 21-cm Signal

    OpenAIRE

    Mesinger, Andrei; Furlanetto, Steven; Cen, Renyue

    2010-01-01

    We introduce a powerful semi-numeric modeling tool, 21cmFAST, designed to efficiently simulate the cosmological 21-cm signal. Our code generates 3D realizations of evolved density, ionization, peculiar velocity, and spin temperature fields, which it then combines to compute the 21-cm brightness temperature. Although the physical processes are treated with approximate methods, we compare our results to a state-of-the-art large-scale hydrodynamic simulation, and find good agreement on scales pe...

  9. 21-cm Intensity Mapping with FAST

    CERN Document Server

    Smoot, George F

    2014-01-01

    This paper describes a program to map large-scale cosmic structures on the largest possible scales by using FAST\\cite{Nan:2011} to make a 21-cm (red-shifted) Intensity Map of the sky for the range $0.5 < z < 2.5$. The goal is to map to the angular and spectral resolution of FAST a large swath of the sky by simple drift scans with a transverse set of beams. This approach would be competitive to galaxy surveys and could be completed before SKA could begin a more detailed and precise effort. The science would be to measure the large-scale structure on the size of the baryon acoustic oscillations and larger scale and the results would be competitive to its contemporary observations and signficant. The survey would be uniquely sensitive to the potential very large-scale features from GUT-scale Inflation and complementary to the CMB observations.

  10. Matched filtering with interferometric 21 cm experiments

    Science.gov (United States)

    White, Martin; Padmanabhan, Nikhil

    2017-10-01

    A new generation of interferometric instruments is emerging, which aims to use intensity mapping of redshifted 21 cm radiation to measure the large-scale structure of the Universe at z ≃ 1-2 over wide areas of the sky. While these instruments typically have limited angular resolution, they cover huge volumes and thus can be used to provide large samples of rare objects. In this paper we study how well such instruments could find spatially extended large-scale structures, such as cosmic voids, using a matched filter formalism. Such a formalism allows us to work in Fourier space, the natural space for interferometers, and to study the impact of finite u - v coverage, noise and foregrounds on our ability to recover voids. We find that in the absence of foregrounds, such instruments would provide enormous catalogs of voids, with high completeness, but that control of foregrounds is key to realizing this goal.

  11. Combining galaxy and 21cm surveys

    CERN Document Server

    Cohn, J D; Chang, Tzu-Ching; Holder, Gil; Padmanabhan, Nikhil; Doré, Olivier

    2015-01-01

    Acoustic waves traveling through the early Universe imprint a characteristic scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale can be used as a standard ruler to map the expansion history of the Universe, a technique known as Baryon Acoustic Oscillations (BAO). BAO offer a high-precision, low-systematics means of constraining our cosmological model. The statistical power of BAO measurements can be improved if the `smearing' of the acoustic feature by non-linear structure formation is undone in a process known as reconstruction. In this paper we use low-order Lagrangian perturbation theory to study the ability of $21\\,$cm experiments to perform reconstruction and how augmenting these surveys with galaxy redshift surveys at relatively low number densities can improve performance. We find that the critical number density which must be achieved in order to benefit $21\\,$cm surveys is set by the linear theory power spectrum near its peak, and corresponds to densities achievable by upcomi...

  12. BAYESIAN SEMI-BLIND COMPONENT SEPARATION FOR FOREGROUND REMOVAL IN INTERFEROMETRIC 21 cm OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Le; Timbie, Peter T. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Bunn, Emory F. [Physics Department, University of Richmond, Richmond, VA 23173 (United States); Karakci, Ata; Korotkov, Andrei; Tucker, Gregory S. [Department of Physics, Brown University, 182 Hope Street, Providence, RI 02912 (United States); Sutter, P. M. [Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States); Wandelt, Benjamin D., E-mail: lzhang263@wisc.edu [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W Green Street, Urbana, IL 61801 (United States)

    2016-01-15

    In this paper, we present a new Bayesian semi-blind approach for foreground removal in observations of the 21 cm signal measured by interferometers. The technique, which we call H i Expectation–Maximization Independent Component Analysis (HIEMICA), is an extension of the Independent Component Analysis technique developed for two-dimensional (2D) cosmic microwave background maps to three-dimensional (3D) 21 cm cosmological signals measured by interferometers. This technique provides a fully Bayesian inference of power spectra and maps and separates the foregrounds from the signal based on the diversity of their power spectra. Relying only on the statistical independence of the components, this approach can jointly estimate the 3D power spectrum of the 21 cm signal, as well as the 2D angular power spectrum and the frequency dependence of each foreground component, without any prior assumptions about the foregrounds. This approach has been tested extensively by applying it to mock data from interferometric 21 cm intensity mapping observations under idealized assumptions of instrumental effects. We also discuss the impact when the noise properties are not known completely. As a first step toward solving the 21 cm power spectrum analysis problem, we compare the semi-blind HIEMICA technique to the commonly used Principal Component Analysis. Under the same idealized circumstances, the proposed technique provides significantly improved recovery of the power spectrum. This technique can be applied in a straightforward manner to all 21 cm interferometric observations, including epoch of reionization measurements, and can be extended to single-dish observations as well.

  13. 21cmFAST: A Fast, Semi-Numerical Simulation of the High-Redshift 21-cm Signal

    Science.gov (United States)

    Mesinger, Andrei; Furlanetto, Steven; Cen, Renyue

    2011-02-01

    21cmFAST is a powerful semi-numeric modeling tool designed to efficiently simulate the cosmological 21-cm signal. The code generates 3D realizations of evolved density, ionization, peculiar velocity, and spin temperature fields, which it then combines to compute the 21-cm brightness temperature. Although the physical processes are treated with approximate methods, the results were compared to a state-of-the-art large-scale hydrodynamic simulation, and the findings indicate good agreement on scales pertinent to the upcoming observations (>~ 1 Mpc). The power spectra from 21cmFAST agree with those generated from the numerical simulation to within 10s of percent, down to the Nyquist frequency. Results were shown from a 1 Gpc simulation which tracks the cosmic 21-cm signal down from z=250, highlighting the various interesting epochs. Depending on the desired resolution, 21cmFAST can compute a redshift realization on a single processor in just a few minutes. The code is fast, efficient, customizable and publicly available, making it a useful tool for 21-cm parameter studies.

  14. Studying the Sources of Cosmic Reionization with 21-cm Fluctuations

    OpenAIRE

    Barkana, Rennan

    2008-01-01

    We explore the ability of measurements of the 21-cm power spectrum during reionization to enable the simultaneous reconstruction of the reionization history and the properties of the ionizing sources. For various sets of simulated 21-cm observations, we perform maximum likelihood fits in order to constrain the reionization and galaxy formation histories. We employ a flexible six-parameter model that parametrizes the uncertainties in the properties of high-redshift galaxies. The computational ...

  15. Cosmological constraints from 21cm surveys after reionization

    OpenAIRE

    Visbal, Eli; Loeb, Abraham; Wyithe, Stuart

    2008-01-01

    21cm emission from residual neutral hydrogen after the epoch of reionization can be used to trace the cosmological power spectrum of density fluctuations. Using a Fisher matrix formulation, we provide a detailed forecast of the constraints on cosmological parameters that are achievable with this probe. We consider two designs: a scaled-up version of the MWA observatory as well as a Fast Fourier Transform Telescope. We find that 21cm observations dedicated to post-reionization redshifts may yi...

  16. Constraining isocurvature perturbations with the 21cm emission from minihaloes

    OpenAIRE

    Takeuchi, Yoshitaka; Chongchitnan, Sirichai

    2013-01-01

    We investigate the effects of isocurvature perturbations on the 21cm radiation from minihaloes (MHs) at high redshifts and examine constraints on the isocurvature amplitude and power spectrum using the next generation of radio telescopes such as the Square Kilometre Array. We find that there is a realistic prospect of observing the isocurvature imprints in the 21cm emission from MHs, but only if the isocurvature spectral index is close to $3$ (i.e., the spectrum is blue). When the isocurvatur...

  17. Baryonic acoustic oscillations from 21cm intensity mapping: the Square Kilometre Array case

    CERN Document Server

    Villaescusa-Navarro, Francisco; Viel, Matteo

    2016-01-01

    We quantitatively investigate the possibility of detecting baryonic acoustic oscillations (BAO) using single-dish 21cm intensity mapping observations in the post-reionization era. We show that the telescope beam smears out the isotropic BAO signature and, in the case of the Square Kilometer Array (SKA) instrument, makes it undetectable at redshifts $z\\gtrsim1$. We however demonstrate that the BAO peak can still be detected in the radial 21cm power spectrum and describe a method to make this type of measurements. By means of numerical simulations, containing the 21cm cosmological signal as well as the most relevant Galactic and extra-Galactic foregrounds and basic instrumental effect, we quantify the precision with which the radial BAO scale can be measured in the 21cm power spectrum. We systematically investigate the signal-to-noise and the precision of the recovered BAO signal as a function of cosmic variance, instrumental noise, angular resolution and foreground contamination. We find that the expected nois...

  18. 21cmFAST: A Fast, Semi-Numerical Simulation of the High-Redshift 21-cm Signal

    CERN Document Server

    Mesinger, Andrei; Cen, Renyue

    2010-01-01

    We introduce a powerful semi-numeric modeling tool, 21cmFAST, designed to efficiently simulate the cosmological 21-cm signal. Our code generates 3D realizations of evolved density, ionization, peculiar velocity, and spin temperature fields, which it then combines to compute the 21-cm brightness temperature. Although the physical processes are treated with approximate methods, we compare our results to a state-of-the-art large-scale hydrodynamic simulation, and find good agreement on scales pertinent to the upcoming observations (>~ 1 Mpc). The power spectra from 21cmFAST agree with those generated from the numerical simulation to within 10s of percent, down to the Nyquist frequency. We show results from a 1 Gpc simulation which tracks the cosmic 21-cm signal down from z=250, highlighting the various interesting epochs. Depending on the desired resolution, 21cmFAST can compute a redshift realization on a single processor in just a few minutes. Our code is fast, efficient, customizable and publicly available, m...

  19. Foreground removal of 21 cm fluctuation with multifrequency fitting

    Institute of Scientific and Technical Information of China (English)

    Li-Ping He

    2009-01-01

    The 21 centimeter (21 cm) line emission from neutral hydrogen in the inter-galactic medium (IGM) at high redshifts is strongly contaminated by foreground sources such as the diffuse Galactic synchrotron emission and free-free emission from the Galaxy, as well as emission from extragalactic radio sources, thus making its observation very complicated. However, the 21 cm signal can be recovered through its structure in fre-quency space, as the power spectrum of the foreground contamination is expected to be smooth over a wide band in frequency space while the 21 cm fluctuations vary signifi-cantly. We use a simple polynomial fitting to reconstruct the 21 cm signal around four frequencies 50, 100, 150 and 200 MHz with an especially small channel width of 20 kHz. Our calculations show that this multifrequency fitting approach can effectively recover the 21 cm signal in the frequency range 100 ~ 200 MHz. However, this method doesn't work well around 50 MHz because of the low intensity of the 21 cm signal at this frequency. We also show that the fluctuation of detector noise can be suppressed to a very low level by taking long integration times, which means that we can reach a sensitivity of ≈ 10 mK at 150 MHz with 40 antennas in 120 hours of observations.

  20. Large 21-cm signals from AGN-dominated reionization

    Science.gov (United States)

    Kulkarni, Girish; Choudhury, Tirthankar Roy; Puchwein, Ewald; Haehnelt, Martin G.

    2017-08-01

    We present predictions for the spatial distribution of 21-cm brightness temperature fluctuations from high-dynamic-range simulations for active galactic nucleus (AGN)-dominated reionization histories that have been tested against available Lyα and cosmic microwave background (CMB) data. We model AGNs by extrapolating the observed Mbh - σ relation to high redshifts and assign them ionizing emissivities consistent with recent UV luminosity function measurements. We assess the observability of the predicted spatial 21-cm fluctuations in the late stages of reionization in the limit in which the hydrogen 21-cm spin temperature is significantly larger than the CMB temperature. Our AGN-dominated reionization histories increase the variance of the 21-cm emission by a factor of up to 10 compared to similar reionization histories dominated by faint galaxies, to values close to 100 mK2 at scales accessible to experiments (k ≲ 1 cMpc-1 h). This is lower than the sensitivity reached by ongoing experiments only by a factor of about 2 or less. When reionization is dominated by AGNs, the 21-cm power spectrum is enhanced on all scales due to the enhanced bias of the clustering of the more massive haloes and the peak in the large scale 21-cm power is strongly enhanced and moved to larger scales due to bigger characteristic bubble sizes. AGN-dominated reionization should be easily detectable by Low Frequency Array (and later Hydrogen Epoch of Reionization Array and Phase 1 of the Square Kilometre Array) at their design sensitivity, assuming successful foreground subtraction and instrument calibration. Conversely, these could become the first non-trivial reionization scenarios to be ruled out by 21-cm experiments, thereby constraining the contribution of AGNs to reionization.

  1. Baryonic acoustic oscillations from 21 cm intensity mapping: the Square Kilometre Array case

    Science.gov (United States)

    Villaescusa-Navarro, Francisco; Alonso, David; Viel, Matteo

    2017-04-01

    We quantitatively investigate the possibility of detecting baryonic acoustic oscillations (BAO) using single-dish 21 cm intensity mapping observations in the post-reionization era. We show that the telescope beam smears out the isotropic BAO signature and, in the case of the Square Kilometre Array (SKA) instrument, makes it undetectable at redshifts z ≳ 1. We however demonstrate that the BAO peak can still be detected in the radial 21 cm power spectrum and describe a method to make this type of measurements. By means of numerical simulations, containing the 21 cm cosmological signal as well as the most relevant Galactic and extra-Galactic foregrounds and basic instrumental effect, we quantify the precision with which the radial BAO scale can be measured in the 21 cm power spectrum. We systematically investigate the signal to noise and the precision of the recovered BAO signal as a function of cosmic variance, instrumental noise, angular resolution and foreground contamination. We find that the expected noise levels of SKA would degrade the final BAO errors by ∼5 per cent with respect to the cosmic-variance limited case at low redshifts, but that the effect grows up to ∼65 per cent at z ∼ 2-3. Furthermore, we find that the radial BAO signature is robust against foreground systematics, and that the main effect is an increase of ∼20 per cent in the final uncertainty on the standard ruler caused by the contribution of foreground residuals as well as the reduction in sky area needed to avoid high-foreground regions. We also find that it should be possible to detect the radial BAO signature with high significance in the full redshift range. We conclude that a 21 cm experiment carried out by the SKA should be able to make direct measurements of the expansion rate H(z) with measure the expansion with competitive per cent level precision on redshifts z ≲ 2.5.

  2. Elucidating Dark Energy with Future 21 cm Observations

    CERN Document Server

    Kohri, Kazunori; Sekiguchi, Toyokazu; Takahashi, Tomo

    2016-01-01

    We investigate how precisely we can determine the nature of dark energy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of dark energy, especially when its EoS varies at high redshifts.

  3. Interpreting Sky-Averaged 21-cm Measurements

    Science.gov (United States)

    Mirocha, Jordan

    2015-01-01

    Within the first ~billion years after the Big Bang, the intergalactic medium (IGM) underwent a remarkable transformation, from a uniform sea of cold neutral hydrogen gas to a fully ionized, metal-enriched plasma. Three milestones during this epoch of reionization -- the emergence of the first stars, black holes (BHs), and full-fledged galaxies -- are expected to manifest themselves as extrema in sky-averaged ("global") measurements of the redshifted 21-cm background. However, interpreting these measurements will be complicated by the presence of strong foregrounds and non-trivialities in the radiative transfer (RT) modeling required to make robust predictions.I have developed numerical models that efficiently solve the frequency-dependent radiative transfer equation, which has led to two advances in studies of the global 21-cm signal. First, frequency-dependent solutions facilitate studies of how the global 21-cm signal may be used to constrain the detailed spectral properties of the first stars, BHs, and galaxies, rather than just the timing of their formation. And second, the speed of these calculations allows one to search vast expanses of a currently unconstrained parameter space, while simultaneously characterizing the degeneracies between parameters of interest. I find principally that (1) physical properties of the IGM, such as its temperature and ionization state, can be constrained robustly from observations of the global 21-cm signal without invoking models for the astrophysical sources themselves, (2) translating IGM properties to galaxy properties is challenging, in large part due to frequency-dependent effects. For instance, evolution in the characteristic spectrum of accreting BHs can modify the 21-cm absorption signal at levels accessible to first generation instruments, but could easily be confused with evolution in the X-ray luminosity star-formation rate relation. Finally, (3) the independent constraints most likely to aide in the interpretation

  4. Redundant Array Configurations for 21 cm Cosmology

    CERN Document Server

    Dillon, Joshua S

    2016-01-01

    Realizing the potential of 21 cm tomography to statistically probe the intergalactic medium before and during the Epoch of Reionization requires large telescopes and precise control of systematics. Next-generation telescopes are now being designed and built to meet these challenges, drawing lessons from first-generation experiments that showed the benefits of densely packed, highly redundant arrays--in which the same mode on the sky is sampled by many antenna pairs--for achieving high sensitivity, precise calibration, and robust foreground mitigation. In this work, we focus on the Hydrogen Epoch of Reionization Array (HERA) as an interferometer with a dense, redundant core designed following these lessons to be optimized for 21 cm cosmology. We show how modestly supplementing or modifying a compact design like HERA's can still deliver high sensitivity while enhancing strategies for calibration and foreground mitigation. In particular, we compare the imaging capability of several array configurations, both ins...

  5. Precision measurement of cosmic magnification from 21 cm emitting galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Pengjie; /Fermilab; Pen, Ue-Li; /Canadian Inst. Theor. Astrophys.

    2005-04-01

    We show how precision lensing measurements can be obtained through the lensing magnification effect in high redshift 21cm emission from galaxies. Normally, cosmic magnification measurements have been seriously complicated by galaxy clustering. With precise redshifts obtained from 21cm emission line wavelength, one can correlate galaxies at different source planes, or exclude close pairs to eliminate such contaminations. We provide forecasts for future surveys, specifically the SKA and CLAR. SKA can achieve percent precision on the dark matter power spectrum and the galaxy dark matter cross correlation power spectrum, while CLAR can measure an accurate cross correlation power spectrum. The neutral hydrogen fraction was most likely significantly higher at high redshifts, which improves the number of observed galaxies significantly, such that also CLAR can measure the dark matter lensing power spectrum. SKA can also allow precise measurement of lensing bispectrum.

  6. Constraining dark matter through 21-cm observations

    Science.gov (United States)

    Valdés, M.; Ferrara, A.; Mapelli, M.; Ripamonti, E.

    2007-05-01

    Beyond reionization epoch cosmic hydrogen is neutral and can be directly observed through its 21-cm line signal. If dark matter (DM) decays or annihilates, the corresponding energy input affects the hydrogen kinetic temperature and ionized fraction, and contributes to the Lyα background. The changes induced by these processes on the 21-cm signal can then be used to constrain the proposed DM candidates, among which we select the three most popular ones: (i) 25-keV decaying sterile neutrinos, (ii) 10-MeV decaying light dark matter (LDM) and (iii) 10-MeV annihilating LDM. Although we find that the DM effects are considerably smaller than found by previous studies (due to a more physical description of the energy transfer from DM to the gas), we conclude that combined observations of the 21-cm background and of its gradient should be able to put constrains at least on LDM candidates. In fact, LDM decays (annihilations) induce differential brightness temperature variations with respect to the non-decaying/annihilating DM case up to ΔδTb = 8 (22) mK at about 50 (15) MHz. In principle, this signal could be detected both by current single-dish radio telescopes and future facilities as Low Frequency Array; however, this assumes that ionospheric, interference and foreground issues can be properly taken care of.

  7. Prospects of probing quintessence with H I 21-cm intensity mapping survey

    Science.gov (United States)

    Hussain, Azam; Thakur, Shruti; Guha Sarkar, Tapomoy; Sen, Anjan A.

    2016-12-01

    We investigate the prospect of constraining scalar field dark energy models using H I 21-cm intensity mapping surveys. We consider a wide class of coupled scalar field dark energy models whose predictions about the background cosmological evolution are different from the Λ cold dark matter (ΛCDM) predictions by a few per cent. We find that these models can be statistically distinguished from ΛCDM through their imprint on the 21-cm angular power spectrum. At the fiducial z = 1.5, corresponding to a radio interferometric observation of the post-reionization H I 21-cm observation at frequency 568 MHz, these models can in fact be distinguished from the ΛCDM model at signal-to-noise ratio >3σ level using a 10 000 h radio observation distributed over 40 pointings of a SKA1-mid-like radio telescope. We also show that tracker models are more likely to be ruled out in comparison with ΛCDM than the thawer models. Future radio observations can be instrumental in obtaining tighter constraints on the parameter space of dark energy models and supplement the bounds obtained from background studies.

  8. Prospects of probing quintessence with HI 21-cm intensity mapping survey

    CERN Document Server

    Hossain, Azam; Sarkar, Tapomoy Guha; Sen, Anjan A

    2016-01-01

    We investigate the prospect of constraining scalar field dark energy models using HI 21-cm intensity mapping surveys. We consider a wide class of coupled scalar field dark energy models whose predictions about the background cosmological evolution are different from the $\\Lambda$CDM predictions by a few percent. We find that these models can be statistically distinguished from $\\Lambda$CDM through their imprint on the 21-cm angular power spectrum. At the fiducial $z= 1.5$, corresponding to a radio interferometric observation of the post-reionization HI 21 cm observation at frequency $568 \\rm MHz$, these models can infact be distinguished from the $\\Lambda$CDM model at $ {\\rm SNR }> 3 \\sigma$ level using a 10,000 hr radio observation distributed over 40 pointings of a SKA1-mid like radio-telescope. We also show that tracker models are more likely to be ruled out in comparison with $\\Lambda$CDM than the thawer models. Future radio observations can be instrumental in obtaining tighter constraints on the paramete...

  9. Precise measurements of inflationary features with 21 cm observations

    CERN Document Server

    Xu, Yidong; Chen, Xuelei

    2016-01-01

    Future observations of 21~cm emission using HI intensity mapping will enable us to probe the large scale structure of the Universe over very large survey volumes within a reasonable observation time. We demonstrate that the three-dimensional information contained in such surveys will be an extremely powerful tool in searching for features that were imprinted in the primordial power spectrum and bispectrum during inflation. Here we focus on the "resonant" and "step" inflation models, and forecast the potential of upcoming 21~cm experiments to detect these inflationary features in the observable power- and bispectrum. We find that the full scale Tianlai experiment and the Square Kilometre Array (SKA) have the potential to improve on the sensitivity of current Cosmic Microwave Background (CMB) experiments by several orders of magnitude.

  10. The Future of Primordial Features with 21 cm Tomography

    CERN Document Server

    Chen, Xingang; Münchmeyer, Moritz

    2016-01-01

    Detecting a deviation from a featureless primordial power spectrum of fluctuations would give profound insight into the physics of the primordial Universe. Depending on their nature, primordial features can either provide direct evidence for the inflation scenario or pin down details of the inflation model. Thus far, using the cosmic microwave background (CMB) we have only been able to put stringent constraints on the amplitude of features, but no significant evidence has been found for such signals. Here we explore the limit of the experimental reach in constraining such features using 21 cm tomography at high redshift. A measurement of the 21 cm power spectrum from the Dark Ages is generally considered as the ideal experiment for early Universe physics, with potentially access to a large number of modes. We consider three different categories of theoretically motivated models: the sharp feature models, resonance models, and standard clock models. We study the improvements on bounds on features as a function...

  11. Intensity Mapping During Reionization: 21 cm and Cross-correlations

    Science.gov (United States)

    Aguirre, James E.; HERA Collaboration

    2016-01-01

    The first generation of 21 cm epoch of reionization (EoR) experiments are now reaching the sensitivities necessary for a detection of the power spectrum of plausible reionization models, and with the advent of next-generation capabilities (e.g. the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometer Array Phase I Low) will move beyond the power spectrum to imaging of the EoR intergalactic medium. Such datasets provide context to galaxy evolution studies for the earliest galaxies on scales of tens of Mpc, but at present wide, deep galaxy surveys are lacking, and attaining the depth to survey the bulk of galaxies responsible for reionization will be challenging even for JWST. Thus we seek useful cross-correlations with other more direct tracers of the galaxy population. I review near-term prospects for cross-correlation studies with 21 cm and CO and CII emission, as well as future far-infrared misions suchas CALISTO.

  12. Gravitational Lensing of Pregalactic 21 cm Radiation

    CERN Document Server

    Metcalf, R Benton

    2008-01-01

    Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic reionization will provide hundreds of quasi-independent source planes, each of precisely known redshift, if a resolution of ~ 1 arcminutes or better can be attained. These planes can be used to reconstruct the projected mass distribution of foreground material. A wide-area survey of 21 cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing although the best constraints come from combining data of the two types. Any radio telescope capable of mapping the 21cm brightness temperature with good frequency resolution (~ 0.05 MHz) over a band of width ~> 10 MHz should be able to make mass maps of high quality. If the reionization epoch is at z ~ 9 very large amounts of cosmological information will be accessible. The planned Square Kilometer Array (SK...

  13. Detailed modelling of the 21-cm Forest

    CERN Document Server

    Semelin, Benoit

    2015-01-01

    The 21-cm forest is a promising probe of the Epoch of Reionization. The local state of the intergalactic medium (IGM) is encoded in the spectrum of a background source (radio-loud quasars or gamma ray burst afterglow) by absorption at the local 21-cm wavelength, resulting in a continuous and fluctuating absorption level. Small-scale structures (filaments and minihaloes) in the IGM are responsible for the strongest absorption features. The absorption can also be modulated on large scales by inhomogeneous heating and Wouthuysen-Field coupling. We present the results from a simulation that attempts to preserve the cosmological environment while resolving some of the small-scale structures (a few kpc resolution in a 50 Mpc/h box). The simulation couples the dynamics and the ionizing radiative transfer and includes X-ray and Lyman lines radiative transfer for a detailed physical modelling. As a result we find that soft X-ray self-shielding, Lyman-alpha self-shielding and shock heating all have an impact on the pre...

  14. Measuring the X-ray Background in the Reionization Era with First Generation 21 cm Experiments

    OpenAIRE

    Christian, Pierre; Loeb, Abraham

    2013-01-01

    The X-ray background during the epoch of reionization is currently poorly constrained. We demonstrate that it is possible to use first generation 21 cm experiments to calibrate it. Using the semi-numerical simulation, 21cmFAST, we calculate the dependence of the 21 cm power spectrum on the X-ray background flux. Comparing the signal to the sensitivity of the Murchison Widefield Array (MWA) we find that in the redshift interval z=8-14 the 21 cm signal is detectable based on the upper limit set...

  15. Foreground Removal in 21cm Surveys of Reionization

    CERN Document Server

    Petrovic, Nada

    2010-01-01

    It is well-known that foreground subtraction in 21cm surveys removes large scale power. We investigate associated systematic biases. We show that removing line-of-sight fluctuations on large scales aliases into suppression of the 3D power spectrum across a broad range of scales. This bias can be eliminated by marginalizing over small k in the 1D power spectrum; however, the unbiased estimator will have unavoidably larger variance. We also show that Gaussian realizations of the power spectrum permit accurate and extremely rapid Monte-Carlo simulations for error analysis; repeated realizations of the fully non-Gaussian field are unnecessary. We perform Monte-Carlo maximum-likelihood simulations of foreground removal which yield unbiased, minimum variance estimates of the power spectrum in agreement with Fisher matrix estimates. Foreground removal also distorts the 21cm PDF, reducing the contrast between neutral and ionized regions. We show that it is the subtraction of large-scales modes which is responsible fo...

  16. Detectability of the 21-cm CMB cross-correlation from the epoch of reionization

    NARCIS (Netherlands)

    Tashiro, Hiroyuki; Aghanim, Nabila; Langer, Mathieu; Douspis, Marian; Zaroubi, Saleem; Jelic, Vibor

    2010-01-01

    The 21-cm line fluctuations and the cosmic microwave background (CMB) are powerful probes of the epoch of reionization of the Universe. We study the potential of the cross-correlation between 21-cm line fluctuations and CMB anisotropy to obtain further constraints on the reionization history. We ana

  17. Update on the BINGO 21cm intensity mapping experiment

    CERN Document Server

    Battye, Richard; Chen, Tianyue; Dickinson, Clive; Harper, Stuart; Olivari, Lucas; Peel, Michael; Remazeilles, Mathieu; Roychowdhury, Sambit; Wilkinson, Peter; Abdalla, Elcio; Abramo, Raul; Ferreira, Elisa; Wuensche, Alex; Vilella, Thyrso; Caldas, Manuel; Tancredi, Gonzalo; Refregier, Alexandre; Monstein, Christian; Abdalla, Filipe; Pourtsidou, Alkistis; Maffei, Bruno; Pisano, Giampaolo; Ma, Yin-Zhe

    2016-01-01

    21cm intensity mapping is a novel approach aimed at measuring the power spectrum of density fluctuations and deducing cosmological information, notably from the Baryonic Acoustic Oscillations (BAO). We give an update on the progress of BAO from Integrated Neutral Gas Observations (BINGO) which is a single dish intensity mapping project. First we explain the basic ideas behind intensity mapping concept before updating the instrument design for BINGO. We also outline the survey we plan to make and its projected science output including estimates of cosmological parameters.

  18. The impact of point source subtraction residuals on 21 cm Epoch of Reionization estimation

    CERN Document Server

    Trott, Cathryn M; Tingay, Steven J

    2012-01-01

    Precise subtraction of foreground sources is crucial for detecting and estimating 21cm HI signals from the Epoch of Reionization (EoR). We quantify how imperfect point source subtraction due to limitations of the measurement dataset yields structured residual signal in the dataset. We use the Cramer-Rao lower bound, as a metric for quantifying the precision with which a parameter may be measured, to estimate the residual signal in a visibility dataset due to imperfect point source subtraction. We then propagate these residuals into two metrics of interest for 21cm EoR experiments - the angular and two-dimensional power spectrum - using a combination of full analytic covariant derivation, analytic variant derivation, and covariant Monte Carlo simulations. This methodology differs from previous work in two ways: (1) it uses information theory to set the point source position error, rather than assuming a global root-mean-square error, and (2) it describes a method for propagating the errors analytically, thereb...

  19. Redshifted 21-cm Signals in the Dark Ages

    CERN Document Server

    Kim, Juhan

    2009-01-01

    We have carried out semianalytic simulations to build redshifted 21-cm maps in the dark ages. An entropy-floor model is adopted for planting protogalaxies in simulated minihaloes. The model allocates gas quantities such as baryonic mass and temperature to every $N$-body particle and extensively exploits the particle nature of the data in the subsequent analysis. We have found that the number density of simulated minihaloes in the early universe is well described by the Sheth & Tormen function and consequently the signal powers of simulated minihaloes are far greater than the Press & Schechter prediction presented by Furlanetto (2006b). Even though the matter power spectrum measured in the halo particles at $z=15$ is about an order of magnitude smaller than the intergalactic medium (IGM), the 21-cm signal fluctuations of haloes are, to the contrary, one order of magnitude higher than the embedding adiabatic IGM on scales, $k\\lesssim 10 h{\\rm Mpc}^{-1}$. But their spectral shapes are almost same to each...

  20. Prospects of Detecting HI using Redshifted 21-cm Radiation at $z \\sim 3$

    Indian Academy of Sciences (India)

    Bharat Kumar Gehlot; J. S. Bagla

    2017-03-01

    Distribution of cold gas in the post-reionization era provides an important link between distribution of galaxies and the process of star formation. Redshifted $21$-cm radiation from the hyperfine transition of neutral hydrogen allows us to probe the neutral component of cold gas, most of which is to be found in the interstellar medium of galaxies. Existing and upcoming radio telescopes can probe the large scale distribution of neutral hydrogen via HI intensity mapping. In this paper, we use an estimate of the HI power spectrum derived using an ansatz to compute the expected signal from the large scale HI distribution at $z \\sim 3$. We find that the scale dependence of bias at small scales makes a significant difference to the expected signal even at large angular scales. We compare the predicted signal strength with the sensitivity of radio telescopes that can observe such radiation and calculate the observation time required for detecting neutral hydrogen at these redshifts. We find that OWFA (Ooty Wide Field Array) offers the best possibility to detect neutral hydrogen at $z \\sim 3$ before the SKA (Square Kilometer Array) becomes operational. We find that the OWFA should be able to make a $3 \\sigma$ or a more significant detection in $2000$ hours of observations at several angular scales. Calculations done using the Fisher matrix approach indicate that a $5\\sigma$ detection of the binned HI power spectrum via measurement of the amplitude of the HI power spectrum is possible in $1000$ h (Sarkar et al. 2017).

  1. Studying topological structure of 21-cm line fluctuations with 3D Minkowski functionals before reionization

    Science.gov (United States)

    Yoshiura, Shintaro; Shimabukuro, Hayato; Takahashi, Keitaro; Matsubara, Takahiko

    2017-02-01

    The brightness temperature of the redshifted 21-cm line brings rich information about the intergalactic medium (IGM) from the cosmic dawn and epoch of reionization (EoR). While the power spectrum is a useful tool to investigate the 21-cm signal statistically, the 21-cm brightness temperature field is highly non-Gaussian and the power spectrum is inadequate to characterize the non-Gaussianity. Minkowski functionals (MFs) are promising tools to extract non-Gaussian features of the 21-cm signal and give topological information, such as morphology of ionized bubbles. In this work, we study the 21-cm line signal in detail with MFs. To promote understanding of basic features of the 21-cm signal, we calculate the MFs of not only the hydrogen neutral fraction but also the matter density and spin temperature, which contribute to brightness-temperature fluctuations. We find that the structure of the brightness temperature depends mainly on the ionized fraction and the spin temperature at late and early stages of the EoR, respectively. Further, we investigate the redshift evolution of MFs at 7 topology of ionized bubbles and we consider the possibility of constraining the parameters using future 21-cm signal observations.

  2. Enhanced Detectability of Pre-reionization 21-cm Structure

    CERN Document Server

    Alvarez, Marcelo A; Chang, Tzu-Ching

    2010-01-01

    Before the universe was reionized, it was likely that the spin temperature of intergalactic hydrogen was decoupled from the CMB by UV radiation from the first stars through the Wouthuysen-Field effect. If the IGM had not yet been heated above the CMB temperature by that time, then the gas would appear in absorption relative to the CMB. Large, rare sources of X-rays could inject sufficient heat into the neutral IGM, so that the differential brightness temperature was greater than zero at comoving distances of tens to hundreds of Mpc, resulting in large 21-cm fluctuations with amplitudes of about 250 mK on arcminute to degree angular scales, an order of magnitude larger in amplitude than that caused by ionized bubbles during reionization, about 25 mK. This signal could therefore be easier to detect and probe higher redshifts than that due to patchy reionization. For the case in which the first objects to heat the IGM are QSOs hosting 10^7-solar mass black holes with an abundance exceeding about 1 per Gpc^3 at z...

  3. A polarimetric approach for constraining the dynamic foreground spectrum for cosmological global 21-cm measurements

    CERN Document Server

    Nhan, Bang D; Burns, Jack O

    2016-01-01

    The cosmological global (sky-averaged) 21-cm signal is a powerful tool to probe the evolution of the intergalactic medium (IGM) in high-redshift Universe ($z \\leq 6$). One of the biggest observational challenges is to remove the foreground spectrum which is at least four orders of magnitude brighter than the cosmological 21-cm emission. Conventional global 21-cm experiments rely on the spectral smoothness of the foreground synchrotron emission to separate it from the unique 21-cm spectral structures in a single total-power spectrum. However, frequency-dependent instrumental and observational effects are known to corrupt such smoothness and complicates the foreground subtraction. We introduce a polarimetric approach to measure the projection-induced polarization of the anisotropic foreground onto a stationary dual-polarized antenna. Due to Earth rotation, when pointing the antenna at a celestial pole, the revolving foreground will modulate this polarization with a unique frequency-dependent sinusoidal signatur...

  4. Epoch of reionization 21 cm forecasting from MCMC-constrained semi-numerical models

    Science.gov (United States)

    Hassan, Sultan; Davé, Romeel; Finlator, Kristian; Santos, Mario G.

    2017-06-01

    The recent low value of Planck Collaboration XLVII integrated optical depth to Thomson scattering suggests that the reionization occurred fairly suddenly, disfavouring extended reionization scenarios. This will have a significant impact on the 21 cm power spectrum. Using a semi-numerical framework, we improve our model from instantaneous to include time-integrated ionization and recombination effects, and find that this leads to more sudden reionization. It also yields larger H ii bubbles that lead to an order of magnitude more 21 cm power on large scales, while suppressing the small-scale ionization power. Local fluctuations in the neutral hydrogen density play the dominant role in boosting the 21 cm power spectrum on large scales, while recombinations are subdominant. We use a Monte Carlo Markov chain approach to constrain our model to observations of the star formation rate functions at z = 6, 7, 8 from Bouwens et al., the Planck Collaboration XLVII optical depth measurements and the Becker & Bolton ionizing emissivity data at z ˜ 5. We then use this constrained model to perform 21 cm forecasting for Low Frequency Array, Hydrogen Epoch of Reionization Array and Square Kilometre Array in order to determine how well such data can characterize the sources driving reionization. We find that the Mock 21 cm power spectrum alone can somewhat constrain the halo mass dependence of ionizing sources, the photon escape fraction and ionizing amplitude, but combining the Mock 21 cm data with other current observations enables us to separately constrain all these parameters. Our framework illustrates how the future 21 cm data can play a key role in understanding the sources and topology of reionization as observations improve.

  5. Non-gaussian CMBR angular power spectra

    CERN Document Server

    Magueijo, J

    1995-01-01

    In this paper we show how the prediction of CMBR angular power spectra C_l in non-Gaussian theories is affected by a cosmic covariance problem, that is (C_l,C_{l'}) correlations impart features on any observed C_l spectrum which are absent from the average C^l spectrum. Therefore the average spectrum is rendered a bad observational prediction, and two new prediction strategies, better adjusted to these theories, are proposed. In one we search for hidden random indices conditional to which the theory is released from the correlations. Contact with experiment can then be made in the form of the conditional power spectra plus the random index distribution. In another approach we apply to the problem a principal component analysis. We discuss the effect of correlations on the predictivity of non-Gaussian theories. We finish by showing how correlations may be crucial in delineating the borderline between predictions made by non-Gaussian and Gaussian theories. In fact, in some particular theories, correlations may ...

  6. Hydrogen 21-cm Intensity Mapping at redshift 0.8

    CERN Document Server

    Chang, Tzu-Ching; Bandura, Kevin; Peterson, Jeffrey B

    2010-01-01

    Observations of 21-cm radio emission by neutral hydrogen at redshifts z ~ 0.5 to ~ 2.5 are expected to provide a sensitive probe of cosmic dark energy. This is particularly true around the onset of acceleration at z ~ 1, where traditional optical cosmology becomes very difficult because of the infrared opacity of the atmosphere. Hitherto, 21-cm emission has been detected only to z=0.24. More distant galaxies generally are too faint for individual detections but it is possible to measure the aggregate emission from many unresolved galaxies in the 'cosmic web'. Here we report a three dimensional 21-cm intensity field at z=0.53 to 1.12. We then co-add HI emission from the volumes surrounding about ten thousand galaxies (from the DEEP2 optical galaxy redshift survey. We detect the aggregate 21-cm glow at a significance of ~ 4 sigma.

  7. Particle decay in the early universe: predictions for 21 cm

    CERN Document Server

    Shchekinov, Yu A; Shchekinov, Yu. A.

    2006-01-01

    The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark matter particles on the emission and absorption characteristics of neutral hydrogen in 21 cm at redshifts $z = 10-50$ is considered. In presence of UHECRs 21 cm can be seen in absorption with the brightness temperature $T_b=-(5\\div 10)$ mK in the range $z=10-30$. Decayng particles can stimulate a 21 cm signal in emission with $T_b\\sim 50-60$~mK at $z =50$, and $T_b \\simeq 10$~mK at $z \\sim 20$. Observational possibilities to detect manifestations of UHECRs and/or decaying particles in 21 cm with the future radio telescopes (LOFAR, PAST and SKA), and to distinguish contributions from them are briefly discussed.

  8. Reconstructing the nature of the first cosmic sources from the anisotropic 21-cm signal

    CERN Document Server

    Fialkov, Anastasia; Cohen, Aviad

    2015-01-01

    The redshifted 21-cm background is expected to be a powerful probe of the early Universe, carrying both cosmological and astrophysical information from a wide range of redshifts. In particular, the power spectrum of fluctuations in the 21-cm brightness temperature is anisotropic due to the line-of-sight velocity gradient, which in principle allows for a simple extraction of this information in the limit of linear fluctuations. However, recent numerical studies suggest that the 21-cm signal is actually rather complex, and its analysis likely depends on detailed model fitting. We present the first realistic simulation of the anisotropic 21-cm power spectrum over a wide period of early cosmic history. We show that on observable scales, the anisotropy is large and thus measurable at most redshifts, and its form tracks the evolution of 21-cm fluctuations as they are produced early on by Lyman-a radiation from stars, then switch to X-ray radiation from early heating sources, and finally to ionizing radiation from s...

  9. BB mode angular power spectrum of CMB from massive gravity

    CERN Document Server

    Malsawmtluangi, N

    2016-01-01

    The primordial massive gravitational waves are placed in the squeezed vacuum state and corresponding $BB$-mode correlation angular power spectrum of the cosmic microwave background is obtained for various slow roll inflation models. The angular power spectrum is compared with the limit of BICEP2/Keck and Planck joint analysis data and the hybrid inflation model is found favorable.

  10. Visibility based angular power spectrum estimation in low frequency radio interferometric observations

    CERN Document Server

    Choudhuri, Samir; Ghosh, Abhik; Ali, SK Saiyad

    2014-01-01

    We present two estimators to quantify the angular power spectrum of the sky signal directly from the visibilities measured in radio interferometric observations. This is relevant for both the foregrounds and the cosmological 21-cm signal buried therein. The discussion here is restricted to the Galactic synchrotron radiation, the most dominant foreground component after point source removal. Our theoretical analysis is validated using simulations at 150 MHz, mainly for GMRT and also briefly for LOFAR. The Bare Estimator uses pairwise correlations of the measured visibilities, while the Tapered Gridded Estimator uses the visibilities after gridding in the uv plane. The former is very precise, but computationally expensive for large data. The latter has a lower precision, but takes less computation time which is proportional to the data volume. The latter also allows tapering of the sky response leading to sidelobe suppression, an useful ingredient for foreground removal. Both estimators avoid the positive bias ...

  11. The cross-correlation of the CMB polarization and the 21-cm line fluctuations from cosmic reionization

    NARCIS (Netherlands)

    Tashiro, Hiroyuki; Aghanim, Nabila; Langer, Mathieu; Douspis, Marian; Zaroubi, Saleem

    2008-01-01

    The cosmic microwave background (CMB) polarization and the 21-cm line fluctuations are powerful probes of cosmological reionization. We study how the cross-correlation between the CMB polarization (E modes) and the 21-cm line fluctuations can be used to gain further understanding of the reionization

  12. Unveiling the nature of dark matter with high redshift 21 cm line experiments

    CERN Document Server

    Evoli, Carmelo; Ferrara, Andrea

    2014-01-01

    Observations of the redshifted 21 cm line from neutral hydrogen will open a new window on the early Universe. By influencing the thermal and ionization history of the intergalactic medium (IGM), annihilating dark matter (DM) can leave a detectable imprint in the 21 cm signal. Building on the publicly available 21cmFAST code, we compute the 21 cm signal for a 10 GeV WIMP DM candidate. The most pronounced role of DM annihilations is in heating the IGM earlier and more uniformly than astrophysical sources of X-rays. This leaves several unambiguous, qualitative signatures in the redshift evolution of the large-scale ($k\\approx0.1$ Mpc$^{-1}$) 21 cm power amplitude: (i) the local maximum (peak) associated with IGM heating can be lower than the other maxima; (ii) the heating peak can occur while the IGM is in emission against the cosmic microwave background (CMB); (iii) there can be a dramatic drop in power (a global minimum) corresponding to the epoch when the IGM temperature is comparable to the CMB temperature. ...

  13. Recovering lost 21 cm radial modes via cosmic tidal reconstruction

    CERN Document Server

    Zhu, Hong-Ming; Yu, Yu; Chen, Xuelei

    2016-01-01

    21 cm intensity mapping has emerged as a promising technique to map the large-scale structure of the Universe, at redshifts $z$ from 1 to 10. Unfortunately, many of the key cross correlations with photo-$z$ galaxies and the CMB have been thought to be impossible due to foreground contamination for radial modes with small wavenumbers. These modes are usually subtracted in the foreground subtraction process. We recover the lost 21 cm radial modes via cosmic tidal reconstruction and find more than 60\\% cross-correlation signal at $\\ell\\lesssim100$ and even more on larger scales can be recovered from null. The tidal reconstruction method opens up a new set of possibilities to probe our Universe and is extremely valuable not only for 21 cm surveys but also for CMB and photometric redshift observations.

  14. Constraining the redshifted 21-cm signal with the unresolved soft X-ray background

    Science.gov (United States)

    Fialkov, Anastasia; Cohen, Aviad; Barkana, Rennan; Silk, Joseph

    2017-01-01

    We use the observed unresolved cosmic X-ray background (CXRB) in the 0.5-2 keV band and existing upper limits on the 21-cm power spectrum to constrain the high-redshift population of X-ray sources, focusing on their effect on the thermal history of the Universe and the cosmic 21-cm signal. Because the properties of these sources are poorly constrained, we consider hot gas, X-ray binaries and mini-quasars (i.e. sources with soft or hard X-ray spectra) as possible candidates. We find that (1) the soft-band CXRB sets an upper limit on the X-ray efficiency of sources that existed before the end of reionization, which is one-to-two orders of magnitude higher than typically assumed efficiencies, (2) hard sources are more effective in generating the CXRB than the soft ones, (3) the commonly assumed limit of saturated heating is not valid during the first half of reionization in the case of hard sources, with any allowed value of X-ray efficiency, (4) the maximal allowed X-ray efficiency sets a lower limit on the depth of the absorption trough in the global 21-cm signal and an upper limit on the height of the emission peak, while in the 21-cm power spectrum it sets a minimum amplitude and frequency for the high-redshift peaks, and (5) the existing upper limit on the 21-cm power spectrum sets a lower limit on the X-ray efficiency for each model. When combined with the 21-cm global signal, the CXRB will be useful for breaking degeneracies and helping constrain the nature of high-redshift heating sources.

  15. Constraining the redshifted 21-cm signal with the unresolved soft X-ray background

    Science.gov (United States)

    Fialkov, Anastasia; Cohen, Aviad; Barkana, Rennan; Silk, Joseph

    2016-10-01

    We use the observed unresolved cosmic X-ray background (CXRB) in the 0.5 - 2 keV band and existing upper limits on the 21-cm power spectrum to constrain the high-redshift population of X-ray sources, focusing on their effect on the thermal history of the Universe and the cosmic 21-cm signal. Because the properties of these sources are poorly constrained, we consider hot gas, X-ray binaries and mini-quasars (i.e., sources with soft or hard X-ray spectra) as possible candidates. We find that (1) the soft-band CXRB sets an upper limit on the X-ray efficiency of sources that existed before the end of reionization, which is one-to-two orders of magnitude higher than typically assumed efficiencies, (2) hard sources are more effective in generating the CXRB than the soft ones, (3) the commonly-assumed limit of saturated heating is not valid during the first half of reionization in the case of hard sources, with any allowed value of X-ray efficiency, (4) the maximal allowed X-ray efficiency sets a lower limit on the depth of the absorption trough in the global 21-cm signal and an upper limit on the height of the emission peak, while in the 21-cm power spectrum it sets a minimum amplitude and frequency for the high-redshift peaks, and (5) the existing upper limit on the 21-cm power spectrum sets a lower limit on the X-ray efficiency for each model. When combined with the 21-cm global signal, the CXRB will be useful for breaking degeneracies and helping constrain the nature of high-redshift heating sources.

  16. Improved foreground removal in GMRT 610 MHz observations towards redshifted 21-cm tomography

    CERN Document Server

    Ghosh, Abhik; Ali, Sk Saiyad; Chengalur, Jayaram N

    2011-01-01

    Foreground removal is a challenge for 21-cm tomography of the high redshift Universe. We use archival GMRT data (obtained for completely different astronomical goals) to estimate the foregrounds at a redshift ~ 1. The statistic we use is the cross power spectrum between two frequencies separated by \\Delta{\

  17. Reionization on Large Scales IV: Predictions for the 21 cm signal incorporating the light cone effect

    CERN Document Server

    La Plante, Paul; Natarajan, Aravind; Peterson, Jeffrey B; Trac, Hy; Cen, Renyue; Loeb, Abraham

    2013-01-01

    We present predictions for the 21 cm brightness temperature power spectrum during the Epoch of Reionization (EoR). We discuss the implications of the "light cone" effect, which incorporates evolution of the 21 cm brightness temperature along the line of sight. Using a novel method calibrated against radiation-hydrodynamic simulations, we model the neutral hydrogen density field and 21 cm signal in large volumes (L = 2 Gpc/h). The inclusion of the light cone effect leads to a relative increase of 2-3 orders of magnitude in the 21 cm signal power spectrum on large scales (k < 0.1 h/Mpc). When we modify the power spectrum to more closely reflect real-world measurement capabilities, we find that the light cone effect leads to a relative decrease of order unity at all scales. The light cone effect also introduces an anisotropy parallel to the line of sight. By decomposing the 3D power spectrum into components perpendicular and parallel to the line of sight, we find that parallel modes contribute about an order ...

  18. Selection between foreground models for global 21-cm experiments

    CERN Document Server

    Harker, Geraint

    2015-01-01

    The precise form of the foregrounds for sky-averaged measurements of the 21-cm line during and before the epoch of reionization is unknown. We suggest that the level of complexity in the foreground models used to fit global 21-cm data should be driven by the data, under a Bayesian model selection methodology. A first test of this approach is carried out by applying nested sampling to simplified models of global 21-cm data to compute the Bayesian evidence for the models. If the foregrounds are assumed to be polynomials of order n in log-log space, we can infer the necessity to use n=4 rather than n=3 with <2h of integration with limited frequency coverage, for reasonable values of the n=4 coefficient. Using a higher-order polynomial does not necessarily prevent a significant detection of the 21-cm signal. Even for n=8, we can obtain very strong evidence distinguishing a reasonable model for the signal from a null model with 128h of integration. More subtle features of the signal may, however, be lost if the...

  19. 21-cm absorption studies with the Square Kilometer Array

    NARCIS (Netherlands)

    Kanekar, N; Briggs, FH

    2004-01-01

    HI 21-cm absorption spectroscopy provides an excellent probe of the neutral gas content of absorbing galaxies, yielding information on their kinematics, mass, physical size and ISM conditions. The high sensitivity, unrivaled frequency coverage and RFI suppression techniques of the SKA will enable it

  20. Exploring 21CM - Lyman Alpha Emitter Synergies for SKA

    NARCIS (Netherlands)

    Dayal, Pratika; Hutter, Anne; Müller, Volker; Trott, C. M.

    2017-01-01

    We study the signatures of reionization and ionizing properties of the early galaxies in the cross-correlations between the 21cm emission from the spin-flip transition of neutral hydrogen (H I ) and the underlying galaxy population, in particular a sub-population of galaxies visible as Lyman Alpha E

  1. The rise of the first stars: Supersonic streaming, radiative feedback, and 21-cm cosmology

    Science.gov (United States)

    Barkana, Rennan

    2016-07-01

    Understanding the formation and evolution of the first stars and galaxies represents one of the most exciting frontiers in astronomy. Since the universe was filled with hydrogen atoms at early times, the most promising method for observing the epoch of the first stars is to use the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on the cosmic reionization era, but observations of the pre-reionization cosmic dawn are also beginning and promise exciting discoveries. While observationally unexplored, theoretical studies predict a rich variety of observational signatures from the astrophysics of the early galaxies that formed during cosmic dawn. As the first stars formed, their radiation (plus that from stellar remnants) produced feedback that radically affected both the intergalactic medium and the character of newly-forming stars. Lyman- α radiation from stars generated a strong 21-cm absorption signal, observation of which is currently the only feasible method of detecting the dominant population of galaxies at redshifts as early as z ∼ 25. Another major player is cosmic heating; if due to soft X-rays, then it occurred fairly early (z ∼ 15) and produced the strongest pre-reionization signal, while if it is due to hard X-rays, as now seems more likely, then it occurred later and may have dramatically affected the 21-cm sky even during reionization. In terms of analysis, much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations, a rich dataset that can be used to reconstruct the astrophysical information of greatest interest. This does not, however, diminish the importance of finding additional probes that are complementary or amenable to a more model-independent analysis. Examples include the global (sky-averaged) 21-cm spectrum, and the line-of-sight anisotropy of the 21-cm power spectrum. Another striking feature may result from a recently recognized effect of a supersonic relative velocity

  2. Cross-correlations between 21 cm,X-ray and infrared backgrounds

    Institute of Scientific and Technical Information of China (English)

    Huan-Yuan Shan; Bo Qin

    2009-01-01

    The history of the cosmological reionization is still unclear. Two ionizing sources, stars and QSOs, are believed to play important roles during this epoch. Besides the 21 cm signals, the infrared emission from Pop Ⅲ stars and X-ray photons from QSOs can be powerful probes of the reionization. Here we present a cross-correlation study of the 21 cm, infrared and X-ray backgrounds. The advantage of doing such cross-correlations is that we could highlight the correlated signals and eliminate irrelevant fore-grounds. We develop a shell model to describe the 21 cm signals and find that PopⅢ stars can provide higher 21 cm signals than QSOs. Using the ROSAT data for X-ray and AKARI data for infrared, we predict various cross power spectra analytically and dis-cuss prospects for detecting these cross-correlation signals in future low frequency radio surveys. We find that, although these cross-correlational signals have distinct features, so far, they have been difficult to detect due to the high noise of the soft X-ray and infrared backgrounds given by ROSAT and AKARI.

  3. 21CMFAST: a fast, seminumerical simulation of the high-redshift 21-cm signal

    Science.gov (United States)

    Mesinger, Andrei; Furlanetto, Steven; Cen, Renyue

    2011-02-01

    We introduce a powerful seminumeric modelling tool, 21CMFAST, designed to efficiently simulate the cosmological 21-cm signal. Our code generates 3D realizations of evolved density, ionization, peculiar velocity and spin temperature fields, which it then combines to compute the 21-cm brightness temperature. Although the physical processes are treated with approximate methods, we compare our results to a state-of-the-art large-scale hydrodynamic simulation, and find good agreement on scales pertinent to the upcoming observations (≳1 Mpc). The power spectra from 21CMFAST agree with those generated from the numerical simulation to within 10s of per cent, down to the Nyquist frequency. We show results from a 1-Gpc simulation which tracks the cosmic 21-cm signal down from z= 250, highlighting the various interesting epochs. Depending on the desired resolution, 21CMFAST can compute a redshift realization on a single processor in just a few minutes. Our code is fast, efficient, customizable and publicly available, making it a useful tool for 21-cm parameter studies.

  4. The Rise of the First Stars: Supersonic Streaming, Radiative Feedback, and 21-cm Cosmology

    CERN Document Server

    Barkana, Rennan

    2016-01-01

    Understanding the formation and evolution of the first stars and galaxies represents one of the most exciting frontiers in astronomy. Since the universe was filled with hydrogen atoms at early times, the most promising probe of the epoch of the first stars is the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on the cosmic reionization era, but observations of the pre-reionization cosmic dawn are also promising. While observationally unexplored, theoretical studies predict a rich variety of observational signatures from cosmic dawn. As the first stars formed, their radiation (plus that from stellar remnants) produced significant cosmic events including Lyman-alpha coupling at z~25, and early X-ray heating. Much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations. Additional probes include the global (sky-averaged) 21-cm spectrum, and the line-of-sight anisotropy of the 21-cm power spectrum. A particularly striking signature may result from t...

  5. Constraining the EoR model parameters with the 21cm bispectrum

    CERN Document Server

    Shimabukuro, Hayato; Takahashi, Keitaro; Yokoyama, Shuichiro; Ichiki, Kiyotomo

    2016-01-01

    We perform a Fisher analysis to estimate expected constraints on the Epoch of Reionization (EoR) model parameters (minimum virial temperature, ionizing efficiency, mean free path of ionizing photons) considering with thermal noise of ongoing telescopes, MWA and LOFAR. We consider how the inclusion of the 21cm bispectrum improves the constraints compared with the power spectrum alone. With assumption that we perfectly remove foreground, we found that the bispectrum, which is calculated by 21cmFAST, can constrain the EoR model parameters more tightly than the power spectrum since the bispectrum is more sensitive to the EoR model parameters than the power spectrum. We also found that degeneracy among the EoR model parameters can be broken by combining the bispectrum with the power spectrum.

  6. Identifying Ionized Regions in Noisy Redshifted 21 cm Data Sets

    CERN Document Server

    Malloy, Matthew

    2012-01-01

    One of the most promising approaches for studying reionization is to use the redshifted 21 cm line. Early generations of redshifted 21 cm surveys will not, however, have the sensitivity to make detailed maps of the reionization process, and will instead focus on statistical measurements. Here we show that it may nonetheless be possible to {\\em directly identify ionized regions} in upcoming data sets by applying suitable filters to the noisy data. The locations of prominent minima in the filtered data correspond well with the positions of ionized regions. In particular, we corrupt semi-numeric simulations of the redshifted 21 cm signal during reionization with thermal noise at the level expected for a 500 antenna tile version of the Murchison Widefield Array (MWA), and mimic the degrading effects of foreground cleaning. Using a matched filter technique, we find that the MWA should be able to directly identify ionized regions despite the large thermal noise. In a plausible fiducial model in which ~20% of the vo...

  7. Organizing the Parameter Space of the Global 21-cm Signal

    CERN Document Server

    Cohen, Aviad; Barkana, Rennan; Lotem, Matan

    2016-01-01

    The early star-forming Universe is still poorly constrained, with the properties of high-redshift stars, the first heating sources, and reionization highly uncertain. This leaves observers planning 21-cm experiments with little theoretical guidance. In this work we explore the possible range of high-redshift parameters including the star formation efficiency and the minimal mass of star-forming halos; the efficiency, spectral energy distribution, and redshift evolution of the first X-ray sources; and the history of reionization. These parameters are only weakly constrained by available observations, mainly the optical depth to the cosmic microwave background. We use realistic semi-numerical simulations to produce the global 21-cm signal over the redshift range $z = 6-40$ for each of 181 different combinations of the astrophysical parameters spanning the allowed range. We show that the expected signal fills a large parameter space, but with a fixed general shape for the global 21-cm curve. Even with our wide s...

  8. Exploring 21cm-Lyman Alpha Emitter Synergies for SKA

    Science.gov (United States)

    Hutter, Anne; Dayal, Pratika; Müller, Volker; Trott, Cathryn M.

    2017-02-01

    We study the signatures of reionization and ionizing properties of early galaxies in the cross-correlations between the 21 cm emission from the spin-flip transition of neutral hydrogen (H i) and the underlying galaxy population. In particular, we focus on a sub-population of galaxies visible as Lyα Emitters (LAEs). With both observables simultaneously derived from a z≃ 6.6 hydrodynamical simulation (GADGET-2) snapshot post-processed with a radiative transfer code (pCRASH) and a dust model, we perform a parameter study and aim to constrain both the average intergalactic medium (IGM) ionization state (1- ) and the reionization topology (outside-in versus inside-out). We find that, in our model, LAEs occupy the densest and most-ionized regions resulting in a very strong anti-correlation between the LAEs and the 21 cm emission. A 1000 hr Square Kilometer Array (SKA)-LOW1—Subaru Hyper Suprime-Cam experiment can provide constraints on , allowing us to distinguish between IGM ionization levels of 50%, 25%, 10%, and fully ionized at scales r≲ 10 comoving Mpc (assuming foreground avoidance for SKA). Our results support the inside-out reionization scenario where the densest knots (under-dense voids) are ionized first (last) for ≳ 0.1. Further, 1000 hr SKA-LOW1 observations should be able to confirm the inside-out scenario by detecting a lower 21 cm brightness temperature (by about 2–10 mK) in the densest regions (≳2 arcmin scales) hosting LAEs, compared to lower-density regions devoid of them.

  9. Simulating the z = 3.35 HI 21-cm Visibility Signal for the Ooty Wide Field Array (OWFA)

    Indian Academy of Sciences (India)

    Suman Chatterjee; Somnath Bharadwaj; Visweshwar Ram Marthi

    2017-03-01

    The upcoming Ooty Wide Field Array (OWFA) will operate at $326.5 \\, {\\rm MHz}$ which corresponds to the redshifted 21-cm signal from neutral hydrogen (HI) at z = 3.35. We present two different prescriptions to simulate this signal and calculate the visibilities expected in radio-interferometric observations with OWFA. In the first method we use an input model for the expected 21-cm power spectrum to directly simulate different random realizations of the brightness temperature fluctuations and calculate the visibilities. This method, which models the HI signal entirely as a diffuse radiation, is completely oblivious to the discrete nature of the astrophysical sources which host the HI. While each discrete source subtends an angle that is much smaller than the angular resolution of OWFA, the velocity structure of the HI inside the individual sources is well within the reach of OWFA’s frequency resolution and this is expected to have an impact on the observed HI signal. The second prescription is based on cosmological N-body simulations. Here we identify each simulation particle with a source that hosts the HI, and we have the freedom to implement any desired line profile for the HI emission from the individual sources. Implementing a simple model for the line profile, we have generated several random realizations of the complex visibilities. Correlations between the visibilities measured at different baselines and channels provides an unique method to quantify the statistical properties of the HI signal. We have used this to quantify the results of our simulations, and explore the relation between the expected visibility correlations and the underlying HI power spectrum.

  10. SPATIALLY EXTENDED 21 cm SIGNAL FROM STRONGLY CLUSTERED UV AND X-RAY SOURCES IN THE EARLY UNIVERSE

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Kyungjin [Department of Earth Sciences, Chosun University, Gwangju, 501-759 (Korea, Republic of); Xu, Hao; Norman, Michael L. [Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States); Alvarez, Marcelo A. [Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada); Wise, John H., E-mail: kjahn@chosun.ac.kr [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332 (United States)

    2015-03-20

    We present our prediction for the local 21 cm differential brightness temperature (δT{sub b}) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early universe, by a numerical simulation of their formation and radiative feedback. These objects are located inside a highly biased environment, which is a rare, high-density peak (“Rarepeak”) extending to ∼7 comoving Mpc. We study the impact of ultraviolet and X-ray photons on the intergalactic medium (IGM) and the resulting δT{sub b}, when Pop III stars are assumed to emit X-ray photons by forming X-ray binaries very efficiently. We parameterize the rest-frame spectral energy distribution of X-ray photons, which regulates X-ray photon-trapping, IGM-heating, secondary Lyα pumping and the resulting morphology of δT{sub b}. A combination of emission (δT{sub b} > 0) and absorption (δT{sub b} < 0) regions appears in varying amplitudes and angular scales. The boost of the signal by the high-density environment (δ ∼ 0.64) and on a relatively large scale combines to make Rarepeak a discernible, spatially extended (θ ∼ 10′) object for 21 cm observation at 13 ≲ z ≲ 17, which is found to be detectable as a single object by SKA with integration time of ∼1000 hr. Power spectrum analysis by some of the SKA precursors (Low Frequency Array, Murchison Widefield Array, Precision Array for Probing the Epoch of Reionization) of such rare peaks is found to be difficult due to the rarity of these peaks, and the contribution only by these rare peaks to the total power spectrum remains subdominant compared to that by all astrophysical sources.

  11. Measuring the Cosmological 21 cm Monopole with an Interferometer

    CERN Document Server

    Presley, Morgan; Parsons, Aaron

    2015-01-01

    A measurement of the cosmological 21 cm signal remains a promising but as-of-yet unattained ambition of radio astronomy. A positive detection would provide direct observations of key unexplored epochs of our cosmic history, including the cosmic dark ages and reionization. In this paper, we concentrate on measurements of the spatial monopole of the 21 cm brightness temperature as a function of redshift (the "global signal"). Most global experiments to date have been single-element experiments. In this paper, we show how an interferometer can be designed to be sensitive to the monopole mode of the sky, thus providing an alternate approach to accessing the global signature. We provide simple rules of thumb for designing a global signal interferometer and use numerical simulations to show that a modest array of tightly packed antenna elements with moderately sized primary beams (full-width-half-max of $\\sim$40$^\\circ$) can compete with typical single-element experiments in their ability to constrain phenomenologi...

  12. Probing patchy reionization through τ-21 cm correlation statistics

    Energy Technology Data Exchange (ETDEWEB)

    Meerburg, P. Daniel; Spergel, David N. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08540 (United States); Dvorkin, Cora, E-mail: meerburg@princeton.edu, E-mail: dns@astro.princeton.edu, E-mail: cdvorkin@ias.edu [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)

    2013-12-20

    We consider the cross-correlation between free electrons and neutral hydrogen during the epoch of reionization (EoR). The free electrons are traced by the optical depth to reionization τ, while the neutral hydrogen can be observed through 21 cm photon emission. As expected, this correlation is sensitive to the detailed physics of reionization. Foremost, if reionization occurs through the merger of relatively large halos hosting an ionizing source, the free electrons and neutral hydrogen are anticorrelated for most of the reionization history. A positive contribution to the correlation can occur when the halos that can form an ionizing source are small. A measurement of this sign change in the cross-correlation could help disentangle the bias and the ionization history. We estimate the signal-to-noise ratio of the cross-correlation using the estimator for inhomogeneous reionization τ-hat {sub ℓm} proposed by Dvorkin and Smith. We find that with upcoming radio interferometers and cosmic microwave background (CMB) experiments, the cross-correlation is measurable going up to multipoles ℓ ∼ 1000. We also derive parameter constraints and conclude that, despite the foregrounds, the cross-correlation provides a complementary measurement of the EoR parameters to the 21 cm and CMB polarization autocorrelations expected to be observed in the coming decade.

  13. A PER-BASELINE, DELAY-SPECTRUM TECHNIQUE FOR ACCESSING THE 21 cm COSMIC REIONIZATION SIGNATURE

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, Aaron R.; Pober, Jonathan C. [Astronomy Department, University of California, Berkeley, CA (United States); Aguirre, James E.; Moore, David F. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA (United States); Carilli, Christopher L. [National Radio Astronomy Observatory, Socorro, NM (United States); Jacobs, Daniel C. [School of Earth and Space Exploration, Arizona State University, Tucson, AZ (United States)

    2012-09-10

    A critical challenge in measuring the power spectrum of 21 cm emission from cosmic reionization is compensating for the frequency dependence of an interferometer's sampling pattern, which can cause smooth-spectrum foregrounds to appear unsmooth and degrade the separation between foregrounds and the target signal. In this paper, we present an approach to foreground removal that explicitly accounts for this frequency dependence. We apply the delay transformation introduced in Parsons and Backer to each baseline of an interferometer to concentrate smooth-spectrum foregrounds within the bounds of the maximum geometric delays physically realizable on that baseline. By focusing on delay modes that correspond to image-domain regions beyond the horizon, we show that it is possible to avoid the bulk of smooth-spectrum foregrounds. We map the point-spread function of delay modes to k-space, showing that delay modes that are uncorrupted by foregrounds also represent samples of the three-dimensional power spectrum, and can be used to constrain cosmic reionization. Because it uses only spectral smoothness to differentiate foregrounds from the targeted 21 cm signature, this per-baseline analysis approach relies on spectrally and spatially smooth instrumental responses for foreground removal. For sufficient levels of instrumental smoothness relative to the brightness of interfering foregrounds, this technique substantially reduces the level of calibration previously thought necessary to detect 21 cm reionization. As a result, this approach places fewer constraints on antenna configuration within an array, and in particular, facilitates the adoption of configurations that are optimized for power-spectrum sensitivity. Under these assumptions, we demonstrate the potential for the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21 cm reionization at an amplitude of 10 mK{sup 2} near k {approx} 0.2 h Mpc{sup -1} with 132 dipoles in 7 months of observing.

  14. Dipole of the Epoch of Reionization 21-cm signal

    CERN Document Server

    Slosar, Anže

    2016-01-01

    The motion of the solar system with respect to the cosmic rest frame modulates the monopole of the Epoch of Reionization 21-cm signal into a dipole. This dipole has a characteristic frequency dependence that is dominated by the frequency derivative of the monopole signal. We argue that although the signal is weaker by a factor of $\\sim200$, there are significant benefits in measuring the dipole. Most importantly, the direction of the cosmic velocity vector is known exquisitely well from the cosmic microwave background and is not aligned with the galaxy velocity vector that modulates the foreground monopole. Moreover, an experiment designed to measure a dipole can rely on differencing patches of the sky rather than making an absolute signal measurement, which helps with some systematic effects.

  15. An HI 21-cm line survey of evolved stars

    CERN Document Server

    Gerard, E; Libert, Y

    2011-01-01

    The HI line at 21 cm is a tracer of circumstellar matter around AGB stars, and especially of the matter located at large distances (0.1-1 pc) from the central stars. It can give unique information on the kinematics and on the physical conditions in the outer parts of circumstellar shells and in the regions where stellar matter is injected into the interstellar medium. However this tracer has not been much used up to now, due to the difficulty of separating the genuine circumstellar emission from the interstellar one. With the Nancay Radiotelescope we are carrying out a survey of the HI emission in a large sample of evolved stars. We report on recent progresses of this long term programme, with emphasis on S-type stars.

  16. Dicke's Superradiance in Astrophysics. I -- The 21 cm Line

    CERN Document Server

    Rajabi, Fereshteh

    2016-01-01

    We have applied the concept of superradiance introduced by Dicke in 1954 to the ISM by extending the corresponding analysis to the magnetic dipole interaction characterizing the atomic hydrogen 21 cm line. Although it is unlikely that superradiance could take place in thermally relaxed regions, in situations where the conditions necessary for superradiance are met (i.e., close atomic spacing, high velocity coherence, population inversion, and long dephasing time-scales compared to those related to coherent behavior), our results suggest that relatively low levels of population inversion over short astronomical length-scales (e.g., as compared to those required for maser amplification) can lead to the cooperative behavior required for superradiance in the ISM. Given the results of our analysis, we expect the observational properties of superradiance to be characterized by the emission of high intensity, spatially compact, burst-like features potentially taking place over short periods ranging from minutes to d...

  17. Effects of the sources of reionization on 21-cm redshift-space distortions

    CERN Document Server

    Majumdar, Suman; Mellema, Garrelt; Chapman, Emma; Abdalla, Filipe B; Lee, Kai-Yan; Iliev, Ilian T; Dixon, Keri L; Datta, Kanan K; Ciardi, Benedetta; Fernandez, Elizabeth R; Jelić, Vibor; Koopmans, Léon V E; Zaroubi, Saleem

    2015-01-01

    The observed 21-cm signal from the epoch of reionization will be distorted along the line-of-sight by the peculiar velocities of matter particles. These redshift-space distortions will affect the contrast in the signal and will also make it anisotropic. This anisotropy contains information about the cross-correlation between the matter density field and the neutral hydrogen field, and could thus potentially be used to extract information about the sources of reionization. In this paper, we study a collection of simulated reionization scenarios assuming different models for the sources of reionization. We show that the 21-cm anisotropy is best measured by the quadrupole moment of the power spectrum. We find that, unless the properties of the reionization sources are extreme in some way, the quadrupole moment evolves very predictably as a function of global neutral fraction. This predictability implies that redshift-space distortions are not a very sensitive tool for distinguishing between reionization sources....

  18. A Bayesian analysis of redshifted 21-cm HI signal and foregrounds: Simulations for LOFAR

    CERN Document Server

    Ghosh, Abhik; Chapman, Emma; Jelic, Vibor

    2015-01-01

    Observations of the EoR with the 21-cm hyperfine emission of neutral hydrogen (HI) promise to open an entirely new window onto the formation of the first stars, galaxies and accreting black holes. In order to characterize the weak 21-cm signal, we need to develop imaging techniques which can reconstruct the extended emission very precisely. Here, we present an inversion technique for LOFAR baselines at NCP, based on a Bayesian formalism with optimal spatial regularization, which is used to reconstruct the diffuse foreground map directly from the simulated visibility data. We notice the spatial regularization de-noises the images to a large extent, allowing one to recover the 21-cm power-spectrum over a considerable $k_{\\perp}-k_{\\para}$ space in the range of $0.03\\,{\\rm Mpc^{-1}}power-spectrum. We find that, in combination with using the GMCA, a non-parametric foreground removal...

  19. Probing the IGM with Ly$\\mathrm{\\alpha}$ and 21 cm fluctuations

    CERN Document Server

    Heneka, Caroline; Feng, Chang

    2016-01-01

    We study 21 cm and Ly$\\mathrm{\\alpha}$ fluctuations, as well as H$\\mathrm{\\alpha}$, while distinguishing for Ly$\\mathrm{\\alpha}$ between emission of galactic, diffuse and scattered IGM origin. Cross-correlation information about the state of the IGM is worked out, testing neutral versus ionized medium with different tracers in a semi-numerical simulation setup. In order to path the way for constraints on reionization history and modelling beyond power spectrum information, we explore parameter dependencies of the cross-power signal between 21$\\,$cm and Ly$\\mathrm{\\alpha}$, which displays characteristic morphology and a turn-over from negative to positive correlation at scales of a couple Mpc$^{-1}$. In a proof of concept for the extraction of further information on the state of the IGM using different tracers, we demonstrate the usage of the 21$\\,$cm and H$\\mathrm{\\alpha}$ cross-correlation signal to determine the relative strength of galactic and IGM emission in Ly$\\mathrm{\\alpha}$. We conclude by showing th...

  20. OPENING THE 21 cm EPOCH OF REIONIZATION WINDOW: MEASUREMENTS OF FOREGROUND ISOLATION WITH PAPER

    Energy Technology Data Exchange (ETDEWEB)

    Pober, Jonathan C.; Parsons, Aaron R.; Ali, Zaki [Astronomy Department, U. California, Berkeley, CA (United States); Aguirre, James E.; Moore, David F. [Department of Physics and Astronomy, U. Pennsylvania, Philadelphia, PA (United States); Bradley, Richard F. [Department of Electrical and Computer Engineering, U. Virginia, Charlottesville, VA (United States); Carilli, Chris L. [National Radio Astronomy Observatory, Socorro, NM (United States); DeBoer, Dave; Dexter, Matthew; MacMahon, Dave [Radio Astronomy Laboratory, U. California, Berkeley, CA (United States); Gugliucci, Nicole E. [Department of Astronomy, U. Virginia, Charlottesville, VA (United States); Jacobs, Daniel C. [School of Earth and Space Exploration, Arizona State U., Tempe, AZ (United States); Klima, Patricia J. [National Radio Astronomy Observatory, Charlottesville, VA (United States); Manley, Jason; Walbrugh, William P. [Square Kilometer Array, South Africa Project, Cape Town (South Africa); Stefan, Irina I. [Cavendish Laboratory, Cambridge (United Kingdom)

    2013-05-10

    We present new observations with the Precision Array for Probing the Epoch of Reionization with the aim of measuring the properties of foreground emission for 21 cm epoch of reionization (EoR) experiments at 150 MHz. We focus on the footprint of the foregrounds in cosmological Fourier space to understand which modes of the 21 cm power spectrum will most likely be compromised by foreground emission. These observations confirm predictions that foregrounds can be isolated to a {sup w}edge{sup -}like region of two-dimensional (k , k{sub Parallel-To })-space, creating a window for cosmological studies at higher k{sub Parallel-To} values. We also find that the emission extends past the nominal edge of this wedge due to spectral structure in the foregrounds, with this feature most prominent on the shortest baselines. Finally, we filter the data to retain only this ''unsmooth'' emission and image its specific k{sub Parallel-To} modes. The resultant images show an excess of power at the lowest modes, but no emission can be clearly localized to any one region of the sky. This image is highly suggestive that the most problematic foregrounds for 21 cm EoR studies will not be easily identifiable bright sources, but rather an aggregate of fainter emission.

  1. Estimating Discrete Power Angular Spectra in Multiprobe OTA Setups

    DEFF Research Database (Denmark)

    Fan, Wei; Nielsen, Jesper Ødum; Pedersen, Gert Frølund

    2014-01-01

    The letter discusses over-the-air (OTA) testing for multiple-input–multiple-output (MIMO) capable terminals with emphasis on estimating discrete power angular spectrum modeled at the receiver (Rx) side in the test zone. Two techniques based on a uniform circular array (UCA) are proposed to obtain...

  2. The angular power spectrum measurement of the Galactic synchrotron emission in two fields of the TGSS survey

    Science.gov (United States)

    Choudhuri, Samir; Bharadwaj, Somnath; Ali, Sk. Saiyad; Roy, Nirupam; Intema, Huib. T.; Ghosh, Abhik

    2017-09-01

    Characterizing the diffuse Galactic synchrotron emission at arcminute angular scales is needed to reliably remove foregrounds in cosmological 21-cm measurements. The study of this emission is also interesting in its own right. Here, we quantify the fluctuations of the diffuse Galactic synchrotron emission using visibility data for two of the fields observed by the TIFR GMRT Sky Survey. We have used the 2D Tapered Gridded Estimator to estimate the angular power spectrum (Cℓ) from the visibilities. We find that the sky signal, after subtracting the point sources, is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 240 ≤ ℓ ≲ 500. We present a power-law fit, C_{ℓ}=A× \\big (1000/l\\big )^{β }, to the measured Cℓ over this ℓ range. We find that (A, β) have values (356 ± 109 mK2, 2.8 ± 0.3) and (54 ± 26 mK2, 2.2 ± 0.4) in the two fields. For the second field, however, there is indication of a significant residual point source contribution and for this field we interpret the measured Cℓ as an upper limit for the diffuse Galactic synchrotron emission. While in both fields the slopes are consistent with earlier measurements, the second field appears to have an amplitude that is considerably smaller compared to similar measurements in other parts of the sky.

  3. On the use of semi-numerical simulations in predicting the 21-cm signal from the epoch of reionization

    CERN Document Server

    Majumdar, Suman; Datta, Kanan K; Jensen, Hannes; Choudhury, T Roy; Bharadwaj, Somnath; Friedrich, Martina M

    2014-01-01

    We perform a detailed comparison of three different simulations of the neutral hydrogen distribution during the epoch of reionization (EoR). Our benchmark is a radiative transfer simulation (C2RAY). Such simulations can produce realistic results, but are computationally expensive. We compare it with two different semi-numerical techniques: one using the same halos as C2RAY as its sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS). These are more computationally efficient than C2RAY, but use more simplistic physics. We evaluate them in terms of how well they can reproduce the history and morphology of EoR. We find that Sem-Num can produce an ionization history and morphology that is very close to C2RAY. Considering the effects of redshift space distortions due to peculiar velocities, we also study a number of statistics such as: the variance, spherically averaged power spectrum and various angular multipole moments of the power spectrum of the 21-cm signal from EoR,that will be obse...

  4. Prospects for Detecting the 326.5MHz Redshifted 21-cm HI Signal with the Ooty Radio Telescope (ORT)

    Indian Academy of Sciences (India)

    Sk. Saiyad Ali; Somnath Bharadwaj

    2014-06-01

    Observations of the redshifted 21-cm HI fluctuations promise to be an important probe of the post-reionization era ( ≤ 6). In this paper we calculate the expected signal and foregrounds for the upgraded Ooty Radio Telescope (ORT) which operates at frequency = 326.5MHz which corresponds to redshift = 3.35. Assuming that the visibilities contain only the HI signal and system noise, we show that a 3 detection of the HI signal (∼ 1 mK) is possible at angular scales 11' to 3° with ≈ 1000 h of observation. Foreground removal is one of the major challenges for a statistical detection of the redshifted 21 cm HI signal. We assess the contribution of different foregrounds and find that the 326.5MHz sky is dominated by the extragalactic point sources at the angular scales of our interest. The expected total foregrounds are 104−105 times higher than the HI signal.

  5. Detecting ionized bubbles in redshifted 21 cm maps

    CERN Document Server

    Datta, K K; Choudhury, T R; Datta, Kanan K.; Bharadwaj, Somnath

    2007-01-01

    The reionization of the Universe, it is believed, occurred by the growth of ionized regions (bubbles) in the neutral intergalactic medium (IGM). We study the possibility of detecting these bubbles in radio-interferometric observations of redshifted neutral hydrogen (HI) 21 cm radiation. The signal ( 40 Mpc (assuming them to be spherical) in 100 hrs of observation and R_b > 22 Mpc in 1000 hrs of observation, provided the bubble is at the center of the field of view. In both these cases the filter effectively removes the expected foreground contribution so that it is below the signal, and the system noise is the deciding criteria. We find that there is a fundamental limitation on the smallest bubble that can be detected arising from the statistical fluctuations in the HI distribution. Assuming that the HI traces the dark matter we find that it will not be possible to detect bubbles with R_b < 8 Mpc using the GMRT and R_b < 16 Mpc using the MWA, however large be the integration time.

  6. Searching for the earliest galaxies in the 21cm forest

    Institute of Scientific and Technical Information of China (English)

    Andrea; FERRARA; Francisco; S.; KITAURA

    2010-01-01

    We use a model developed by Xu,Ferrara,and Chen(Mon Not Roy Astron Soc,submitted) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies(DGs) and starless minihalos(MHs). The method,based on a statistical comparison of the equivalent width(W ν ) distribution and flux correlation function,allows us to derive a simple selection criteria for candidate DGs at very high(z ≤ 8) redshift. We find that ≈18% of the total number of DGs along a line of sight to a target radio source(GRB or quasar) can be identified by the condition W ν<0; these objects correspond to the high-mass tail of the DG distribution at high redshift,and are embedded in large HII regions. The criterion W ν>0.37 kHz instead selects ≈11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency,thus providing a direct probe of the most likely reionization sources.

  7. Primordial non-gaussianity from the bispectrum of 21-cm fluctuations in the dark ages

    CERN Document Server

    Muñoz, Julian B; Kamionkowski, Marc

    2015-01-01

    A measurement of primordial non-gaussianity will be of paramount importance to distinguish between different models of inflation. Cosmic microwave background (CMB) anisotropy observations have set unprecedented bounds on the non-gaussianity parameter f_NL but the interesting regime f_NL <~ 1 is beyond their reach. Brightness-temperature fluctuations in the 21-cm line during the dark ages (z ~ 30-100) are a promising successor to CMB studies, giving access to a much larger number of modes. They are, however, intrinsically non-linear, which results in secondary non-gaussianities orders of magnitude larger than the sought-after primordial signal. In this paper we carefully compute the primary and secondary bispectra of 21-cm fluctuations on small scales. We use the flat-sky formalism, which greatly simplifies the analysis, while still being very accurate on small angular scales. We show that the secondary bispectrum is highly degenerate with the primordial one, and argue that even percent-level uncertainties ...

  8. Reconstructing the galaxy redshift distribution from angular cross power spectra

    CERN Document Server

    Sun, L; Tao, C

    2015-01-01

    The control of photometric redshift (photo-$z$) errors is a crucial and challenging task for precision weak lensing cosmology. The spacial cross-correlations (equivalently, the angular cross power spectra) of galaxies between tomographic photo-$z$ bins are sensitive to the true redshift distribution $n_i(z)$ of each bin and hence can help calibrate the photo-$z$ error distribution for weak lensing surveys. Using Fisher matrix analysis, we investigate the contributions of various components of the angular power spectra to the constraints of $n_i(z)$ parameters and demonstrate the importance of the cross power spectra therein, especially when catastrophic photo-$z$ errors are present. We further study the feasibility of reconstructing $n_i(z)$ from galaxy angular power spectra using Markov Chain Monte Carlo estimation. Considering an LSST-like survey with $10$ photo-$z$ bins, we find that the underlying redshift distribution can be determined with a fractional precision ($\\sigma(\\theta)/\\theta$ for parameter $\\...

  9. Limits on Foreground Subtraction from Chromatic Beam Effects in Global Redshifted 21 cm Measurements

    CERN Document Server

    Mozdzen, Thomas J; Monsalve, Raul A; Rogers, Alan E E

    2015-01-01

    Foreground subtraction in global redshifted 21 cm measurements is limited by frequency-dependent (chromatic) structure in antenna beam patterns. Chromatic beams couple angular structures in Galactic foreground emission to spectral structures that may not be removed by smooth functional forms. We report results for simulations based on two dipole antennas used by the Experiment to Detect the Global EoR Signature (EDGES). The residual levels in simulated foreground-subtracted spectra are found to differ substantially between the two antennas, suggesting that antenna design must be carefully considered. Residuals are also highly dependent on the right ascension and declination of the antenna pointing, with RMS values differing by as much as a factor of 20 across pointings. For EDGES and other ground-based experiments with zenith pointing antennas, right ascension and declination correspond directly to the local sidereal time and the latitude of the deployment site, hence chromatic beam effects should be taken in...

  10. SETHI@Berkeley- A Piggyback 21-cm Sky Survey at Arecibo

    CERN Document Server

    Korpela, E J; Heien, E; Heiles, C; Werthimer, D; Korpela, Eric J.; Demorest, Paul; Heien, Eric; Heiles, Carl; Werthimer, Dan

    2001-01-01

    SETI@home observes a 2.5 MHz bandwidth centered on 1420 MHz near the 21-cm line using a short line feed at Arecibo which provides a 6' beam. This feed sits on Carriage House 1. During normal astronomical observations with the new Gregorian dome the feed scans across the sky at twice the sidereal rate. We are using the SETI@home receiver to obtain about 4.4x10^6 HI spectra per year with integration time of 5 seconds per spectrum. We have accumulated 2.6 years of data covering most of the sky observable from Arecibo. This survey has much better angular resolution than previous single dish surveys and better sensitivity than existing or planned interferometric surveys.

  11. A new Tolman test of a cosmic distance duality relation at 21 cm.

    Science.gov (United States)

    Khedekar, Satej; Chakraborti, Sayan

    2011-06-01

    Under certain general conditions in an expanding universe, the luminosity distance (d(L)) and angular diameter distance (d(A)) are connected by the Etherington relation as d(L)=d(A)(1+z)2. The Tolman test suggests the use of objects of known surface brightness, to test this relation. In this Letter, we propose the use of a redshifted 21 cm signal from disk galaxies, where neutral hydrogen (HI) masses are seen to be almost linearly correlated with surface area, to conduct a new Tolman test. We construct simulated catalogs of galaxies, with the observed size-luminosity relation and realistic redshift evolution of HI mass functions, likely to be detected with the planned Square Kilometer Array. We demonstrate that these observations may soon provide the best implementation of the Tolman test to detect any violation of the cosmic distance duality relation.

  12. Erasing the variable: Empirical foreground discovery for global 21 cm spectrum experiments

    CERN Document Server

    Switzer, Eric R

    2014-01-01

    Spectral measurements of the 21 cm monopole background have the promise of revealing the bulk energetic properties and ionization state of our universe from z ~ 6-30. Synchrotron foregrounds are orders of magnitude larger than the cosmological signal, and are the principal challenge faced by these experiments. While synchrotron radiation is thought to be spectrally smooth and described by relatively few degrees of freedom, the instrumental response to bright foregrounds may be much more complex. To deal with such complexities, we develop an approach that discovers contaminated spectral modes using spatial fluctuations of the measured data. This approach exploits the fact that foregrounds vary across the sky while the signal does not. The discovered modes are projected out of each line-of-sight of a data cube. An angular weighting then optimizes the cosmological signal amplitude estimate by giving preference to lower-noise regions. Using this method, we show that it is essential for the passband to be stable t...

  13. Second order cross-correlation between kinetic Sunyaev-Zel'dovich effect and 21-cm fluctuations from the epoch of reionization

    NARCIS (Netherlands)

    Tashiro, Hiroyuki; Aghanim, Nabila; Langer, Mathieu; Douspis, Marian; Zaroubi, Saleem; Jelić, Vibor

    2011-01-01

    The measurement of the brightness temperature fluctuations of neutral hydrogen 21-cm lines from the epoch of reionization (EoR) is expected to be a powerful tool for revealing the reionization process. We study the 21-cm cross-correlation with cosmic microwave background (CMB) temperature anisotropi

  14. The Impact of Foregrounds on Redshift Space Distortion Measurements With the Highly-Redshifted 21 cm Line

    CERN Document Server

    Pober, Jonathan C

    2014-01-01

    The highly redshifted 21 cm line of neutral hydrogen has become recognized as a unique probe of cosmology from relatively low redshifts (z ~ 1) up through the Epoch of Reionization (z ~ 8) and even beyond. To date, most work has focused on recovering the spherically averaged power spectrum of the 21 cm signal, since this approach maximizes the signal-to-noise in the initial measurement. However, like galaxy surveys, the 21 cm signal is effected by redshift space distortion effects, and is inherently anisotropic between the line-of-sight and transverse directions. A full measurement of this anisotropy can yield unique cosmological information, potentially even isolating the matter power spectrum from astrophysical effects at high redshifts. However, foregrounds also have an anisotropic footprint between the line-of-sight and transverse directions: the so-called foreground "wedge". Although techniques to subtract foregrounds are actively being developed, a "foreground avoidance" approach of simply ignoring cont...

  15. Analysing the 21 cm signal from the epoch of reionization with artificial neural networks

    Science.gov (United States)

    Shimabukuro, Hayato; Semelin, Benoit

    2017-07-01

    The 21 cm signal from the epoch of reionization should be observed within the next decade. While a simple statistical detection is expected with Square Kilometre Array (SKA) pathfinders, the SKA will hopefully produce a full 3D mapping of the signal. To extract from the observed data constraints on the parameters describing the underlying astrophysical processes, inversion methods must be developed. For example, the Markov Chain Monte Carlo method has been successfully applied. Here, we test another possible inversion method: artificial neural networks (ANNs). We produce a training set that consists of 70 individual samples. Each sample is made of the 21 cm power spectrum at different redshifts produced with the 21cmFast code plus the value of three parameters used in the seminumerical simulations that describe astrophysical processes. Using this set, we train the network to minimize the error between the parameter values it produces as an output and the true values. We explore the impact of the architecture of the network on the quality of the training. Then we test the trained network on the new set of 54 test samples with different values of the parameters. We find that the quality of the parameter reconstruction depends on the sensitivity of the power spectrum to the different parameters at a given redshift, that including thermal noise and sample variance decreases the quality of the reconstruction and that using the power spectrum at several redshifts as an input to the ANN improves the quality of the reconstruction. We conclude that ANNs are a viable inversion method whose main strength is that they require a sparse exploration of the parameter space and thus should be usable with full numerical simulations.

  16. The processes of reionization simulated with the LICORICE and 21cmFAST codes

    OpenAIRE

    Zawada, Karolina; Semelin, Benoît

    2012-01-01

    One of the possible sources of an anisotropy in the power spectrum of 21 cm brightness uctuations from the epoch of reionization (EoR) is the delay in light traveltime along the line-of-sight (LOS). We examine the anisotropy between the parallel and transverse directions with respect to the LOS. The inhomogeneous distribution of ionized clouds at the redshift of z gt; 6 should provide an enhanced level of inhomogeneity in the Thomson optical depth. Evolution of the optical depth, the correlat...

  17. Imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA

    CERN Document Server

    Ghara, Raghunath; Datta, Kanan K; Choudhuri, Samir

    2016-01-01

    Understanding properties of the first sources in the Universe using the redshifted \\HI ~21-cm signal is one of the major aims of present and upcoming low-frequency experiments. We investigate the possibility of imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA1-low. We model the \\HI ~21-cm image maps, appropriate for the SKA1-low, around the first sources consisting of stars and X-ray sources within galaxies. In addition to the system noise, we account also for the astrophysical foregrounds by adding them to the signal maps. We find that after subtracting the foregrounds using a polynomial fit and suppressing the noise by smoothing the maps over $10^{'} - 30^{'}$ angular scale, the isolated sources at $z \\sim 15$ are detectable with $\\sim 4 - 9 \\, \\sigma$ confidence level in 2000 h of observation with the SKA1-low. Although the 21-cm profiles around the sources get altered because of the Gaussian smoothing, the images can still be used to extract some of the so...

  18. Power calculation of linear and angular incremental encoders

    Science.gov (United States)

    Prokofev, Aleksandr V.; Timofeev, Aleksandr N.; Mednikov, Sergey V.; Sycheva, Elena A.

    2016-04-01

    Automation technology is constantly expanding its role in improving the efficiency of manufacturing and testing processes in all branches of industry. More than ever before, the mechanical movements of linear slides, rotary tables, robot arms, actuators, etc. are numerically controlled. Linear and angular incremental photoelectric encoders measure mechanical motion and transmit the measured values back to the control unit. The capabilities of these systems are undergoing continual development in terms of their resolution, accuracy and reliability, their measuring ranges, and maximum speeds. This article discusses the method of power calculation of linear and angular incremental photoelectric encoders, to find the optimum parameters for its components, such as light emitters, photo-detectors, linear and angular scales, optical components etc. It analyzes methods and devices that permit high resolutions in the order of 0.001 mm or 0.001°, as well as large measuring lengths of over 100 mm. In linear and angular incremental photoelectric encoders optical beam is usually formulated by a condenser lens passes through the measuring unit changes its value depending on the movement of a scanning head or measuring raster. Past light beam is converting into an electrical signal by the photo-detecter's block for processing in the electrical block. Therefore, for calculating the energy source is a value of the desired value of the optical signal at the input of the photo-detecter's block, which reliably recorded and processed in the electronic unit of linear and angular incremental optoelectronic encoders. Automation technology is constantly expanding its role in improving the efficiency of manufacturing and testing processes in all branches of industry. More than ever before, the mechanical movements of linear slides, rotary tables, robot arms, actuators, etc. are numerically controlled. Linear and angular incremental photoelectric encoders measure mechanical motion and

  19. Exploring the Cosmic Reionization Epoch in Frequency Space: An Improved Approach to Remove the Foreground in 21 cm Tomography

    CERN Document Server

    Wang, Jingying; An, Tao; Gu, Junhua; Guo, Xueying; Li, Weitian; Wang, Yu; Liu, Chengze; Martineau-Huynh, Olivier; Wu, Xiang-Ping

    2012-01-01

    Aiming to correctly restore the redshifted 21 cm signals emitted by the neutral hydrogen during the cosmic reionization processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space to investigate whether they works satisfactorily with complex foreground, by quantitatively evaluate the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterize both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias $b$ and average ionization fraction $x_e$ of the reionization processes, at $z=8$ and the noise level of 60 mK we find that, although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of Mpc-scale components ...

  20. 21 cm Fluctuations of the Cosmic Dawn with the Owens Valley Long Wavelength Array

    Science.gov (United States)

    Eastwood, Michael; Hallinan, Gregg; Owens Valley LWA Collaboration

    2016-01-01

    The Owens Valley Long Wavelength Array (OVRO LWA) is a 288-antenna interferometer covering 30 to 80 MHz located at the Owens Valley Radio Observatory (OVRO) near Big Pine, California. I am leading the effort to detect spatial fluctuations of the 21 cm transition from the cosmic dawn (z~20) with the OVRO LWA. These spatial fluctuations are primarily sourced by inhomogeneous X-ray heating from early star formation. The spectral hardness of early X-ray sources, stellar feedback mechanisms, and baryon streaming therefore all play a role in shaping the power spectrum. I will present the application of m-mode analysis (Shaw et al. 2014, Shaw et al. 2015) to OVRO LWA data to: 1. compress the data set, 2. create maps of the northern sky that can be fed back into the calibration pipeline, and 3. filter foreground emission. Finally I will present the current status and future prospects of the OVRO LWA for detecting the 21 cm power spectrum at z~20.

  1. Models of the cosmological 21 cm signal from the epoch of reionization calibrated with Ly α and CMB data

    Science.gov (United States)

    Kulkarni, Girish; Choudhury, Tirthankar Roy; Puchwein, Ewald; Haehnelt, Martin G.

    2016-12-01

    We present here 21 cm predictions from high dynamic range simulations for a range of reionization histories that have been tested against available Ly α and cosmic microwave background (CMB) data. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen spin temperature is significantly larger than the CMB temperature. Models consistent with the available Ly α data and CMB measurement of the Thomson optical depth predict typical values of 10-20 mK2 for the variance of the 21 cm brightness temperature at redshifts z = 7-10 at scales accessible to ongoing and upcoming experiments (k ≲ 1 cMpc-1h). This is within a factor of a few magnitude of the sensitivity claimed to have been already reached by ongoing experiments in the signal rms value. Our different models for the reionization history make markedly different predictions for the redshift evolution and thus frequency dependence of the 21 cm power spectrum and should be easily discernible by Low-Frequency Array (and later Hydrogen Epoch of Reionization Array and Square Kilometre Array1) at their design sensitivity. Our simulations have sufficient resolution to assess the effect of high-density Lyman limit systems that can self-shield against ionizing radiation and stay 21 cm bright even if the hydrogen in their surroundings is highly ionized. Our simulations predict that including the effect of the self-shielded gas in highly ionized regions reduces the large-scale 21 cm power by about 30 per cent.

  2. A comparative study of intervening and associated H I 21-cm absorption profiles in redshifted galaxies

    Science.gov (United States)

    Curran, S. J.; Duchesne, S. W.; Divoli, A.; Allison, J. R.

    2016-11-01

    The star-forming reservoir in the distant Universe can be detected through H I 21-cm absorption arising from either cool gas associated with a radio source or from within a galaxy intervening the sightline to the continuum source. In order to test whether the nature of the absorber can be predicted from the profile shape, we have compiled and analysed all of the known redshifted (z ≥ 0.1) H I 21-cm absorption profiles. Although between individual spectra there is too much variation to assign a typical spectral profile, we confirm that associated absorption profiles are, on average, wider than their intervening counterparts. It is widely hypothesized that this is due to high-velocity nuclear gas feeding the central engine, absent in the more quiescent intervening absorbers. Modelling the column density distribution of the mean associated and intervening spectra, we confirm that the additional low optical depth, wide dispersion component, typical of associated absorbers, arises from gas within the inner parsec. With regard to the potential of predicting the absorber type in the absence of optical spectroscopy, we have implemented machine learning techniques to the 55 associated and 43 intervening spectra, with each of the tested models giving a ≳ 80 per cent accuracy in the prediction of the absorber type. Given the impracticability of follow-up optical spectroscopy of the large number of 21-cm detections expected from the next generation of large radio telescopes, this could provide a powerful new technique with which to determine the nature of the absorbing galaxy.

  3. Late-time cosmology with 21cm intensity mapping experiments

    CERN Document Server

    Bull, Philip; Patel, Prina; Santos, Mario G

    2014-01-01

    We present a framework for forecasting cosmological constraints from future neutral hydrogen intensity mapping experiments at low to intermediate redshifts. In the process, we establish a simple way of comparing such surveys with optical galaxy redshift surveys. We explore a wide range of experimental configurations and assess how well a number of cosmological observables (the expansion rate, growth rate, and angular diameter distance) and parameters (the densities of dark energy and dark matter, spatial curvature, the dark energy equation of state, etc.) will be measured by an extensive roster of upcoming experiments. A number of potential contaminants and systematic effects are also studied in detail. The overall picture is encouraging - Phase I of the SKA should be able to constrain the dark energy equation of state about as well as a DETF Stage IV galaxy redshift survey like Euclid or LSST, in roughly the same timeframe.

  4. Determination of z~0.8 neutral hydrogen fluctuations using the 21 cm intensity mapping auto-correlation

    CERN Document Server

    Switzer, E R; Bandura, K; Calin, L -M; Chang, T -C; Chen, X -L; Li, Y -C; Liao, Y -W; Natarajan, A; Pen, U -L; Peterson, J B; Shaw, J R; Voytek, T C

    2013-01-01

    The large-scale distribution of neutral hydrogen in the universe will be luminous through its 21 cm emission. Here, for the first time, we use the auto-power spectrum of 21 cm intensity fluctuations to constrain neutral hydrogen fluctuations at z~0.8. Our data were acquired with the Green Bank Telescope and span the redshift range 0.6 < z < 1 over two fields totaling ~41 deg. sq. and 190 hr of radio integration time. The dominant synchrotron foregrounds exceed the signal by ~10^3, but have fewer degrees of freedom and can be removed efficiently. Even in the presence of residual foregrounds, the auto-power can still be interpreted as an upper bound on the 21 cm signal. Our previous measurements of the cross-correlation of 21 cm intensity and the WiggleZ galaxy survey provide a lower bound. Through a Bayesian treatment of signal and foregrounds, we can combine both fields in auto- and cross-power into a measurement of Omega_HI b_HI = [0.62^{+0.23}_{-0.15}] * 10^{-3} at 68% confidence with 9% systematic ca...

  5. HIPSR: A Digital Signal Processor for the Parkes 21-cm Multibeam Receiver

    Science.gov (United States)

    Price, D. C.; Staveley-Smith, L.; Bailes, M.; Carretti, E.; Jameson, A.; Jones, M. E.; van Straten, W.; Schediwy, S. W.

    2016-11-01

    HIPSR (HI-Pulsar) is a digital signal processing system for the Parkes 21-cm Multibeam Receiver that provides larger instantaneous bandwidth, increased dynamic range, and more signal processing power than the previous systems in use at Parkes. The additional computational capacity enables finer spectral resolution in wideband HI observations and real-time detection of Fast Radio Bursts during pulsar surveys. HIPSR uses a heterogeneous architecture, consisting of FPGA-based signal processing boards connected via high-speed Ethernet to high performance compute nodes. Low-level signal processing is conducted on the FPGA-based boards, and more complex signal processing routines are conducted on the GPU-based compute nodes. The development of HIPSR was driven by two main science goals: to provide large bandwidth, high-resolution spectra suitable for 21-cm stacking and intensity mapping experiments; and to upgrade the Berkeley-Parkes-Swinburne Recorder (BPSR), the signal processing system used for the High Time Resolution Universe (HTRU) Survey and the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB).

  6. 21CMMC: An MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21cm signal

    CERN Document Server

    Greig, Bradley

    2015-01-01

    We introduce 21CMMC: a parallelized, Monte Carlo Markov Chain analysis tool, incorporating the epoch of reionization (EoR) semi-numerical simulation 21CMFAST. 21CMMC estimates astrophysical parameter constraints from 21cm EoR experiments, accommodating a variety of EoR models, as well as priors on model parameters and the reionization history. To illustrate its utility, we consider two different EoR scenarios, one with a single population of galaxies (with a mass-independent ionizing efficiency) and a second, more general model with two different, feedback-regulated populations (each with mass-dependent ionizing efficiencies). As an example, combining three observations (z=8, 9 and 10) of the 21cm power spectrum with a conservative noise estimate and uniform model priors, we find that LOFAR/HERA/SKA can constrain common reionization parameters: the ionizing efficiency (or similarly the escape fraction), the mean free path of ionizing photons, and the log of the minimum virial temperature of star-forming halos...

  7. Impact of Wind Power on the Angular Stability of a Power System

    Directory of Open Access Journals (Sweden)

    Djemai NAIMI

    2008-06-01

    Full Text Available Wind energy conversion systems are very different in nature from conventional generators. Therefore dynamic studies must be addressed in order to integrate wind power into the power system. Angular stability assessment of wind power generator is one of main issues in power system security and operation. The angular stability for the wind power generator is determined by its corresponding Critical Clearing Time (CCT. In this paper, the effect of wind power on the transient fault behavior is investigated by replacing the power generated by two main types of wind turbine, increasing gradually a rate of wind power penetration and changing the location of wind resources. The simulation analysis was established on a 14 bus IEEE test system by PSAT/Matlab, which gives access to an extensive library of grid components, and relevant wind turbine model.

  8. MITEoR: A Scalable Interferometer for Precision 21 cm Cosmology

    CERN Document Server

    Zheng, Haoxuan; Buza, Victor; Dillon, Joshua S; Gharibyan, Hrant; Hickish, Jack; Kunz, Eben; Liu, Adrian; Losh, Jon; Lutomirski, Andrew; Morrison, Scott; Narayanan, Sruthi; Perko, Ashley; Rosner, Devon; Sanchez, Nevada; Schutz, Katelin; Tribiano, Shana M; Valdez, Michael; Yang, Hung-I; Adami, Kristian Zarb; Zelko, Ioana; Zheng, Kevin; Armstrong, Richard; Bradley, Richard F; Dexter, Matthew R; Ewall-Wice, Aaron; Magro, Alessio; Matejek, Michael; Morgan, Edward; Neben, Abraham R; Pan, Qinxuan; Penna, Robert F; Peterson, Courtney M; Su, Meng; Villasenor, Joel; Williams, Christopher L; Zhu, Yan

    2014-01-01

    Tomographically mapping our universe using the redshifted 21 cm line of neutral hydrogen can revolutionize our picture of the early universe, providing a unique probe of the "cosmic dawn" and the Epoch of Reionization. By mapping a vast comoving volume, it can potentially overtake the cosmic microwave background as our most powerful cosmological probe. We report on MIT Epoch of Reionization (MITEoR), a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce the cost of such high-sensitivity 3D mapping. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction. For an $N$ antenna instrument, the cost scaling is reduced from $N^2$ to $N\\log N$. We demonstrate and quantify the power and robustness of redundancy for scalability and precision. We find that our calibration parameters precisely describe the effect of the instrument upon our measurements, all...

  9. Models of the Cosmological 21 cm Signal from the Epoch of Reionization Calibrated with Lyman-alpha and CMB Data

    CERN Document Server

    Kulkarni, Girish; Puchwein, Ewald; Haehnelt, Martin G

    2016-01-01

    We present here 21 cm predictions from high dynamic range simulations for a range of reionization histories that have been tested against available Lyman-alpha and CMB data. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen spin temperature is significantly larger than the CMB temperature. Models consistent with the available Lyman-alpha data and CMB measurement of the Thomson optical depth predict typical values of 10--20 mK^2 for the variance of the 21 cm brightness temperature at redshifts z=7--10 at scales accessible to ongoing and upcoming experiments (k < 1 h/cMpc). This is only a factor of a few below the sensitivity claimed to have been already reached by ongoing experiments. Our different models for the reionization history make markedly different predictions for the redshift evolution and thus frequency dependence of the 21 cm power spectrum and should be easily discerni...

  10. Unveiling the nature of dark matter with high redshift 21 cm line experiments

    OpenAIRE

    Evoli, Carmelo; Mesinger, Andrei; Ferrara, Andrea

    2014-01-01

    Observations of the redshifted 21 cm line from neutral hydrogen will open a new window on the early Universe. By influencing the thermal and ionization history of the intergalactic medium (IGM), annihilating dark matter (DM) can leave a detectable imprint in the 21 cm signal. Building on the publicly available 21cmFAST code, we compute the 21 cm signal for a 10 GeV WIMP DM candidate. The most pronounced role of DM annihilations is in heating the IGM earlier and more uniformly than astrophysic...

  11. Small-scale structure and 21cm fluctuations by primordial black holes

    Science.gov (United States)

    Gong, Jinn-Ouk; Kitajima, Naoya

    2017-08-01

    We discuss early structure formation of small scales sourced by primordial black holes (PBHs) which constitute a small part of present cold dark matter component. We calculate the mass function and power spectrum of haloes originated from the Poisson fluctuations of PBH number and show that the number of small haloes is significantly modified in the presence of PBHs even if their fraction accounts for only 10-4-10-3 of total dark matter abundance. We then compute the subsequent 21cm signature from those haloes. We find that PBHs can provide major contributions at high redshifts within the detectability of future experiments such as Square Kilometer Array, and provide a forecast constraint on the PBH fraction.

  12. Measuring cosmic velocities with 21cm intensity mapping and galaxy redshift survey cross-correlation dipoles

    CERN Document Server

    Hall, Alex

    2016-01-01

    We investigate the feasibility of measuring the effects of peculiar velocities in large-scale structure using the dipole of the redshift-space cross-correlation function. We combine number counts of galaxies with brightness-temperature fluctuations from 21cm intensity mapping, demonstrating that the dipole may be measured at modest significance ($\\lesssim 2\\sigma$) by combining the upcoming radio survey CHIME with the future redshift surveys of DESI and Euclid. More significant measurements ($\\lesssim~10\\sigma$) will be possible by combining intensity maps from the SKA with these of DESI or Euclid, and an even higher significance measurement ($\\lesssim 100\\sigma$) may be made by combining observables completely internally to the SKA. We account for effects such as contamination by wide-angle terms, interferometer noise and beams in the intensity maps, non-linear enhancements to the power spectrum, stacking multiple populations, sensitivity to the magnification slope, and the possibility that number counts and...

  13. Erasing the Variable: Empirical Foreground Discovery for Global 21 cm Spectrum Experiments

    Science.gov (United States)

    Switzer, Eric R.; Liu, Adrian

    2014-01-01

    Spectral measurements of the 21 cm monopole background have the promise of revealing the bulk energetic properties and ionization state of our universe from z approx. 6 - 30. Synchrotron foregrounds are orders of magnitude larger than the cosmological signal, and are the principal challenge faced by these experiments. While synchrotron radiation is thought to be spectrally smooth and described by relatively few degrees of freedom, the instrumental response to bright foregrounds may be much more complex. To deal with such complexities, we develop an approach that discovers contaminated spectral modes using spatial fluctuations of the measured data. This approach exploits the fact that foregrounds vary across the sky while the signal does not. The discovered modes are projected out of each line-of-sight of a data cube. An angular weighting then optimizes the cosmological signal amplitude estimate by giving preference to lower-noise regions. Using this method, we show that it is essential for the passband to be stable to at least approx. 10(exp -4). In contrast, the constraints on the spectral smoothness of the absolute calibration are mainly aesthetic if one is able to take advantage of spatial information. To the extent it is understood, controlling polarization to intensity leakage at the approx. 10(exp -2) level will also be essential to rejecting Faraday rotation of the polarized synchrotron emission. Subject headings: dark ages, reionization, first stars - methods: data analysis - methods: statistical

  14. H-I 21 cm absorption in Mg (II)-selected systems at moderate redshifts

    NARCIS (Netherlands)

    Lane, WM; Briggs, FH; Hibbard, JE; Rupen, MP; VanGorkom, JH

    2001-01-01

    We present results from a Westerbork Synthesis Radio Telescope (WSRT) survey for HI 21 cm absorption in 62 MgII-selected absorption systems, among which we identify three now HI 21cm absorbers. We use the redshift evolution of the number density of MgII-absorbers and the Hi detection rate to estimat

  15. Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data.

    Science.gov (United States)

    Choudhuri, Samir; Bharadwaj, Somnath; Roy, Nirupam; Ghosh, Abhik; Ali, Sk Saiyad

    2016-06-11

    It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase centre. Here, we show that it is possible to overcome this problem by tapering the sky response. Using simulated 150 MHz observations, we demonstrate that it is possible to suppress the contribution due to point sources from the outer parts by using the Tapered Gridded Estimator to measure the angular power spectrum Cℓ of the sky signal. We also show from the simulation that this method can self-consistently compute the noise bias and accurately subtract it to provide an unbiased estimation of Cℓ.

  16. Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data

    CERN Document Server

    Choudhuri, Samir; Roy, Nirupam; Ghosh, Abhik; Ali, Sk Saiyad

    2016-01-01

    It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase center. Here we show that it is possible to overcome this problem by tapering the sky response. Using simulated 150 MHz observations, we demonstrate that it is possible to suppress the contribution due to point sources from the outer parts by using the Tapered Gridded Estimator to measure the angular power spectrum C_l of the sky signal. We also show from the simulation that this method can self-consistently compute the noise bias and accurately subtract it t...

  17. The Angular Power Spectra of Photometric SDSS LRGs

    CERN Document Server

    Thomas, Shaun A; Lahav, Ofer

    2010-01-01

    We construct new galaxy angular power spectra based on the extended, updated and final SDSS II Luminous Red Galaxy (LRG) photometric redshift survey: MegaZ DR7. Encapsulating 7746 deg^{2} we utilise 723,556 photometrically determined LRGs between 0.45 < z < 0.65 in a 3.3 (Gpc h^{-1})^3 spherical harmonic analysis of the galaxy distribution. By combining four photometric redshift bins we find preliminary parameter constraints of f_{b} = \\Omega_{b}/\\Omega_{m} = 0.173 +/- 0.046 and \\Omega_{m} = 0.260 +/- 0.035 assuming H_{0} = 75 km s^{-1} Mpc^{-1}, n_{s}=1 and \\Omega_{k} = 0. These limits are consistent with the CMB and the previous data release (DR4). The C_{\\ell} are sensitive to redshift space distortions and therefore we also recast our constraints into a measurement of \\beta ~ \\Omega_{m}^{0.55}/b in different redshift shells. The robustness of these power spectra with respect to a number of potential systematics such as extinction, photometric redshift and ANNz training set extrapolation are examined...

  18. Constraints on massive neutrinos from the CFHTLS angular power spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Jun-Qing [Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy); Granett, Benjamin R.; Guzzo, Luigi [INAF — Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Brera (Italy); Viel, Matteo [INAF — Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste (Italy); Bird, Simeon [School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540 (United States); Haehnelt, Martin G. [Institute of Astronomy and Kavli Institute for Cosmology, Madingley Road, CB3 0HA, Cambridge (United Kingdom); Coupon, Jean [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); McCracken, Henry Joy; Mellier, Yannick, E-mail: xia@sissa.it, E-mail: ben.granett@brera.inaf.it, E-mail: viel@oats.inaf.it, E-mail: spb@ias.edu, E-mail: luigi.guzzo@brera.inaf.it, E-mail: haehnelt@ast.cam.ac.uk, E-mail: coupon@asiaa.sinica.edu.tw, E-mail: hjmcc@iap.fr, E-mail: mellier@iap.fr [Institut d' Astrophysique de Paris, UMR 7095 CNRS, Universitè Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris (France)

    2012-06-01

    We use the galaxy angular power spectrum at z ∼ 0.5–1.2 from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass Σm{sub ν} and the effective number of neutrino species N{sub eff}. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of Σm{sub ν} < 0.29 eV and N{sub eff} = 4.17{sup +1.62}{sub −1.26} (2 σ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become Σm{sub ν} < 0.41 eV and N{sub eff} = 3.98{sup +2.02}{sub −1.20} (2 σ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass.

  19. Can 21-cm observations discriminate between high-mass and low-mass galaxies as reionization sources?

    Science.gov (United States)

    Iliev, Ilian T.; Mellema, Garrelt; Shapiro, Paul R.; Pen, Ue-Li; Mao, Yi; Koda, Jun; Ahn, Kyungjin

    2012-07-01

    The prospect of detecting the first galaxies by observing their impact on the intergalactic medium (IGM) as they reionized it during the first billion years leads us to ask whether such indirect observations are capable of diagnosing which types of galaxies were most responsible for reionization. We attempt to answer this with new large-scale radiative transfer simulations of reionization including the entire mass range of atomically cooling haloes (M > 108 M⊙). We divide these haloes into two groups, high-mass, atomically cooling haloes, or HMACHs (M > 109 M⊙), and low-mass, atomically cooling haloes, or LMACHs (108 regulation. We focus here on predictions of the redshifted 21-cm emission, to see if upcoming observations are capable of distinguishing a universe ionized primarily by HMACHs from one in which both HMACHs and LMACHs are responsible, and to see how these results depend upon the uncertain source efficiencies. We find that 21-cm fluctuation power spectra observed by the first-generation Epoch of Reionization 21-cm radio interferometer arrays should be able to distinguish the case of reionization by HMACHs alone from that by both HMACHs and LMACHs, together. Some reionization scenarios, e.g. one with abundant low-efficiency sources versus one with self-regulation, yield very similar power spectra and rms evolution and thus can only be discriminated by their different mean reionization history and 21-cm probability distribution function (PDF) distributions. We also find that the skewness of the 21-cm PDF distribution smoothed with Low Frequency Array (LOFAR)-like resolution shows a clear feature correlated with the rise of the rms due to patchiness. This is independent of the reionization scenario and thus provides a new approach for detecting the rise of large-scale patchiness. The peak epoch of the 21-cm rms fluctuations depends significantly on the beam and bandwidth smoothing size as well as on the reionization scenario and can occur for ionized

  20. A Method to Measure the Mass of Damped Ly-alpha Absorber Host Galaxies Using Fluctuations in 21cm Emission

    CERN Document Server

    Wyithe, Stuart

    2008-01-01

    Observations of damped Ly-alpha absorbers (DLA) indicate that the fraction of hydrogen in its neutral form (HI) is significant by mass at all redshifts. This gas represents the reservoir of material that is available for star formation at late times. As a result, observational identification of the systems in which this neutral hydrogen resides is an important missing ingredient in models of galaxy formation. Precise identification of DLA host mass via traditional clustering studies is not practical owing to the small numbers of known systems being spread across sparsely distributed sight lines. However following the completion of reionization, 21cm surface brightness fluctuations will be dominated by neutral hydrogen in DLAs. Observations of these fluctuations will measure the combined clustering signal from all DLAs within a large volume. We show that measurement of the spherically averaged power-spectrum of 21cm intensity fluctuations due to DLAs could be used to measure the galaxy bias for DLA host galaxi...

  1. Inferring the distances of fast radio bursts through associated 21-cm absorption

    Science.gov (United States)

    Margalit, Ben; Loeb, Abraham

    2016-07-01

    The distances of fast radio burst (FRB) sources are currently unknown. We show that the 21-cm absorption line of hydrogen can be used to infer the redshifts of FRB sources, and determine whether they are Galactic or extragalactic. We calculate a probability of ˜10 per cent for the host galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width ≳10 km s-1. Arecibo, along with several future radio observatories, should be capable of detecting such associated 21-cm absorption signals for strong bursts of ≳several Jy peak flux densities.

  2. Bayesian constraints on the global 21-cm signal from the Cosmic Dawn

    CERN Document Server

    Bernardi, G; Price, D; Greenhill, L J; Mesinger, A; Dowell, J; Eftekhari, T; Ellingson, S W; Kocz, J; Schinzel, F

    2016-01-01

    The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work we present a fully-Bayesian method, \\textsc{hibayes}, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible), Gaussian model of the 21-cm emission from the Cosmic Dawn epoch ($15 \\lesssim z \\lesssim 30$), parameterized by an amplitude $A_{\\rm HI}$, a frequency peak $\

  3. The prospects of measuring the angular power spectrum of the diffuse Galactic synchrotron emission with SKA1 Low

    CERN Document Server

    Ali, Sk Saiyad; Choudhuri, Samir; Ghosh, Abhik; Roy, Nirupam

    2016-01-01

    The diffuse Galactic syncrotron emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our Galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are (1.) it deals with the gridded data which makes it computationally very fast (2.) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3.) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the sidelobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C_l of the DGSE using 1...

  4. The angular power spectrum of radio emission at 2.3 GHz

    CERN Document Server

    Giardino, G; Fosalba, P; Górski, K M; Jonas, J L; O'Mullane, W; Tauber, J A

    2001-01-01

    We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global angular power spectrum of Galactic continuum emission. In order to measure the angular power spectrum of the diffuse component, point sources were removed from the map by median filtering. A least-square fit to the angular power spectrum of the entire survey with a power law spectrum C_l proportional to l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power spectrum of radio emission appears to steepen at high Galactic latitudes and for observed regions with |b| > 20 deg, the fitted spectral index is alpha = 2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency channel of Planck) and estimate that no significant contribution to the sky temperature fluctuation is likely to come from synchrotron at degree-angular scales

  5. 21-cm signal from cosmic dawn - II: Imprints of the light-cone effects

    CERN Document Server

    Ghara, Raghunath; Choudhury, T Roy

    2015-01-01

    Details of various unknown physical processes during the cosmic dawn and the epoch of reionization can be extracted from observations of the redshifted 21-cm signal. These observations, however, will be affected by the evolution of the signal along the line-of-sight which is known as the "light-cone effect". We model this effect by post-processing a dark matter $N-$body simulation with a 1-D radiative transfer code. We find that the effect is much stronger and dramatic in presence of inhomogeneous heating and Ly$\\alpha$ coupling compared to the case where these processes are not accounted for. One finds increase (decrease) in the coeval spherically averaged power spectrum up to a factor of 3 (0.6) at large scales ($k \\sim 0.05\\, \\rm Mpc^{-1}$), though these numbers are highly dependent on the source model. Consequently, the peak and trough-like features seen in the evolution of the large-scale power spectrum can be smoothed out to a large extent if the width of the frequency bands used in the experiment is la...

  6. Blind search for 21-cm absorption systems using a new generation of Chinese radio telescopes

    Science.gov (United States)

    Yu, Hao-Ran; Pen, Ue-Li; Zhang, Tong-Jie; Li, Di; Chen, Xuelei

    2017-05-01

    Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese radio telescopes through a blind search of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China -the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and Tianlai 21-cm cosmology experiment (Tianlai). Facilitated by either the high sensitivity (FAST) or wide field of view (Tianlai) of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.

  7. An intensity map of hydrogen 21-cm emission at redshift z approximately 0.8.

    Science.gov (United States)

    Chang, Tzu-Ching; Pen, Ue-Li; Bandura, Kevin; Peterson, Jeffrey B

    2010-07-22

    Observations of 21-cm radio emission by neutral hydrogen at redshifts z approximately 0.5 to approximately 2.5 are expected to provide a sensitive probe of cosmic dark energy. This is particularly true around the onset of acceleration at z approximately 1, where traditional optical cosmology becomes very difficult because of the infrared opacity of the atmosphere. Hitherto, 21-cm emission has been detected only to z = 0.24. More distant galaxies generally are too faint for individual detections but it is possible to measure the aggregate emission from many unresolved galaxies in the 'cosmic web'. Here we report a three-dimensional 21-cm intensity field at z = 0.53 to 1.12. We then co-add neutral-hydrogen (H i) emission from the volumes surrounding about 10,000 galaxies (from the DEEP2 optical galaxy redshift survey). We detect the aggregate 21-cm glow at a significance of approximately 4sigma.

  8. Inferring the Distances of Fast Radio Bursts Through 21-cm Absorption

    CERN Document Server

    Margalit, Ben

    2015-01-01

    The distances of Fast Radio Burst (FRB) sources are currently unknown. We show that the 21-cm absorption line of hydrogen can be used to infer the redshifts of FRB sources, and determine whether they are Galactic or extragalactic. We calculate a probability of $\\sim 10\\%$ for detecting a 21-cm equivalent width $\\gtrsim 4 ~\\mathrm{km}~\\mathrm{s}^{-1}$. The forthcoming SKA observatory provides ideal prospects for detecting our predicted signal.

  9. Can 21-cm observations discriminate between high-mass and low-mass galaxies as reionization sources?

    CERN Document Server

    Iliev, Ilian T; Shapiro, Paul R; Pen, Ue-Li; Mao, Yi; Koda, Jun; Ahn, Kyungjin

    2011-01-01

    The prospect of detecting the first galaxies by observing their impact on the intergalactic medium as they reionized it during the first billion years leads us to ask whether such indirect observations are capable of diagnosing which types of galaxies were most responsible for reionization. We attempt to answer this by considering a set of large-scale radiative transfer simulations of reionization in sufficiently large volumes to make statistically meaningful predictions of observable signatures, while also directly resolving all atomically-cooling halos down to 10^8 M_solar. We focus here on predictions of the 21-cm background, to see if upcoming observations are capable of distinguishing a universe ionized primarily by high-mass halos from one in which both high-mass and low-mass halos are responsible, and to see how these results depend upon the uncertain source efficiencies. We find that 21-cm fluctuation power spectra observed by the first generation EoR/21-cm radio interferometer arrays should be able t...

  10. Non-parametric foreground subtraction for 21cm epoch of reionization experiments

    CERN Document Server

    Harker, Geraint; Bernardi, Gianni; Brentjens, Michiel A; De Bruyn, A G; Ciardi, Benedetta; Jelic, Vibor; Koopmans, Leon V E; Labropoulos, Panagiotis; Mellema, Garrelt; Offringa, Andre; Pandey, V N; Schaye, Joop; Thomas, Rajat M; Yatawatta, Sarod

    2009-01-01

    An obstacle to the detection of redshifted 21cm emission from the epoch of reionization (EoR) is the presence of foregrounds which exceed the cosmological signal in intensity by orders of magnitude. We argue that in principle it would be better to fit the foregrounds non-parametrically - allowing the data to determine their shape - rather than selecting some functional form in advance and then fitting its parameters. Non-parametric fits often suffer from other problems, however. We discuss these before suggesting a non-parametric method, Wp smoothing, which seems to avoid some of them. After outlining the principles of Wp smoothing we describe an algorithm used to implement it. We then apply Wp smoothing to a synthetic data cube for the LOFAR EoR experiment. The performance of Wp smoothing, measured by the extent to which it is able to recover the variance of the cosmological signal and to which it avoids leakage of power from the foregrounds, is compared to that of a parametric fit, and to another non-parame...

  11. The 21-cm signature of the first stars during the Lyman-Werner feedback era

    CERN Document Server

    Fialkov, Anastasia; Visbal, Eli; Tseliakhovich, Dmitriy; Hirata, Christopher M

    2012-01-01

    The formation of the first stars is an exciting frontier area in astronomy. Early redshifts z ~ 20 have become observationally promising as a result of a recently recognized effect of a supersonic relative velocity between the dark matter and gas. This effect produces prominent structure on 100 comoving Mpc scales, which makes it much more feasible to detect 21-cm fluctuations from the epoch of first heating. We use semi-numerical hybrid methods to follow for the first time the joint evolution of the X-ray and Lyman-Werner radiative backgrounds, including the effect of the supersonic streaming velocity on the cosmic distribution of stars. We incorporate self-consistently the negative feedback on star formation induced by the Lyman-Werner radiation, which dissociates molecular hydrogen and thus suppresses gas cooling. We find that the feedback delays the X-ray heating transition by a Delta z ~ 2, but leaves a promisingly large fluctuation signal over a broad redshift range. The large-scale power spectrum is pr...

  12. The angular magnetothermoelectric power of a charge density wave system

    Science.gov (United States)

    Krstovska, D.; Choi, E. S.; Steven, E.; Brooks, J. S.

    2012-07-01

    The angular dependence of the magnetothermopower of a charge transfer organic salt α-(ET)2KHg(SCN)4 below (4 K) and above (9 K) the phase transition temperature, Tp = 8 K, and under fields of 15 T and 25 T, below and above the ‘kinkfield’, has been studied. We find that for a longitudinal thermoelectric measurement both an interlayer thermopower (the Seebeck effect), Szz, and a transverse thermopower (the Nernst effect), Syz, exist in all three different B-T phases (the CDW 0, CDW x and metallic states) with large amplitude. Both thermoelectric effects display a resonant-like behavior without a sign reversal at the angles corresponding to angular magnetoresistance oscillation minima and maxima in this compound. The resonant behavior is most evident in the CDW0 state, indicating a mechanism involving the Fermi surface nesting. Angular dependences reveal different behaviors of the thermopower and Nernst effect in the high magnetic field (CDWx) state.

  13. Cross-correlation of the cosmic 21-cm signal and Lyman α emitters during reionization

    Science.gov (United States)

    Sobacchi, Emanuele; Mesinger, Andrei; Greig, Bradley

    2016-07-01

    Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal to noise, limited by systematics. To confirm a putative 21-cm detection, and check the accuracy of 21-cm data analysis pipelines, it would be very useful to cross-correlate against a genuine cosmological signal. The most promising cosmological signals are wide-field maps of Lyman α emitting galaxies (LAEs), expected from the Subaru Hyper-Suprime Cam ultradeep field (UDF). Here we present estimates of the correlation between LAE maps at z ˜ 7 and the 21-cm signal observed by both the Low Frequency Array (LOFAR) and the planned Square Kilometre Array Phase 1 (SKA1). We adopt a systematic approach, varying both: (i) the prescription of assigning LAEs to host haloes; and (ii) the large-scale structure of neutral and ionized regions (i.e. EoR morphology). We find that the LAE-21cm cross-correlation is insensitive to (i), thus making it a robust probe of the EoR. A 1000 h observation with LOFAR would be sufficient to discriminate at ≳ 1σ a fully ionized Universe from one with a mean neutral fraction of bar{x}_{H I}≈ 0.50, using the LAE-21 cm cross-correlation function on scales of R ≈ 3-10 Mpc. Unlike LOFAR, whose detection of the LAE-21 cm cross-correlation is limited by noise, SKA1 is mostly limited by ignorance of the EoR morphology. However, the planned 100 h wide-field SKA1-Low survey will be sufficient to discriminate an ionized Universe from one with bar{x}_{H I}=0.25, even with maximally pessimistic assumptions.

  14. A Halo Model Approach to the 21 cm and Lyα Cross-correlation

    Science.gov (United States)

    Feng, Chang; Cooray, Asantha; Keating, Brian

    2017-09-01

    We present a halo-model-based approach to calculate the cross-correlation between 21 {cm} H i intensity fluctuations and {Ly}α emitters (LAE) during the epoch of reionization (EoR). Ionizing radiation around dark matter halos are modeled as bubbles with the size and growth determined based on the reionization photon production, among other physical parameters. The cross-correlation shows a clear negative-to-positive transition, associated with transition from ionized to neutral hydrogen in the intergalactic medium during EoR. The cross-correlation is subject to several foreground contaminants, including foreground radio point sources important for 21 {cm} experiments and low-z interloper emission lines, such as {{H}}α , O iii, and O ii, for {Ly}α experiments. Our calculations show that by masking out high fluxes in the {Ly}α measurement, the correlated foreground contamination on the 21 {cm}–{Ly}α cross-correlation can be dramatically reduced. We forecast the detectability of 21 {cm}–{Ly}α cross-correlation at different redshifts and adopt a Fisher matrix approach to estimate uncertainties on the key EoR parameters that have not been well constrained by other observations of reionization. This halo-model-based approach enables us to explore the EoR parameter space rapidly for different 21 {cm} and {Ly}α experiments.

  15. Cross-correlation of the cosmic 21-cm signal and Lyman Alpha Emitters during reionization

    CERN Document Server

    Sobacchi, Emanuele; Greig, Bradley

    2016-01-01

    Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal-to-noise, limited by systematics. To confirm a putative 21-cm detection, and check the accuracy of 21-cm data analysis pipelines, it would be very useful to cross-correlate against a genuine cosmological signal. The most promising cosmological signals are wide-field maps of Lyman alpha emitting galaxies (LAEs), expected from the Subaru Hyper-Suprime Cam (HSC) Ultra-Deep field. Here we present estimates of the correlation between LAE maps at z~7 and the 21-cm signal observed by both the Low Frequency Array (LOFAR) and the planned Square Kilometer Array Phase 1 (SKA1). We adopt a systematic approach, varying both: (i) the prescription of assigning LAEs to host halos; and (ii) the large-scale structure of neutral and ionized regions (i.e. EoR morphology). We find that the LAE-21cm cross-correlation...

  16. THE IMPORTANCE OF WIDE-FIELD FOREGROUND REMOVAL FOR 21 cm COSMOLOGY: A DEMONSTRATION WITH EARLY MWA EPOCH OF REIONIZATION OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Pober, J. C. [Department of Physics, Brown University, Providence, RI 02912 (United States); Hazelton, B. J.; Beardsley, A. P.; Barry, N. A.; Martinot, Z. E.; Sullivan, I. S.; Morales, M. F.; Carroll, P. [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Bell, M. E. [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia); Bernardi, G. [Square Kilometre Array South Africa (SKA SA), Pinelands 7405 (South Africa); Bhat, N. D. R.; Emrich, D. [International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102 (Australia); Bowman, J. D. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Briggs, F. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Cappallo, R. J.; Corey, B. E. [MIT Haystack Observatory, Westford, MA 01886 (United States); De Oliveira-Costa, A. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Deshpande, A. A. [Raman Research Institute, Bangalore 560080 (India); Dillon, Joshua S. [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720 (United States); Ewall-Wice, A. M. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); and others

    2016-03-01

    In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing a foreground model that includes sources in both the main field of view and the first sidelobes reduces the contamination in high k{sub ∥} modes by several per cent relative to a model that only includes sources in the main field of view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. While small, a percent-level amount of foreground power is in itself more than enough to prevent recovery of any Epoch of Reionization signal from these modes. This result demonstrates that foreground subtraction for redshifted 21 cm experiments is truly a wide-field problem, and algorithms and simulations must extend beyond the instrument’s main field of view to potentially recover the full 21 cm power spectrum.

  17. Contributions of dark matter annihilation within ultracompact minihalos to the 21 cm background signal

    Science.gov (United States)

    Yang, Yupeng

    2016-12-01

    In the dark age of the Universe, any exotic sources, e.g. the dark matter annihilation, which inject the energy into the intergalactic medium (IGM) will left some imprint on the 21cm background signal. Recently, one new kind of dark matter structure named ultracompact dark matter minihalos (UCMHs) was proposed. Near the inner part of UCMHs, the distribution of dark matter particles is steeper than that of the general dark matter halos, ρ_{UCMHs}(r) ˜ r^{-2.25}, and the formation time of UCMHs is earlier, zc ˜ 1000. Therefore, it is excepted that the dark matter annihilation within UCMHs can effect the 21cm background signal. In this paper, we investigated the contributions of the dark matter annihilation within UCMHs to the 21cm background signal.

  18. The mass angular scattering power method for determining the kinetic energies of clinical electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Blais, N.; Podgorsak, E.B. (Montreal General Hospital, PQ (Canada). Dept. of Medical Physics)

    1992-10-01

    A method for determining the kinetic energy of clinical electron beams is described, based on the measurement in air of the spatial spread of a pencil electron beam which is produced from the broad clinical electron beam. As predicted by the Fermi-Eyges theory, the dose distribution measured in air on a plane, perpendicular to the incident direction of the initial pencil electron beam, is Gaussian. The square of its spatial spread is related to the mass angular scattering power which in turn is related to the kinetic energy of the electron beam. The measured spatial spread may thus be used to determine the mass angular scattering power, which is then used to determine the kinetic energy of the electron beam from the known relationship between mass angular scattering power and kinetic energy. Energies obtained with the mass angular scattering power method agree with those obtained with the electron range method. (author).

  19. FOREGROUND MODEL AND ANTENNA CALIBRATION ERRORS IN THE MEASUREMENT OF THE SKY-AVERAGED λ21 cm SIGNAL AT z∼ 20

    Energy Technology Data Exchange (ETDEWEB)

    Bernardi, G. [SKA SA, 3rd Floor, The Park, Park Road, Pinelands, 7405 (South Africa); McQuinn, M. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Greenhill, L. J., E-mail: gbernardi@ska.ac.za [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2015-01-20

    The most promising near-term observable of the cosmic dark age prior to widespread reionization (z ∼ 15-200) is the sky-averaged λ21 cm background arising from hydrogen in the intergalactic medium. Though an individual antenna could in principle detect the line signature, data analysis must separate foregrounds that are orders of magnitude brighter than the λ21 cm background (but that are anticipated to vary monotonically and gradually with frequency, e.g., they are considered {sup s}pectrally smooth{sup )}. Using more physically motivated models for foregrounds than in previous studies, we show that the intrinsic spectral smoothness of the foregrounds is likely not a concern, and that data analysis for an ideal antenna should be able to detect the λ21 cm signal after subtracting a ∼fifth-order polynomial in log ν. However, we find that the foreground signal is corrupted by the angular and frequency-dependent response of a real antenna. The frequency dependence complicates modeling of foregrounds commonly based on the assumption of spectral smoothness. Our calculations focus on the Large-aperture Experiment to detect the Dark Age, which combines both radiometric and interferometric measurements. We show that statistical uncertainty remaining after fitting antenna gain patterns to interferometric measurements is not anticipated to compromise extraction of the λ21 cm signal for a range of cosmological models after fitting a seventh-order polynomial to radiometric data. Our results generalize to most efforts to measure the sky-averaged spectrum.

  20. Inferring the Distances of Fast Radio Bursts Through Associated 21-cm Absorption

    OpenAIRE

    Margalit, Ben; Loeb, Abraham

    2015-01-01

    The distances of Fast Radio Burst (FRB) sources are currently unknown. We show that the 21-cm absorption line of hydrogen can be used to infer the redshifts of FRB sources, and determine whether they are Galactic or extragalactic. We calculate a probability of $\\sim 10\\%$ for the host galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width $\\gtrsim 10 ~\\mathrm{km}~\\mathrm{s}^{-1}$. Arecibo, along with several future radio observatories, should be capable of detecting such a...

  1. From Darkness to Light: Signatures of the Universe's First Galaxies in the Cosmic 21-cm Background

    Science.gov (United States)

    Mirocha, Jordan

    Within the first billion years after the Big Bang, the intergalactic medium (IGM) underwent a remarkable transformation, from a uniform sea of cold neutral hydrogen gas to a fully ionized, metal-enriched plasma. Three milestones during this Epoch of Reionization -- the emergence of the first stars, black holes, and full-fledged galaxies -- are expected to manifest as spectral "turning points" in the sky-averaged ("global") 21-cm background. However, interpreting these measurements will be complicated by the presence of strong foregrounds and non-trivialities in the radiative transfer (RT) required to model the signal. In this thesis, I make the first attempt to build the final piece of a global 21-cm data analysis pipeline: an inference tool capable of extracting the properties of the IGM and the Universe's first galaxies from the recovered signal. Such a framework is valuable even prior to a detection of the global 21-cm signal as it enables end-to-end simulations of 21-cm observations that can be used to optimize the design of upcoming instruments, their observing strategies, and their signal extraction algorithms. En route to a complete pipeline, I found that (1) robust limits on the physical properties of the IGM, such as its temperature and ionization state, can be derived analytically from the 21-cm turning points within two-zone models for the IGM, (2) improved constraints on the IGM properties can be obtained through simultaneous fitting of the global 21-cm signal and foregrounds, though biases can emerge depending on the parameterized form of the signal one adopts, (3) a simple four-parameter galaxy formation model can be constrained in only 100 hours of integration provided a stable instrumental response over a broad frequency range (~80 MHz), and (4) frequency-dependent RT solutions in physical models for the global 21-cm signal will be required to properly interpret the 21-cm absorption minimum, as the IGM thermal history is highly sensitive to the

  2. Whole-body angular momentum during stair walking using passive and powered lower-limb prostheses.

    Science.gov (United States)

    Pickle, Nathaniel T; Wilken, Jason M; Aldridge, Jennifer M; Neptune, Richard R; Silverman, Anne K

    2014-10-17

    Individuals with a unilateral transtibial amputation have a greater risk of falling compared to able-bodied individuals, and falling on stairs can lead to serious injuries. Individuals with transtibial amputations have lost ankle plantarflexor muscle function, which is critical for regulating whole-body angular momentum to maintain dynamic balance. Recently, powered prostheses have been designed to provide active ankle power generation with the goal of restoring biological ankle function. However, the effects of using a powered prosthesis on the regulation of whole-body angular momentum are unknown. The purpose of this study was to use angular momentum to evaluate dynamic balance in individuals with a transtibial amputation using powered and passive prostheses relative to able-bodied individuals during stair ascent and descent. Ground reaction forces, external moment arms, and joint powers were also investigated to interpret the angular momentum results. A key result was that individuals with an amputation had a larger range of sagittal-plane angular momentum during prosthetic limb stance compared to able-bodied individuals during stair ascent. There were no significant differences in the frontal, transverse, or sagittal-plane ranges of angular momentum or maximum magnitude of the angular momentum vector between the passive and powered prostheses during stair ascent or descent. These results indicate that individuals with an amputation have altered angular momentum trajectories during stair walking compared to able-bodied individuals, which may contribute to an increased fall risk. The results also suggest that a powered prosthesis provides no distinct advantage over a passive prosthesis in maintaining dynamic balance during stair walking. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. A deep search for 21-cm absorption in high redshift damped Lyman-alpha systems

    NARCIS (Netherlands)

    Kanekar, N; Chengalur, JN

    2003-01-01

    We present deep GMRT 21-cm absorption spectra of 10 damped Lyman-alpha systems (DLAs), of which 8 are at redshifts zgreater than or similar to1.3. HI absorption was detected in only one DLA, the z=0.5318 absorber toward PKS 1629+12. This absorber has been identified with a luminous spiral galaxy; th

  4. Nancay blind 21cm line survey of the Canes Venatici group region

    NARCIS (Netherlands)

    Kraan-Korteweg, R. C.; Driel, W. van; Briggs, F.; Binggeli, B.; Mostefaoui, T. I.

    1998-01-01

    Submitted to: Astron. Astrophys. Abstract: A radio spectroscopic driftscan survey in the 21cm line with the Nancay Radio Telescope of 0.08 steradians of sky in the direction of the constellation Canes Venatici covering a heliocentric velocity range of -350 < V_hel < 2350 km/s produced 53 spectral fe

  5. Bayesian constraints on the global 21-cm signal from the Cosmic Dawn

    Science.gov (United States)

    Bernardi, G.; Zwart, J. T. L.; Price, D.; Greenhill, L. J.; Mesinger, A.; Dowell, J.; Eftekhari, T.; Ellingson, S. W.; Kocz, J.; Schinzel, F.

    2016-09-01

    The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work, we present a fully Bayesian method, HIBAYES, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible) Gaussian model of the 21-cm emission from the Cosmic Dawn epoch (15 ≲ z ≲ 30), parametrized by an amplitude A_{H I}, a frequency peak ν _{H I} and a width σ _{H I}, can be extracted even in the presence of a structured foreground frequency spectrum (parametrized as a seventh-order polynomial), provided sufficient signal-to-noise (400 h of observation with a single dipole). We apply our method to an early, 19-min-long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be -890 6.5 MHz (corresponding to Δz > 1.9 at redshift z ≃ 20) respectively at the 95-per cent confidence level in the range 13.2 ν > 50 MHz).

  6. Nancay "blind" 21 cm line survey of the Canes Venatici group region

    NARCIS (Netherlands)

    Kraan-Korteweg, RC; van Driel, W; Briggs, F; Binggeli, B; Mostefaoui, TI

    1999-01-01

    A radio spectroscopic driftscan survey in the 21 cm line with the Nancay decimetric radio telescope of 0.08 steradians of sky in the direction of the constellation Canes Venatici covering a heliocentric velocity range of -350

  7. Prospects of Measuring the Angular Power Spectrum of the Diffuse Galactic Synchrotron Emission with SKA1 Low

    Indian Academy of Sciences (India)

    Sk. Saiyad Ali; Somnath Bharadwaj; Samir Choudhuri; Abhik Ghosh; Nirupam Roy

    2016-12-01

    The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum $C_\\ell$ of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the $C_\\ell$ of the DGSE using 150 MHz GMRT data. Earlier measurements of $C_\\ell$ are restricted to $\\ell \\le \\ell _{\\max } \\sim 10^{3}$ for the DGSE, the signal at the larger $\\ell$ values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the $C_\\ell$ of the DGSE to larger values of $\\ell _{\\max }$ with SKA1 Low. Our results show that it should be possible to achieve $\\ell _{\\max }\\sim 10^{4}$ and $∼10^5$ with 2 minutes and 10 hours of observations respectively.

  8. Prospects of Measuring the Angular Power Spectrum of the Diffuse Galactic Synchrotron Emission with SKA1 Low

    Science.gov (United States)

    Ali, Sk. Saiyad; Bharadwaj, Somnath; Choudhuri, Samir; Ghosh, Abhik; Roy, Nirupam

    2016-12-01

    The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum C ℓ of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C ℓ of the DGSE using 150 MHz GMRT data. Earlier measurements of C ℓ are restricted to ℓ ≤ ℓ _{max } ˜ 103 for the DGSE, the signal at the larger ℓ values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the C ℓ of the DGSE to larger values of ℓ _{max } with SKA1 Low. Our results show that it should be possible to achieve ℓ _{max }˜ 104 and ˜105 with 2 minutes and 10 hours of observations respectively.

  9. A FLUX SCALE FOR SOUTHERN HEMISPHERE 21 cm EPOCH OF REIONIZATION EXPERIMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Jacobs, Daniel C.; Bowman, Judd [School of Earth and Space Exploration, Arizona State University, Tempe, AZ (United States); Parsons, Aaron R.; Ali, Zaki; Pober, Jonathan C. [Astronomy Department, University of California, Berkeley, CA (United States); Aguirre, James E.; Moore, David F. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA (United States); Bradley, Richard F. [Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, VA (United States); Carilli, Chris L. [National Radio Astronomy Observatory, Socorro, NM (United States); DeBoer, David R.; Dexter, Matthew R.; MacMahon, Dave H. E. [Radio Astronomy Lab., University of California, Berkeley, CA (United States); Gugliucci, Nicole E.; Klima, Pat [National Radio Astronomy Observatory, Charlottesville, VA (United States); Manley, Jason R.; Walbrugh, William P. [Square Kilometer Array, South Africa Project, Cape Town (South Africa); Stefan, Irina I. [Cavendish Laboratory, Cambridge (United Kingdom)

    2013-10-20

    We present a catalog of spectral measurements covering a 100-200 MHz band for 32 sources, derived from observations with a 64 antenna deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. For transit telescopes such as PAPER, calibration of the primary beam is a difficult endeavor and errors in this calibration are a major source of error in the determination of source spectra. In order to decrease our reliance on an accurate beam calibration, we focus on calibrating sources in a narrow declination range from –46° to –40°. Since sources at similar declinations follow nearly identical paths through the primary beam, this restriction greatly reduces errors associated with beam calibration, yielding a dramatic improvement in the accuracy of derived source spectra. Extrapolating from higher frequency catalogs, we derive the flux scale using a Monte Carlo fit across multiple sources that includes uncertainty from both catalog and measurement errors. Fitting spectral models to catalog data and these new PAPER measurements, we derive new flux models for Pictor A and 31 other sources at nearby declinations; 90% are found to confirm and refine a power-law model for flux density. Of particular importance is the new Pictor A flux model, which is accurate to 1.4% and shows that between 100 MHz and 2 GHz, in contrast with previous models, the spectrum of Pictor A is consistent with a single power law given by a flux at 150 MHz of 382 ± 5.4 Jy and a spectral index of –0.76 ± 0.01. This accuracy represents an order of magnitude improvement over previous measurements in this band and is limited by the uncertainty in the catalog measurements used to estimate the absolute flux scale. The simplicity and improved accuracy of Pictor A's spectrum make it an excellent calibrator in a band important for experiments seeking to measure 21 cm emission from the epoch of reionization.

  10. Angular Differential Imaging: a Powerful High-Contrast Imaging Technique

    Energy Technology Data Exchange (ETDEWEB)

    Marois, C; Lafreniere, D; Doyon, R; Macintosh, B; Nadeau, D

    2005-11-07

    Angular differential imaging is a high-contrast imaging technique that reduces speckle noise from quasi-static optical aberrations and facilitates the detection of faint nearby companions. A sequence of images is acquired with an altitude/azimuth telescope, the instrument rotator being turned off. This keeps the instrument and telescope optics aligned, stabilizes the instrumental PSF and allows the field of view to rotate with respect to the instrument. For each image, a reference PSF obtained from other images of the sequence is subtracted. All residual images are then rotated to align the field and are median combined. Observed performances are reported for Gemini Altair/NIRI data. Inside the speckle dominated region of the PSF, it is shown that quasi-static PSF noise can be reduced by a factor {approx}5 for each image subtraction. The combination of all residuals then provides an additional gain of the order of the square root of the total number of images acquired. To our knowledge, this is the first time an acquisition strategy and reduction pipeline designed for speckle attenuation and high contrast imaging is demonstrated to significantly get better detection limits with longer integration times at all angular separations. A PSF noise attenuation of 100 was achieved from 2-hour long sequences of images of Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 7''. This technique can be used with currently available instruments to search for {approx} 1 M{sub Jup} exoplanets with orbits of radii between 50 and 300 AU around nearby young stars. The possibility of combining the technique with other high-contrast imaging methods is briefly discussed.

  11. Modelling the 21 cm Signal From the Epoch of Reionization and Cosmic Dawn

    CERN Document Server

    Choudhury, T Roy; Majumdar, Suman; Ghara, Raghunath; Paranjape, Aseem; Mondal, Rajesh; Bharadwaj, Somnath; Samui, Saumyadip

    2016-01-01

    Studying the cosmic dawn and the epoch of reionization through the redshifted 21 cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21 cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data.

  12. Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn

    Indian Academy of Sciences (India)

    T. Roy Choudhury; Kanan Datta; Suman Majumdar; Raghunath Ghara; Aseem Paranjape; Rajesh Mondal; Somnath Bharadwaj; Saumyadip Samui

    2016-12-01

    Studying the cosmic dawn and the epoch of reionization through the redshifted 21-cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the Universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21-cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data.

  13. The Global 21-cm Signal in the Context of the High-z Galaxy Luminosity Function

    CERN Document Server

    Mirocha, Jordan; Sun, G

    2016-01-01

    Motivated by recent progress in studies of the high-$z$ Universe, we build a new model for the global 21-cm signal that is explicitly calibrated to measurements of the galaxy luminosity function (LF) and further tuned to match the Thomson scattering optical depth of the cosmic microwave background, $\\tau_e$. Assuming that the $z \\lesssim 8$ galaxy population can be smoothly extrapolated to higher redshifts, the recent decline in best-fit values of $\\tau_e$ and the inefficient heating induced by X-ray binaries (HMXBs; the presumptive sources of the X-ray background at high-$z$) imply that the entirety of cosmic reionization and reheating occurs at redshifts $z \\lesssim 12$. In contrast to past global 21-cm models, whose $z \\sim 20$ ($\

  14. Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation

    CERN Document Server

    Masui, K W; Banavar, N; Bandura, K; Blake, C; Calin, L -M; Chang, T -C; Chen, X; Li, Y -C; Liao, Y -W; Natarajan, A; Pen, U -L; Peterson, J B; Shaw, J R; Voytek, T C

    2012-01-01

    In this letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in the WiggleZ Dark Energy Survey. The data span the redshift range 0.6 < z < 1 over two fields totaling ~41 deg. sq. and 190 hours of radio integration time. The cross-correlation constrains Omega_HI b_HI r = [0.43 \\pm 0.07 (stat.) \\pm 0.04(sys.)] x 10^-3, where Omega_HI is the neutral hydrogen HI fraction, r is the galaxy-hydrogen correlation coefficient, and b_HI is the HI bias parameter. This is the most precise constraint on neutral hydrogen density fluctuations in a challenging redshift range. Our measurement improves the previous 21 cm cross-correlation at z ~ 0.8 both in its precision and in the range of scales probed.

  15. The Application of Continuous Wavelet Transform Based Foreground Subtraction Method in 21 cm Sky Surveys

    CERN Document Server

    Gu, Junhua; Wang, Jingying; An, Tao; Chen, Wen

    2013-01-01

    We propose a continuous wavelet transform based non-parametric foreground subtraction method for the detection of redshifted 21 cm signal from the epoch of reionization. This method works based on the assumption that the foreground spectra are smooth in frequency domain, while the 21 cm signal spectrum is full of saw-tooth-like structures, thus their characteristic scales are significantly different. We can distinguish them in the wavelet coefficient space easily and perform the foreground subtraction. Compared with the traditional spectral fitting based method, our method is more tolerant to complex foregrounds. Furthermore, we also find that when the instrument has uncorrected response error, our method can also work significantly better than the spectral fitting based method. Our method can obtain similar results with the Wp smoothing method, which is also a non-parametric method, but our method consumes much less computing time.

  16. The 21 cm signal and the interplay between dark matter annihilations and astrophysical processes

    CERN Document Server

    Lopez-Honorez, Laura; Moliné, Ángeles; Palomares-Ruiz, Sergio; Vincent, Aaron C

    2016-01-01

    Future dedicated radio interferometers, including HERA and SKA, are very promising tools that aim to study the epoch of reionization and beyond via measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM) annihilations into charged particles change the thermal history of the Universe and, as a consequence, affect the 21 cm signal. Accurately predicting the effect of DM strongly relies on the modeling of annihilations inside halos. In this work, we use up-to-date computations of the energy deposition rates by the products from DM annihilations, a proper treatment of the contribution from DM annihilations in halos, as well as values of the annihilation cross section allowed by the most recent cosmological measurements from the Planck satellite. Given current uncertainties on the description of the astrophysical processes driving the epochs of reionization, X-ray heating and Lyman-$\\alpha$ pumping, we find that disentangling DM signatures from purely astrophysical effects, related to early-time s...

  17. Will Nonlinear Peculiar Velocity and Inhomogeneous Reionization Spoil 21cm Cosmology from the Epoch of Reionization?

    OpenAIRE

    Shapiro, Paul R.; Mao, Yi; Iliev, Ilian T.; Mellema, Garrelt; Datta, Kanan K.; Ahn, Kyungjin; Koda, Jun

    2012-01-01

    The 21cm background from the epoch of reionization is a promising cosmological probe: line-of-sight velocity fluctuations distort redshift, so brightness fluctuations in Fourier space depend upon angle, which linear theory shows can separate cosmological from astrophysical information. Nonlinear fluctuations in ionization, density and velocity change this, however. The validity and accuracy of the separation scheme are tested here for the first time, by detailed reionization simulations. The ...

  18. The 21-cm Background from the Cosmic Dark Ages: Minihalos and the Intergalactic Medium before Reionization

    CERN Document Server

    Ahn, K; Alvarez, M A; Iliev, I T; Martel, H; Ryu, D; Ahn, Kyungjin; Shapiro, Paul R.; Alvarez, Marcelo A.; Iliev, Ilian T.; Martel, Hugo

    2006-01-01

    The H atoms inside minihalos (i.e. halos with virial temperatures T_vir 8) to compute the mean brightness temperature of this background from both minihalos and the intergalactic medium (IGM) prior to the onset of Ly-alpha radiative pumping. We find that the 21-cm signal from gas in collapsed, virialized minihalos dominates over that from the diffuse shocked gas in the IGM.

  19. The Importance of Wide-field Foreground Removal for 21 cm Cosmology: A Demonstration With Early MWA Epoch of Reionization Observations

    CERN Document Server

    Pober, J C; Beardsley, A P; Barry, N A; Martinot, Z E; Sullivan, I S; Morales, M F; Bell, M E; Bernardi, G; Bhat, N D R; Bowman, J D; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Deshpande, A A; Dillon, Joshua S; Emrich, D; Ewall-Wice, A M; Feng, L; Goeke, R; Greenhill, L J; Hewitt, J N; Hindson, L; Hurley-Walker, N; Jacobs, D C; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kim, Han-Seek; Kittiwisit, P; Kratzenberg, E; Kudryavtseva, N; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morgan, E; Neben, A R; Oberoi, D; Offringa, A R; Ord, S M; Paul, Sourabh; Pindor, B; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Sethi, Shiv K; Shankar, N Udaya; Srivani, K S; Subrahmanyan, R; Tegmark, M; Thyagarajan, Nithyanandan; Tingay, S J; Trott, C M; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wyithe, J S B

    2016-01-01

    In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing a foreground model which includes sources in both the main field-of-view and the first sidelobes reduces the contamination in high k_parallel modes by several percent relative to a model which only includes sources in the main field-of-view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. ...

  20. Z > 6 Galaxy Signatures in the Infrared Background and the 21-cm background

    Science.gov (United States)

    Cooray, A.

    2006-08-01

    We will discuss the signatures of the high-redshift galaxy formation in the near-infrared background. Ionizing sources at high redshift generically imprint a distinctive Lyman-cutoff feature and a unique spatial anisotropy signature to the IRB, both of which may be detectable in a short rocket flight. We will discuss the Cosmic Infrared Background ExpeRiment (CIBER), a rocket-borne instrument to probe the absolute spectrum and spatial anisotropy of the extragalactic InfraRed Background (IRB) optimized for detection of the integrated spatial anisotropies in the IR background from high-redshift galaxies. We will also discuss the signatures of first galaxies in the low radio frequency 21-cm background from the neutral Hydrogen distribution at z > 6; When combined with arcminute-scale temperature anisotropy and the polarization of the cosmic microwave background, the 21-cm background will allow a determination of inhomogeneous distribution of Lyman-alpha photons from first galaxies. We will discuss these and other possibilities to understand the first galaxy population with IR, 21-cm, and CMB backgrounds.

  1. The imprint of the cosmic supermassive black hole growth history on the 21 cm background radiation

    CERN Document Server

    Tanaka, Takamitsu L; Perna, Rosalba

    2015-01-01

    The redshifted 21 cm transition line of hydrogen tracks the thermal evolution of the neutral intergalactic medium (IGM) at "cosmic dawn," during the emergence of the first luminous astrophysical objects (~100 Myr after the Big Bang) but before these objects ionized the IGM (~400-800 Myr after the Big Bang). Because X-rays, in particular, are likely to be the chief energy courier for heating the IGM, measurements of the 21 cm signature can be used to infer knowledge about the first astrophysical X-ray sources. Using analytic arguments and a numerical population synthesis algorithm, we argue that the progenitors of supermassive black holes (SMBHs) should be the dominant source of hard astrophysical X-rays---and thus the primary driver of IGM heating and the 21 cm signature---at redshifts $z 20$. An absence of such a signature in the forthcoming observational data would imply that SMBH formation occurred later (e.g. via so-called direct collapse scenarios), that it was not a common occurrence in early galaxies ...

  2. Detecting the integrated Sachs-Wolfe effect with high-redshift 21-cm surveys

    CERN Document Server

    Raccanelli, Alvise; Dai, Liang; Kamionkowski, Marc

    2015-01-01

    We investigate the possibility to detect the integrated Sachs-Wolfe (ISW) effect by cross-correlating 21-cm surveys at high redshifts with galaxies, in a way similar to the usual CMB-galaxy cross-correlation. The high-redshift 21-cm signal is dominated by CMB photons that travel freely without interacting with the intervening matter, and hence its late-time ISW signature should correlate extremely well with that of the CMB at its peak frequencies. Using the 21-cm temperature brightness instead of the CMB would thus be a further check of the detection of the ISW effect, measured by different instruments at different frequencies and suffering from different systematics. We also study the ISW effect on the photons that are scattered by HI clouds. We show that a detection of the unscattered photons is achievable with planned radio arrays, while one using scattered photons will require advanced radio interferometers, either an extended version of the planned Square Kilometre Array or futuristic experiments such as...

  3. Exploiting 21cm - Ly$\\alpha$ emitter synergies: constraints on reionization

    CERN Document Server

    Hutter, Anne; Müller, Volker; Trott, Cathryn

    2016-01-01

    We couple a $z \\simeq 6.6$ hydrodynamical simulation (GADGET-2) with a radiative transfer code (pCRASH) and a dust model to simultaneously obtain the 21cm emission from the spin-flip transition of neutral hydrogen (HI) as well as the sub-population of galaxies visible as Lyman Alpha Emitters (LAEs). Cross-correlating 21cm data with the underlying galaxy population, and especially the subset visible as LAEs, our aim is to constrain both the average intergalactic medium (IGM) ionization state ($\\langle \\chi_{HI} \\rangle$) and the reionization topology (outside-in versus inside-out). We find that LAEs occupy the densest and most-ionized regions resulting in a very strong anti-correlation between the LAEs and the 21cm emission. Within errors, a 1000h SKA-LOW1 - Subaru Hyper Suprime Cam experiment can provide exquisite constraints on $\\langle \\chi_{HI} \\rangle$, allowing us to distinguish between IGM ionization levels of 50%, 25%, 10% and fully ionized at scales $\\leq 10$ comoving Mpc. Our results support the insi...

  4. Detection of architectural distortion in prior mammograms using fractal analysis and angular spread of power

    Science.gov (United States)

    Banik, Shantanu; Rangayyan, Rangaraj M.; Desautels, J. E. L.

    2010-03-01

    This paper presents methods for the detection of architectural distortion in mammograms of interval-cancer cases taken prior to the diagnosis of breast cancer, using Gabor filters, phase portrait analysis, fractal dimension (FD), and analysis of the angular spread of power in the Fourier spectrum. In the estimation of FD using the Fourier power spectrum, only the distribution of power over radial frequency is considered; the information regarding the angular spread of power is ignored. In this study, the angular spread of power in the Fourier spectrum is used to generate features for the detection of spiculated patterns related to architectural distortion. Using Gabor filters and phase portrait analysis, a total of 4224 regions of interest (ROIs) were automatically obtained from 106 prior mammograms of 56 interval-cancer cases, including 301 ROIs related to architectural distortion, and from 52 mammograms of 13 normal cases. For each ROI, the FD and measures of the angular spread of power were computed. Feature selection was performed using stepwise logistic regression. The best result achieved, in terms of the area under the receiver operating characteristic curve, is 0.75 +/- 0.02 with an artificial neural network including radial basis functions. Analysis of the performance of the methods with free-response receiver operating characteristics indicated a sensitivity of 0.82 at 7.7 false positives per image.

  5. The concept of mass angular scattering power and its relation to the diffusion constant

    CERN Document Server

    Sandison, G A

    1998-01-01

    An understanding of the scattering of high energy charged particle beams by tissue is required in radiotherapy since the particle trajectories determine the pattern of radiation dose deposition in patients. Numerical calculations of radiation dose often utilize energy dependent values of the angular scattering power. However, the physics literature is replete with confused interpretations of the concept of angular scattering power and its relation to the single scattering cross section for the medium or the diffusion constant in the diffusional limit. The purpose of this article is to clarify these notions.

  6. Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole

    CERN Document Server

    Bernardi, G; Brentjens, M A; Ciardi, B; Jelić, V; Koopmans, L V E; Labropoulos, P; Offringa, A; Pandey, V N; Schaye, J; Thomas, R M; Yatawatta, S; Zaroubi, S

    2010-01-01

    In the coming years a new insight into galaxy formation and the thermal history of the Universe is expected to come from the detection of the highly redshifted cosmological 21 cm line. The cosmological 21 cm line signal is buried under Galactic and extragalactic foregrounds which are likely to be a few orders of magnitude brighter. Strategies and techniques for effective subtraction of these foreground sources require a detailed knowledge of their structure in both intensity and polarization on the relevant angular scales of 1-30 arcmin. We present results from observations conducted with the Westerbork telescope in the 140-160 MHz range with 2 arcmin resolution in two fields located at intermediate Galactic latitude, centred around the bright quasar 3C196 and the North Celestial Pole. They were observed with the purpose of characterizing the foreground properties in sky areas where actual observations of the cosmological 21 cm line could be carried out. The polarization data were analysed through the rotatio...

  7. Relationships between the HI 21-cm line strength, MgII equivalent width and metallicity in damped Lyman-alpha absorption systems

    CERN Document Server

    Curran, S J; Pihlström, Y M; Webb, J K

    2007-01-01

    We present the results of a survey for 21-cm absorption in four never previously searched damped Lyman-alpha absorption systems (DLAs) with the Westerbork Synthesis Radio Telescope. We add our results to other recent studies in order to address the important issues regarding the detection of cold gas, through 21-cm absorption, in DLAs: Although, due to the DLAs identified with spiral galaxies, there is a mix of spin temperature/covering factor ratios at low redshift, two recent high redshift end points confirm that this ratio does not generally rise over the whole redshift range searched (up to z = 3.39). That is, if the covering factors of many of these galaxies were a factor of >2 smaller than for the spirals, then no significant difference in the spin temperatures between these two classes would be required. Furthermore, although it is difficult to separate the relative contributions of the spin temperature and covering factor, the new results confirm that 21-cm detections tend to occur at low angular diam...

  8. ON THE DETECTION OF GLOBAL 21-cm SIGNAL FROM REIONIZATION USING INTERFEROMETERS

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Saurabh; Subrahmanyan, Ravi; Shankar, N. Udaya; Raghunathan, A., E-mail: saurabhs@rri.res.in [Raman Research Institute, C V Raman Avenue, Sadashivanagar, Bangalore 560080 (India)

    2015-12-20

    Detection of the global redshifted 21-cm signal is an excellent means of deciphering the physical processes during the Dark Ages and subsequent Epoch of Reionization (EoR). However, detection of this faint monopole is challenging due to the high precision required in instrumental calibration and modeling of substantially brighter foregrounds and instrumental systematics. In particular, modeling of receiver noise with mK accuracy and its separation remains a formidable task in experiments aiming to detect the global signal using single-element spectral radiometers. Interferometers do not respond to receiver noise; therefore, here we explore the theory of the response of interferometers to global signals. In other words, we discuss the spatial coherence in the electric field arising from the monopole component of the 21-cm signal and methods for its detection using sensor arrays. We proceed by first deriving the response to uniform sky of two-element interferometers made of unit dipole and resonant loop antennas, then extend the analysis to interferometers made of one-dimensional arrays and also consider two-dimensional aperture antennas. Finally, we describe methods by which the coherence might be enhanced so that the interferometer measurements yield improved sensitivity to the monopole component. We conclude (a) that it is indeed possible to measure the global 21-cm from EoR using interferometers, (b) that a practically useful configuration is with omnidirectional antennas as interferometer elements, and (c) that the spatial coherence may be enhanced using, for example, a space beam splitter between the interferometer elements.

  9. The global 21-cm signal in the context of the high- z galaxy luminosity function

    Science.gov (United States)

    Mirocha, Jordan; Furlanetto, Steven R.; Sun, Guochao

    2017-01-01

    We build a new model for the global 21-cm signal that is calibrated to measurements of the high-z galaxy luminosity function (LF) and further tuned to match the Thomson scattering optical depth of the cosmic microwave background, τe. Assuming that the z ≲ 8 galaxy population can be smoothly extrapolated to higher redshifts, the recent decline in best-fitting values of τe and the inefficient heating induced by X-ray binaries (the presumptive sources of the high-z X-ray background) imply that the entirety of cosmic reionization and reheating occurs at z ≲ 12. In contrast to past global 21-cm models, whose z ˜ 20 (ν ˜ 70 MHz) absorption features and strong ˜25 mK emission features were driven largely by the assumption of efficient early star formation and X-ray heating, our new models peak in absorption at ν ˜ 110 MHz at depths ˜-160 mK and have negligible emission components. Current uncertainties in the faint-end of the LF, binary populations in star-forming galaxies, and UV and X-ray escape fractions introduce ˜20 MHz (˜50 mK) deviations in the trough's frequency (amplitude), while emission signals remain weak (≲10 mK) and are confined to ν ≳ 140 MHz. These predictions, which are intentionally conservative, suggest that the detection of a 21-cm absorption minimum at frequencies below ˜90 MHz and/or emission signals stronger than ˜10mK at ν ≲ 140 MHz would provide strong evidence for `new' sources at high redshifts, such as Population III stars and their remnants.

  10. 21-cm lensing and the cold spot in the cosmic microwave background.

    Science.gov (United States)

    Kovetz, Ely D; Kamionkowski, Marc

    2013-04-26

    An extremely large void and a cosmic texture are two possible explanations for the cold spot seen in the cosmic microwave background. We investigate how well these two hypotheses can be tested with weak lensing of 21-cm fluctuations from the epoch of reionization measured with the Square Kilometer Array. While the void explanation for the cold spot can be tested with Square Kilometer Array, given enough observation time, the texture scenario requires significantly prolonged observations, at the highest frequencies that correspond to the epoch of reionization, over the field of view containing the cold spot.

  11. Full-sky formulae for weak lensing power spectra from total angular momentum method

    Energy Technology Data Exchange (ETDEWEB)

    Yamauchi, Daisuke; Taruya, Atsushi [Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Namikawa, Toshiya, E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: namikawa@yukawa.kyoto-u.ac.jp, E-mail: ataruya@utap.phys.s.u-tokyo.ac.jp [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2013-08-01

    We systematically derive full-sky formulae for the weak lensing power spectra generated by scalar, vector and tensor perturbations from the total angular momentum (TAM) method. Based on both the geodesic and geodesic deviation equations, we first give the gauge-invariant expressions for the deflection angle and Jacobi map as observables of the CMB lensing and cosmic shear experiments. We then apply the TAM method, originally developed in the theoretical studies of CMB, to a systematic derivation of the angular power spectra. The TAM representation, which characterizes the total angular dependence of the spatial modes projected along a line-of-sight, can carry all the information of the lensing modes generated by scalar, vector, and tensor metric perturbations. This greatly simplifies the calculation, and we present a complete set of the full-sky formulae for angular power spectra in both the E-/B-mode cosmic shear and gradient-/curl-mode lensing potential of deflection angle. Based on the formulae, we give illustrative examples of non-vanishing B-mode cosmic shear and curl-mode of deflection angle in the presence of the vector and tensor perturbations, and explicitly compute the power spectra.

  12. Slow-roll inflation and BB-mode angular power spectrum of CMB

    Energy Technology Data Exchange (ETDEWEB)

    Malsawmtluangi, N.; Suresh, P.K. [University of Hyderabad, School of Physics, Hyderabad (India)

    2016-05-15

    The BB-mode correlation angular power spectrum of CMB is obtained by considering the primordial gravitational waves in the squeezed vacuum state for various inflationary models and results are compared with the joint analysis of the BICEP2/Keck Array and Planck 353 GHz data. The present results may constrain several models of inflation. (orig.)

  13. Piezoelectric generator based on torsional modes for power harvesting from angular vibrations

    Institute of Scientific and Technical Information of China (English)

    CHEN Zi-guang; HU Yuan-tai; YANG Jia-shi

    2007-01-01

    Torsional vibration of a circular piezoelectric shell of polarized ceramics mounted on a rotationally vibrating base is analyzed. The shell is properly electroded and connected to a circuit such that an electric output is generated. The structure analyzed represents a piezoelectric generator for converting mechanical energy from angular vibrations to electrical energy. Analytical expressions and numerical results for the output voltage, current, power, efficiency and power density are given.

  14. The existence and detection of optically dark galaxies by 21-cm surveys

    Science.gov (United States)

    Davies, J. I.; Disney, M. J.; Minchin, R. F.; Auld, R.; Smith, R.

    2006-05-01

    One explanation for the disparity between cold dark matter (CDM) predictions of galaxy numbers and observations could be that there are numerous dark galaxies in the Universe. These galaxies may still contain baryons, but no stars, and may be detectable in the 21-cm line of atomic hydrogen. The results of surveys for such objects, and simulations that do/do not predict their existence, are controversial. In this paper, we use an analytical model of galaxy formation, consistent with CDM, to first show that dark galaxies are certainly a prediction of the model. Secondly, we show that objects like VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are predicted by the model. Thirdly, we show that previous `blind' HI surveys have placed few constraints on the existence of dark galaxies. This is because they have either lacked the sensitivity and/or velocity resolution or have not had the required detailed optical follow up. We look forward to new 21-cm blind surveys [Arecibo Legacy Fast ALFA (ALFALFA) survey and Arecibo Galactic Environments Survey (AGES)] using the Arecibo multibeam instrument which should find large numbers of dark galaxies if they exist.

  15. Cosmological evolution of atomic gas and implications for 21 cm HI absorption

    CERN Document Server

    Braun, Robert

    2012-01-01

    Galaxy disks are shown to contain a significant population of atomic clouds of 100pc linear size which are self-opaque in the 21cm transition. These objects have HI column densities as high as 10^23 and contribute to a global opacity correction factor of 1.34+/-0.05 that applies to the integrated 21cm emission to obtain a total HI mass estimate. Opacity-corrected images of the nearest external galaxies have been used to form a robust z=0 distribution function of HI, f(N_HI,X,z=0), the probability of encountering a specific HI column density per unit comoving distance. This is contrasted with previously published determinations of f(N_HI,X) at z=1 and 3. A systematic decline of moderate column density (1820.3) has also declined systematically over this redshift interval by a similar amount, while the cosmological mass density in such systems has declined by only a factor of two to its current, opacity corrected value of Omega_HI^DLA(z=0) = 5.4 +/- 0.9x10^-4. We utilize the tight, but strongly non-linear depend...

  16. Probing individual sources during reionization and cosmic dawn using SKA HI 21-cm observations

    CERN Document Server

    Datta, Kanan K; Majumdar, Suman; Choudhury, T Roy; Bharadwaj, Somnath; Roy, Himadri; Datta, Abhirup

    2016-01-01

    Detection of individual luminous sources during the reionization epoch and cosmic dawn through their signatures in the HI 21-cm signal is one of the direct approaches to probe the epoch. Here, we summarize our previous works on this and present preliminary results on the prospects of detecting such sources using the SKA1-low experiment. We first discuss the expected HI 21-cm signal around luminous sources at different stages of reionization and cosmic dawn. We then introduce two visibility based estimators for detecting such signal: one based on the matched filtering technique and the other relies on simply combing the visibility signal from different baselines and frequency channels. We find that that the SKA1-low should be able to detect ionized bubbles of radius $R_b \\gtrsim 10$ Mpc with $\\sim 100$ hr of observations at redshift $z \\sim 8$ provided that the mean outside neutral Hydrogen fraction $ x_{\\rm HI} \\gtrsim 0.5$. We also investigate the possibility of detecting HII regions around known bright QSOs...

  17. MEASUREMENT OF 21 cm BRIGHTNESS FLUCTUATIONS AT z {approx} 0.8 IN CROSS-CORRELATION

    Energy Technology Data Exchange (ETDEWEB)

    Masui, K. W.; Switzer, E. R.; Calin, L.-M.; Pen, U.-L.; Shaw, J. R. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George St., Toronto, Ontario, M5S 3H8 (Canada); Banavar, N. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, Ontario, M5S 3H4 (Canada); Bandura, K. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec, H3A 2T8 (Canada); Blake, C. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia); Chang, T.-C.; Liao, Y.-W. [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 10617, Taiwan (China); Chen, X.; Li, Y.-C. [National Astronomical Observatories, Chinese Academy of Science, 20A Datun Road, Beijing 100012 (China); Natarajan, A.; Peterson, J. B.; Voytek, T. C. [McWilliams Center for Cosmology, Carnegie Mellon University, Department of Physics, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States)

    2013-01-20

    In this Letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in the WiggleZ Dark Energy Survey. The data span the redshift range 0.6 < z < 1 over two fields totaling {approx}41 deg. sq. and 190 hr of radio integration time. The cross-correlation constrains {Omega}{sub HI} b{sub HI} r = [0.43 {+-} 0.07(stat.) {+-} 0.04(sys.)] Multiplication-Sign 10{sup -3}, where {Omega}{sub HI} is the neutral hydrogen (H I) fraction, r is the galaxy-hydrogen correlation coefficient, and b{sub HI} is the H I bias parameter. This is the most precise constraint on neutral hydrogen density fluctuations in a challenging redshift range. Our measurement improves the previous 21 cm cross-correlation at z {approx} 0.8 both in its precision and in the range of scales probed.

  18. The existence and detection of optically dark galaxies by 21cm surveys

    CERN Document Server

    Davies, J I; Minchin, R F; Auld, R; Smith, R

    2006-01-01

    One explanation for the disparity between Cold Dark Matter (CDM) predictions of galaxy numbers and observations could be that there are numerous dark galaxies in the Universe. These galaxies may still contain baryons, but no stars, and may be detectable in the 21cm line of atomic hydrogen. The results of surveys for such objects, and simulations that do/do not predict their existence, are controversial. In this paper we use an analytical model of galaxy formation, consistent with CDM, to firstly show that dark galaxies are certainly a prediction of the model. Secondly, we show that objects like VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are predicted by the model. Thirdly, we show that previous 'blind' HI surveys have placed few constraints on the existence of dark galaxies. This is because they have either lacked the sensitivity and/or velocity resolution or have not had the required detailed optical follow up. We look forward to new 21cm blind surveys (ALFALFA and AGES) using t...

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

    CERN Document Server

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

    2015-01-01

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

  20. A comparative study of intervening and associated HI 21-cm absorption profiles in redshifted galaxies

    CERN Document Server

    Curran, S J; Divoli, A; Allison, J R

    2016-01-01

    The star-forming reservoir in the distant Universe can be detected through HI 21-cm absorption arising from either cool gas associated with a radio source or from within a galaxy intervening the sight-line to the continuum source. In order to test whether the nature of the absorber can be predicted from the profile shape, we have compiled and analysed all of the known redshifted (z > 0.1) HI 21-cm absorption profiles. Although between individual spectra there is too much variation to assign a typical spectral profile, we confirm that associated absorption profiles are on average, wider than their intervening counterparts. It is widely hypothesised that this is due to high velocity nuclear gas feeding the central engine, absent in the more quiescent intervening absorbers. Modelling the column density distribution of the mean associated and intervening spectra, we confirm that the additional low optical depth, wide dispersion component, typical of associated absorbers, arises from gas within the inner parsec. W...

  1. The effect of Galactic foreground subtraction on redshifted 21-cm observations of quasar HII regions

    CERN Document Server

    Geil, Paul M; Petrovic, Nada; Oh, Peng

    2008-01-01

    We assess the impact of Galactic synchrotron foreground removal on the observation of high-redshift quasar HII regions in redshifted 21-cm emission. We consider the case where a quasar is observed in an intergalactic medium (IGM) whose ionisation structure evolves slowly relative to the light crossing time of the HII region, as well as the case where the evolution is rapid. The latter case is expected towards the end of the reionisation era where the highest redshift luminous quasars will be observed. In the absence of foregrounds the fraction of neutral hydrogen in the IGM could be measured directly from the contrast between the HII region and surrounding IGM. However, we find that foreground removal lowers the observed contrast between the HII region and the IGM. This indicates that measurement of the neutral fraction would require modelling to correct for this systematic effect. On the other hand, foreground removal does not modify the most prominent features of the 21-cm maps. Using a simple algorithm we ...

  2. Q-switched fibre laser using 21 cm Bismuth-erbium doped fibre and graphene oxide as saturable absorber

    Science.gov (United States)

    Ahmad, Harith; Zulkifli, Ahmad Zarif; Kiat, Yap Yuen; Harun, Sulaiman Wadi

    2014-01-01

    A compact, Q-switched fibre laser is proposed and demonstrated using a compact Bismuth-based erbium doped fibre (Bi-EDF) together with a Graphene Oxide (GO) Saturable Absorber (SA). The 21 cm long Bi-EDF has an erbium dopant concentration of 6300 ppm with absorption rates of about 83 and 133 dB/m at 1480 and 1530 nm. The SA is fabricated from graphene flakes dissolved in water, forming a GO film that is sandwiched between two FC/PC connectors. The Q-switched Bi-EDF laser has an Amplified Spontaneous Emission (ASE) spectrum of 120 nm, stretching from 1490 to 1610 nm and a Q-switching threshold power of about 65 mW. At the maximum pump power of 118 mW, the pulses are generated with an average output power and pulse energy of 0.11 mW and 4.3 nJ, with a repetition rate and pulse width of 27.2 kHz and 7.7 μs. The output can be tuned over the amplified spontaneous emission spectrum with an average peak power of about -16.8 dBm, and observation under a radio frequency spectrum analyser shows a highly stable output at 21.8 kHz. The proposed Bi-EDF laser will have substantial uses in applications requiring short and stable pulses such as rangefinding and sensing.

  3. Fisher Matrix Predictions for Detecting the Cosmological 21-cm Signal with the Ooty Wide Field Array (OWFA)

    Indian Academy of Sciences (India)

    S. Bharadwaj; A. K. Sarkar; Sk. Saiyad Ali

    2015-09-01

    We have used the Fisher matrix formalism to quantify the prospects of detecting the = 3.35 redshifted 21-cm HI power spectrum with the upcoming radio-imterferometric array OWFA. OWFA’s frequency and baseline coverage spans comoving Fourier modes in the range 1.8 × 10−2 ≤ k ≤ 2.7 Mpc−1. The OWFA HI signal, however, is predominantly from the range ≤ 0.2 Mpc−1. The larger modes, though abundant, do not contribute much to the HI signal. In this work, we have focused on combining the entire signal to achieve a detection. We find that a 5 - detection of HI is possible with ∼ 150 h of observations, here $A^{2}_{\\text{HI}}$ is the amplitude of the HI power spectrum. We have also carried out a joint analysis for HI and the redshift space distortion parameter. Our study shows that OWFA is very sensitive to the amplitude of the HI power spectrum. However, the anisotropic distribution of the k modes does not make it very suitable for measuring .

  4. Fisher matrix predictions for detecting the cosmological 21 cm signal with the Ooty Wide Field Array (OWFA)

    CERN Document Server

    Bharadwaj, Somnath; Ali, Sk Saiyad

    2015-01-01

    We have used the Fisher matrix formalism to quantify the prospects of detecting the z = 3.35 redshifted 21-cm HI power spectrum with the upcoming radio-imterferometric array OWFA. OWFA's frequency and baseline coverage spans comoving Fourier modes (k) in the range 0.018 to 2.7 [1/Mpc]. The OWFA HI signal, however, is predominantly from the range k below 0.2 [1/Mpc]. The larger modes, though abundant, do not contribute much to the HI signal. In this work we have focused on combining the entire signal to achieve a detection. We find that a 5-sigma detection of A_{HI} is possible with ~ 150 hr of observations, here A^2 _{HI} is the amplitude of the HI power spectrum. We have also carried out a joint analysis for A_{HI} and the redshift space distortion parameter. Our study shows that OWFA is very sensitive to the amplitude of the HI power spectrum. However, the anisotropic distribution of the k modes does not make it very suitable for measuring the redshift space distortion parameter.

  5. Search for cold gas in z>2 damped Lyman-alpha systems: 21-cm and H_2 absorption

    CERN Document Server

    Srianand, R; Petitjean, P; Noterdaeme, P; Ledoux, C; Salter, C J; Saikia, D J

    2011-01-01

    (Abridged) We present the results of a systematic GBT and GMRT survey for 21-cm absorption in a sample of 10 DLAs at 2 2 is predominantly constituted by WNM. The detection rate of 21-cm absorption seems to be higher for systems with higher N(HI) or metallicity. However, no clear correlation is found between the integrated 21-cm optical depth (or spin temperature) and either N(HI), metallicity or velocity spread of the low ionization species. There are 13 DLAs in our sample for which high resolution optical spectra covering the expected wavelength range of H_2 absorption are available. We report the detection of H_2 molecules in the z_abs = 3.3871 21-cm absorber towards J0203+1134 (PKS 0201+113). In 8 cases, neither H_2 nor 21-cm absorption are detected. The lack of 21-cm and H_2 absorption in these systems can be explained if most of the HI in these DLAs originate from low density high temperature gas. In one case we have a DLA with 21-cm absorption not showing H_2 absorption. In two cases, both species are d...

  6. HI 21 cm Emission Line Study of Southern Galactic Supernova Remnants

    CERN Document Server

    Koo, B C; McClure-Griffiths, N M; Koo, Bon-Chul; Kang, Ji-hyun

    2004-01-01

    We have searched for HI 21 cm line emission from shocked atomic gas associated with southern supernova remnants (SNRs) using data from the Southern Galactic Plane Survey. Among the 97 sources studied, we have detected 10 SNRs with high-velocity HI emission confined to the SNR. The large velocity and the spatial confinement suggest that the emission is likely from the gas accelerated by the SN blast wave. We also detected 22 SNRs which show HI emission significantly brighter than the surrounding regions over a wide ($>10$\\kms) velocity interval. The association with these SNRs is less certain. We present the parameters and maps of the excess emission in these SNRs. We discuss in some detail the ten individual SNRs with associated high-velocity HI emission.

  7. Driftscan Surveys in the 21 cm Line with the Arecibo and Nancay Telescopes

    CERN Document Server

    Briggs, F H; Kraan-Korteweg, R C; Van Driel, W

    1997-01-01

    Driftscan methods are highly efficient, stable techniques for conducting extragalactic surveys in the 21cm line of neutral hydrogen. Holding the telescope still while the beam scans the sky at the sidereal rate produces exceptionally stable spectral baselines, increased stability for RFI signals, and excellent diagnostic information about system performance. Data can be processed naturally and efficiently by grouping long sequences of spectra into an image format, thereby allowing thousands of individual spectra to be calibrated, inspected and manipulated as a single data structure with standard tools that already exist in astronomical software. The behavior of spectral standing waves (multi-path effects) can be appraised and excised in this environment, making observations possible while the Sun is up. The method is illustrated with survey data from Arecibo and Nancay.

  8. Probing Individual Sources during Reionization and Cosmic Dawn using Square Kilometre Array HI 21-cm Observations

    Indian Academy of Sciences (India)

    Kanan K. Datta; Raghunath Ghara; Suman Majumdar; T. Roy Choudhury; Somnath Bharadwaj; Himadri Roy; Abhirup Datta

    2016-12-01

    Detection of individual luminous sources during the reionization epoch and cosmic dawn through their signatures in the HI 21-cm signal is one of the direct approaches to probe the epoch. Here, we summarize our previous works on this and present preliminary results on the prospects of detecting such sources using the SKA1-low experiment. We first discuss the expected HI 21-cm signal around luminous sources at different stages of reionization and cosmic dawn. We then introduce two visibility based estimators for detecting such signals: one based on the matched filtering technique and the other relies on simply combing the visibility signal from different baselines and frequency channels. We find that the SKA1-low should be able to detect ionized bubbles of radius $R_{\\mathrm {b}} \\gtrsim 10$ Mpc with $\\sim100 \\rm h$ of observations at redshift $z\\sim8$ provided that the mean outside neutral hydrogen fraction $\\mathrm {x}_{\\text {HI}} \\gtrsim 0.5$. We also investigate the possibility of detecting HII regions around known bright QSOs such as around ULASJ1120+0641 discovered by Mortlock et al. (Nature 474, 7353 (2011)). We find that a $5σ$ detection is possible with 600 h of SKA1-low observations if the QSO age and the outside $\\mathrm {x}_{\\text {HI}}$ are at least $\\sim2 \\times 10^7$ Myr and $\\sim0.2$ respectively. Finally, we investigate the possibility of detecting the very first X-ray and Ly- α sources during the cosmic dawn. We consider mini-QSOs like sources which emits in X-ray frequency band. We find that with a total $\\sim 1000 \\rm h$ of observations, SKA1-low should be able to detect those sources individually with a $∼ 9σ$ significance at redshift z=15. We summarize how the SNR changes with various parameters related to the source properties.

  9. An MCMC approach to extracting the global 21-cm signal during the cosmic dawn from sky-averaged radio observations

    CERN Document Server

    Harker, Geraint J A; Burns, Jack O; Bowman, Judd D

    2011-01-01

    Efforts are being made to observe the 21-cm signal from the 'cosmic dawn' using sky-averaged observations with individual radio dipoles. In this paper, we develop a model of the observations accounting for the 21-cm signal, foregrounds, and several major instrumental effects. Given this model, we apply Markov Chain Monte Carlo techniques to demonstrate the ability of these instruments to separate the 21-cm signal from foregrounds and quantify their ability to constrain properties of the first galaxies. For concreteness, we investigate observations between 40 and 120 MHz with the proposed DARE mission in lunar orbit, showing its potential for science return.

  10. Nonparametric Forecasts of the CMB Angular Power Spectra for the Planck Mission

    CERN Document Server

    Aghamousa, Amir; Souradeep, Tarun

    2013-01-01

    The Planck mission, designed for making measurements of the cosmic microwave background (CMB) radiation with unprecedented accuracy and angular resolution, is expected to release its first data set in the near future. For the first time in the CMB history, extensive measurements of the CMB polarization will be made available for the entire sky. Such precise and rich data are expected to contain a great wealth of information about the Universe. The information in the CMB data is conveniently represented in terms of angular power spectra for temperature and polarization. A proper estimation of these CMB power spectra from data is the first step in making inferences about the Universe and, in particular, cosmological parameters that govern the Universe. In this paper, we provide forecasts for the $TT$, $EE$, and $TE$ angular power spectra for the Planck mission. Our forecasts are made using synthetic data based on the best-fit $\\Lambda$CDM model while conforming to the characteristics and parameters of the Planc...

  11. The 21 cm Forest as a Probe of the Reionization and the Temperature of the Intergalactic Medium

    CERN Document Server

    Xu, Yidong; Fan, Zuhui; Trac, Hy; Cen, Renyue

    2009-01-01

    Using high redshift radio sources as background, the 21cm forest observations probe the neutral hydrogen absorption signatures of early structures along the lines of sight. Directly sensitive to the spin temperature of the hydrogen atoms, it complements the 21cm tomography observations, and provides information on the temperature as well as the ionization state of the intergalactic medium (IGM). We use a radiative transfer simulation to investigate the 21cm forest signals during the epoch of reionization. We first check whether the equivalent width (EW) can be a representative indicator of the ionization and thermal state of the IGM, and find that the optical depth and EW are good representation of the reionization process. The features selected by their relative optical depth are excellent tracers of ionization fields, and the features selected by their absolute optical depth are very sensitive to the IGM temperature, so the IGM temperature information could potentially be extracted from 21cm forest observat...

  12. New Limits on 21cm EoR From PAPER-32 Consistent with an X-Ray Heated IGM at z=7.7

    CERN Document Server

    Parsons, Aaron R; Aguirre, James E; Ali, Zaki S; Bradley, Richard F; Carilli, Chris L; DeBoer, David R; Dexter, Matthew R; Gugliucci, Nicole E; Jacobs, Daniel C; Klima, Pat; MacMahon, David H E; Manley, Jason R; Moore, David F; Pober, Jonathan C; Stefan, Irina I; Walbrugh, William P

    2013-01-01

    We present new constraints on the 21cm Epoch of Reionization (EoR) power spectrum derived from 3 months of observing with a 32-antenna, dual-polarization deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. In this paper, we demonstrate the efficacy of the delay-spectrum approach to avoiding foregrounds, achieving over 8 orders of magnitude of foreground suppression (in mK^2). Combining this approach with a procedure for removing off-diagonal covariances arising from instrumental systematics, we achieve a best 2-sigma upper limit of 52 mK^2 for k=0.11 h Mpc^-1 at z=7.7. This limit falls within an order of magnitude of the brighter predictions of the expected 21cm EoR signal level. Using the upper limits set by these measurements, we generate new constraints on the brightness temperature of 21cm emission in neutral regions for various reionization models. We show that for several ionization models, heating of the neutral intergalactic medium (IGM) is...

  13. Incidence of H I 21-cm absorption in strong Fe II systems at 0.5 < z < 1.5

    Science.gov (United States)

    Dutta, R.; Srianand, R.; Gupta, N.; Joshi, R.; Petitjean, P.; Noterdaeme, P.; Ge, J.; Krogager, J.-K.

    2017-03-01

    We present the results from our search for H I 21-cm absorption in a sample of 16 strong Fe II systems [Wr(Mg II λ2796) ≥ 1.0 Å and Wr(Fe II λ2600) or W_{Fe II} ≥ 1 Å] at 0.5 measurements with those in the literature, we find that the detection rate of H I 21-cm absorption increases with W_{Fe II}, being four times higher in systems with W_{Fe II} ≥ 1 Å compared to systems with W_{Fe II} measurements of damped Lyman α systems at this redshift range) and unit covering factor. We find that H I 21-cm absorption arises on an average in systems with stronger metal absorption. We also find that quasars with H I 21-cm absorption detected towards them have systematically higher E(B - V) values than those which do not. Further, by comparing the velocity widths of H I 21-cm absorption lines detected in absorption- and galaxy-selected samples, we find that they show an increasing trend (significant at 3.8σ) with redshift at z < 3.5, which could imply that the absorption originates from more massive galaxy haloes at high z. Increasing the number of H I 21-cm absorption detections at these redshifts is important to confirm various trends noted here with higher statistical significance.

  14. WIND TURBINE SIMULATION FOR TIME-DEPENDENT ANGULAR VELOCITY, TORQUE, AND POWER

    Directory of Open Access Journals (Sweden)

    YONGHO LEE

    2013-02-01

    Full Text Available Albeit the prediction of time-dependent properties of wind turbines is not required for common applications, such time-varying properties may play an important role during transient operations occurring due to various reasons. Unlike the conventional numerical simulations of wind turbine rotations that fix the angular velocity to an assumed value, the present work numerically simulates the time-varying turbine rotation in both unsteady and quasi-steady operation regimes, without specifying the angular velocity of the turbine a priori, but by calculating the actual time-dependent angular velocity and aerodynamic torque along with other properties in the course of simulation. In the present work, successful results obtained by an efficient computational fluid dynamics technique are shown, as a demonstration, for a vertical-axis wind turbine with a two-dimensionalSavonius rotor, and the cycle-averaged output powers are compared with experimental power curves and a theory developed on the basis of experimental observations.

  15. Constraints on the temperature of the intergalactic medium at z=8.4 with 21-cm observations

    CERN Document Server

    Greig, Bradley; Pober, Jonathan C

    2015-01-01

    We compute robust lower limits on the spin temperature, $T_{\\rm S}$, of the $z=8.4$ intergalactic medium (IGM), implied by the upper limits on the 21-cm power spectrum recently measured by PAPER-64. Unlike previous studies which used a single epoch of reionization (EoR) model, our approach samples a large parameter space of EoR models: the dominant uncertainty when estimating constraints on $T_{\\rm S}$. Allowing $T_{\\rm S}$ to be a free parameter and marginalising over EoR parameters in our Markov Chain Monte Carlo code 21CMMC, we infer $T_{\\rm S}\\ge3 {\\rm K}$ for a mean IGM neutral fraction of $\\bar{x}_{H{\\scriptsize I}}\\gtrsim0.1$. We further improve on these limits by folding-in additional EoR constraints based on: (i) the dark fraction in QSO spectra, which implies a strict upper limit of $\\bar{x}_{H{\\scriptsize I}}[z=5.9]\\leq 0.06+0.05 \\,(1\\sigma)$; and (ii) the electron scattering optical depth, $\\tau_{e}=0.066\\pm0.016\\,(1\\sigma)$ measured by the Planck satellite. By restricting the allowed EoR models, ...

  16. Spatially Extended 21 cm Signal from Strongly Clustered Uv and X-Ray Sources in the Early Universe

    Science.gov (United States)

    Ahn, Kyungjin; Xu, Hao; Norman, Michael L.; Alvarez, Marcelo A.; Wise, John H.

    2015-03-01

    We present our prediction for the local 21 cm differential brightness temperature (δTb) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early universe, by a numerical simulation of their formation and radiative feedback. These objects are located inside a highly biased environment, which is a rare, high-density peak (“Rarepeak”) extending to ∼7 comoving Mpc. We study the impact of ultraviolet and X-ray photons on the intergalactic medium (IGM) and the resulting δTb, when Pop III stars are assumed to emit X-ray photons by forming X-ray binaries very efficiently. We parameterize the rest-frame spectral energy distribution of X-ray photons, which regulates X-ray photon-trapping, IGM-heating, secondary Lyα pumping and the resulting morphology of δTb. A combination of emission (δTb > 0) and absorption (δTb Frequency Array, Murchison Widefield Array, Precision Array for Probing the Epoch of Reionization) of such rare peaks is found to be difficult due to the rarity of these peaks, and the contribution only by these rare peaks to the total power spectrum remains subdominant compared to that by all astrophysical sources.

  17. Faint HI 21-cm Emission Line Wings at Forbidden-Velocities

    CERN Document Server

    Kang, Ji-hyun

    2007-01-01

    We present the results of a search for faint HI 21-cm emission line wings at velocities forbidden by Galactic rotation in the Galactic plane using the Leiden/Dwingeloo HI Survey data and the HI Southern Galactic Plane Survey data. These ``forbidden-velocity wings (FVWs)'' appear as protruding excessive emission in comparison with their surroundings in limited (< 2 deg) spatial regions over velocity extent more than ~20 km/s in large-scale (l-v) diagrams. Their high-velocities imply that there should be some dynamical phenomena associated. We have identified 87 FVWs. We present their catalog, and discuss their distribution and statistical properties. We found that 85% of FVWs are not coincident with known supernova remnants (SNRs), galaxies, or high-velocity clouds. Their natures are currently unknown. We suspect that many of them are fast-moving HI shells and filaments associated with the oldest SNRs that are essentially invisible except via their HI line emission. We discuss other possible origins.

  18. Radiative Transfer Effect on Ultraviolet Pumping of the 21cm Line in the High Redshift Universe

    CERN Document Server

    Chuzhoy, Leonid

    2007-01-01

    During the epoch of reionization the 21cm signal is sensitive to the scattering rate of the ultraviolet photons, redshifting across the Lyman_alpha resonance. Here we calculate the photon scattering rate profile for a single ultraviolet source. After taking into account previously neglected natural broadening of the resonance line, we find that photons approach the resonance frequency and experience most scatterings at a significantly smaller distance from the source than naively expected r=(dnu/nu_0)(c/H), where dnu=nu-nu_0 is the initial frequency offset, and the discrepancy increases as the initial frequency offset decreases. As a consequence, the scattering rate P(r) drops much faster with increasing distance than the previously assumed 1/r^2 profile. Near the source (r<1Mpc comoving), the scattering rate of photons that redshift into the Ly_alpha resonance converges to P(r) \\propto r^{-7/3}. The scattering rate of Ly_alpha photons produced by splitting of photons that redshift into a higher resonance ...

  19. A "Missing" Supernova Remnant revealed by the 21-cm Line of Atomic Hydrogen

    CERN Document Server

    Koo, B C; Salter, C J

    2006-01-01

    Although some 20--30,000 supernova remnants (SNRs) are expected to exist in the Milky Way, only about 230 are presently known. This implies that most SNRs are ``missing''. Recently, we proposed that small ($\\simlt 1^\\circ$), faint, high-velocity features seen in large-scale 21-cm line surveys of atomic hydrogen ({\\sc Hi}) in the Galactic plane could be examples of such {\\it missing} old SNRs. Here we report on high-resolution \\schi observations of one such candidate, FVW 190.2+1.1, which is revealed to be a rapidly expanding ($\\sim 80$ \\kms) shell. The parameters of this shell seem only consistent with FVW 190.2+1.1 being the remnant of a SN explosion that occurred in the outermost fringes of the Galaxy some $\\sim 3\\times 10^5$ yr ago. This shell is not seen in any other wave band suggesting that it represents the oldest type of SNR, that which is essentially invisible except via its \\schi line emission. FVW 190.2+1.1 is one of a hundred "forbidden-velocity wings" (FVWs) recently identified in the Galactic pl...

  20. A Search for Mass Loss on the Cepheid Instability Strip using HI 21-cm Line Observations

    CERN Document Server

    Matthews, L D; Evans, N R

    2016-01-01

    We present the results of a search for HI 21-cm line emission from the circumstellar environments of four Galactic Cepheids (RS Pup, X Cyg, $\\zeta$ Gem, and T Mon) based on observations with the Karl G. Jansky Very Large Array. The observations were aimed at detecting gas associated with previous or ongoing mass loss. Near the long-period Cepheid T Mon, we report the detection of a partial shell-like structure whose properties appear consistent with originating from an earlier epoch of Cepheid mass loss. At the distance of T Mon, the nebula would have a mass (HI+He) of $\\sim0.5M_{\\odot}$, or $\\sim$6\\% of the stellar mass. Assuming that one-third of the nebular mass comprises swept-up interstellar gas, we estimate an implied mass-loss rate of ${\\dot M}\\sim (0.6-2)\\times10^{-5} M_{\\odot}$ yr$^{-1}$. No clear signatures of circumstellar emission were found toward $\\zeta$ Gem, RS Pup, or X Cyg, although in each case, line-of-sight confusion compromised portions of the spectral band. For the undetected stars, we d...

  1. Tracing the Milky Way Nuclear Wind with 21cm Atomic Hydrogen Emission

    CERN Document Server

    Lockman, Felix J

    2016-01-01

    There is evidence in 21cm HI emission for voids several kpc in size centered approximately on the Galactic centre, both above and below the Galactic plane. These appear to map the boundaries of the Galactic nuclear wind. An analysis of HI at the tangent points, where the distance to the gas can be estimated with reasonable accuracy, shows a sharp transition at Galactic radii $R\\lesssim 2.4$ kpc from the extended neutral gas layer characteristic of much of the Galactic disk, to a thin Gaussian layer with FWHM $\\sim 125$ pc. An anti-correlation between HI and $\\gamma$-ray emission at latitudes $10^{\\circ} \\leq |b| \\leq 20^{\\circ}$ suggests that the boundary of the extended HI layer marks the walls of the Fermi Bubbles. With HI we are able to trace the edges of the voids from $|z| > 2$ kpc down to $z\\approx0$, where they have a radius $\\sim 2$ kpc. The extended HI layer likely results from star formation in the disk, which is limited largely to $R \\gtrsim 3$ kpc, so the wind may be expanding into an area of rela...

  2. A practical theorem on using interferometry to measure the global 21-cm signal

    CERN Document Server

    Venumadhav, Tejaswi; Doré, Olivier; Hirata, Christopher M

    2015-01-01

    The sky-averaged, or global, background of redshifted 21-cm radiation is expected to be a rich source of information on the history of re-heating and re-ionization of the intergalactic medium. However, measuring the signal is technically challenging: one must extract the small, frequency-dependent signal from under the much brighter spectrally smooth foregrounds. Traditional approaches to study the global signal have used single-antenna systems, where one must calibrate out frequency-dependent structure in the overall system gain (due e.g. to internal reflections) as well as remove the noise bias from auto-correlating a single amplifier output. This has motivated several proposals to measure the global background using interferometric setups, where the signal appears in cross-correlation and where additional calibration techniques are available. In this paper, we focus on the general principles that drive the sensitivity of any interferometric setup to the global signal. In particular, we prove that this sens...

  3. Wouthuysen-Field coupling strength and application to high-redshift 21 cm radiation

    CERN Document Server

    Hirata, C M

    2006-01-01

    The first UV sources in the universe are expected to have coupled the HI spin temperature to the gas kinetic temperature via scattering in the Lyman-alpha resonance [the Wouthuysen-Field (WF) effect]. By establishing an HI spin temperature different from the temperature of the CMB, the WF effect should allow observations of HI during the reionization epoch in the redshifted 21 cm line. This paper investigates four mechanisms that can affect the strength of the WF effect that were not previously considered: (1) Photons redshifting into the HI Lyman resonances may excite an H atom and result in a radiative cascade terminating in two-photon 2s->1s emission, rather than always degrading to Lyman-alpha as usually assumed. (2) The fine structure of the Lyman-alpha resonance alters the photon frequency distribution and leads to a suppression of the scattering rate. (3) The spin-flip scatterings change the frequency of the photon and cause the photon spectrum to relax not to the kinetic temperature of the gas but to ...

  4. 2MTF II. New Parkes 21-cm observations of 303 southern galaxies

    CERN Document Server

    Hong, Tao; Masters, Karen L; Springob, Christopher M; Macri, Lucas M; Koribalski, Barbel S; Jones, D Heath; Jarrett, Tom H; Crook, Aidan C

    2013-01-01

    We present new 21-cm neutral hydrogen (HI) observations of spiral galaxies for the 2MASS Tully Fisher (2MTF) survey. Using the 64-m Parkes radio telescope multibeam system we obtain 152 high signal-to-noise HI spectra from which we extract 148 high-accuracy (< 5% error) velocity widths and derive reliable rotation velocities. The observed sample consists of 303 southern (\\delta < -40\\deg) galaxies selected from the MASS Redshift Survey (2MRS) with K_s <11.25 mag, cz < 10,000 km/s and axis ratio b/a < 0.5. The HI observations reported in this paper will be combined with new HI spectra from the Green Bank and Arecibo telescopes, together producing the most uniform Tully-Fisher survey ever constructed (in terms of sky coverage). In particular, due to its near infrared selection, 2MTF will be significantly more complete at low Galactic latitude (|b|<15\\deg) and will provide a more reliable map of peculiar velocities in the local universe.

  5. A Dark Galaxy in the Virgo Cluster Imaged at 21-cm

    CERN Document Server

    Minchin, R F; Disney, M J; Marble, A R; Impey, C D; Boyce, P J; García, D A; Grossi, M; Jordan, C A; Lang, R H; Roberts, S; Sabatini, S; Van Driel, W

    2005-01-01

    Dark Matter supposedly dominates the extragalactic, yet no totally dark structure of galactic proportions has ever been convincingly identified. Earlier (Minchin et al. 2005) we suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster at Jodrell Bank using single-dish observations (Davies et al. 2004), was probably such a dark galaxy because of its broad line-width (~ 200 km/s) unaccompanied by any visible gravitational source to account for it. Now we have managed to image VIRGOHI 21 in the neutral-hydrogen line, and indeed we find what appears to be a dark, edge-on, spinning disc with the mass and diameter of a typical spiral galaxy. Moreover the disc has unquestionably interacted with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor invariably responsible for such a feature. Published numerical models (Vollmer, Huchtmeier & van Driel 2005) of NGC 4254 call for a close interaction ~ 10^8 years ago with a perturber of 10^11 solar masses. This...

  6. 21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster

    CERN Document Server

    Minchin, Robert; Disney, Michael; Grossi, Marco; Sabatini, Sabina; Boyce, Peter; Garcia, Diego; Impey, Chris; Jordan, Christine; Lang, Robert; Marble, Andrew; Roberts, Sarah; van Driel, Wim

    2007-01-01

    Many observations indicate that dark matter dominates the extra-galactic Universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible gravitational source to account for it. We have now imaged VIRGOHI 21 in the neutral-hydrogen line and find what could be a dark, edge-on, spinning disk with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has unquestionably been involved in an interaction with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor normally linked with such a feature. Numerical models of NGC 4254 call for a close interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we take as additional evidence for the massive nature of VIRGOHI 21 as there does not appear to be...

  7. Constraining the redshifted 21-cm signal with the unresolved soft X-ray background

    CERN Document Server

    Fialkov, Anastasia; Barkana, Rennan; Silk, Joseph

    2016-01-01

    We use the observed unresolved cosmic X-ray background (CXRB) in the soft 0.5-2 keV band to constrain the population of high redshift X-ray sources existing before the end of reionization. Because the nature of these sources is poorly understood, we consider hot gas, X-ray binaries and mini-quasars (i.e., sources with soft and hard X-ray spectra) as possible candidates. We show that all types of the considered sources naturally generate a soft band CXRB, but if they actually generate the observed background their efficiency in producing X-rays must be one-to-two orders of magnitude higher than what is normally assumed. We find that the efficiency of hard sources does not have to be increased as strongly as that of the soft ones in order to generate the observed background. In addition, we show that when models are normalized to the CXRB, cosmic heating occurs quite early, and in some cases X-rays become a significant driver of reionization competing with the UV photons, while the expected high-redshift 21-cm ...

  8. 2MTF III. HI 21cm observations of 1194 spiral galaxies with the Green Bank Telescope

    CERN Document Server

    Masters, Karen L; Hong, Tao; Jarrett, T H; Koribalski, Baerbel S; Macri, Lucas; Springob, Christopher M; Staveley-Smith, Lister

    2014-01-01

    We present HI 21cm observations of 1194 galaxies out to a redshift of 10,000 km/s selected as inclined spirals (i>60deg) from the 2MASS Redshift Survey. These observations were carried out at the National Radio Astronomy Observatory Robert C. Byrd Green Bank Telescope (GBT). This observing program is part of the 2MASS Tully-Fisher (2MTF) survey. This project will combine HI widths from these GBT observations with those from further dedicated observing at the Parkes Telescope, from the ALFALFA survey at Arecibo, and S/N>10 and spectral resolution, v_res < 10km/s published widths from a variety of telescopes. We will use these HI widths along with 2MASS photometry to estimate Tully-Fisher distances to nearby spirals and investigate the peculiar velocity field of the local Universe. In this paper we report on detections of neutral hydrogen in emission in 727 galaxies, and measure good signal-to-noise and symmetric HI global profiles suitable for use in the Tully-Fisher relation in 484.

  9. Spectral Polarization of the Redshifted 21 cm Absorption Line Toward 3C 286

    CERN Document Server

    Wolfe, Arthur M; Robishaw, Timothy; Heiles, Carl; Prochaska, J Xavier

    2011-01-01

    A re-analysis of the Stokes-parameter spectra obtained of the z=0.692 21 cm absorption line toward 3C 286 shows that our original claimed detection of Zeeman splitting by a line-of-sight magnetic field, B_los = 87 microgauss is incorrect. Because of an insidious software error, what we reported as Stokes V is actually Stokes U: the revised Stokes V spectrum indicates a 3-sigma upper limit of B_los < 17 microgauss. The correct analysis reveals an absorption feature in fractional polarization that is offset in velocity from the Stokes I spectrum by -1.9 km/s. The polarization position-angle spectrum shows a dip that is also significantly offset from the Stokes I feature, but at a velocity that differs slightly from the absorption feature in fractional polarization. We model the absorption feature with 3 velocity components against the core-jet structure of 3C 286. Our chisquare minimization fitting results in components with differing (1) ratios of H I column density to spin temperature, (2) velocity centroi...

  10. The optimal redshift for detecting ionized bubbles in HI 21-cm maps

    CERN Document Server

    Datta, Kanan K; Choudhury, T Roy

    2009-01-01

    The detection of individual ionized bubbles in HI 21-cm maps is one of the most promising, direct probes of the epoch of reionization(EoR). Atleast 1000 hrs of observation would be required for such a detection with either the currently functioning GMRT or the upcoming MWA. Considering the large investment of telescope time it is essential to identify the``optimal redshift'' where the prospects of a detection are most favourable. We find that the optimal redshift is determined by a combination of instrument dependent factors and the evolution of the neutral fraction x_HI. We find that the redshift range 8.1 +/- 1.1 and 9.8 +/- 1 are optimum for detecting ionized bubbles with the GMRT and MWA respectively. The prospects of a detection, we find, are more favourable in a scenario with late reionization with x_HI \\approx 0.5 at z \\approx 7.5 as compared to an early reionization model where x_HI \\approx 0.5 at z \\approx 10. In the late reionization scenario, for both instruments a 3 \\sigma detection is possible fo...

  11. Eliminating Polarized Leakage as a Systematic for 21 cm Epoch of Reionization Experiments

    Science.gov (United States)

    Aguirre, James E.; HERA Collaboration, PAPER Collaboration

    2016-01-01

    Because of the extreme brightness of foreground emission relative to the desired signal, experiments seeking the 21 cm HI signal from the epoch of reionization must employ foreground removal or avoidance strategies with high dynamic range. Almost all of these techniques rely on the spectral smoothness of the foreground emission, which is dominated by synchrotron emission. The polarized component of such emission can suffer Faraday rotation through the interstellar medium of the Milky Way, thereby inducing frequency structure which can be mistaken for real reionization signal. Therefore, it is of great importance for such experiments to eliminate leakage of Faraday-rotated, polarized emission into the unpolarized (Stokes I) component where the reionization signal lives. We discuss a number of approaches under investigation for mitigating this leakage in the PAPER and HERA experiments, including calibration and careful instrument design. Importantly, however, we show that the ionosphere may provide a very strong suppression of the polarized signal, when averaged over the integration times required for EoR experiments, by scrambling the phase of polarized sources. Moreover, this attenuation comes with very little suppression of the desired unpolarized signal. We consider the implications of this strategy for PAPER and HERA.

  12. Rotation Measures in AGN jets seen by VLA at 21 cm to 6 mm

    CERN Document Server

    Kravchenko, E V; Kovalev, Y Y

    2014-01-01

    We present Faraday Rotation Measure (RM) properties of seven active galactic nuclei (AGN), observed with the NRAO VLA at three epochs in 2012-2014. Data was taken at 1.4, 2.2, 5.0, 8.2, 15.4, 22.4, 33.5 and 43.1 GHz quasi simultaneously in full polarization mode. For the first time RMs were calculated in a range of wavelengths covering more than one order of magnitude: from 21 cm up to 6 mm. We measured RM for each source and showed a tendency to increase its value toward high frequencies according to the law |RM|~f^a with a=1.6+/-0.1. For 0710+439, we observed an increase over the frequency range of 4 orders of magnitude and measured one of the highest RM ever, (-89+/-1)*10^3 rad/m^2. Analysis of different epochs shows variations of the value and the sign of RM on short and long time-scales. This may be caused by changing physical conditions in the compact regions of the AGN jets, e.g. strength of magnetic field, particle density and so on.

  13. Effect of the length of inflation on angular TT and TE power spectra in power-law inflation

    CERN Document Server

    Hirai, S; Hirai, Shiro; Takami, Tomoyuki

    2006-01-01

    The effect of the length of inflation on the power spectra of scalar and tensor perturbations is estimated using the power-law inflation model with a scale factor of a(t) = t^q. Considering various pre-inflation models with radiation-dominated or scalar matter-dominated periods before inflation in combination with two matching conditions, the temperature angular power spectrum (TT) and temperature-polarization cross-power spectrum (TE) are calculated and a likelihood analysis is performed. It is shown that the discrepancies between the Wilkinson Microwave Anisotropy Probe (WMAP) data and the LCDM model, such as suppression of the spectrum at l = 2,3 and oscillatory behavior, may be explained by the finite length of inflation model if the length of inflation is near 60 e-folds and q > 300. The proposed models retain similar values of chi^2 to that achieved by the LCDM model with respect to fit to the WMAP data, but display different characteristics of the angular TE power spectra at l < 20.

  14. The Properties of Primordial Stars and Galaxies measured from the 21-cm Global Spectrum using the Dark Ages Radio Explorer (DARE)

    Science.gov (United States)

    Burns, Jack O.; Bowman, Judd D.; Bradley, Richard F.; Fialkov, Anastasia; Furlanetto, Steven R.; Jones, Dayton L.; Kasper, Justin; Loeb, Abraham; Mirocha, Jordan; Monsalve, Raul A.; Rapetti, David; Tauscher, Keith; Wollack, Edward

    2017-01-01

    DARE is a mission concept designed to observe the formation of primordial stars, black holes, and galaxies (z=11-35) by measuring their spectral effects on the redshifted 21-cm hydrogen line. The UV and X-ray radiation emitted by these first objects ionized and heated the intergalactic medium and imprinted characteristic features in the 21-cm spectrum. The 1.4 GHz signal is redshifted into the radio band 40-120 MHz. DARE will take advantage of the quietest RF environment in the inner solar system by using the Moon as a shield from human radio frequency interference and solar emissions via observations on the lunar farside. DARE’s science objectives are to determine: when the first stars turned on and their properties, when the first black holes began accreting and their masses, the reionization history of the early Universe, and if evidence exists for exotic physics in the Dark Ages such as Dark Matter decay. Wideband crossed-dipole antennas, pilot tone stablized radiometric receivers, a polarimeter, and a digital spectrometer constitute the science instrument. DARE’s radiometer is precisely calibrated with a featureless spectral response, controlled systematics, and heritage from CMB missions. Models for the instrument main beam and sidelobes, antenna reflection coefficient, gain variations, and calibrations will be validated with electromagnetic simulations, laboratory and anechoic chamber measurements, and verified on-orbit. The unique frequency structure of the 21-cm spectrum, its uniformity over large angular scales, and its unpolarized state are unlike the spectrally featureless, spatially-varying, polarized emission of the bright Galactic foreground, allowing the signal to be cleanly separated from the foreground. The 21-cm signal will be extracted in the presence of foregrounds using a Bayesian framework with a Markov Chain Monto Carlo (MCMC) numerical inference technique. The DARE data analysis pipeline enables efficient, simultaneous, and self

  15. 21-cm Observations with the Morehead Radio Telescope: Involving Undergraduates in Observing Programs

    Science.gov (United States)

    Malphrus, B. K.; Combs, M. S.; Kruth, J.

    2000-12-01

    Herein we report astronomical observations made by undergraduate students with the Morehead Radio Telescope (MRT). The MRT, located at Morehead State University, Morehead, Kentucky, is small aperture (44-ft.) instrument designed by faculty, students, and industrial partners to provide a research instrument and active laboratory for undergraduate astronomy, physics, pre-engineering, and computer science students. Small aperture telescopes like the MRT have numerous advantages as active laboratories and as research instruments. The benefits to students are based upon a hands-on approach to learning concepts in astrophysics and engineering. Students are provided design and research challenges and are allowed to pursue their own solutions. Problem-solving abilities and research design skills are cultivated by this approach. Additionally, there are still contributions that small aperture centimeter-wave instruments can make. The MRT operates over a 6 MHz bandwidth centered at 1420 MHz (21-cm), which corresponds to the hyperfine transition of atomic hydrogen (HI). The HI spatial distribution and flux density associated with cosmic phenomena can be observed and mapped. The dynamics and kinematics of celestial objects can be investigated by observing over a range of frequencies (up to 2.5 MHz) with a 2048-channel back-end spectrometer, providing up to 1 KHz frequency resolution. The sensitivity and versatility of the telescope design facilitate investigation of a wide variety of cosmic phenomena, including supernova remnants, emission and planetary nebulae, extended HI emission from the Milky Way, quasars, radio galaxies, and the sun. Student observations of galactic sources herein reported include Taurus A, Cygnus X, and the Rosette Nebula. Additionally, we report observations of extragalactic phenomena, including Cygnus A, 3C 147, and 3C 146. These observations serve as a performance and capability test-bed of the MRT. In addition to the astronomical results of these

  16. A Practical Theorem on Using Interferometry to Measure the Global 21-cm Signal

    Science.gov (United States)

    Venumadhav, Tejaswi; Chang, Tzu-Ching; Doré, Olivier; Hirata, Christopher M.

    2016-08-01

    The sky-averaged, or global, background of redshifted 21 cm radiation is expected to be a rich source of information on cosmological reheating and reionization. However, measuring the signal is technically challenging: one must extract a small, frequency-dependent signal from under much brighter spectrally smooth foregrounds. Traditional approaches to study the global signal have used single antennas, which require one to calibrate out the frequency-dependent structure in the overall system gain (due to internal reflections, for example) as well as remove the noise bias from auto-correlating a single amplifier output. This has motivated proposals to measure the signal using cross-correlations in interferometric setups, where additional calibration techniques are available. In this paper we focus on the general principles driving the sensitivity of the interferometric setups to the global signal. We prove that this sensitivity is directly related to two characteristics of the setup: the cross-talk between readout channels (i.e., the signal picked up at one antenna when the other one is driven) and the correlated noise due to thermal fluctuations of lossy elements (e.g., absorbers or the ground) radiating into both channels. Thus in an interferometric setup, one cannot suppress cross-talk and correlated thermal noise without reducing sensitivity to the global signal by the same factor—instead, the challenge is to characterize these effects and their frequency dependence. We illustrate our general theorem by explicit calculations within toy setups consisting of two short-dipole antennas in free space and above a perfectly reflecting ground surface, as well as two well-separated identical lossless antennas arranged to achieve zero cross-talk.

  17. Incidence of HI 21-cm absorption in strong FeII systems at $0.5

    CERN Document Server

    Dutta, R; Gupta, N; Joshi, R; Petitjean, P; Noterdaeme, P; Ge, J; Krogager, J -K

    2016-01-01

    We present the results from our search for HI 21-cm absorption in a sample of 16 strong FeII systems ($W_{\\rm r}$(MgII $\\lambda2796$) $\\ge1.0$ \\AA\\ and $W_{\\rm r}$(FeII $\\lambda2600$) or $W_{\\rm FeII}$ $\\ge1$ \\AA) at $0.521-cm absorption detections from our sample, which have increased the known number of detections in strong MgII systems at this redshift range by $\\sim50$%. Combining our measurements with those in the literature, we find that the detection rate of HI 21-cm absorption increases with $W_{\\rm FeII}$, being four times higher in systems with $W_{\\rm FeII}$ $\\ge1$ \\AA\\ compared to systems with $W_{\\rm FeII}$ $<1$ \\AA. The $N$(HI) associated with the HI 21-cm absorbers would be $\\ge 2 \\times 10^{20}$ cm$^{-2}$, assuming a spin temperature of $\\sim500$ K (based on HI 21-cm absorption measurements of damped Lyman-$\\alpha$ systems at this redshift range) and unit covering factor. We find that ...

  18. Design method for a laser line beam shaper of a general 1D angular power distribution

    Science.gov (United States)

    Oved, E.; Oved, A.

    2016-05-01

    Laser line is a beam of laser, spanned in one direction using a beam shaper to form a fan of light. This illumination tool is important in laser aided machine vision, 3D scanners, and remote sensing. For some applications the laser line should have a specific angular power distribution. If the distribution is nonsymmetrical, the beam shaper is required to be nonsymmetrical freeform, and its design process using optical design software is time consuming due to the long optimization process which usually converges to some local minimum. In this paper we introduce a new design method of a single element refractive beam shaper of any predefined general 1D angular power distribution. The method makes use of a notion of "prism space", a geometrical representation of all double refraction prisms, and any 1D beam shaper can be described by a continuous curve in this space. It is shown that infinitely many different designs are possible for any given power distribution, and it is explained how an optimal design is selected among them, based on criteria such as high transmission, low surface slopes, robustness to manufacturing errors etc. The method is non-parametric and hence does not require initial guess of a functional form, and the resultant optical surfaces are described by a sequence of points, rather than by an analytic function.

  19. Redshifted HI 21-cm Signal from the Post-Reionization Epoch: Cross-Correlations with Other Cosmological Probes

    Indian Academy of Sciences (India)

    T. Guha Sarkar; K. K. Datta; A. K. Pal; T. Roy Choudhury; S. Bharadwaj

    2016-12-01

    Tomographic intensity mapping of the HI using the redshifted 21-cm observations opens up a new window towards our understanding of cosmological background evolution and structure formation. This is a key science goal of several upcoming radio telescopes including the Square Kilometer Array (SKA). In this article, we focus on the post-reionization signal and investigate the cross correlating of the 21-cm signal with other tracers of the large scale structure. We consider the cross-correlation of the post-reionization 21-cm signal with the Lyman- α forest, Lyman-break galaxies and late time anisotropies in the CMBR maps like weak lensing and the integrated Sachs Wolfe effect. We study the feasibility of detecting the signal and explore the possibility of obtaining constraints on cosmological models using it.

  20. The redshifted HI 21 cm signal from the post-reionization epoch: Cross-correlations with other cosmological probes

    CERN Document Server

    Sarkar, T Guha; Pal, A K; Choudhury, T Roy; Bharadwaj, S

    2016-01-01

    Tomographic intensity mapping of the HI using the redshifted 21 cm observations opens up a new window towards our understanding of cosmological background evolution and structure formation. This is a key science goal of several upcoming radio telescopes including the Square Kilometer Array (SKA). In this article we focus on the post-reionization signal and investigate the of cross correlating the 21 cm signal with other tracers of the large scale structure. We consider the cross-correlation of the post-reionization 21 cm signal with the Lyman-alpha forest, Lyman-break galaxies and late time anisotropies in the CMBR maps like weak lensing and the Integrated Sachs Wolfe effect. We study the feasibility of detecting the signal and explore the possibility of obtaining constraints on cosmological models using it.

  1. It's Always Darkest Before the Cosmic Dawn: Early Results from Novel Tools and Telescopes for 21 cm Cosmology

    CERN Document Server

    Dillon, Joshua S

    2015-01-01

    21 cm cosmology, the statistical observation of the high redshift universe using the hyperfine transition of neutral hydrogen, has the potential to revolutionize our understanding of cosmology and the astrophysical processes that underlie the formation of the first stars, galaxies, and black holes during the "Cosmic Dawn." By making tomographic maps with low frequency radio interferometers, we can study the evolution of the 21 cm signal with time and spatial scale and use it to understand the density, temperature, and ionization evolution of the intergalactic medium over this dramatic period in the history of the universe. For my Ph.D. thesis, I explore a number of advancements toward detecting and characterizing the 21 cm signal from the Cosmic Dawn, especially during its final stage, the epoch of reionization. In seven different previously published papers, I explore new techniques for the statistical analysis of interferometric measurements, apply them to data from current generation telescopes like the Mu...

  2. Impact of Instrument Responses on the Detectability of One-point Statistics from Redshifted 21 cm Observations

    CERN Document Server

    Kittiwisit, Piyanat; Jacobs, Daniel C; Thyagarajan, Nithyanandan; Beardsley, Adam P

    2016-01-01

    We study the impact of instrumental systematics on the variance, skewness, and kurtosis of redshifted 21 cm intensity fluctuation observations from the Epoch of Reionization. We simulate realistic 21 cm observations based on the Murchison Widefield Array (MWA) Phase I reionization experiment, using the array's point spread function (PSF) and antenna beam patterns, full-sky 21 cm models, and the FHD imaging pipeline. We measure the observed redshift evolution of pixel probability density functions (PDF) and one-point statistics from the simulated maps, comparing them to the measurements derived from simpler simulations that represent the instrument PSFs with Gaussian kernels. We find that both methods yield statistics with similar trends with greater than 80% correlation. We perform additional simulations based on the Hydrogen Epoch of Reionization Array (HERA), using Gaussian kernels as the instrument PSFs, and study the effect of frequency binning on the statistics. We find that PSF smoothing and sampling va...

  3. A High Galactic Latitude HI 21 cm-line Absorption Survey using the GMRT: I. Observations and Spectra

    Indian Academy of Sciences (India)

    Rekhesh Mohan; K. S. Dwarakanath; G. Srinivasan

    2004-09-01

    We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (|| > 15°) Galactic latitudes. The Declination coverage of the present survey is ≳ -45°. With a mean rms optical depth of ∼ 0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components. A subsequent paper will discuss the interpretation of these results.

  4. The cross-correlation between 21cm intensity mapping maps and the Lyman-alpha forest in the post-reionization era

    CERN Document Server

    Carucci, Isabella P; Viel, Matteo

    2016-01-01

    We investigate the cross-correlation signal between 21cm intensity mapping maps and the Lyman-alpha forest in the fully non-linear regime using state-of-the-art hydrodynamic simulations. The cross-correlation signal between these fields can provide a coherent and comprehensive picture of the neutral hydrogen (HI) content of our Universe in the post-reionization era, probing both its mass content and volume distribution. We compute the auto-power spectra of both fields together with their cross-power spectrum at z = 2.4 and find that on large scales the fields are completely anti-correlated. This anti-correlation arises because regions with high (low) 21cm emission, such as those with a large (low) concentration of damped Lyman-alpha systems, will show up as regions with low (high) transmitted flux. We find that on scales smaller than k = 0.2 h/Mpc the cross-correlation coefficient departs from -1, at a scale where non-linearities show up. We use the anisotropy of the power spectra in redshift-space to determi...

  5. Angular Power Spectrum and Dilatonic Inflation in Modular-Invariant Supergravity

    CERN Document Server

    Hayashi, M J; Okame, Y; Watanabe, T; Hayashi, Mitsuo J.; Hirai, Shiro; Okame, Yusuke; Watanabe, Tomoki

    2006-01-01

    The angular power spectrum is investigated in the model of supergravity, incorporating the target-space duality and the non-perturbative gaugino condensation in the hidden sector. The inflation and supersymmetry breaking occur at once by the interplay between the dilaton field as inflaton and the condensate gauge-singlet field. The model satisfies the slow-roll condition which solves the \\eta-problem. When the particle rolls down along the minimized trajectory of the potential at a duality invariant fixed point T=1, we can obtain the e-fold value \\sim 57. And then the cosmological parameters obtained from our model well match with the recent WMAP data combined with other experiments. The TT and TE angular power spectra also show that our model is compatible with the data for l > 20. However, the best fit value of \\tau in our model is smaller than that of the \\Lambda CDM model. These results suggest that, among supergravity models of inflation, the modular-invariant supergravity seems to open a hope to constru...

  6. First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations Angular Power Spectrum

    CERN Document Server

    Hinshaw, G; Verde, L; Hill, R S; Meyer, S S; Barnes, C; Bennett, C L; Halpern, M; Jarosik, N C; Kogut, A J; Komatsu, E; Limon, M; Page, L; Tucker, G S; Weiland, J; Wollack, E; Wright, E L

    2003-01-01

    We present the angular power spectrum derived from the first-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power spectrum estimation methods and data combinations and demonstrate that the results are robust. The data are modestly contaminated by diffuse Galactic foreground emission, but we show that a simple Galactic template model is sufficient to remove the signal. Point sources produce a modest contamination in the low frequency data. After masking ~700 known bright sources from the maps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130 uK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic errors are negligible compared to the (modest) level of foreground emission. Our best estimate of the power spectrum is derived from 28 cross-power spectra of statistically independent channels. The final spectrum is essentially independent of the noise properties of an individual radiometer. The resulting spectrum provides a definitive mea...

  7. Stars and reionization: the cross-correlation of the 21 cm line and the near-infrared background

    NARCIS (Netherlands)

    Fernandez, Elizabeth R.; Zaroubi, Saleem; Iliev, Ilian T.; Mellema, Garrelt; Jelić, Vibor

    2014-01-01

    With improving telescopes, it may now be possible to observe the Epoch of Reionization in multiple ways. We examine two of these observables - the excess light in the near-infrared background that may be due to high-redshift stars and ionized HII bubbles, and the 21 cm emission from neutral hydrogen

  8. The Evolution of 21-cm Structure (EOS): public, large-scale simulations of Cosmic Dawn and Reionization

    CERN Document Server

    Mesinger, Andrei; Sobacchi, Emanuele

    2016-01-01

    We introduce the Evolution of 21-cm Structure (EOS) project: providing periodic, public releases of the latest cosmological 21-cm simulations. 21-cm interferometry is set to revolutionize studies of the Cosmic Dawn (CD) and epoch of reionization (EoR), eventually resulting in 3D maps of the first billion years of our Universe. Progress will depend on sophisticated data analysis pipelines, which are in turn tested on large-scale mock observations. Here we present the 2016 EOS data release, consisting of the largest (1.6 Gpc on side with a 1024^3 grid), public 21-cm simulations of the CD and EoR. We include calibrated, sub-grid prescriptions for inhomogeneous recombinations and photo-heating suppression of star formation in small mass galaxies. We present two simulation runs that approximately bracket the contribution from faint unseen galaxies. From these two extremes, we predict that the duration of reionization (defined as a change in the mean neutral fraction from 0.9 to 0.1) should be between 2.7 < Delt...

  9. A search for HI 21cm absorption in strong MgII absorbers in the redshift desert

    CERN Document Server

    Kanekar, N; Ellison, S L; Chengalur, J N

    2009-01-01

    We report results from a deep search for redshifted HI 21cm absorption in 55 strong MgII$\\lambda$2796 absorbers (having $W (MgII) > 0.5 \\AA$) at intermediate redshifts, $0.58 3\\sigma$ significance in 32 other MgII absorbers, with 26 of these providing strong upper limits to the HI 21cm optical depth, $\\tau_{3\\sigma} [800 \\times f]$ K (where $f$ is the covering factor), if the HI column density is $\\ge 2 \\times 10^{20}$ cm$^{-2}$, i.e. if the absorber is a damped Lyman-$\\alpha$ system (DLA). Data on the remaining 13 systems of the sample were affected by radio frequency interference and were hence not useful. Excluding "associated" systems (within 3000 km/s of the quasar redshift), the detection rate of HI 21cm absorption in strong MgII absorbers is $x_{\\rm 21,MgII} ({\\bar z} = 1.1) = 25^{+11}_{-8}$%, at a $3\\sigma$ optical depth sensitivity of $\\sim 0.013$ per 10 km/s. Comparing the detection rates of HI 21cm and damped Lyman-$\\alpha$ absorption in strong MgII absorber samples yields a detection rate of HI ...

  10. Stars and reionization: the cross-correlation of the 21 cm line and the near-infrared background

    NARCIS (Netherlands)

    Fernandez, Elizabeth R.; Zaroubi, Saleem; Iliev, Ilian T.; Mellema, Garrelt; Jelic, Vibor

    With improving telescopes, it may now be possible to observe the Epoch of Reionization in multiple ways. We examine two of these observables - the excess light in the near-infrared background that may be due to high-redshift stars and ionized HII bubbles, and the 21 cm emission from neutral

  11. New limits on 21 cm epoch of reionization from paper-32 consistent with an x-ray heated intergalactic medium at z = 7.7

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, Aaron R.; Liu, Adrian; Ali, Zaki S.; Pober, Jonathan C. [Astronomy Department, University of California, Berkeley, CA (United States); Aguirre, James E.; Moore, David F. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA (United States); Bradley, Richard F. [Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, VA (United States); Carilli, Chris L. [National Radio Astronomy Observatory, Socorro, NM (United States); DeBoer, David R.; Dexter, Matthew R.; MacMahon, David H. E. [Radio Astronomy Laboratory, University of California, Berkeley, CA (United States); Gugliucci, Nicole E. [Department of Astronomy, University of Virginia, Charlottesville, VA (United States); Jacobs, Daniel C. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ (United States); Klima, Pat [National Radio Astronomy Observatory, Charlottesville, VA (United States); Manley, Jason R.; Walbrugh, William P. [Square Kilometer Array, South Africa Project, Cape Town (South Africa); Stefan, Irina I. [Cavendish Laboratory, Cambridge (United Kingdom)

    2014-06-20

    We present new constraints on the 21 cm Epoch of Reionization (EoR) power spectrum derived from three months of observing with a 32 antenna, dual-polarization deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization in South Africa. In this paper, we demonstrate the efficacy of the delay-spectrum approach to avoiding foregrounds, achieving over eight orders of magnitude of foreground suppression (in mK{sup 2}). Combining this approach with a procedure for removing off-diagonal covariances arising from instrumental systematics, we achieve a best 2σ upper limit of (41 mK){sup 2} for k = 0.27 h Mpc{sup –1} at z = 7.7. This limit falls within an order of magnitude of the brighter predictions of the expected 21 cm EoR signal level. Using the upper limits set by these measurements, we generate new constraints on the brightness temperature of 21 cm emission in neutral regions for various reionization models. We show that for several ionization scenarios, our measurements are inconsistent with cold reionization. That is, heating of the neutral intergalactic medium (IGM) is necessary to remain consistent with the constraints we report. Hence, we have suggestive evidence that by z = 7.7, the H I has been warmed from its cold primordial state, probably by X-rays from high-mass X-ray binaries or miniquasars. The strength of this evidence depends on the ionization state of the IGM, which we are not yet able to constrain. This result is consistent with standard predictions for how reionization might have proceeded.

  12. Results from EDGES High-band. I. Constraints on Phenomenological Models for the Global 21 cm Signal

    Science.gov (United States)

    Monsalve, Raul A.; Rogers, Alan E. E.; Bowman, Judd D.; Mozdzen, Thomas J.

    2017-09-01

    We report constraints on the global 21 cm signal due to neutral hydrogen at redshifts 14.8≥slant z≥slant 6.5. We derive our constraints from low-foreground observations of the average sky brightness spectrum conducted with the EDGES High-band instrument between 2015 September 7 and October 26. Observations were calibrated by accounting for the effects of antenna beam chromaticity, antenna and ground losses, signal reflections, and receiver parameters. We evaluate the consistency between the spectrum and phenomenological models for the global 21 cm signal. For tanh-based representations of the ionization history during the epoch of reionization, we rule out, at ≥slant 2σ significance, models with duration of up to {{Δ }}z=1 at z≈ 8.5 and higher than {{Δ }}z=0.4 across most of the observed redshift range under the usual assumption that the 21 cm spin temperature is much larger than the temperature of the cosmic microwave background during reionization. We also investigate a “cold” intergalactic medium (IGM) scenario that assumes perfect Lyα coupling of the 21 cm spin temperature to the temperature of the IGM, but that the latter is not heated by early stars or stellar remants. Under this assumption, we reject tanh-based reionization models of duration {{Δ }}z≲ 2 over most of the observed redshift range. Finally, we explore and reject a broad range of Gaussian models for the 21 cm absorption feature expected in the First Light era. As an example, we reject 100 mK Gaussians with duration (full width at half maximum) {{Δ }}z≤slant 4 over the range 14.2≥slant z≥slant 6.5 at ≥slant 2σ significance.

  13. Whole-body angular momentum during sloped walking using passive and powered lower-limb prostheses.

    Science.gov (United States)

    Pickle, Nathaniel T; Wilken, Jason M; Aldridge Whitehead, Jennifer M; Silverman, Anne K

    2016-10-03

    Sloped walking requires altered strategies for maintaining dynamic balance relative to level-ground walking, as evidenced by changes in sagittal-plane whole-body angular momentum (H) in able-bodied individuals. The ankle plantarflexor muscles are critical for regulating H, and functional loss of these muscles from transtibial amputation affects this regulation. However, it is unclear if a powered prosthesis, which more closely emulates intact ankle function than a passive energy-storage-and-return prosthesis, affects H differently during sloped walking. Therefore, our purpose was to investigate H in individuals with unilateral transtibial amputation when using powered and passive prostheses. Overall, the range of H was greater in people with a transtibial amputation relative to able-bodied individuals. On a -10° decline, individuals with amputation did not decrease H as much as able-bodied individuals, and had reduced prosthetic limb braking ground reaction forces and knee power absorption. On a +10° incline, individuals with amputation had a greater relative increase of H than able-bodied individuals, a more anterior placement of the prosthetic foot, and higher peak hip power generation. The powered prosthesis condition resulted in a smaller range of H during prosthetic stance relative to the passive condition, although it was still larger than able-bodied individuals. Our results suggest that prosthetic ankle power generation may help regulate dynamic balance during prosthetic stance, but alone is not sufficient for restoring H to that of able-bodied individuals on slopes. Contributions of knee extensor muscles and the biarticular gastrocnemius in regulating H on slopes should be further investigated. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Planck early results. XVIII. The power spectrum of cosmic infrared background anisotropies

    DEFF Research Database (Denmark)

    Bucher, M.; Delabrouille, J.; Giraud-Héraud, Y.

    2011-01-01

    Using Planck maps of six regions of low Galactic dust emission with a total area of about 140 deg2, we determine the angular power spectra of cosmic infrared background (CIB) anisotropies from multipole = 200 to = 2000 at 217, 353, 545 and 857 GHz. We use 21-cm observations of Hi as a tracer of t...

  15. Hydrogen and the First Stars: First Results from the SCI-HI 21-cm all-sky spectrum experiment

    Science.gov (United States)

    Voytek, Tabitha; Peterson, Jeffrey; Lopez-Cruz, Omar; Jauregui-Garcia, Jose-Miguel; SCI-HI Experiment Team

    2015-01-01

    The 'Sonda Cosmologica de las Islas para la Deteccion de Hidrogeno Neutro' (SCI-HI) experiment is an all-sky 21-cm brightness temperature spectrum experiment studying the cosmic dawn (z~15-35). The experiment is a collaboration between Carnegie Mellon University (CMU) and Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) in Mexico. Initial deployment of the SCI-HI experiment occurred in June 2013 on Guadalupe; a small island about 250 km off of the Pacific coast of Baja California in Mexico. Preliminary measurements from this deployment have placed the first observational constraints on the 21-cm all-sky spectrum around 70 MHz (z~20), see Voytek et al (2014).Neutral Hydrogen (HI) is found throughout the universe in the cold gas that makes up the intergalactic medium (IGM). HI can be observed through the spectral line at 21 cm (1.4 GHz) due to hyperfine structure. Expansion of the universe causes the wavelength of this spectral line to stretch at a rate defined by the redshift z, leading to a signal which can be followed through time.Now the strength of the 21-cm signal in the IGM is dependent only on a small number of variables; the temperature and density of the IGM, the amount of HI in the IGM, the UV energy density in the IGM, and the redshift. This means that 21-cm measurements teach us about the history and structure of the IGM. The SCI-HI experiment focuses on the spatially averaged 21-cm spectrum, looking at the temporal evolution of the IGM during the cosmic dawn before reionization.Although the SCI-HI experiment placed first constraints with preliminary data, this data was limited to a narrow frequency regime around 60-85 MHz. This limitation was caused by instrumental difficulties and the presence of residual radio frequency interference (RFI) in the FM radio band (~88-108 MHz). The SCI-HI experiment is currently undergoing improvements and we plan to have another deployment soon. This deployment would be to Socorro and Clarion, two

  16. GMRT Detection of HI 21cm Associated Absorption towards the = 1.2 Red Quasar 3C 190

    Indian Academy of Sciences (India)

    C. H. Ishwara-Chandra; K. S. Dwarakanath; K. R. Anantharamaiah

    2003-03-01

    We report the GMRT detection of associated HI 21 cm-line absorption in the = 1.1946 red quasar 3C 190. Most of the absorption is blue-shifted with respect to the systemic redshift. The absorption, at ∼ 647.7MHz, is broad and complex, spanning a velocity width of ∼ 600 kms-1. Since the core is self-absorbed at this frequency, the absorption is most likely towards the hotspots. Comparison of the radio and deep optical images reveal linear filaments in the optical which overlap with the brighter radio jet towards the south-west.We therefore suggest that most of the HI 21 cm-line absorption could be occurring in the atomic gas shocked by the south-west jet.

  17. Fast large volume simulations of the 21-cm signal from the reionization and pre-reionization epochs

    Science.gov (United States)

    Santos, M. G.; Ferramacho, L.; Silva, M. B.; Amblard, A.; Cooray, A.

    2010-08-01

    While limited to low spatial resolution, the next-generation low-frequency radio interferometers that target 21-cm observations during the era of reionization and prior will have instantaneous fields of view that are many tens of deg2 on the sky. Predictions related to various statistical measurements of the 21-cm brightness temperature must then be pursued with numerical simulations of reionization with correspondingly large volume box sizes, of the order of 1000 Mpc on one side. We pursue a semi-numerical scheme to simulate the 21-cm signal during and prior to reionization by extending a hybrid approach where simulations are performed by first laying down the linear dark matter density field, accounting for the non-linear evolution of the density field based on second-order linear perturbation theory as specified by the Zel'dovich approximation, and then specifying the location and mass of collapsed dark matter haloes using the excursion-set formalism. The location of ionizing sources and the time evolving distribution of ionization field is also specified using an excursion-set algorithm. We account for the brightness temperature evolution through the coupling between spin and gas temperature due to collisions, radiative coupling in the presence of Lyman α photons and heating of the intergalactic medium, such as due to a background of X-ray photons. The hybrid simulation method we present is capable of producing the required large volume simulations with adequate resolution in a reasonable time, so a large number of realizations can be obtained with variations in assumptions related to astrophysics and background cosmology that govern the 21-cm signal.

  18. First measurement of HI 21cm emission from a GRB host galaxy indicates a post-merger system

    CERN Document Server

    Arabsalmani, Maryam; Zwaan, Martin; Kanekar, Nissim; Michałowski, Michał J

    2015-01-01

    We report the detection and mapping of atomic hydrogen in HI 21cm emission from ESO 184-G82, the host galaxy of the gamma ray burst 980425. This is the first instance where HI in emission has been detected from a galaxy hosting a gamma ray burst. ESO 184-G82 is an isolated galaxy and contains a Wolf-Rayet region close to the location of the gamma ray burst and the associated supernova, SN 1998bw. This is one of the most luminous HII regions identified in the local Universe, with a very high inferred density of star formation. The HI 21cm observations reveal a high HI mass for the galaxy, twice as large as the stellar mass. The spatial and velocity distribution of the HI 21cm emission reveals a disturbed rotating gas disk, which suggests that the galaxy has undergone a recent minor merger that disrupted its rotation. We find that the Wolf-Rayet region and the gamma ray burst are both located in the highest HI column density region of the galaxy. We speculate that the merger event has resulted in shock compress...

  19. PRECISE MEASUREMENT OF THE REIONIZATION OPTICAL DEPTH FROM THE GLOBAL 21 cm SIGNAL ACCOUNTING FOR COSMIC HEATING

    Energy Technology Data Exchange (ETDEWEB)

    Fialkov, Anastasia; Loeb, Abraham, E-mail: anastasia.fialkov@cfa.harvard.edu, E-mail: aloeb@cfa.harvard.edu [Department of Astronomy, Harvard University, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)

    2016-04-10

    As a result of our limited data on reionization, the total optical depth for electron scattering, τ, limits precision measurements of cosmological parameters from the Cosmic Microwave Background (CMB). It was recently shown that the predicted 21 cm signal of neutral hydrogen contains enough information to reconstruct τ with sub-percent accuracy, assuming that the neutral gas was much hotter than the CMB throughout the entire epoch of reionization (EoR). Here we relax this assumption and use the global 21 cm signal alone to extract τ for realistic X-ray heating scenarios. We test our model-independent approach using mock data for a wide range of ionization and heating histories and show that an accurate measurement of the reionization optical depth at a sub-percent level is possible in most of the considered scenarios even when heating is not saturated during the EoR, assuming that the foregrounds are mitigated. However, we find that in cases where heating sources had hard X-ray spectra and their luminosity was close to or lower than what is predicted based on low-redshift observations, the global 21 cm signal alone is not a good tracer of the reionization history.

  20. Broad, weak 21 cm absorption in an early type galaxy: spectral-line finding and parameterisation for future surveys

    CERN Document Server

    Allison, J R; Sadler, E M; Reeves, S N

    2012-01-01

    We report conclusive verification of the detection of associated HI 21cm absorption in the early-type host of the compact radio source PMN J2054-4242. We estimate an equivalent spectral-line width of 415 +/- 20 km/s, and observed peak optical depth of 2.5 +/- 0.2 per cent, making this one of the broadest and weakest 21cm absorption-lines yet discovered. For Tspin/f > 100K the column density is NHI > 2 x 10^{21} cm^{-2}. The observed spectral-line profile is redshifted by v = 179 +/- 46 km/s, with respect to the spectroscopic optical measurement, perhaps indicating that the HI gas is infalling toward the central active galactic nucleus. The broad width of the line suggests that the cold gas is either rotating at very high velocity, or that the infall is accelerating (perhaps as a blended series of line-of-sight gas clouds). Our initial tentative detection would likely have been dismissed by visual inspection, and hence its verification here is an excellent test of our spectral-line detection technique, current...

  1. The cross correlation between the 21-cm radiation and the CMB lensing field: a new cosmological signal

    Energy Technology Data Exchange (ETDEWEB)

    Vallinotto, Alberto [Los Alamos National Laboratory

    2011-01-01

    The measurement of Baryon Acoustic Oscillations through the 21-cm intensity mapping technique at redshift z {<=} 4 has the potential to tightly constrain the evolution of dark energy. Crucial to this experimental effort is the determination of the biasing relation connecting fluctuations in the density of neutral hydrogen (HI) with the ones of the underlying dark matter field. In this work I show how the HI bias relevant to these 21-cm intensity mapping experiments can successfully be measured by cross-correlating their signal with the lensing signal obtained from CMB observations. In particular I show that combining CMB lensing maps from Planck with 21-cm field measurements carried out with an instrument similar to the Cylindrical Radio Telescope, this cross-correlation signal can be detected with a signal-to-noise (S/N) ratio of more than 5. Breaking down the signal arising from different redshift bins of thickness {Delta}z = 0.1, this signal leads to constraining the large scale neutral hydrogen bias and its evolution to 4{sigma} level.

  2. e-MERLIN 21cm constraints on the mass-loss rates of OB stars in Cyg OB2

    CERN Document Server

    Morford, Jack; Prinja, Raman; Blomme, Ronnie; Yates, Jeremy

    2016-01-01

    We present e-MERLIN 21 cm (L-band) observations of single luminous OB stars in the Cygnus OB2 association, from the COBRaS Legacy programme. The radio observations potentially offer the most straightforward, least model-dependent, determinations of mass-loss rates, and can be used to help resolve current discrepancies in mass-loss rates via clumped and structured hot star winds. We report here that the 21 cm flux densities of O3 to O6 supergiant and giant stars are less than ~ 70 microJy. These fluxes may be translated to `smooth' wind mass-loss upper limits of ~ 4.4 - 4.8 x 10^(-6) M_sol/yr for O3 supergiants and < 2.9 x 10^(-6) M_sol/yr for B0 to B1 supergiants. The first ever resolved 21 cm detections of the hypergiant (and LBV candidate) Cyg OB2 #12 are discussed; for multiple observations separated by 14 days, we detect a ~ 69% increase in its flux density. Our constraints on the upper limits for the mass-loss rates of evolved OB stars in Cyg OB2 support the model that the inner wind region close to t...

  3. HI 21-cm absorption survey of quasar-galaxy pairs: Distribution of cold gas around z<0.4 galaxies

    CERN Document Server

    Dutta, R; Gupta, N; Momjian, E; Noterdaeme, P; Petitjean, P; Rahmani, H

    2016-01-01

    We present the results from our survey of HI 21-cm absorption, using GMRT, VLA and WSRT, in a sample of 55 z<0.4 galaxies towards radio sources with impact parameters (b) in the range ~0-35 kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy-pairs (QGPs), probed by 45 sightlines, we have found seven HI 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity ($\\int\\tau dv$ <= 0.3 km/s) from the literature, we find a weak anti-correlation (rank correlation coefficient = -0.20 at 2.42sigma level) between $\\int\\tau dv$ and b, consistent with previous literature results. The covering factor of HI 21-cm absorbers (C_21) is estimated to be 0.24 (+0.12/-0.08) at b <= 15 kpc and 0.06 (+0.09/-0.04) at b = 15-35 kpc. $\\int\\tau dv$ and C_21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective HI radius. The...

  4. e-MERLIN 21 cm constraints on the mass-loss rates of OB stars in Cyg OB2

    Science.gov (United States)

    Morford, J. C.; Fenech, D. M.; Prinja, R. K.; Blomme, R.; Yates, J. A.

    2016-11-01

    We present e-MERLIN 21 cm (L-band) observations of single luminous OB stars in the Cygnus OB2 association, from the Cyg OB2 Radio Survey Legacy programme. The radio observations potentially offer the most straightforward, least model-dependent, determinations of mass-loss rates, and can be used to help resolve current discrepancies in mass-loss rates via clumped and structured hot star winds. We report here that the 21 cm flux densities of O3 to O6 supergiant and giant stars are less than ˜70 μJy. These fluxes may be translated to `smooth' wind mass-loss upper limits of ˜4.4-4.8 × 10-6 M⊙ yr -1 for O3 supergiants and ≲2.9 × 10-6 M⊙ yr -1 for B0 to B1 supergiants. The first ever resolved 21 cm detections of the hypergiant (and luminous blue variable candidate) Cyg OB2 #12 are discussed; for multiple observations separated by 14 d, we detect an ˜69 per cent increase in its flux density. Our constraints on the upper limits for the mass-loss rates of evolved OB stars in Cyg OB2 support the model that the inner wind region close to the stellar surface (where Hα forms) is more clumped than the very extended geometric region sampled by our radio observations.

  5. The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological parameters

    CERN Document Server

    Komatsu, E; Komatsu, Eiichiro; Seljak, Uros

    2002-01-01

    The angular power spectrum of the SZ effect, C_l, is a powerful probe of cosmology. It is easier to detect than individual clusters in the field, is insensitive to observational selection effects and does not require a calibration between cluster mass and flux, reducing the systematic errors which dominate the cluster-counting constraints. It receives a dominant contribution from cluster region between 20-40% of the virial radius and is thus insensitive to the poorly known gas physics in the cluster centre, such as cooling or (pre)heating. In this paper we derive a refined analytic prediction for C_l using the universal gas-density and temperature profile and the dark-matter halo mass function. The predicted C_l has no free parameters and fits all of the published hydrodynamic simulation results to better than a factor of two around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and is almost independent of all of the other cosmological parameters. This differs from the local cluster abund...

  6. INTERPRETING THE GLOBAL 21-cm SIGNAL FROM HIGH REDSHIFTS. II. PARAMETER ESTIMATION FOR MODELS OF GALAXY FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Mirocha, Jordan; Burns, Jack O. [Center for Astrophysics and Space Astronomy and Department of Astrophysical and Planetary Science, University of Colorado, Campus Box 389, Boulder, CO 80309 (United States); Harker, Geraint J. A., E-mail: mirocha@astro.ucla.edu [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

    2015-11-01

    Following our previous work, which related generic features in the sky-averaged (global) 21-cm signal to properties of the intergalactic medium, we now investigate the prospects for constraining a simple galaxy formation model with current and near-future experiments. Markov-Chain Monte Carlo fits to our synthetic data set, which includes a realistic galactic foreground, a plausible model for the signal, and noise consistent with 100 hr of integration by an ideal instrument, suggest that a simple four-parameter model that links the production rate of Lyα, Lyman-continuum, and X-ray photons to the growth rate of dark matter halos can be well-constrained (to ∼0.1 dex in each dimension) so long as all three spectral features expected to occur between 40 ≲ ν/MHz ≲ 120 are detected. Several important conclusions follow naturally from this basic numerical result, namely that measurements of the global 21-cm signal can in principle (i) identify the characteristic halo mass threshold for star formation at all redshifts z ≳ 15, (ii) extend z ≲ 4 upper limits on the normalization of the X-ray luminosity star formation rate (L{sub X}–SFR) relation out to z ∼ 20, and (iii) provide joint constraints on stellar spectra and the escape fraction of ionizing radiation at z ∼ 12. Though our approach is general, the importance of a broadband measurement renders our findings most relevant to the proposed Dark Ages Radio Explorer, which will have a clean view of the global 21-cm signal from ∼40 to 120 MHz from its vantage point above the radio-quiet, ionosphere-free lunar far-side.

  7. INVISIBLE ACTIVE GALACTIC NUCLEI. II. RADIO MORPHOLOGIES AND FIVE NEW H i 21 cm ABSORPTION LINE DETECTORS

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Ting; Stocke, John T.; Darling, Jeremy [Center for Astrophysics and Space Astronomy, UCB 389, University of Colorado, Boulder, CO 80309-0389 (United States); Momjian, Emmanuel [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Sharma, Soniya [Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory, ACT 2611 (Australia); Kanekar, Nissim [National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007 (India)

    2016-03-15

    This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Paper I. In this paper, we present both high-resolution radio continuum images for all of these sources and H i 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0.″5 and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H i 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral “window” (i.e., the percentage of H i 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H i detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H i absorption may well be present but is masked by

  8. Extraction of global 21-cm signal from simulated data for the Dark Ages Radio Explorer (DARE) using an MCMC pipeline

    Science.gov (United States)

    Tauscher, Keith A.; Burns, Jack O.; Rapetti, David; Mirocha, Jordan; Monsalve, Raul A.

    2017-01-01

    The Dark Ages Radio Explorer (DARE) is a mission concept proposed to NASA in which a crossed dipole antenna collects low frequency (40-120 MHz) radio measurements above the farside of the Moon to detect and characterize the global 21-cm signal from the early (z~35-11) Universe's neutral hydrogen. Simulated data for DARE includes: 1) the global signal modeled using the ares code, 2) spectrally smooth Galactic foregrounds with spatial structure taken from multiple radio foreground maps averaged over a large, well characterized beam, 3) systematics introduced in the data by antenna/receiver reflections, and 4) the Moon. This simulated data is fed into a signal extraction pipeline. As the signal is 4-5 orders of magnitude below the Galactic synchrotron contribution, it is best extracted from the data using Bayesian techniques which take full advantage of prior knowledge of the instrument and foregrounds. For the DARE pipeline, we use the affine-invariant MCMC algorithm implemented in the Python package, emcee. The pipeline also employs singular value decomposition to use known spectral features of the antenna and receiver to form a natural basis with which to fit instrumental systematics. Taking advantage of high-fidelity measurements of the antenna beam (to ~20 ppm) and precise calibration of the instrument, the pipeline extracts the global 21-cm signal with an average RMS error of 10-15 mK for multiple signal models.

  9. Three Dimensional Hydrodynamic Simulations of Multiphase Galactic Disks with Star Formation Feedback: II. Synthetic HI 21 cm Line Observations

    CERN Document Server

    Kim, Chang-Goo; Kim, Woong-Tae

    2014-01-01

    We use three-dimensional numerical hydrodynamic simulations of the turbulent, multiphase atomic interstellar medium (ISM) to construct and analyze synthetic HI 21 cm emission and absorption lines. Our analysis provides detailed tests of 21 cm observables as physical diagnostics of the atomic ISM. In particular, we construct (1) the "observed" spin temperature, $T_{s,obs}(v_{ch})\\equiv T_B(v_{ch})/[1-e^{-{\\tau}(v_{ch})}]$, and its optical-depth weighted mean T_s,obs; (2) the absorption-corrected "observed" column density, $N_{H,obs}\\propto \\int dv_{ch} T_B(v_{ch}){\\tau}(v_{ch})/[[1-e^{-{\\tau}(v_{ch})}]$; and (3) the "observed" fraction of cold neutral medium (CNM), $f_{c,obs}\\equiv T_c/T_{s,obs}$ for T_c the CNM temperature; we compare each observed parameter with true values obtained from line-of-sight (LOS) averages in the simulation. Within individual velocity channels, T_s,obs(v_ch) is within a factor 1.5 of the true value up to ${\\tau}(v_{ch})\\approx10$. As a consequence, N_H,obs and T_s,obs are respectiv...

  10. The impact of the supersonic baryon-dark matter velocity difference on the z~20 21cm background

    CERN Document Server

    McQuinn, Matthew

    2012-01-01

    Recently, Tseliakhovich and Hirata (2010) showed that during the cosmic Dark Ages the baryons were typically moving supersonically with respect to the dark matter with a spatially variable Mach number. Such supersonic motion may source shocks that heat the Universe. This motion may also suppress star formation in the first halos. Even a small amount of coupling of the 21cm signal to this motion has the potential to vastly enhance the 21cm brightness temperature fluctuations at 15

  11. Simulating the 21cm forest detectable with LOFAR and SKA in the spectra of high-z GRBs

    CERN Document Server

    Ciardi, B; Abdalla, F B; Asad, K; Bernardi, G; Bolton, J S; Brentjens, M; de Bruyn, A G; Chapman, E; Daiboo, S; Fernandez, E R; Ghosh, A; Graziani, L; Harker, G J A; Iliev, I T; Jelic, V; Jensen, H; Kazemi, S; Koopmans, L V E; Martinez, O; Maselli, A; Mellema, G; Offringa, A R; Pandey, V N; Schaye, J; Thomas, R; Vedantham, H; Yatawatta, S; Zaroubi, S

    2015-01-01

    We investigate the feasibility of detecting 21cm absorption features in the afterglow spectra of high redshift long Gamma Ray Bursts (GRBs). This is done employing simulations of cosmic reionization, together with the instrumental characteristics of the LOw Frequency ARray (LOFAR). We find that absorption features could be marginally (with a S/N larger than a few) detected by LOFAR at z>7 if the GRB originated from PopIII stars, while the detection would be easier if the noise were reduced by one order of magnitude, i.e. similar to what is expected for the first phase of the Square Kilometer Array (SKA1-low). On the other hand, more standard GRBs are too dim to be detected even with ten times the sensitivity of SKA1-low, and only in the most optimistic case can a S/N larger than a few be reached at z>9.

  12. Interpreting the Global 21-cm Signal from High Redshifts. II. Parameter Estimation for Models of Galaxy Formation

    CERN Document Server

    Mirocha, Jordan; Burns, Jack O

    2015-01-01

    Following our previous work, which related generic features in the sky-averaged (global) 21-cm signal to properties of the intergalactic medium, we now investigate the prospects for constraining a simple galaxy formation model with current and near-future experiments. Markov-Chain Monte Carlo fits to our synthetic dataset, which includes a realistic galactic foreground, a plausible model for the signal, and noise consistent with 100 hours of integration by an ideal instrument, suggest that a simple four-parameter model that links the production rate of Lyman-$\\alpha$, Lyman-continuum, and X-ray photons to the growth rate of dark matter halos can be well-constrained (to $\\sim 0.1$ dex in each dimension) so long as all three spectral features expected to occur between $40 \\lesssim \

  13. Calibration of the EDGES Receiver to Observe the Global 21-cm Signature from the Epoch of Reionization

    CERN Document Server

    Monsalve, Raul A; Bowman, Judd D; Mozdzen, Thomas J

    2016-01-01

    The EDGES experiment strives to detect the the sky-average brightness temperature from the $21$-cm line emitted during the Epoch of Reionization (EoR) in the redshift range $14 \\gtrsim z \\gtrsim 6$. To probe this signal, EDGES conducts single-antenna measurements in the frequency range $\\sim 100-200$ MHz from the Murchison Radio-astronomy Observatory in Western Australia. In this paper we describe the current strategy for calibration of the EDGES instrument and, in particular, of its receiver. The calibration involves measuring accurately modeled passive and active noise sources connected to the receiver input in place of the antenna. We model relevant uncertainties that arise during receiver calibration and propagate them to the calibrated antenna temperature using a Monte Carlo approach. Calibration effects are isolated by assuming that the sky foregrounds and the antenna beam are perfectly known. We find that if five polynomial terms are used to account for calibration systematics, most of the calibration ...

  14. Surveys of the Milky Way and Magellanic System in the λ21-cm line of atomic hydrogen

    Directory of Open Access Journals (Sweden)

    Dickey J.M.

    2012-02-01

    Full Text Available In the next three years, surveys of the Northern and Southern skies using focal plane arrays on aperture synthesis radio telescopes will lead to a breakthrough in our knowledge of the warm and cool atomic phases of the interstellar medium and their relationship with the diffuse molecular gas. The sensitivity and resolution of these surveys will give an order of magnitude or more improvement over existing interstellar medium data. The GASKAP (South and GAMES (North projects together constitute a complete survey of the Milky Way plane and the Magellanic Clouds and Stream in both emission and absorption in the H I 21-cm line and the OH 18-cm lines. The overall goal of this project is to understand the mechanism of galaxy evolution, through a detailed tracing of the astrophysical processes that drive the cycle of star formation in very different environments. Comparison of 21-cm emission and absorption highlights the transition from the warm, diffuse medium to cool clouds. Tracing turbulence in the Magellanic Stream shows how extra-galactic gas makes the difficult passage through the halo to replenish the disk. Finally, high resolution images of OH masers trace outflows from evolved stars that enrich the medium with heavy elements. To understand how the Milky Way was assembled and how it has evolved since, the speed and efficiency of these processes must be measured, as functions of Galactic radius and height above the plane. Observations of similar processes in the Magellanic Clouds show how differently they might have worked in conditions typical of the early universe.

  15. Probing small-scale cosmological fluctuations with the 21 cm forest: effects of neutrino mass, running spectral index and warm dark matter

    CERN Document Server

    Shimabukuro, Hayato; Inoue, Susumu; Yokoyama, Shuichiro

    2014-01-01

    Although the cosmological paradigm based on cold dark matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller than those of massive galaxies, and various alternatives have been proposed that differ significantly in the consequent small-scale power spectrum (SSPS) of large-scale structure. Here we show that a powerful probe of the SSPS at $k\\gtrsim 10$ Mpc$^{-1}$ can be provided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. Such features are expected to be caused predominantly by collapsed gas in starless minihalos, whose mass function can be very sensitive to the SSPS. As specific examples, we consider the effects of neutrino mass, running spectral index (RSI) and warm dark matter (WDM) on the SSPS, and evaluate the expected distribut...

  16. Temperature and polarization angular power spectra of Galactic dust radiation at 353 GHz as measured by Archeops

    CERN Document Server

    Ponthieu, N; Tristram, M; Ade, P; Amblard, A; Ansari, R; Aumont, J; Aubourg, E; Beno^it, A; Bernard, J P; Blanchard, A; Bock, J J; Bouchet, F R; Bourrachot, A; Camus, P; Cardoso, J F; Couchot, F; De Bernardis, P

    2005-01-01

    We present the first measurement of temperature and polarization angular power spectra of the diffuse emission of Galactic dust at 353 GHz as seen by Archeops on 20% of the sky. The temperature angular power spectrum is compatible with that provided by the extrapolation to 353 GHz of IRAS and DIRBE maps using \\cite{fds} model number 8. For Galactic latitudes $|b| \\geq 5$ deg we report a 4 sigma detection of large scale ($3\\leq \\ell \\leq 8$) temperature-polarization cross-correlation $(\\ell+1)C_\\ell^{TE}/2\\pi = 76\\pm 21 \\mu\\rm{K_{RJ}}^2$ and set upper limits to the $E$ and $B$ modes at $11 \\mu\\rm{K_{RJ}}^2$. For Galactic latitudes $|b| \\geq 10$ deg, on the same angular scales, we report a 2 sigma detection of temperature-polarization cross-correlation $(\\ell+1)C_\\ell^{TE}/2\\pi = 24\\pm 13 \\mu\\rm{K_{RJ}}^2$. These results are then extrapolated to 100 GHz to estimate the contamination in CMB measurements by polarized diffuse Galactic dust emission. The $TE$ signal is then $1.7\\pm0.5$ and $0.5\\pm0.3 \\mu\\rm{K^2_{CM...

  17. Optical imaging and high spatial resolution 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215)

    Science.gov (United States)

    Smith, Beverly J.

    1994-01-01

    We have used the Very Large Array (VLA) B and C Arrays to make 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215). These observations are complementary to previously published D Array VLA data, which revealed the presence of a long (5 min to 54 kpc) H I plume near the western side of this galaxy. We have also obtained BVRI H alpha images of the main body of this galaxy using the McDonald Observatory 30 inch telescope. The optical images of this galaxy show a strong stellar tail extending to the east, opposite the H I plume. Within the disk of NGC 2782, unsharp masking of the optical images at all 4 broadband wavelengths reveals three bright 'ripples', separated by approximately 15 sec. The light profiles across these ripples are symmetric, without a sharp outer edge. H alpha is strong at the starburst nucleus and along the northern and western sections of the inner ripple. The new higher resolution H I data show that the atomic gas is very clumpy. We have identified ten H I clumps in the long western plume, with H I masses of approximately 10(exp 8) solar mass, similar to those of dwarf galaxies, and column densities of approximately 10(exp 21) cm(exp -2) over surface areas of approximately 10 kpc(exp 2). No CO (1-0) emission has been detected from this plume, suggesting that it is material stripped from the outer edge of a disk galaxy. The H alpha peaks, in contrast, are generally not coincident with H I peaks. No H I is seen at the tip of the eastern extension. The H I distribution near this structure is ring-like rather than tail-like as in the optical data. We have detected redshifted H I absorption toward the central continuum source, indicating gas infall into the nuclear region. Using a restricted 3-body dynamical model, we have successfully reproduced the basic properties of NGC 2782 with an off-center collision between two galaxies, where a lower mass disk companion (M(sub 2)/M(sub 1) approximately 0.25) collides almost head-on with a larger

  18. A Measurement of the Angular Power Spectrum of the CMB from l = 100 to 400

    CERN Document Server

    Miller, A D; Devlin, M J; Dorwart, W B; Herbig, T; Nolta, M R; Page, L A; Puchalla, J; Torbet, E; Tran, H T

    1999-01-01

    We report on a measurement of the angular spectrum of the CMB between $l\\approx 100$ and $l\\approx 400$ made at 144 GHz from Cerro Toco in the Chilean altiplano. When the new data are combined with previous data at 30 and 40 GHz, taken with the same instrument observing the same section of sky, we find: 1) a rise in the angular spectrum to a maximum with $\\delta T_l \\approx 85~\\mu$K at $l\\approx 200$ and a fall at $l>300$, thereby localizing the peak near $l\\approx 200$; and 2) that the anisotropy at $l\\approx 200$ has the spectrum of the CMB.

  19. Calibration of the EDGES High-band Receiver to Observe the Global 21 cm Signature from the Epoch of Reionization

    Science.gov (United States)

    Monsalve, Raul A.; Rogers, Alan E. E.; Bowman, Judd D.; Mozdzen, Thomas J.

    2017-01-01

    The EDGES High-Band experiment aims to detect the sky-average brightness temperature of the 21 cm signal from the epoch of reionization in the redshift range 14.8≳ z≳ 6.5. To probe this redshifted signal, EDGES High-Band conducts single-antenna measurements in the frequency range 90–190 MHz from the Murchison Radio-astronomy Observatory in Western Australia. In this paper, we describe the current strategy for calibration of the EDGES High-Band receiver and report calibration results for the instrument used in the 2015–2016 observational campaign. We propagate uncertainties in the receiver calibration measurements to the antenna temperature using a Monte Carlo approach. We define a performance objective of 1 mK residual rms after modeling foreground subtraction from a fiducial temperature spectrum using a five-term polynomial. Most of the calibration uncertainties yield residuals of 1 mK or less at 95 % confidence. However, current uncertainties in the antenna and receiver reflection coefficients can lead to residuals of up to 20 mK even in low-foreground sky regions. These dominant residuals could be reduced by (1) improving the accuracy in reflection measurements, especially their phase, (2) improving the impedance match at the antenna-receiver interface, and (3) decreasing the changes with frequency of the antenna reflection phase.

  20. Spectral performance of SKA Log-periodic Antennas I: mitigating spectral artefacts in SKA1-LOW 21 cm cosmology experiments

    Science.gov (United States)

    de Lera Acedo, Eloy; Trott, Cathryn M.; Wayth, Randall B.; Fagnoni, Nicolas; Bernardi, Gianni; Wakley, Brett; Koopmans, Léon V. E.; Faulkner, Andrew J.; bij de Vaate, Jan Geralt

    2017-08-01

    This paper is the first in a series of papers describing the impact of antenna instrumental artefacts on the 21 cm cosmology experiments to be carried out by the low frequency instrument (SKA1-LOW) of the Square Kilometre Array telescope (SKA), i.e. the Cosmic Dawn (CD) and the Epoch of Reionization (EoR). The smoothness of the passband response of the current log-periodic antenna being developed for the SKA1-LOW is analysed using numerical electromagnetic simulations. The amplitude variations over the frequency range are characterized using low-order polynomials defined locally, in order to study the impact of the passband smoothness in the instrument calibration and CD/EoR Science. A solution is offered to correct a fast ripple found at 60 MHz during a test campaign at the SKA site at the Murchison Radio-astronomy Observatory, Western Australia in 2015 September with a minor impact on the telescope's performance and design. A comparison with the Hydrogen Epoch of Reionization Array antenna is also shown demonstrating the potential use of the SKA1-LOW antenna for the delay-spectrum technique to detect the EoR.

  1. Characterizing the peak in the cosmic microwave background angular power spectrum

    Science.gov (United States)

    Knox; Page

    2000-08-14

    A peak has been unambiguously detected in the cosmic microwave background angular spectrum. Here we characterize its properties with fits to phenomenological models. We find that the TOCO and BOOM/NA data determine the peak location to be in the range 175-243 and 151-259, respectively (at 95% confidence) and determine the peak amplitude to be between approximately 70 and 90 &mgr;K. The peak shape is consistent with inflation-inspired flat, cold dark matter plus cosmological constant models of structure formation with adiabatic, nearly scale invariant initial conditions. It is inconsistent with open models and presents a great challenge to defect models.

  2. Older men are more fatigable than young when matched for maximal power and knee extension angular velocity is unconstrained.

    Science.gov (United States)

    Dalton, Brian H; Power, Geoffrey A; Paturel, Justin R; Rice, Charles L

    2015-06-01

    The underlying factors related to the divergent findings of age-related fatigue for dynamic tasks are not well understood. The purpose here was to investigate age-related fatigability and recovery between a repeated constrained (isokinetic) and an unconstrained velocity (isotonic) task, in which participants performed fatiguing contractions at the velocity (isokinetic) or resistance (isotonic) corresponding with maximal power. To compare between tasks, isotonic torque-power relationships were constructed prior to and following both fatiguing tasks and during short-term recovery. Contractile properties were recorded from 9 old (~75 years) and 11 young (~25 years) men during three testing sessions. In the first session, maximal power was assessed, and sessions 2 and 3 involved an isokinetic or an isotonic concentric fatigue task performed until maximal power was reduced by 40 %. Compared with young, the older men performed the same number of contractions to task failure for the isokinetic task (~45 contractions), but 20 % fewer for the isotonic task (p contraction strength, angular velocity, and power were reduced by ~30, ~13, and ~25 %, respectively, immediately following task failure, and only isometric torque was not recovered fully by 10 min. In conclusion, older men are more fatigable than the young when performing a repetitive maximal dynamic task at a relative resistance (isotonic) but not an absolute velocity (isokinetic), corresponding to maximal power.

  3. A High Galactic Latitude HI 21 cm-line Absorption Survey using the GMRT: II. Results and Interpretation

    Indian Academy of Sciences (India)

    Rekhesh Mohan; K. S. Dwarakanath; G. Srinivasan

    2004-09-01

    We have carried out a sensitive high-latitude (|| > 15°) HI 21 cm-line absorption survey towards 102 sources using the GMRT. With a 3 detection limit in optical depth of ∼ 0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the absorption features is well-fit by two Gaussians centered at lsr ∼ 0 km s−1 with velocity dispersions of 7.6 ± 0.3 km s-1 and 21 ± 4 km s-1 respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) × 1020 cm-2, and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04 ± 0.02, a mean HI column density of (4.3 ± 3.4)× 1019 cm-2, and a mean spin temperature of 125 ± 82 K. The HI column densities of these fast clouds decrease with their increasing random velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic Halo.

  4. H I 21-cm absorption survey of quasar-galaxy pairs: distribution of cold gas around z < 0.4 galaxies

    Science.gov (United States)

    Dutta, R.; Srianand, R.; Gupta, N.; Momjian, E.; Noterdaeme, P.; Petitjean, P.; Rahmani, H.

    2017-02-01

    We present the results from our survey of H I 21-cm absorption, using Giant Metrewave Radio Telescope, Very Large Array and Westerbork Radio Synthesis Telescope, in a sample of 55 z level) between ∫τdv and b, consistent with previous literature results. The covering factor of H I 21-cm absorbers (C21) is estimated to be 0.24^{+0.12}_{-0.08} at b ≤ 15 kpc and 0.06^{+0.09}_{-0.04} at b = 15-35 kpc. ∫τdv and C21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective H I radius. There is also tentative indication that most of the H I 21-cm absorbers could be co-planar with the extended H I discs. No significant dependence of ∫τdv and C21 on galaxy luminosity, stellar mass, colour and star formation rate is found, though the H I 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ˜4) of H I 21-cm absorption in z < 1 damped Lyman-α systems compared to the quasar-galaxy pairs indicates towards small covering factor and patchy distribution of cold gas clouds around low-z galaxies.

  5. Effects Of The Ionosphere On Ground-Based Detection Of The Global 21 CM Signal From The Cosmic Dawn And The Dark Ages

    CERN Document Server

    Datta, Abhirup; Burns, Jack O; Harker, Geraint; Komjathy, Attila; Lazio, T Joseph W

    2014-01-01

    Detection of global HI 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground/space based experiments. The crucial spectral features in the global 21cm signal (turning points) occurs at low radio frequencies < 100 MHz. In addition to the human-generated RFI (Radio Frequency Interference), Earth's ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21cm experiments. Our results indicate that the spectral features in the global 21cm signal below 100 MHz cannot be detected from the ground under even "quiet" night-time ionospheric conditions. Any attempt to calibrate the ionospheric effect will ...

  6. An Analytical and Experimental Investigation of Average Laser Power and Angular Scanning Speed Effects on Laser Tube Bending Process

    Directory of Open Access Journals (Sweden)

    Imhan Khalil Ibraheem

    2017-01-01

    Full Text Available Laser tube bending is a new technique of laser material forming to produce a complex and accurate shape due to its flexibility and high controllability. Moreover, the defects during conventional tube forming such as thinning, wrinkling, spring back and ovalization can be avoided in laser tube bending process, because there is no external force used. In this paper an analytical investigation has been conducted to analyses the effects of average laser power and laser scanning speed on laser tube bending process, the analytical results have been verified experimentally. The model used in this study is in the same trend of the experiment. The results show that the bending angle increased with the increasing of average laser power and decreased with the increasing of angular scanning speed.

  7. Neural-net based calculation of voltage dips at maximum angular swing in direct transient stability analysis [of power systems

    Energy Technology Data Exchange (ETDEWEB)

    Djukanovic, M. (Inst. ' Nikola Tesla' , Belgrade (Yugoslavia)); Sobajic, D.J.; Yohhan Pao (Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Electrical Engineering and Applied Physics Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Computer Engineering and Science AI WARE inc., Cleveland, OH (United States))

    1992-10-01

    In heavily stressed power systems, post-fault transient voltage dips can lead to undesired tripping of industrial drives and large induction motors. The lowest transient voltage dips occur when fault clearing times are less than critical ones. In this paper, we propose a new iterative analytical methodology to obtain more accurate estimates of voltage dips at maximum angular swing in direct transient stability analysis. We also propose and demonstrate the possibility of storing the results of these computations in the associative memory (AM) system, which exhibits remarkable generalization capabilities. Feature-based models stored in the AM can be utilized for fast and accurate prediction of the location, duration and the amount of the worst voltage dips, thereby avoiding the need and cost for lengthy time-domain simulations. Numerical results obtained using the example of the New England power system are presented to illustrate our approach. (Author)

  8. Characterizing the Peak in the Cosmic Microwave Background Angular Power Spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Knox, Lloyd [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States); Page, Lyman [Department of Physics, Princeton University, Princeton, New Jersey (United States)

    2000-08-14

    A peak has been unambiguously detected in the cosmic microwave background angular spectrum. Here we characterize its properties with fits to phenomenological models. We find that the TOCO and BOOM/NA data determine the peak location to be in the range 175-243 and 151-259, respectively (at 95% confidence) and determine the peak amplitude to be between {approx_equal}70 and 90 {mu}K . The peak shape is consistent with inflation-inspired flat, cold dark matter plus cosmological constant models of structure formation with adiabatic, nearly scale invariant initial conditions. It is inconsistent with open models and presents a great challenge to defect models. (c) 2000 The American Physical Society.

  9. Foreground Model and Antenna Calibration Errors in the Measurement of the Sky-Averaged $\\lambda21$ cm Signal at z$\\sim$20

    CERN Document Server

    Bernardi, G; Greenhill, L J

    2014-01-01

    The most promising near-term observable of the cosmic dark age prior to widespread reionization ($z\\sim15-200$) is the sky-averaged $\\lambda21$ cm background arising from hydrogen in the intergalactic medium. Though an individual antenna could in principle detect the line signature, data analysis must separate foregrounds that are orders of magnitude brighter than the $\\lambda21$ cm background (but that are anticipated to vary monotonically and gradually with frequency). Using more physically motivated models for foregrounds than in previous studies, we show that the intrinsic "spectral smoothness" of the foregrounds is likely not a concern, and that data analysis for an ideal antenna should be able to detect the $\\lambda21$ cm signal after deprojecting a $\\sim 5^{\\rm th}$ order polynomial in $\\log \

  10. The Effects of the Ionosphere on Ground-based Detection of the Global 21 cm Signal from the Cosmic Dawn and the Dark Ages

    Science.gov (United States)

    Datta, Abhirup; Bradley, Richard; Burns, Jack O.; Harker, Geraint; Komjathy, Attila; Lazio, T. Joseph W.

    2016-11-01

    Detection of the global H i 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground-/space-based experiments. The crucial spectral features in the global 21 cm signal (turning points) occur at low radio frequencies ≲ 100 {{MHz}}. In addition to the human-generated radio frequency interference, Earth’s ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption, and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21 cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21 cm experiments. The fluctuations in the ionosphere are influenced by solar activity with flicker noise characteristics. The same characteristics are reflected in the ionospheric corruption to any radio signal passing through the ionosphere. As a result, any ground-based observations of the faint global 21 cm signal are corrupted by flicker noise (or 1/f noise, where f is the dynamical frequency) which scales as {ν }-2 (where ν is the frequency of radio observation) in the presence of a bright galactic foreground (\\propto {ν }-s, where s is the radio spectral index). Hence, the calibration of the ionosphere for any such experiment is critical. Any attempt to calibrate the ionospheric effects will be subject to the inaccuracies in the current ionospheric measurements using Global Positioning System (GPS) ionospheric measurements, riometer measurements, ionospheric soundings, etc. Even considering an optimistic improvement in the accuracy of GPS-total electron content measurements, we conclude that Earth’s ionosphere poses a significant challenge in the absolute detection of the global 21 cm signal below 100 MHz.

  11. Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes

    Science.gov (United States)

    Planck Collaboration; Adam, R.; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Guillet, V.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hivon, E.; Hobson, M.; Holmes, W. A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Krachmalnicoff, N.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Remazeilles, M.; Renault, C.; Renzi, A.; Ricciardi, S.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rouillé d'Orfeuil, B.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Soler, J. D.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vibert, L.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Watson, R.; Wehus, I. K.; White, M.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-02-01

    The polarized thermal emission from diffuse Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100 GHz. In this paper we exploit the uniqueness of the Planck HFI polarization data from 100 to 353 GHz to measure the polarized dust angular power spectra CℓEE and CℓBB over the multipole range 40 <ℓ< 600 well away from the Galactic plane. These measurements will bring new insights into interstellar dust physics and allow a precise determination of the level of contamination for CMB polarization experiments. Despite the non-Gaussian and anisotropic nature of Galactic dust, we show that general statistical properties of the emission can be characterized accurately over large fractions of the sky using angular power spectra. The polarization power spectra of the dust are well described by power laws in multipole, Cℓ ∝ ℓα, with exponents αEE,BB = -2.42 ± 0.02. The amplitudes of the polarization power spectra vary with the average brightness in a way similar to the intensity power spectra. The frequency dependence of the dust polarization spectra is consistent with modified blackbody emission with βd = 1.59 and Td = 19.6 K down to the lowest Planck HFI frequencies. We find a systematic difference between the amplitudes of the Galactic B- and E-modes, CℓBB/CℓEE = 0.5. We verify that these general properties are preserved towards high Galactic latitudes with low dust column densities. We show that even in the faintest dust-emitting regions there are no "clean" windows in the sky where primordial CMB B-mode polarization measurements could be made without subtraction of foreground emission. Finally, we investigate the level of dust polarization in the specific field recently targeted by the BICEP2 experiment. Extrapolation of the Planck 353 GHz data to 150 GHz gives a dust power 𝒟ℓBB ≡ ℓ(ℓ+1)CℓBB/(2π) of 1.32 × 10-2 μKCMB2 over the multipole range

  12. 21-cm Observations with the NASA ADAS 18-meter Antenna System: Baseline Astronomical Observations and Measurements of Performance Characteristics

    Science.gov (United States)

    Malphrus, B. K.; Combs, M. S.; Kruth, J.

    2001-12-01

    Herein we report astronomical observations made with the NASA Advanced Data Acquisition System (ADAS). The NASA ADAS antenna, located at NASA Goddard Spaceflight Center's Wallops Flight Facility, Virginia, is an 18-meter X-band antenna system that has been primarily used for satellite tracking and served as the telecommunication station for the NASA IUE satellite until ca. 1997. A joint NASA-Morehead State University (MSU)-Kentucky NSF EPSCoR venture has been initiated to upgrade and relocate the antenna system to MSU's Astrophysics Laboratory where it will provide a research instrument and active laboratory for undergraduate students as well as be engaged in satellite tracking missions. As part of the relocation efforts, many systems will be upgraded including replacement of a hydrostatic azimuth bearing with a high-precision electromechanical bearing, a new servo system, and Ku-capable reflector surface. It is widely believed that there are still contributions that small aperture centimeter-wave instruments can make utilizing three primary observing strategies: 1.) longitudinal studies of RF variations in cosmic phenomena, 2.) surveys of large areas of sky, and 3.) fast reactions to transient phenomena. MSU faculty and staff along with NASA engineers re-outfitted the ADAS system with RF systems and upgraded servo controllers during the spring and summer of 2001. Empirical measurements of primary system performance characteristics were made including G/T (at S- and L bands), noise figures, pointing and tracking accuracies, and drive speeds and accelerations. Baseline astronomical observations were made with the MSU L-band receiver using a 6 MHz bandwidth centered at 1420 MHz (21-cm) and observing over a range of frequencies (up to 2.5 MHz, tunable over the 6 MHz window) with a 2048-channel back-end spectrometer, providing up to 1 KHz frequency resolution. Baseline observations of radio sources herein reported include Cygnus A, 3C 157, 3C 48 and the Andromeda

  13. Does use of a powered ankle-foot prosthesis restore whole-body angular momentum during walking at different speeds?

    Science.gov (United States)

    D'Andrea, Susan; Wilhelm, Natalie; Silverman, Anne K; Grabowski, Alena M

    2014-10-01

    Whole-body angular momentum (H) influences fall risk, is tightly regulated during walking, and is primarily controlled by muscle force generation. People with transtibial amputations using passive-elastic prostheses typically have greater H compared with nonamputees. (1) Do people with unilateral transtibial amputations using passive-elastic prostheses have greater sagittal and frontal plane H ranges of motion during walking compared with nonamputees and compared with using powered prostheses? (2) Does use of powered ankle-foot prostheses result in equivalent H ranges in all planes of motion compared with nonamputees during walking as a result of normative prosthetic ankle power generation? Eight patients with a unilateral transtibial amputation and eight nonamputees walked 0.75, 1.00, 1.25, 1.50, and 1.75 m/s while we measured kinematics and ground reaction forces. We calculated H for participants using their passive-elastic prosthesis and a powered ankle-foot prosthesis and for nonamputees at each speed. Patients using passive-elastic prostheses had 32% to 59% greater sagittal H ranges during the affected leg stance phase compared with nonamputees at 1.00 to 1.75 m/s (p passive-elastic prostheses had 5% and 9% greater sagittal H ranges compared with using powered prostheses at 1.25 and 1.50 m/s, respectively (p passive-elastic prostheses had 29% and 17% greater frontal H ranges at 0.75 and 1.50 m/s, respectively, compared with nonamputees (p walking speeds when using powered compared with passive-elastic prostheses. Our results support the hypothesis that an ankle-foot prosthesis capable of providing net positive work during the stance phase of walking reduces sagittal plane H; future studies are needed to validate our biomechanical findings with larger numbers of patients and should determine whether powered prostheses can decrease the risk of falls in patients with a transtibial amputation.

  14. Normalization of the Matter Power Spectrum via Higher-Order Angular Correlations of Luminous Red Galaxies

    CERN Document Server

    Ross, Ashley J; Myers, Adam D

    2008-01-01

    We present a novel technique to measure $\\sigma_8$, by measuring the dependence of the second-order bias of a density field on $\\sigma_8$ using two separate techniques. Each technique employs area-averaged angular correlation functions ($\\bar{\\omega}_N$), one relying on the shape of $\\bar{\\omega}_2$, the other relying on the amplitude of $s_3$ ($s_3 =\\bar{\\omega}_3/\\bar{\\omega}_2^2$). We confirm the validity of the method by testing it on a mock catalog drawn from Millennium Simulation data and finding $\\sigma_8^{measured}- \\sigma_8^{true} = -0.002 \\pm 0.062$. We create a catalog of photometrically selected LRGs from SDSS DR5 and separate it into three distinct data sets by photometric redshift, with median redshifts of 0.47, 0.53, and 0.61. Measurements of $c_2$, and $\\sigma_8$ are made for each data set, assuming flat geometry and WMAP3 best-fit priors on $\\Omega_m$, $h$, and $\\Gamma$. We find, with increasing redshfit, $c_2 = 0.09 \\pm 0.04$, $0.09 \\pm 0.05$, and $0.09 \\pm 0.03$ and $\\sigma_8 = 0.78 \\pm 0.0...

  15. Planck intermediate results XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes

    DEFF Research Database (Denmark)

    Adam, R.; Ade, P. A. R.; Aghanim, N.

    2016-01-01

    The polarized thermal emission from diffuse Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100 GHz. In this paper we exploit the uniqueness of the Planck HFI polarization data from 100 to 353 GHz...... to measure the polarized dust angular power spectra C-l(EE) and C-l(BB) over the multipole range 40 CMB polarization...... dust column densities. We show that even in the faintest dust-emitting regions there are no "clean" windows in the sky where primordial CMB B-mode polarization measurements could be made without subtraction of foreground emission. Finally, we investigate the level of dust polarization in the specific...

  16. CMB Lensing Power Spectrum Biases from Galaxies and Clusters using High-angular Resolution Temperature Maps

    CERN Document Server

    van Engelen, A; Sehgal, N; Holder, G P; Zahn, O; Nagai, D

    2013-01-01

    The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to ACT and SPT. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on sigma_8 and an uncertainty on the total neutrino mass of approximately 50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 15...

  17. On Angular Momentum

    Science.gov (United States)

    Schwinger, J.

    1952-01-26

    The commutation relations of an arbitrary angular momentum vector can be reduced to those of the harmonic oscillator. This provides a powerful method for constructing and developing the properties of angular momentum eigenvectors. In this paper many known theorems are derived in this way, and some new results obtained. Among the topics treated are the properties of the rotation matrices; the addition of two, three, and four angular momenta; and the theory of tensor operators.

  18. Impact of Scale Dependent Bias and Nonlinear Structure Growth on the ISW Effect: Angular Power Spectra

    CERN Document Server

    Smith, Robert E; Seljak, Uros

    2009-01-01

    We investigate the impact of nonlinear evolution of the gravitational potentials in the LCDM model on the Integrated Sachs-Wolfe (ISW) contribution to the CMB temperature power spectrum, and on the cross-power spectrum of the CMB and a set of biased tracers of the mass. We use an ensemble of N-body simulations to directly follow the potentials and compare results to perturbation theory (PT). The predictions from PT match the results to high precision for k100 the departures are more significant, however the CMB signal is more than a factor 10^3 larger at this scale. Nonlinear ISW effects therefore play no role in shaping the CMB power spectrum for l<1500. We analyze the CMB--density tracer cross-spectrum using simulations and renormalized bias PT, and find good agreement. The usual assumption is that nonlinear evolution enhances the growth of structure and counteracts linear ISW on small scales, leading to a change in sign of the CMB-LSS cross-spectrum at small scales. However, PT analysis suggests that th...

  19. CMB lensing power spectrum biases from galaxies and clusters using high-angular resolution temperature maps

    Energy Technology Data Exchange (ETDEWEB)

    Van Engelen, A.; Sehgal, N. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Bhattacharya, S. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Holder, G. P. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Zahn, O. [Berkeley Center for Cosmological Physics, Department of Physics, University of California, and Lawrence Berkeley National Labs, Berkeley, CA 94720 (United States); Nagai, D. [Department of Physics, Department of Astronomy and Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06520 (United States)

    2014-05-01

    The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to the Atacama Cosmology Telescope and the South Pole Telescope. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on σ{sub 8} and an uncertainty on the total neutrino mass of ∼50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with masses above M {sub vir} = 10{sup 14} M {sub ☉}. To achieve such percent level bias, we find that only modes up to a maximum multipole of l {sub max} ∼ 2500 should be included in the lensing reconstruction. We also discuss ways to minimize additional bias induced by such aggressive foreground masking by, for example, exploring a two-step masking and in-painting algorithm.

  20. Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes

    CERN Document Server

    Adam, R; Aghanim, N; Arnaud, M; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Bartlett, J G; Bartolo, N; Battaner, E; Benabed, K; Benoit-Lévy, A; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Boulanger, F; Bracco, A; Bucher, M; Burigana, C; Butler, R C; Calabrese, E; Cardoso, J -F; Catalano, A; Challinor, A; Chamballu, A; Chary, R -R; Chiang, H C; Christensen, P R; Clements, D L; Colombi, S; Colombo, L P L; Combet, C; Couchot, F; Coulais, A; Curto, A; Cuttaia, F; Danese, L; Davies, R D; Davis, R J; de Bernardis, P; de Zotti, G; Delabrouille, J; Delouis, J -M; Désert, F -X; Dickinson, C; Diego, J M; Dolag, K; Dole, H; Donzelli, S; Doré, O; Douspis, M; Ducout, A; Dunkley, J; Dupac, X; Efstathiou, G; Elsner, F; Enßlin, T A; Eriksen, H K; Falgarone, E; Finelli, F; Forni, O; Frailis, M; Fraisse, A A; Franceschi, E; Frejsel, A; Galeotta, S; Galli, S; Ganga, K; Ghosh, T; Giard, M; Giraud-Héraud, Y; Gjerløw, E; González-Nuevo, J; Górski, K M; Gratton, S; Gregorio, A; Gruppuso, A; Guillet, V; Hansen, F K; Hanson, D; Harrison, D L; Helou, G; Henrot-Versillé, S; Hernández-Monteagudo, C; Herranz, D; Hivon, E; Holmes, W A; Huffenberger, K M; Hurier, G; Jaffe, A H; Jaffe, T R; Jewell, J; Jones, W C; Juvela, M; Keihänen, E; Keskitalo, R; Kisner, T S; Kneissl, R; Knoche, J; Knox, L; Krachmalnicoff, N; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Lasenby, A; Lattanzi, M; Lawrence, C R; Leahy, J P; Leonardi, R; Lesgourgues, J; Levrier, F; Liguori, M; Lilje, P B; Linden-Vørnle, M; López-Caniego, M; Lubin, P M; Macías-Pérez, J F; Maffei, B; Maino, D; Mandolesi, N; Mangilli, A; Maris, M; Martin, P G; Martínez-González, E; Masi, S; Matarrese, S; Mazzotta, P; Melchiorri, A; Mendes, L; Mennella, A; Migliaccio, M; Mitra, S; Miville-Deschênes, M -A; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Moss, A; Munshi, D; Murphy, J A; Naselsky, P; Nati, F; Natoli, P; Netterfield, C B; Nørgaard-Nielsen, H U; Noviello, F; Novikov, D; Novikov, I; Pagano, L; Pajot, F; Paladini, R; Paoletti, D; Partridge, B; Pasian, F; Patanchon, G; Pearson, T J; Perdereau, O; Perotto, L; Perrotta, F; Pettorino, V; Piacentini, F; Piat, M; Pierpaoli, E; Pietrobon, D; Plaszczynski, S; Pointecouteau, E; Polenta, G; Ponthieu, N; Popa, L; Pratt, G W; Prunet, S; Puget, J -L; Rachen, J P; Reach, W T; Rebolo, R; Remazeilles, M; Renault, C; Renzi, A; Ricciardi, S; Ristorcelli, I; Rocha, G; Rosset, C; Rossetti, M; Roudier, G; d'Orfeuil, B Rouillé; Rubiño-Martín, J A; Rusholme, B; Sandri, M; Santos, D; Savelainen, M; Savini, G; Scott, D; Soler, J D; Spencer, L D; Stolyarov, V; Stompor, R; Sudiwala, R; Sunyaev, R; Sutton, D; Suur-Uski, A -S; Sygnet, J -F; Tauber, J A; Terenzi, L; Tomasi, M; Tristram, M; Tucci, M; Tuovinen, J; Valenziano, L; Valiviita, J; Van Tent, B; Vibert, L; Vielva, P; Villa, F; Wade, L A; Wandelt, B D; Watson, R; Wehus, I K; White, M; White, S D M; Yvon, D; Zacchei, A; Zonca, A

    2016-01-01

    The polarized thermal emission from Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100GHz. We exploit the Planck HFI polarization data from 100 to 353GHz to measure the dust angular power spectra $C_\\ell^{EE,BB}$ over the range $40<\\ell<600$. These will bring new insights into interstellar dust physics and a precise determination of the level of contamination for CMB polarization experiments. We show that statistical properties of the emission can be characterized over large fractions of the sky using $C_\\ell$. For the dust, they are well described by power laws in $\\ell$ with exponents $\\alpha^{EE,BB}=-2.42\\pm0.02$. The amplitudes of the polarization $C_\\ell$ vary with the average brightness in a way similar to the intensity ones. The dust polarization frequency dependence is consistent with modified blackbody emission with $\\beta_d=1.59$ and $T_d=19.6$K. We find a systematic ratio between the amplitudes of ...

  1. H I Structure and Topology of the Galaxy Revealed by the I-GALFA H I 21-cm Line Survey

    Science.gov (United States)

    Koo, Bon-Chul; Park, G.; Cho, W.; Gibson, S. J.; Kang, J.; Douglas, K. A.; Peek, J. E. G.; Korpela, E. J.; Heiles, C. E.

    2011-05-01

    The I-GALFA survey mapping all the H I in the inner Galactic disk visible to the Arecibo 305m telescope within 10 degrees of the Galactic plane (longitudes of 32 to 77 degrees at b = 0) completed observations in 2009 September and will soon be made publicly available. The high (3.4 arcmin) resolution and tremendous sensitivity of the survey offer a great opportunity to observe the fine details of H I both in the inner and in the far outer Galaxy. The reduced HI column density maps show that the HI structure is highly filamentary and clumpy, pervaded by shell-like structures, vertical filaments, and small clumps. By inspecting individual maps, we have found 36 shell candidates of angular sizes ranging from 0.4 to 12 degrees, half of which appear to be expanding. In order to characterize the filamentary/clumpy morphology of the HI structure, we have carried out statistical analyses of selected areas representing the spiral arms in the inner and outer Galaxy. Genus statistics that can distinguish the ``meatball'' and ``swiss-cheese'' topologies show that the HI topology is clump-like in most regions. The two-dimensional Fourier analysis further shows the HI structures are filamentary and mainly parallel to the plane in the outer Galaxy. We also examine the level-crossing statistics, the results of which are described in detail in an accompanying poster by Park et al.

  2. High-power Bessel beams with orbital angular momentum in the terahertz range

    Science.gov (United States)

    Choporova, Yu. Yu.; Knyazev, B. A.; Kulipanov, G. N.; Pavelyev, V. S.; Scheglov, M. A.; Vinokurov, N. A.; Volodkin, B. O.; Zhabin, V. N.

    2017-08-01

    In this paper, we have performed experimental, analytical, and numerical studies of beams with topological charges of ±1 and ±2 formed by silicon binary phase axicons (BPAs) with spiral zone structures. The axicons were illuminated with the Novosibirsk free electron laser radiation (a continuous stream of 100-ps pulses at f =5.6 MHz). The cw power of the beams produced reached 30 W and can by doubled via antireflection coating of the axicons. The intensity distribution in the beam cross sections was in good agreement with the Bessel functions and was kept constant within a distance of about L /r ≈190 and 100, where the first ring radii of the beams r were 0.9 and 1.5 mm for the Bessel beams of the first and second orders, respectively. Although the characteristics of the beams (Bessel cross section, "diffraction-free" propagation, self-recovery after passing obstacles, and randomly inhomogeneous media) corresponded to the properties of ideal Bessel beams, their spatial Fourier spectrum (the image in the focal plane of the lens) was, instead of an ideal ring, intertwined segments of arcs with phases shifted by π , the number of which was equal to the double value of the topological charge. This feature can be used, for example, in a demultiplexing unit of a free vortex-wave communication system or for identification of beam topological charge. We also revisited Young's double-slit diffraction and rotation of beams obstructed by a half-plane, previously applied to Laguerre-Gaussian beam characterization, in the case of the Bessel beams. The Young diffraction pattern demonstrated in this case a complicated intensity-phase distribution. It was shown that the Bessel beams formed by BPAs have two important advantages, which can be used in applications, in comparison with other methods of generation, e.g., a combination of an axicon lens with a spiral phase plate. Although the phase jumps of the axicons are designed for a determined wavelength (141 μ m in our case

  3. Giant Metrewave Radio Telescope detection of associated H I 21-cm absorption at z = 1.2230 towards TXS 1954+513

    Science.gov (United States)

    Aditya, J. N. H. S.; Kanekar, Nissim; Prochaska, J. Xavier; Day, Brandon; Lynam, Paul; Cruz, Jocelyn

    2017-03-01

    We have used the 610-MHz receivers of the Giant Metrewave Radio Telescope (GMRT) to detect associated H I 21-cm absorption from the z = 1.2230 blazar TXS 1954+513. The GMRT H I 21-cm absorption is likely to arise against either the milliarcsecond-scale core or the one-sided milliarcsecond-scale radio jet, and is blueshifted by ≈328 km s-1 from the blazar redshift. This is consistent with a scenario in which the H I cloud giving rise to the absorption is being driven outwards by the radio jet. The integrated H I 21-cm optical depth is (0.716 ± 0.037) km s-1, implying a high H I column density, N_{H I} = (1.305 ± 0.067) × ({ T_s/100 K}) × 10^{20} cm-2, for an assumed H I spin temperature of 100 K. We use Nickel Telescope photometry of TXS 1954+513 to infer a high rest-frame 1216 Å luminosity of (4.1 ± 1.2) × 1023 W Hz-1. The z = 1.2230 absorber towards TXS 1954+513 is only the fifth case of a detection of associated H I 21-cm absorption at z > 1, and is also the first case of such a detection towards an active galactic nucleus (AGN) with a rest-frame ultraviolet (UV) luminosity ≫1023 W Hz-1, demonstrating that neutral hydrogen can survive in AGN environments in the presence of high UV luminosities.

  4. HI 21cm emission from the sub-damped Lyman-alpha absorber at z=0.0063 towards PG1216+069

    CERN Document Server

    Chengalur, Jayaram N; Salter, C J; Kanekar, N; Momjian, E; Keeney, B A; Stocke, J T

    2015-01-01

    We present HI 21cm emission observations of the z ~ 0.00632 sub-damped Lyman-alpha absorber (sub-DLA) towards PG1216+069 made using the Arecibo Telescope and the Very Large Array (VLA). The Arecibo 21cm spectrum corresponds to an HI mass of ~ 3.2x10^7 solar masses, two orders of magnitude smaller than that of a typical spiral galaxy. This is surprising since in the local Universe the cross-section for absorption at high HI column densities is expected to be dominated by spirals. The 21cm emission detected in the VLA spectral cube has a low signal-to-noise ratio, and represents only half the total flux seen at Arecibo. Emission from three other sources is detected in the VLA observations, with only one of these sources having an optical counterpart. This group of HI sources appears to be part of complex "W", believed to lie in the background of the Virgo cluster. While several HI cloud complexes have been found in and around the Virgo cluster, it is unclear whether the ram pressure and galaxy harassment proces...

  5. Hi Shells and Supershells in the I-GALFA Hi 21-cm Line Survey: I. Fast-Expanding Hi Shells Associated with Supernova Remnants

    CERN Document Server

    Park, Geumsook; Gibson, Steven J; Kang, Ji-hyun; Lane, Daria C; Douglas, Kevin A; Peek, Joshua E G; Korpela, Eric J; Heiles, Carl E; Newton, Jonathan H

    2013-01-01

    We search for fast-expanding Hi shells associated with Galactic supernova remnants (SNRs) in the longitude range l \\approx 32\\arcdeg to 77\\arcdeg using 21-cm line data from the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) Hi survey. Among the 39 known Galactic SNRs in this region, we find such Hi shells in four SNRs: W44, G54.4-0.3, W51C, and CTB 80. All four were previously identified in low-resolution surveys, and three of those (excluding G54.4-0.3) were previously studied with the Arecibo telescope. A remarkable new result, however, is the detection of Hi emission at both very high positive and negative velocities in W44 from the receding and approaching parts of the Hi expanding shell, respectively. This is the first detection of both sides of an expanding shell associated with an SNR in Hi 21-cm emission. The high-resolution I-GALFA survey data also reveal a prominent expanding Hi shell with high circular symmetry associated with G54.4-0.3. We explore the physical characteristics of four SNRs and di...

  6. The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds

    CERN Document Server

    Goldsmith, P F; Krco, M; Goldsmith, Paul F.; Li, Di; Krco, Marko

    2006-01-01

    We have investigated the time scale for formation of molecular clouds by examining the conversion of HI to H2 using a time-dependent model. H2 formation on dust grains and cosmic ray and photo destruction are included in one-dimensional model slab clouds which incorporate time-independent density and temperature distributions. We calculate 21cm spectral line profiles seen in absorption against a background provided by general Galactic HI emission, and compare the model spectra with HI Narrow Self-Absorption, or HINSA, profiles absorbed in a number of nearby molecular clouds. The time evolution of the HI and H2 densities is dramatic, with the atomic hydrogen disappearing in a wave propagating from the central, denser regions which have a shorter H2 formation time scale, to the edges, where the density is lower and the time scale for H2 formation longer. The model 21cm spectra are characterized by very strong absorption at early times, when the HI column density through the model clouds is extremely large. The ...

  7. Power Stroke Angular Velocity Profiles of Archaeal A-ATP Synthase Versus Thermophilic and Mesophilic F-ATP Synthase Molecular Motors.

    Science.gov (United States)

    Sielaff, Hendrik; Martin, James; Singh, Dhirendra; Biuković, Goran; Grüber, Gerhard; Frasch, Wayne D

    2016-12-02

    The angular velocities of ATPase-dependent power strokes as a function of the rotational position for the A-type molecular motor A3B3DF, from the Methanosarcina mazei Gö1 A-ATP synthase, and the thermophilic motor α3β3γ, from Geobacillus stearothermophilus (formerly known as Bacillus PS3) F-ATP synthase, are resolved at 5 μs resolution for the first time. Unexpectedly, the angular velocity profile of the A-type was closely similar in the angular positions of accelerations and decelerations to the profiles of the evolutionarily distant F-type motors of thermophilic and mesophilic origins, and they differ only in the magnitude of their velocities. M. mazei A3B3DF power strokes occurred in 120° steps at saturating ATP concentrations like the F-type motors. However, because ATP-binding dwells did not interrupt the 120° steps at limiting ATP, ATP binding to A3B3DF must occur during the catalytic dwell. Elevated concentrations of ADP did not increase dwells occurring 40° after the catalytic dwell. In F-type motors, elevated ADP induces dwells 40° after the catalytic dwell and slows the overall velocity. The similarities in these power stroke profiles are consistent with a common rotational mechanism for A-type and F-type rotary motors, in which the angular velocity is limited by the rotary position at which ATP binding occurs and by the drag imposed on the axle as it rotates within the ring of stator subunits.

  8. The angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its Dark Matter interpretation

    CERN Document Server

    Fornasa, Mattia; Zavala, Jesus; Gaskins, Jennifer M; Sanchez-Conde, Miguel A; Gomez-Vargas, German; Komatsu, Eiichiro; Linden, Tim; Prada, Francisco; Zandanel, Fabio; Morselli, Aldo

    2016-01-01

    The isotropic gamma-ray background arises from the contribution of unresolved sources, including members of confirmed source classes and proposed gamma-ray emitters such as the radiation induced by dark matter annihilation and decay. Clues about the properties of the contributing sources are imprinted in the anisotropy characteristics of the gamma-ray background. We use 81 months of Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a measurement of the anisotropy angular power spectrum of the gamma-ray background. We analyze energies between 0.5 and 500 GeV, extending the range considered in the previous measurement based on 22 months of data. We also compute, for the first time, the cross-correlation angular power spectrum between different energy bins. We find that the derived angular spectra are compatible with being Poissonian, i.e. constant in multipole. Moreover, the energy dependence of the anisotropy suggests that the signal is due to two populations of sources, contributing, resp...

  9. Regression relationships of landing height with ground reaction forces, knee flexion angles, angular velocities and joint powers during double-leg landing.

    Science.gov (United States)

    Yeow, C H; Lee, Peter V S; Goh, James C H

    2009-10-01

    Ground reaction forces (GRF), knee flexion angles, angular velocities and joint powers are unknown at large landing heights, which are infeasible for laboratory testing. However, this information is important for understanding lower extremity injury mechanisms. We sought to determine regression relationships of landing height with these parameters during landing so as to facilitate estimation of these parameters at large landing heights. Five healthy male subjects performed landing tasks from heights of 0.15-1.05 m onto a force-plate. Motion capture system was used to obtain knee flexion angles during landing via passive markers placed on the lower body. An iterative regression model, involving simple linear/exponential/natural logarithmic functions, was used to fit regression equations to experimental data. Peak GRF followed an exponential regression relationship (R(2)=0.90-0.99, p<0.001; power=0.987-0.998). Peak GRF slope and impulse also had an exponential relationship (R(2)=0.90-0.96, p<0.001; power=0.980-0.997 and R(2)=0.90-0.99, p<0.001; power=0.990-1.000 respectively) with landing height. Knee flexion angle at initial contact and at peak GRF had an inverse-exponential regression relationship (R(2)=0.81-0.99, p<0.001-p=0.006; power=0.834-0.978 and R(2)=0.84-0.97, p<0.001-p=0.004; power=0.873-0.999 respectively). There was also an inverse-exponential relationship between peak knee flexion angular velocity and landing height (R(2)=0.86-0.96, p<0.001; power=0.935-0.994). Peak knee joint power demonstrated a substantial linear relationship (R(2)=0.98-1.00, p<0.001; power=0.990-1.000). The parameters analyzed in this study are highly dependent on landing height. The exponential increase in peak GRF parameters and the relatively slower increase in knee flexion angles, angular velocities and joint power may synergistically lead to an exacerbated lower extremity injury risk at large landing heights.

  10. Angular Momentum

    Science.gov (United States)

    Shakur, Asif; Sinatra, Taylor

    2013-01-01

    The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in…

  11. THE ANGULAR POWER SPECTRUM OF DUST-OBSCURED GALAXIES AND ITS IMPACT ON SUNYAEV ZEL'DOVICH STUDIES

    Directory of Open Access Journals (Sweden)

    A. A. Montaña

    2011-01-01

    Full Text Available En este trabajo medimos el espectro angular de potencias de la población de galaxias milimétricas (SMGs a partir de observaciones a 1.1 mm realizadas con la cámara AzTEC en el Atacama Submillimeter Telescope Experiment (ASTE y el James Clerk Maxwell Telecope (JCMT. La muestra de campos observados nos permite comparar el espectro angular de potencias de las SMGs medido en la dirección de regiones del Universo sin sesgo y otras sobre densas. Nuestras mediciones permiten acotar el impacto que tiene la población de SMGs en mediciones del espectro de potencias de las fluctuaciones primarias y secundarias del fondo cósmico de radiación de microndas (CMB, que actualmente están siendo medidas por una nueva generación de experimentos con resoluciones espaciales del orden de minutos de arco y que operan a longitudes de onda milimétricas.

  12. Constraints on the neutrino parameters by future cosmological 21cm line and precise CMB polarization observations (PhD thesis, The Graduate University for Advanced Studies (SOKENDAI))

    CERN Document Server

    Oyama, Yoshihiko

    2015-01-01

    Observations of the 21 cm line radiation coming from the epoch of reionization have a great capacity to study the cosmological growth of the Universe. Also, CMB polarization produced by gravitational lensing has a large amount of information about the growth of matter fluctuations at late time. In this thesis, we investigate their sensitivities to the impact of neutrino property on the growth of density fluctuations, such as the total neutrino mass, the neutrino mass hierarchy, the effective number of neutrino species (extra radiation), and the lepton asymmetry of our Universe. We will show that by combining the precise CMB polarization observations with Square Kilometer Array (SKA) we can measure the impact of non-zero neutrino mass on the growth of density fluctuation, and determine the neutrino mass hierarchy at 2 sigma level if the total neutrino mass is smaller than 0.1 eV. Additionally, we will show that by using these combinations we can constrain the lepton asymmetry better than big-bang nucleosynthes...

  13. The LOFAR EoR Data Model: (I) Effects of Noise and Instrumental Corruptions on the 21-cm Reionization Signal-Extraction Strategy

    CERN Document Server

    Labropoulos, Panagiotis; Jelic, Vibor; Yatawatta, Sarod; Thomas, Rajat M; Bernardi, Gianni; Brentjens, Michiel; de Bruyn, Ger; Ciardi, Benedetta; Harker, Geraint; Offringa, Andre; Pandey, Vishambar N; Schaye, Joop; Zaroubi, Saleem

    2009-01-01

    A number of experiments are set to measure the 21-cm signal of neutral hydrogen from the Epoch of Reionization (EoR). The common denominator of these experiments are the large data sets produced, contaminated by various instrumental effects, ionospheric distortions, RFI and strong Galactic and extragalactic foregrounds. In this paper, the first in a series, we present the Data Model that will be the basis of the signal analysis for the LOFAR (Low Frequency Array) EoR Key Science Project (LOFAR EoR KSP). Using this data model we simulate realistic visibility data sets over a wide frequency band, taking properly into account all currently known instrumental corruptions (e.g. direction-dependent gains, complex gains, polarization effects, noise, etc). We then apply primary calibration errors to the data in a statistical sense, assuming that the calibration errors are random Gaussian variates at a level consistent with our current knowledge based on observations with the LOFAR Core Station 1. Our aim is to demons...

  14. Revisiting the radio interferometer measurement equation. III. Addressing direction-dependent effects in 21 cm WSRT observations of 3C 147

    CERN Document Server

    Smirnov, Oleg M

    2011-01-01

    Papers I and II of this series have extended the radio interferometry measurement equation (RIME) formalism to the full-sky case, and provided a RIME-based description of calibration and the problem of direction-dependent effects (DDEs). This paper aims to provide a practical demonstration of a RIME-based approach to calibration, via an example of extremely high-dynamic range calibration of WSRT observations of 3C 147 at 21 cm, with full treatment of DDEs. A version of the RIME incorporating differential gains has been implemented in MeqTrees, and applied to the 3C 147 data. This was used to perform regular selfcal, then solve for interferometer-based errors and for differential gains. The resulting image of the field around 3C 147 is thermal noise-limited, has a very high dynamic range (1.6 million), and none of the off-axis artefacts that plague regular selfcal. The differential gain solutions show a high signal-to-noise ratio, and may be used to extract information on DDEs and errors in the sky model. The ...

  15. Systematic effects in large-scale angular power spectra of photometric quasars and implications for constraining primordial nongaussianity

    CERN Document Server

    Pullen, Anthony R

    2013-01-01

    Primordial non-Gaussianity of local type is predicted to lead to enhanced halo clustering on very large scales. Photometric quasars, which can be seen from cosmological redshifts z>2 even in wide-shallow optical surveys, are promising tracers for constraining non-Gaussianity using this effect. However, large-scale systematics can also mimic this signature of non-Gaussianity. In order to assess the contribution of systematic effects, we cross-correlate overdensity maps of photometric quasars from the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) in different redshift ranges. We find that the maps are significantly correlated on large scales, even though we expect the angular distributions of quasars at different redshifts to be uncorrelated. This implies that the quasar maps are contaminated with systematic errors. We investigate the use of external templates that provide information on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the quasar data. W...

  16. Older men are more fatigable than young when matched for maximal power and knee extension angular velocity is unconstrained

    OpenAIRE

    Brian H. Dalton; Geoffrey A Power; Paturel, Justin R.; Rice, Charles L.

    2015-01-01

    The underlying factors related to the divergent findings of age-related fatigue for dynamic tasks are not well understood. The purpose here was to investigate age-related fatigability and recovery between a repeated constrained (isokinetic) and an unconstrained velocity (isotonic) task, in which participants performed fatiguing contractions at the velocity (isokinetic) or resistance (isotonic) corresponding with maximal power. To compare between tasks, isotonic torque–power relationships were...

  17. Multiple Peaks in the Angular Power Spectrum of the CosmicMicrowave Background: Significance and Consequences for Cosmology

    Energy Technology Data Exchange (ETDEWEB)

    de Bernardis, P.; Ade, P.A.R.; Bock, J.J.; Bond, J.R.; Borrill,J.; Boscaleri, A.; Coble, K.; Contaldi, C.R.; Crill, B.P.; De Troia, G.; Farese, P.; Ganga, K.; Giacometti, M.; Hivon, E.; Hristov, V.V.; Iacoangeli, A.; Jaffe, A.H.; Jones, W.C.; Lange, A.E.; Martinis, L.; Masi, S.; Mason, P.; Mauskopf, P.D.; Melchiorri, A.; Montroy, T.; Netterfield, C.B.; Pascale, E.; Piacentini, F.; Pogosyan, D.; Polenta,G.; Pongetti, F.; Prunet, S.; Romeo, G.; Ruhl, J.E.; Scaramuzzi, F.

    2001-05-17

    Three peaks and two dips have been detected in the power spectrum of the cosmic microwave background from the BOOMERANG experiment, at {ell} {approx} 210, 540, 840 and {ell} {approx} 420, 750, respectively. Using model-independent analyses, we find that all five features are statistically significant and we measure their location and amplitude. These are consistent with the adiabatic inflationary model. We also calculate the mean and variance of the peak and dip locations and amplitudes in a large 7-dimensional parameter space of such models, which gives good agreement with the model-independent estimates, and forecast where the next few peaks and dips should be found if the basic paradigm is correct. We test the robustness of our results by comparing Bayesian marginalization techniques on this space with likelihood maximization techniques applied to a second 7-dimensional cosmological parameter space, using an independent computational pipeline, and find excellent agreement: {Omega}{sub tot} = 1.02{sub -0.05}{sup +0.06} vs. 1.04 {+-} 0.05, {Omega}{sub b}h{sup 2} = 0.022{sub -0.003}{sup +0.004} vs. 0.019{sub -0.004}{sup +0.005}, and n{sub s} = 0.96{sub -0.09}{sup +0.10} vs. 0.90 {+-} 0.08. The deviation in primordial spectral index n{sub s} is a consequence of the strong correlation with the optical depth.

  18. Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO$_x$ film growth

    CERN Document Server

    Franz, Robert; Kolbeck, Jonathan; Anders, André

    2016-01-01

    The ion energies and fluxes in the high power impulse magnetron sputtering plasma from a Nb target were analysed angularly resolved along the tangential direction of the racetrack. A reactive oxygen-containing atmosphere was used as such discharge conditions are typically employed for the synthesis of thin films. Asymmetries in the flux distribution of the recorded ions as well as their energies and charge states were noticed when varying the angle between mass-energy analyser and target surface. More positively charged ions with higher count rates in the medium energy range of their distributions were detected in $+\\mathbf{E}\\times \\mathbf{B}$ than in $-\\mathbf{E}\\times \\mathbf{B}$ direction, thus confirming the notion that ionisation zones are associated with moving potential humps. The motion of the recorded negatively charged high-energy oxygen ions was unaffected. NbO$_x$ thin films at different angles and positions were synthesised and analysed as to their structure and properties in order to correlate ...

  19. Professional AngularJS

    CERN Document Server

    Karpov, Valeri

    2015-01-01

    A comprehensive guide to AngularJS, Google's open-source client-side framework for app development. Most of the existing guides to AngularJS struggle to provide simple and understandable explanations for more advanced concepts. As a result, some developers who understand all the basic concepts of AngularJS struggle when it comes to building more complex real-world applications. Professional AngularJS provides a thorough understanding of AngularJS, covering everything from basic concepts, such as directives and data binding, to more advanced concepts like transclusion, build systems, and auto

  20. On Angular Sampling Methods for 3-D Spatial Channel Models

    DEFF Research Database (Denmark)

    Fan, Wei; Jämsä, Tommi; Nielsen, Jesper Ødum

    2015-01-01

    This paper discusses generating three dimensional (3D) spatial channel models with emphasis on the angular sampling methods. Three angular sampling methods, i.e. modified uniform power sampling, modified uniform angular sampling, and random pairing methods are proposed and investigated in detail....

  1. Study on the factors of the angular dispersion power for the triple prism%三棱镜角色散性能的影响因素研究

    Institute of Scientific and Technical Information of China (English)

    王玉梅

    2013-01-01

    In this paper, the refractive index of visible light in the triple prism was measured by the methord of minimum deviation. Based on the expirical foumula of Cauchy, the experimental data was investigated in Origin software, and the dispersion curvers of the triple prism were obtained. The parameters A0 and B0 of the ZF1 optical glass and the K9 optical glass were determined and the angular diapersion power of two optical glass were obtained. The experimental results show that the angular dispersion power of triple prism related to not only prism materials but also the wave length of the incident light. The angular dispersion power increases with the increase of refraction index and increases with the decrease of wave length.%用最小偏向角法测定了可见光中不同波长的光在三棱镜中的折射率,按照Cauchy经验公式用Origin软件拟合实验数据,得出了三棱镜材料的色散关系曲线;确定了玻璃ZF1和玻璃K9色散关系中的参量A0、B0值;确定了两种玻璃棱镜的角色散本领;分析得出了三棱镜的角色散本领与棱镜材料的折射率及入射波的波长有关,三棱镜的角色散本领随棱镜材料折射率的增大而增大,随入射波波长的减小而增大.

  2. Sequential amplitude divided angular multiplexing encoding optical system design for high power excimer laser system%连续分振幅式高功率准分子激光角多路编码光路设计

    Institute of Scientific and Technical Information of China (English)

    胡云; 王大辉; 赵学庆

    2016-01-01

    In high power excimer laser system, angular multiplexing technique is employed to achieve both high energy and narrow pulse output. In this article, angular multiplexing technique was introduced, and a multiplexing encoding method was presented. This method encoded seed beam in two steps by sequential amplitude splitting. The optical elements were arranged in rectangle arrays and piled by layers. A specific optical design was made for XeCl high power excimer laser system in this laboratory. This method of angular multiplexing encoding has advantages of compacted space, small encoding error, good compatibility with alignment and measurement, and is also easy to fabricate and assemble. This design is adopted in the system and performs well.%在高功率准分子激光系统中,一般采用光学角多路技术来获得高能量窄脉冲输出。文中介绍了角多路技术原理,提出了一种采用矩形阵列和空间层叠光路结构的连续分振幅两次编码方式,并针对该实验室的XeCl高功率准分子激光系统进行了具体的编码光路设计,给出了设计实例。该方法具有编码结构紧凑,编码精度高,与光路准直、激光参数测量系统等兼容性好,便于加工制作和安装调节等优点,目前已在系统中应用,效果良好。

  3. Quark Orbital Angular Momentum

    Directory of Open Access Journals (Sweden)

    Burkardt Matthias

    2015-01-01

    Full Text Available Definitions of orbital angular momentum based on Wigner distributions are used as a framework to discuss the connection between the Ji definition of the quark orbital angular momentum and that of Jaffe and Manohar. We find that the difference between these two definitions can be interpreted as the change in the quark orbital angular momentum as it leaves the target in a DIS experiment. The mechanism responsible for that change is similar to the mechanism that causes transverse single-spin asymmetries in semi-inclusive deep-inelastic scattering.

  4. Kinematics of the Local Universe XIV. Measurements from the 21 cm line and the HI mass function from a homogeneous catalog gathered with the Nan\\c{c}ay radio telescope

    CERN Document Server

    Theureau, Gilles; Hallet, Nicole; Hanski, Mikko; Poulain, Mélina

    2016-01-01

    This paper presents 828 new 21 cm neutral hydrogen line measurements carried out with the FORT receiver of the meridian transit Nan\\c{c}ay radio telescope (NRT) in the years 2000 -- 2007. This observational program was part of a larger project aimed at collecting an exhaustive and magnitude-complete HI extragalactic catalog for Tully-Fisher applications. Through five massive data releases, the KLUN series has collected a homogeneous sample of 4876 HI-spectra of spiral galaxies, complete down to a flux of 5 Jy.km.s^{-1} and with declination delta > -40{\\deg}. We publish here the last release of the KLUN HI observational program, corresponding to the faint end of the survey, with HI masses ranging from 5 10^8 to 5 10^{10} solar masses. The size of this final sample is comparable to the catalogs based on the Arecibo and Parkes radio telescope campaigns, and it allows general HI mass distribution studies from a set of homogeneous radio measurements.

  5. Kinematics of the Local Universe. XIV. Measurements from the 21 cm line and the HI mass function from a homogeneous catalog gathered with the Nançay radio telescope

    Science.gov (United States)

    Theureau, G.; Coudreau, N.; Hallet, N.; Hanski, M. O.; Poulain, M.

    2017-03-01

    Aims: This paper presents 828 new 21 cm neutral hydrogen line measurements carried out with the FORT receiver of the meridian transit Nançay radio telescope (NRT) in the years 2000-2007. Methods: This observational program was part of a larger project aimed at collecting an exhaustive and magnitude-complete HI extragalactic catalog for Tully-Fisher applications. Through five massive data releases, the KLUN series has collected a homogeneous sample of 4876 HI-spectra of spiral galaxies, complete down to a flux of 5 Jy km s-1 and with declination δ > -40°. Results: We publish here the last release of the KLUN HI observational program, corresponding to the faint end of the survey, with HI masses ranging from 5 × 108 to 5 × 1010 solar masses. The size of this final sample is comparable to the catalogs based on the Arecibo and Parkes radio telescope campaigns, and it allows general HI mass distribution studies from a set of homogeneous radio measurements. Full Tables 2 and 3, together with HI profiles in ascii format, are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A104

  6. Recurrence of angular cheilitis.

    Science.gov (United States)

    Ohman, S C; Jontell, M; Dahlen, G

    1988-08-01

    The incidence of recurrence of angular cheilitis following a successful antimicrobial treatment was studied in 48 patients. Clinical assessments including a microbial examination were carried out 8 months and 5 yr after termination of treatment. Eighty percent of the patients reported recurrence of their angular cheilitis on one or more occasions during the observation period. Patients with cutaneous disorders associated with dry skin or intraoral leukoplakia had an increased incidence of recrudescence. Neither the presence of denture stomatitis nor the type of microorganisms isolated from the original lesions of angular cheilitis, i.e. Candida albicans and/or Staphylococcus aureus, were associated with the number of recurrences. The present observations indicate that treatment of the majority of patients with angular cheilitis should be considered in a longer perspective than previously supposed, due to the short lasting therapeutic effects of the antimicrobial therapy.

  7. [Malignant angular cheilitis].

    Science.gov (United States)

    Seoane, J; Vázquez, J; Cazenave, A; de la Cruz Mera, A; Argila, F; Aguado, A

    1996-01-01

    A case of chronic angular cheilitis is reported. Candida albicans was isolated repeatedly and the process developed into epitheliomatous carcinoma. The etiopathogenic role of Candida albicans and possible mechanism of action are discussed.

  8. Angular Cheilitis Pada Anak

    OpenAIRE

    Gema Nazriyanti

    2008-01-01

    Angular cheilitis adalah inflamasi akut atau kronis pada sudut mulut yang ditandai dengan adanya flsur-fisur, retak-retak pada sudut bibir, berwarna kemerahan, mengalami ulserasi disertai rasa terbakar, nyeri dan rasa kering pada sudut mulut. Dapat mengenai orang tua, dewasa dan anak-anak. Banyak pendapat yang mengemukakan tentang etiologi dari angular cheilitis, antara lain defisiensi vitamin B kompleks, denture soremouth, defisiensi besi, kebiasaan bernafas melalui mulut, membasahi bib...

  9. Optical orbital angular momentum

    Science.gov (United States)

    Barnett, Stephen M.; Babiker, Mohamed; Padgett, Miles J.

    2017-01-01

    We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069775

  10. Angular shear plate

    Science.gov (United States)

    Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ

    2009-07-14

    One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

  11. Optical orbital angular momentum

    Science.gov (United States)

    Barnett, Stephen M.; Babiker, Mohamed; Padgett, Miles J.

    2017-02-01

    We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next. This article is part of the themed issue 'Optical orbital angular momentum'.

  12. Induced Angular Momentum

    Science.gov (United States)

    Parker, G. W.

    1978-01-01

    Discusses, classically and quantum mechanically, the angular momentum induced in the bound motion of an electron by an external magnetic field. Calculates the current density and its magnetic moment, and then uses two methods to solve the first-order perturbation theory equation for the required eigenfunction. (Author/GA)

  13. "Angular" plasma cell cheilitis.

    Science.gov (United States)

    da Cunha Filho, Roberto Rheingantz; Tochetto, Lucas Baldissera; Tochetto, Bruno Baldissera; de Almeida, Hiram Larangeira; Lorencette, Nádia Aparecida; Netto, José Fillus

    2014-03-17

    Plasma cell cheilitis is an extremely rare disease, characterized by erythematous-violaceous, ulcerated and asymptomatic plaques, which evolve slowly. The histological characteristics include dermal infiltrate composed of mature plasmocytes. We report a case of Plasma cell angular cheilitis in a 58-year-old male, localized in the lateral oral commissure.

  14. "Angular" plasma cell cheilitis

    OpenAIRE

    da Cunha Filho, Roberto Rheingantz; Tochetto, Lucas Baldissera; Tochetto, Bruno Baldissera; de Almeida Jr, Hiram Larangeira; Lorencette, Nadia Aparecida; Netto, Jose Fillus

    2014-01-01

    Plasma cell cheilitis is an extremely rare disease, characterized by erythematous-violaceous, ulcerated and asymptomatic plaques, which evolve slowly. The histological characteristics include dermal infiltrate composed of mature plasmocytes. We report a case of Plasma cell angular cheilitis in a 58-year-old male, localized in the lateral oral commissure.

  15. Angular Accelerating White Light

    CSIR Research Space (South Africa)

    Dudley, Angela L

    2015-08-01

    Full Text Available Shaping XVI, 958104, San Diego, California, United States, 09 August 2015 Angular Accelerating White Light Angela Dudley*a,b, Christian Vetterc , Alexander Szameitc , and Andrew Forbesa,b a CSIR National Laser Centre, PO Box 395, Pretoria 0001...

  16. Quantum Heuristics of Angular Momentum

    Science.gov (United States)

    Levy-Leblond, Jean-Marc

    1976-01-01

    Discusses the quantization of angular momentum components, Heisenberg-type inequalities for their spectral dispersions, and the quantization of the angular momentum modulus, without using operators or commutation relations. (MLH)

  17. Angular cheilitis after tonsillectomy.

    Science.gov (United States)

    England, R J; Lau, M; Ell, S R

    1999-08-01

    The operation of tonsillectomy requires the oral cavity to be held open mechanically in an unconscious patient, and intra-oral instrumentation to occur. Angular cheilitis may arise as a result of this after operation. This can cause morbidity and delay the re-establishment of a normal diet. The aim of this study was to identify what factors increase the likelihood of developing this problem postoperatively. Sixty patients were randomly selected in a prospective manner. Preoperative, intraoperative and postoperative variables were recorded. The frequency of development of postoperative angular cheilitis was recorded. The prevalence of the condition was related to the prerecorded variables. Parametric analysis showed that the chance of developing angular cheilitis was directly related to the use of diathermy haemostasis (P = 0.05). Logistic regression analysis showed that the odds ratio of developing this complication if diathermy was used is 3.5 (95% confidence intervals 0.99, 12.4) and operation difficulty may also be a relevant variable. No other recorded variables were found to be significant.

  18. Optical angular momentum and atoms.

    Science.gov (United States)

    Franke-Arnold, Sonja

    2017-02-28

    Any coherent interaction of light and atoms needs to conserve energy, linear momentum and angular momentum. What happens to an atom's angular momentum if it encounters light that carries orbital angular momentum (OAM)? This is a particularly intriguing question as the angular momentum of atoms is quantized, incorporating the intrinsic spin angular momentum of the individual electrons as well as the OAM associated with their spatial distribution. In addition, a mechanical angular momentum can arise from the rotation of the entire atom, which for very cold atoms is also quantized. Atoms therefore allow us to probe and access the quantum properties of light's OAM, aiding our fundamental understanding of light-matter interactions, and moreover, allowing us to construct OAM-based applications, including quantum memories, frequency converters for shaped light and OAM-based sensors.This article is part of the themed issue 'Optical orbital angular momentum'. © 2017 The Author(s).

  19. AngularJS directives

    CERN Document Server

    Vanston, Alex

    2013-01-01

    This book uses a practical, step-by-step approach, starting with how to build directives from the ground up before moving on to creating web applications comprised of multiple modules all working together to provide the best user experience possible.This book is intended for intermediate JavaScript developers who are looking to enhance their understanding of single-page web application development with a focus on AngularJS and the JavaScript MVC frameworks.It is expected that readers will understand basic JavaScript patterns and idioms and can recognize JSON formatted data.

  20. Orbital angular momentum microlaser

    Science.gov (United States)

    Miao, Pei; Zhang, Zhifeng; Sun, Jingbo; Walasik, Wiktor; Longhi, Stefano; Litchinitser, Natalia M.; Feng, Liang

    2016-07-01

    Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.

  1. γ - γ Angular Correlation Measurements With GRIFFIN

    Science.gov (United States)

    Maclean, Andrew; Griffin Collaboration

    2015-10-01

    When an excited nuclear state emits successive γ-rays causing a γ - γ cascade an anisotropy is found in the spatial distribution of γ2 with respect to γ1. Defining the direction of γ1 as the z-axis, the intermediate level, in general will have an uneven distribution of m-states. This causes an anisotropy in the angular correlation of the second γ-ray with respect to the first. These angular correlations are expressed by the W (θ) that depends on numerical coefficients described by the sequence of spin-parity values for the nuclear states involved, the multipolarities and mixing ratios. Angular correlations can be used for the assignment of spins and parities for the nuclear states, and thus provide a powerful means to elucidate the structure of nuclei far from stability through β - γ - γ coincidence measurements. In order to explore the sensitivity of the new 16 clover-detector GRIFFIN γ-ray spectrometer at TRIUMF-ISAC to such γ - γ angular correlations, and to optimize its performance for these measurements we have studied a well known γ - γ cascade from 60Co decay through both experimental measurements and Geant4 simulation. Results will be shown in this talk. Work supported by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada and the National Research Council of Canada.

  2. Intrinsic Angular Momentum of Light.

    Science.gov (United States)

    Santarelli, Vincent

    1979-01-01

    Derives a familiar torque-angular momentum theorem for the electromagnetic field, and includes the intrinsic torques exerted by the fields on the polarized medium. This inclusion leads to the expressions for the intrinsic angular momentum carried by the radiation traveling through a charge-free medium. (Author/MA)

  3. Angular integrals in d dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Somogyi, Gabor

    2011-01-15

    We discuss the evaluation of certain d dimensional angular integrals which arise in perturbative field theory calculations. We find that the angular integral with n denominators can be computed in terms of a certain special function, the so-called H-function of several variables. We also present several illustrative examples of the general result and briefly consider some applications. (orig.)

  4. Angular momentum of sound pulses.

    Science.gov (United States)

    Lekner, John

    2006-07-05

    Three-dimensionally localized acoustic pulses in an isotropic fluid medium necessarily have transverse components of momentum density. Those with an azimuthal component of momentum density can carry angular momentum. The component of total pulse angular momentum along the direction of the total momentum is an invariant (constant in time and independent of choice of origin). The pulse energy, momentum and angular momentum are evaluated analytically for a family of localized solutions of the wave equation. In the limit where the pulses have many oscillations within their spatial extent ([Formula: see text], where k is the wavenumber and a determines the size of a pulse), the energy, momentum and angular momentum are consistent with a multiphonon representation of the pulse, each phonon having energy [Formula: see text], momentum [Formula: see text] and angular momentum [Formula: see text] (with integer m).

  5. Mitigation of radiation-pressure-induced angular instability of a Fabry–Perot cavity consisting of suspended mirrors

    Energy Technology Data Exchange (ETDEWEB)

    Nagano, Koji, E-mail: knagano@icrr.u-tokyo.ac.jp [KAGRA Observatory, Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba 277-8582 (Japan); Enomoto, Yutaro; Nakano, Masayuki [KAGRA Observatory, Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba 277-8582 (Japan); Furusawa, Akira [Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Kawamura, Seiji [KAGRA Observatory, Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba 277-8582 (Japan)

    2016-12-01

    To observe radiation pressure noise in optical cavities consisting of suspended mirrors, high laser power is necessary. However, because the radiation pressure on the mirrors could cause an angular anti-spring effect, the high laser power could induce angular instability to the cavity. An angular control system using radiation pressure as an actuator, which was previously invented to reduce the anti-spring effect for the low power case, was applied to the higher power case where the angular instability would occur. As a result the angular instability was mitigated. It was also demonstrated that the cavity was unstable without this control system. - Highlights: • High laser power could cause angular instability to a suspended Fabry–Perot cavity. • To mitigate the instability, the control system using radiation pressure is applied. • Mitigating the radiation-pressure-induced angular instability is demonstrated. • It is also confirmed that the cavity would be unstable without the control system.

  6. AngularJS testing cookbook

    CERN Document Server

    Bailey, Simon

    2015-01-01

    This book is intended for developers who have an understanding of the basic principles behind both AngularJS and test-driven development. You, as a developer, are interested in eliminating the fear related to either introducing tests to an existing codebase or starting out testing on a fresh AngularJS application. If you're a team leader or part of a QA team with the responsibility of ensuring full test coverage of an application, then this book is ideal for you to comprehend the full testing scope required by your developers. Whether you're new to or are well versed with AngularJS, this book

  7. The Cosmology Large Angular Scale Surveyor (CLASS)

    Science.gov (United States)

    Harrington, Kathleen; Marriange, Tobias; Aamir, Ali; Appel, John W.; Bennett, Charles L.; Boone, Fletcher; Brewer, Michael; Chan, Manwei; Chuss, David T.; Colazo, Felipe; Denis, Kevin; Moseley, Samuel H.; Rostem, Karwan; Wollack, Edward

    2016-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to characterize relic primordial gravitational waves from in ation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on the largest angular scales. The frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one dichroic system at 145/217 GHz, are chosen to avoid spectral regions of high atmospheric emission and span the minimum of the polarized Galactic foregrounds: synchrotron emission at lower frequencies and dust emission at higher frequencies. Low-noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique combination of high sensitivity, stability, and control of systematics. The CLASS site, at 5200 m in the Chilean Atacama desert, allows for daily mapping of up to 70% of the sky and enables the characterization of CMB polarization at the largest angular scales. Using this combination of a broad frequency range, large sky coverage, control over systematics, and high sensitivity, CLASS will observe the reionization and recombination peaks of the CMB E- and B-mode power spectra. CLASS will make a cosmic variance limited measurement of the optical depth to reionization and will measure or place upper limits on the tensor-to-scalar ratio, r, down to a level of 0.01 (95% C.L.).

  8. Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development

    CERN Document Server

    Chuss, D T; Amiri, M; Appel, J; Bennett, C L; Colazo, F; Denis, K L; Dünner, R; Essinger-Hileman, T; Eimer, J; Fluxa, P; Gothe, D; Halpern, M; Harrington, K; Hilton, G; Hinshaw, G; Hubmayr, J; Iuliano, J; Marriage, T A; Miller, N; Moseley, S H; Mumby, G; Petroff, M; Reintsema, C; Rostem, K; U-Yen, K; Watts, D; Wagner, E; Wollack, E J; Xu, Z; Zeng, L

    2015-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe $\\sim$70% of the sky. A variable-delay polarization modulator (VPM) modulates the polarization at $\\sim$10 Hz to suppress the 1/f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that span both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously d...

  9. Systematic Effects in Large Scale Angular Power Spectra and Implications for Constraining Primordial Non-gaussianity%宇宙大尺度结构和原初扰动非高斯性研究进展

    Institute of Scientific and Technical Information of China (English)

    杨圣

    2015-01-01

    big difference between the derived cosmic parameters and the actual counterparts. Therefore removing the systematic errors' effect for the LSS tracers on constraining primordial non-gaussianity is very meaningful so that we could get more real cosmic truth and know the early cosmology more clearly. In this paper, we will review the way how the CMB and LSS tracer's maps restrict on the cosmological parameters firstly and then we will disicuss about the systematic errors' effect on the observed angular power spectrum and also we introduce two important methods to remove the systematics. Finally, we will compare the modified parameter and the original one to discuss the goodness.

  10. Power

    DEFF Research Database (Denmark)

    Elmholdt, Claus Westergård; Fogsgaard, Morten

    2016-01-01

    In this chapter, we will explore the dynamics of power in processes of creativity, and show its paradoxical nature as both a bridge and a barrier to creativity in organisations. Recent social psychological experimental research (Slighte, de Dreu & Nijstad, 2011) on the relation between power...... and creativity suggests that when managers give people the opportunity to gain power and explicate that there is reason to be more creative, people will show a boost in creative behaviour. Moreover, this process works best in unstable power hierarchies, which implies that power is treated as a negotiable...... and floating source for empowering people in the organisation. We will explore and discuss here the potentials, challenges and pitfalls of power in relation to creativity in the life of organisations today. The aim is to demonstrate that power struggles may be utilised as constructive sources of creativity...

  11. Probing protoplanetary disk evolution with the HI 21 cm line

    NARCIS (Netherlands)

    Kamp, Inga; Freudling, Wolfram; Robberto, Massimo; Chengalur, Jayaram; Keto, Eric

    2008-01-01

    Little is known about the gas disk dispersal timescales in the planet formation process. Disks have a complex chemical structure and a wide range of excitation conditions, making the interpretation of line observations difficult. Here, we use detailed chemo-physical models to predict the Hi abundanc

  12. Associated 21-cm absorption towards the cores of radio galaxies

    OpenAIRE

    Chandola, Yogesh; Gupta, Neeraj; Saikia, D.J.

    2012-01-01

    We present the results of Giant Metrewave Radio Telescope (GMRT) observations to detect H{\\sc i} in absorption towards the cores of a sample of radio galaxies. From observations of a sample of 16 sources, we detect H{\\sc i} in absorption towards the core of only one source, the FR\\,II radio galaxy 3C\\,452 which has been reported earlier by Gupta & Saikia (2006a). In this paper we present the results for the remaining sources which have been observed to a similar optical depth as for a compari...

  13. Instant AngularJS starter

    CERN Document Server

    Menard, Dan

    2013-01-01

    Get to grips with a new technology, understand what it is and what it can do for you, and then get to work with the most important features and tasks. This book is written in an easytoread style, with a strong emphasis on realworld, practical examples. Stepbystep explanations are provided for performing important tasks.This book is for web developers familiar with JavascriptIt doesn't cover the history of AngularJS, and it's not a pitch to convince you that AngularJS is the best framework on the entire web. It's a guide to help you learn everything you need to know about AngularJS in as few pa

  14. Angular momentum in human walking.

    Science.gov (United States)

    Herr, Hugh; Popovic, Marko

    2008-02-01

    Angular momentum is a conserved physical quantity for isolated systems where no external moments act about a body's center of mass (CM). However, in the case of legged locomotion, where the body interacts with the environment (ground reaction forces), there is no a priori reason for this relationship to hold. A key hypothesis in this paper is that angular momentum is highly regulated throughout the walking cycle about all three spatial directions [|Lt| approximately 0], and therefore horizontal ground reaction forces and the center of pressure trajectory can be explained predominantly through an analysis that assumes zero net moment about the body's CM. Using a 16-segment human model and gait data for 10 study participants, we found that calculated zero-moment forces closely match experimental values (Rx2=0.91; Ry2=0.90). Additionally, the centroidal moment pivot (point where a line parallel to the ground reaction force, passing through the CM, intersects the ground) never leaves the ground support base, highlighting how closely the body regulates angular momentum. Principal component analysis was used to examine segmental contributions to whole-body angular momentum. We found that whole-body angular momentum is small, despite substantial segmental momenta, indicating large segment-to-segment cancellations ( approximately 95% medio-lateral, approximately 70% anterior-posterior and approximately 80% vertical). Specifically, we show that adjacent leg-segment momenta are balanced in the medio-lateral direction (left foot momentum cancels right foot momentum, etc.). Further, pelvis and abdomen momenta are balanced by leg, chest and head momenta in the anterior-posterior direction, and leg momentum is balanced by upper-body momentum in the vertical direction. Finally, we discuss the determinants of gait in the context of these segment-to-segment cancellations of angular momentum.

  15. Non-Colinearity of Angular Velocity and Angular Momentum

    Science.gov (United States)

    Burr, A. F.

    1974-01-01

    Discusses the principles, construction, and operation of an apparatus which serves to demonstrate the non-colinearity of the angular velocity and momentum vectors as well as the inertial tensors. Applications of the apparatus to teaching of advanced undergraduate mechanics courses are recommended. (CC)

  16. Olympic Wrestling and Angular Momentum.

    Science.gov (United States)

    Carle, Mark

    1988-01-01

    Reported is the use of a wrestling photograph in a noncalculus introductory physics course. The photograph presents a maneuver that could serve as an example for a discussion on equilibrium, forces, torque, and angular motion. Provided are some qualitative thoughts as well as quantitative calculations. (YP)

  17. CMB anisotropies: Total angular momentum method

    Science.gov (United States)

    Hu, Wayne; White, Martin

    1997-07-01

    A total angular momentum representation simplifies the radiation transport problem for temperature and polarization anisotropy in the cosmic microwave background (CMB). Scattering terms couple only the quadrupole moments of the distributions and each moment corresponds directly to the observable angular pattern on the sky. We develop and employ these techniques to study the general properties of anisotropy generation from scalar, vector, and tensor perturbations to the metric and the matter, both in the cosmological fluids and from any seed perturbations (e.g., defects) that may be present. The simpler, more transparent form and derivation of the Boltzmann equations brings out the geometric and model-independent aspects of temperature and polarization anisotropy formation. Large angle scalar polarization provides a robust means to distinguish between isocurvature and adiabatic models for structure formation in principle. Vector modes have the unique property that the CMB polarization is dominated by magnetic-type parity at small angles (a factor of 6 in power compared with 0 for the scalars and 8/13 for the tensors) and hence potentially distinguishable independent of the model for the seed. The tensor modes produce a different sign from the scalars and vectors for the temperature-polarization correlations at large angles. We explore conditions under which one perturbation type may dominate over the others including a detailed treatment of the photon-baryon fluid before recombination.

  18. Plate tectonics conserves angular momentum

    Directory of Open Access Journals (Sweden)

    C. Bowin

    2009-03-01

    Full Text Available A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s−1. Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates. Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth. The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive

  19. The integration of angular velocity

    CERN Document Server

    Boyle, Michael

    2016-01-01

    A common problem in physics and engineering is determination of the orientation of an object given its angular velocity. When the direction of the angular velocity changes in time, this is a nontrivial problem involving coupled differential equations. Several possible approaches are examined, along with various improvements over previous efforts. These are then evaluated numerically by comparison to a complicated but analytically known rotation that is motivated by the important astrophysical problem of precessing black-hole binaries. It is shown that a straightforward solution directly using quaternions is most efficient and accurate, and that the norm of the quaternion is irrelevant. Integration of the generator of the rotation can also be made roughly as efficient as integration of the rotation. Both methods will typically be twice as efficient naive vector- or matrix-based methods. Implementation by means of standard general-purpose numerical integrators is stable and efficient, so that such problems can ...

  20. Angular momentum in QGP holography

    Directory of Open Access Journals (Sweden)

    Brett McInnes

    2014-10-01

    Full Text Available The quark chemical potential is one of the fundamental parameters describing the quark–gluon plasma produced by sufficiently energetic heavy-ion collisions. It is not large at the extremely high temperatures probed by the LHC, but it plays a key role in discussions of the beam energy scan programmes at the RHIC and other facilities. On the other hand, collisions at such energies typically (that is, in peripheral collisions give rise to very high values of the angular momentum density. Here we explain that holographic estimates of the quark chemical potential of a rotating sample of plasma can be very considerably improved by taking the angular momentum into account.

  1. Phonons with orbital angular momentum

    Energy Technology Data Exchange (ETDEWEB)

    Ayub, M. K. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

    2011-10-15

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  2. Effects of Angular Momentum on Halo Profiles

    CERN Document Server

    Lentz, Erik W; Rosenberg, Leslie J

    2016-01-01

    The near universality of DM halo density profiles provided by N-body simulations has proven to be robust against changes in total mass density, power spectrum, and some forms of initial velocity dispersion. In this letter 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 ($\\lambda \\lesssim 0.20$) produce profiles with negligible deviations from the universal form. Only when the spin becomes quite large ($\\lambda \\gtrsim 0.20$) do departures become evident. The angular momentum distribution also exhibits a near universal form, which is also independent of halo spin up to $\\lambda \\lesssim 0.20$. 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.

  3. Moon influence on equatorial atmospheric angular momentum

    Science.gov (United States)

    Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

    2014-05-01

    The variation of the equatorial atmospheric angular momentum function, coordinated with respect to a star-fixed system, is investigated in relation with the lunar tide. We isolate the rapid fluctuations, below 30 days, where Moon motion has a possible influence. First we notice that pressure term and wind term are almost proportional, by contrast to celestial seasonal band (S1). This would mean that, in this frequency band, the torque of the atmosphere on the solid Earth mostly results from the equatorial bulge. Spectrum reveals sharp lunar tidal peaks at 13.66 days (O1 diurnal tide in the terrestrial frame) and 13.63 days, reflecting the Moon influence on meridional circulation. We also observe powerful episodic fluctuations between 5 and 8 days (up to 10 mas), possibly resulting from non linear effect of the O1 tide, or tidal waves 2Q1 (6.86 days) and σ1 (7.095 days).

  4. The Angular Trispectrum of the CMB

    CERN Document Server

    Hu, W

    2001-01-01

    We study the general properties of the CMB temperature four-point function, specifically its harmonic analogue the angular trispectrum, and illustrate its utility in finding optimal quadratic statistics through the weak gravitational lensing effect. We determine the general form of the trispectrum, under the assumptions of rotational, permutation, and parity invariance, its estimators on the sky, and their Gaussian noise properties. The signal-to-noise in the trispectrum can be highly configuration dependent and any quadratic statistic used to compress the information to a manageable two-point level must be carefully chosen. Through a systematic study, we determine that for the case of lensing a specific statistic, the divergence of a filtered temperature-weighted temperature-gradient map, contains the maximal signal-to-noise and reduces the variance of estimates of the large-scale convergence power spectrum by over an order of magnitude over previous gradient-gradient techniques. The total signal-to-noise fo...

  5. AngularJS test-driven development

    CERN Document Server

    Chaplin, Tim

    2015-01-01

    This book is for developers who want to learn about AngularJS development by applying testing techniques. You are assumed to have a basic knowledge and understanding of HTML, JavaScript, and AngularJS.

  6. Optical angular momentum in dispersive media

    CERN Document Server

    Philbin, T G

    2012-01-01

    The angular momentum density and flux of light in a dispersive, rotationally symmetric medium are derived from Noether's theorem. Optical angular momentum in a dispersive medium has no simple relation to optical linear momentum, even if the medium is homogeneous. A circularly polarized monochromatic beam in a homogeneous, dispersive medium carries a spin angular momentum per unit energy of $\\pm\\omega^{-1}$, as in vacuum. This result demonstrates the non-trivial interplay of dispersive contributions to optical angular momentum and energy.

  7. AngularJS web application development

    CERN Document Server

    Darwin, Peter Bacon

    2013-01-01

    The book will be a step-by-step guide showing the readers how to build a complete web app with AngularJSJavaScript developers who want to learn AngularJS for developing web apps. Knowledge of JavaScript and HTML is expected. No knowledge of AngularJS is required.

  8. Optical angular momentum in classical electrodynamics

    Science.gov (United States)

    Mansuripur, Masud

    2017-06-01

    Invoking Maxwell’s classical equations in conjunction with expressions for the electromagnetic (EM) energy, momentum, force, and torque, we use a few simple examples to demonstrate the nature of the EM angular momentum. The energy and the angular momentum of an EM field will be shown to have an intimate relationship; a source radiating EM angular momentum will, of necessity, pick up an equal but opposite amount of mechanical angular momentum; and the spin and orbital angular momenta of the EM field, when absorbed by a small particle, will be seen to elicit different responses from the particle.

  9. Dependency injection with AngularJS

    CERN Document Server

    Knol, Alex

    2013-01-01

    This book is a practical, hands-on approach to using dependency injection and implementing test-driven development using AngularJS. Dependency Injection with AngularJS is aimed at developers who are aware of AngularJS but need to get started with using it in real life applications. Also, developers who want to get into test-driven development with AngularJS can use this book as practical guide. Even if you know about dependency injection, it can serve as a good reference on how it is used within AngularJS. Readers are expected to have some experience with JavaScript.

  10. AngularJS lietotnes migrācija uz Angular

    OpenAIRE

    Andrucis, Edgars

    2017-01-01

    Darbā tiek aprakstītas un apkopotas dažādas stratēģijas un pieejas “AngularJS” projektu migrācijai uz jauno “Angular” ietvaru. Tai skaitā dažādi migrāciju priekšdarbi un stratēģijas, kā lielā sprādziena migrācijas stratēģija un inkrementālā migrācijas stratēģija. Šīs stratēģijas tiek novērtētas aprakstot to trūkumus un priekšrocības. Balstoties uz tā, darba autors veica tīmekļa pieteikumu formu “AngularJS” lietotnes migrāciju uz jauno “Angular” ietvaru. Pēc kā tas novērtēja apkopoto informāci...

  11. Two-axis angular effector

    Energy Technology Data Exchange (ETDEWEB)

    Vaughn, Mark R. (Albuquerque, NM); Robinett, III, Rush D. (Tijeras, NM); Phelan, John R. (Albuquerque, NM); Van Zuiden, Don M. (Albuquerque, NM)

    1997-01-21

    A new class of coplanar two-axis angular effectors. These effectors combine a two-axis rotational joint analogous to a Cardan joint with linear actuators in a manner to produce a wider range of rotational motion about both axes defined by the joint. This new class of effectors also allows design of robotic manipulators having very high strength and efficiency. These effectors are particularly suited for remote operation in unknown surroundings, because of their extraordinary versatility. An immediate application is to the problems which arise in nuclear waste remediation.

  12. Two-axis angular effector

    Energy Technology Data Exchange (ETDEWEB)

    Vaughn, M.R.; Robinett, R.D. III; Phelan, J.R.; Zuiden, D.M. Van

    1997-01-21

    A new class of coplanar two-axis angular effectors is described. These effectors combine a two-axis rotational joint analogous to a Cardan joint with linear actuators in a manner to produce a wider range of rotational motion about both axes defined by the joint. This new class of effectors also allows design of robotic manipulators having very high strength and efficiency. These effectors are particularly suited for remote operation in unknown surroundings, because of their extraordinary versatility. An immediate application is to the problems which arise in nuclear waste remediation. 11 figs.

  13. The tetrahexahedric angular Calogero model

    Energy Technology Data Exchange (ETDEWEB)

    Correa, Francisco [Centro de Estudios Científicos (CECs),Casilla 1468, Valdivia (Chile); Institut für Theoretische Physik and Riemann Center for Geometry and Physics,Leibniz Universität Hannover,Appelstraße 2, 30167 Hannover (Germany); Lechtenfeld, Olaf [Institut für Theoretische Physik and Riemann Center for Geometry and Physics,Leibniz Universität Hannover,Appelstraße 2, 30167 Hannover (Germany)

    2015-10-28

    The spherical reduction of the rational Calogero model (of type A{sub n−1} and after removing the center of mass) is considered as a maximally superintegrable quantum system, which describes a particle on the (n−2)-sphere subject to a very particular potential. We present a detailed analysis of the simplest non-separable case, n=4, whose potential is singular at the edges of a spherical tetrahexahedron. A complete set of independent conserved charges and of Hamiltonian intertwiners is constructed, and their algebra is elucidated. They arise from the ring of polynomials in Dunkl-deformed angular momenta, by classifying the subspaces invariant and antiinvariant under all Weyl reflections, respectively.

  14. Variable Distance Angular Symbology Reader

    Science.gov (United States)

    Schramm, Harry F., Jr. (Inventor); Corder, Eric L. (Inventor)

    2006-01-01

    A variable distance angular symbology, reader utilizes at least one light source to direct light through a beam splitter and onto a target. A target may be angled relative to the impinging light beam up to and maybe even greater than 45deg. A reflected beam from the target passes through the beam splitter and is preferably directed 90deg relative to the light source through a telecentric lens to a scanner which records an image of the target such as a direct part marking code.

  15. Angular output of hollow, metal-lined, waveguide Raman sensors

    Energy Technology Data Exchange (ETDEWEB)

    Biedrzycki, Stephen; Buric, Michael P.; Falk, Joel; Woodruff, Steven D.

    2012-04-20

    Hollow, metal-lined waveguides used as gas sensors based on spontaneous Raman scattering are capable of large angular collection. The collection of light from a large solid angle implies the collection of a large number of waveguide modes. An accurate estimation of the propagation losses for these modes is required to predict the total collected Raman power. We report a theory/experimental comparison of the Raman power collected as a function of the solid angle and waveguide length. New theoretical observations are compared with previous theory appropriate only for low-order modes. A cutback experiment is demonstrated to verify the validity of either theory. The angular distribution of Raman light is measured using aluminum and silver-lined waveguides of varying lengths.

  16. Transverse and longitudinal angular momenta of light

    CERN Document Server

    Bliokh, Konstantin Y

    2015-01-01

    We review basic physics and novel types of optical angular momentum. We start with a theoretical overview of momentum and angular momentum properties of generic optical fields, and discuss methods for their experimental measurements. In particular, we describe the well-known longitudinal (i.e., aligned with the mean momentum) spin and orbital angular momenta in polarized vortex beams. Then, we focus on the transverse (i.e., orthogonal to the mean momentum) spin and orbital angular momenta, which were recently actively discussed in theory and observed in experiments. First, the recently-discovered transverse spin angular momenta appear in various structured fields: evanescent waves, interference fields, and focused beams. We show that there are several kinds of transverse spin angular momentum, which differ strongly in their origins and physical properties. We describe extraordinary features of the transverse optical spins and overview recent experiments. In particular, the helicity-independent transverse spin...

  17. Electromagnetic Angular Momentum and Relativity

    CERN Document Server

    Milton, Kimball A

    2012-01-01

    Recently there have been suggestions that the Lorentz force law is inconsistent with special relativity. This is difficult to understand, since Einstein invented relativity in order to reconcile electrodynamics with mechanics. Here we investigate the momentum of an electric charge and a magnetic dipole in the frame in which both are at rest, and in an infinitesimally boosted frame in which both have a common velocity. We show that for a dipole composed of a magnetic monopole-antimonopole pair the torque is zero in both frames, while if the dipole is a point dipole, the torque is not zero, but is balanced by the rate of change of the angular momentum of the electromagnetic field, so there is no mechanical torque on the dipole.

  18. Angular distributions as lifetime probes

    Energy Technology Data Exchange (ETDEWEB)

    Dror, Jeff Asaf; Grossman, Yuval [Department of Physics, LEPP, Cornell University,Ithaca, NY 14853 (United States)

    2014-06-27

    If new TeV scale particles are discovered, it will be important to determine their width. There is, however, a problematic region, where the width is too small to be determined directly, and too large to generate a secondary vertex. For a collection of colored, spin polarized particles, hadronization depolarizes the particles prior to their decay. The amount of depolarization can be used to probe the lifetime in the problematic region. In this paper we apply this method to a realistic scenario of a top-like particle that can be produced at the LHC. We study how depolarization affects the angular distributions of the decay products and derive an equation for the distributions that is sensitive to the lifetime.

  19. Angular Distributions as Lifetime Probes

    CERN Document Server

    Dror, Jeff Asaf

    2013-01-01

    If new TeV scale particles are discovered, it will be important to determine their width. There is, however, a problematic region, where the width is too small to be determined directly, and too large to generate a secondary vertex. For a collection of colored, spin polarized particles, hadronization depolarizes the particles prior to their decay. The amount of depolarization can be used to probe the lifetime in the problematic region. In this paper we apply this method to a realistic scenario of a top-like particle that can be produced at the LHC. We study how depolarization affects the angular distributions of the decay products and derive an equation for the distributions that is sensitive to the lifetime.

  20. Oral candidiasis and angular cheilitis.

    Science.gov (United States)

    Sharon, Victoria; Fazel, Nasim

    2010-01-01

    Candidiasis, an often encountered oral disease, has been increasing in frequency. Most commonly caused by the overgrowth of Candida albicans, oral candidiasis can be divided into several categories including acute and chronic forms, and angular cheilitis. Risk factors for the development of oral candidiasis include immunosuppression, wearing of dentures, pharmacotherapeutics, smoking, infancy and old age, endocrine dysfunction, and decreased salivation. Oral candidiasis may be asymptomatic. More frequently, however, it is physically uncomfortable, and the patient may complain of burning mouth, dysgeusia, dysphagia, anorexia, and weight loss, leading to nutritional deficiency and impaired quality of life. A plethora of antifungal treatments are available. The overall prognosis of oral candidiasis is good, and rarely is the condition life threatening with invasive or recalcitrant disease.

  1. Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development

    Science.gov (United States)

    Chuss, D. T.; Ali, A.; Amiri, M.; Appel, J.; Bennett, C. L.; Colazo, F.; Denis, K. L.; Dunner, R.; Essinger-Hileman, T.; Eimer, J.; Fluxa, P.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G.; Hubmayr, J.; Iuliano, J.; Marriage, T. A.; Miller, N.; Moseley, S. H.; Mumby, G.; Petroff, M.; Reintsema, C.; Rostem, K.; U-yen, K.; Watts, D.; Wagner, E.; Wollack, E. J.; Xu, Z.; Zeng, L.

    2015-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe approx.70% of the sky. A variable-delay polarization modulator provides modulation of the polarization at approx.10Hz to suppress the 1/f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that spans both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously detect two orthogonal linear polarizations. The use of single-crystal silicon as the dielectric for the on-chip transmission lines enables both high efficiency and uniformity in fabrication. Integrated band definition has been implemented that both controls the bandpass of the single-mode transmission on the chip and prevents stray light from coupling to the detectors.

  2. Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development

    Science.gov (United States)

    Chuss, D. T.; Ali, A.; Amiri, M.; Appel, J.; Bennett, C. L.; Colazo, F.; Denis, K. L.; Dünner, R.; Essinger-Hileman, T.; Eimer, J.; Fluxa, P.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G.; Hubmayr, J.; Iuliano, J.; Marriage, T. A.; Miller, N.; Moseley, S. H.; Mumby, G.; Petroff, M.; Reintsema, C.; Rostem, K.; U-Yen, K.; Watts, D.; Wagner, E.; Wollack, E. J.; Xu, Z.; Zeng, L.

    2016-08-01

    The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe ˜ 70 % of the sky. A variable-delay polarization modulator provides modulation of the polarization at ˜ 10 Hz to suppress the 1/ f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that spans both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously detect two orthogonal linear polarizations. The use of single-crystal silicon as the dielectric for the on-chip transmission lines enables both high efficiency and uniformity in fabrication. Integrated band definition has been implemented that both controls the bandpass of the single-mode transmission on the chip and prevents stray light from coupling to the detectors.

  3. Chirality and the angular momentum of light

    Science.gov (United States)

    Cameron, Robert P.; Götte, Jörg B.; Barnett, Stephen M.; Yao, Alison M.

    2017-02-01

    Chirality is exhibited by objects that cannot be rotated into their mirror images. It is far from obvious that this has anything to do with the angular momentum of light, which owes its existence to rotational symmetries. There is nevertheless a subtle connection between chirality and the angular momentum of light. We demonstrate this connection and, in particular, its significance in the context of chiral light-matter interactions. This article is part of the themed issue 'Optical orbital angular momentum'.

  4. Management of angular cheilitis for children

    Directory of Open Access Journals (Sweden)

    Fajriani Fajriani

    2016-06-01

    Full Text Available Angular cheilitis is one type of oral soft tissue disease that can occur in both children and adults, the condition is characterized by cracks and inflammation in both corners of the mouth. Although this disease does not cause severe disruption but quite disturbing activity and also one's physical appearance. Angular cheilitis light will disappear on their own over time.Severe conditions that can cause pain and bleading. aims to give feedback on peers about managment angular cheilitis in children.

  5. The difficulty of measuring orbital angular momentum

    Directory of Open Access Journals (Sweden)

    D. Preece

    2011-09-01

    Full Text Available Light can carry angular momentum as well as energy and momentum; the transfer of this angular momentum to an object results in an optical torque. The development of a rotational analogue to the force measurement capability of optical tweezers is hampered by the difficulty of optical measurement of orbital angular momentum. We present an experiment with encouraging results, but emphasise the difficulty of the task.

  6. A Novel Permanent Magnetic Angular Acceleration Sensor

    OpenAIRE

    Hao Zhao; Hao Feng

    2015-01-01

    Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it h...

  7. Magnetic Modulation of Stellar Angular Momentum Loss

    CERN Document Server

    Garraffo, Cecilia; Cohen, Ofer

    2014-01-01

    Angular Momentum Loss is important for understanding astrophysical phenomena such as stellar rotation, magnetic activity, close binaries, and cataclysmic variables. Magnetic breaking is the dominant mechanism in the spin down of young late-type stars. We have studied angular momentum loss as a function of stellar magnetic activity. We argue that the complexity of the field and its latitudinal distribution are crucial for angular momentum loss rates. In this work we discuss how angular momentum is modulated by magnetic cycles, and how stellar spin down is not just a simple function of large scale magnetic field strength.

  8. N(HI) and Jet Power/Emission in AGNs

    Indian Academy of Sciences (India)

    Zhongzu Wu; Minfeng Gu; Ming Zhu

    2011-03-01

    Neutral hydrogen (HI) 21-cm absorption has been detected against very powerful radio jets. In this paper, based on Gupta’s sample (Gupta et al. 2006), we present our preliminary study of the correlations between the HI column density N(HI) and the jet power, N(HI) versus the low frequency luminosity at 408 MHz, and N(HI) versus the radio luminosity at 1400 MHz.

  9. Transverse and longitudinal angular momenta of light

    Energy Technology Data Exchange (ETDEWEB)

    Bliokh, Konstantin Y., E-mail: k.bliokh@gmail.com [Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Nonlinear Physics Centre, RSPhysE, The Australian National University, Canberra, ACT 0200 (Australia); Nori, Franco [Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)

    2015-08-26

    We review basic physics and novel types of optical angular momentum. We start with a theoretical overview of momentum and angular momentum properties of generic optical fields, and discuss methods for their experimental measurements. In particular, we describe the well-known longitudinal (i.e., aligned with the mean momentum) spin and orbital angular momenta in polarized vortex beams. Then, we focus on the transverse (i.e., orthogonal to the mean momentum) spin and orbital angular momenta, which were recently actively discussed in theory and observed in experiments. First, the recently-discovered transverse spin  angular momenta appear in various structured fields: evanescent waves, interference fields, and focused beams. We show that there are several kinds of transverse spin angular momentum, which differ strongly in their origins and physical properties. We describe extraordinary features of the transverse optical spins and overview recent experiments. In particular, the helicity-independent transverse spin inherent in edge evanescent waves offers robust spin–direction coupling at optical interfaces (the quantum spin Hall effect of light). Second, we overview the transverse orbital angular momenta of light, which can be both extrinsic and intrinsic. These two types of the transverse orbital angular momentum are produced by spatial shifts of the optical beams (e.g., in the spin Hall effect of light) and their Lorentz boosts, respectively. Our review is underpinned by a unified theory of the angular momentum of light based on the canonical momentum and spin densities, which avoids complications associated with the separation of spin and orbital angular momenta in the Poynting picture. It allows us to construct a comprehensive classification of all known optical angular momenta based on their key parameters and main physical properties.

  10. Time-delay cosmography: increased leverage with angular diameter distances

    Science.gov (United States)

    Jee, I.; Komatsu, E.; Suyu, S. H.; Huterer, D.

    2016-04-01

    Strong lensing time-delay systems constrain cosmological parameters via the so-called time-delay distance and the angular diameter distance to the lens. In previous studies, only the former information was used in forecasting cosmographic constraints. In this paper, we show that the cosmological constraints improve significantly when the latter information is also included. Specifically, the angular diameter distance plays a crucial role in breaking the degeneracy between the curvature of the Universe and the time-varying equation of state of dark energy. Using a mock sample of 55 bright quadruple lens systems based on expectations for ongoing/future imaging surveys, we find that adding the angular diameter distance information to the time-delay distance information and the Planck's measurements of the cosmic microwave background anisotropies improves the constraint on the constant equation of state by 30%, on the time variation in the equation of state by a factor of two, and on the Hubble constant in the flat ΛCDM model by a factor of two. Therefore, previous forecasts for the statistical power of time-delay systems were overly pessimistic, i.e., time-delay systems are more powerful than previously appreciated.

  11. Angular velocity and centripetal acceleration relationship

    Science.gov (United States)

    Monteiro, Martín; Cabeza, Cecilia; Marti, Arturo C.; Vogt, Patrik; Kuhn, Jochen

    2014-05-01

    During the last few years, the growing boom of smartphones has given rise to a considerable number of applications exploiting the functionality of the sensors incorporated in these devices. A sector that has unexpectedly taken advantage of the power of these tools is physics teaching, as reflected in several recent papers. In effect, the use of smartphones has been proposed in several physics experiments spanning mechanics, electromagnetism, optics, oscillations, and waves, among other subjects. Although mechanical experiments have received considerable attention, most of them are based on the use of the accelerometer. An aspect that has received less attention is the use of rotation sensors or gyroscopes. An additional advance in the use of these devices is given by the possibility of obtaining data using the accelerometer and the gyroscope simultaneously. The aim of this paper is to consider the relation between the centripetal acceleration and the angular velocity. Instead of using a formal laboratory setup, in this experiment a smartphone is attached to the floor of a merry-go-round, found in many playgrounds. Several experiments were performed with the roundabout rotating in both directions and with the smart-phone at different distances from the center. The coherence of the measurements is shown.

  12. CLASS: The Cosmology Large Angular Scale Surveyor

    CERN Document Server

    Essinger-Hileman, Thomas; Amiri, Mandana; Appel, John W; Araujo, Derek; Bennett, Charles L; Boone, Fletcher; Chan, Manwei; Cho, Hsiao-Mei; Chuss, David T; Colazo, Felipe; Crowe, Erik; Denis, Kevin; Dünner, Rolando; Eimer, Joseph; Gothe, Dominik; Halpern, Mark; Harrington, Kathleen; Hilton, Gene; Hinshaw, Gary F; Huang, Caroline; Irwin, Kent; Jones, Glenn; Karakla, John; Kogut, Alan J; Larson, David; Limon, Michele; Lowry, Lindsay; Marriage, Tobias; Mehrle, Nicholas; Miller, Amber D; Miller, Nathan; Moseley, Samuel H; Novak, Giles; Reintsema, Carl; Rostem, Karwan; Stevenson, Thomas; Towner, Deborah; U-Yen, Kongpop; Wagner, Emily; Watts, Duncan; Wollack, Edward; Xu, Zhilei; Zeng, Lingzhen

    2014-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravita-tional-wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70\\% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low $\\ell$. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of $r=0.01$ and make a cosmi...

  13. CLASS: The Cosmology Large Angular Scale Surveyor

    Science.gov (United States)

    Essinger-Hileman, Thomas; Ali, Aamir; Amiri, Mandana; Appel, John W.; Araujo, Derek; Bennett, Charles L.; Boone, Fletcher; Chan, Manwei; Cho, Hsiao-Mei; Chuss, David T.; Colazo, Felipe; Crowe, Erik; Denis, Kevin; Dunner, Rolando; Eimer, Joseph; Gothe, Dominik; Halpern, Mark; Kogut, Alan J.; Miller, Nathan; Moseley, Samuel; Rostem, Karwan; Stevenson, Thomas; Towner, Deborah; U-Yen, Kongpop; Wollack, Edward

    2014-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravitational wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low-length. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of r = 0:01 and make a cosmic-variance-limited measurement of the optical depth to the surface of last scattering, tau. (c) (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  14. Angular Momentum Distribution in the Transverse Plane

    CERN Document Server

    Adhikari, Lekha

    2016-01-01

    Several possibilities to relate the $t$-dependence of Generalized Parton Distributions (GPDs) to the distribution of angular momentum in the transverse plane are discussed. Using a simple spectator model we demonstrate that non of them correctly describes the orbital angular momentum distribution that for a longitudinally polarized nucleon obtained directly from light-front wavefunctions.

  15. Responsive web design with AngularJS

    CERN Document Server

    Patel, Sandeep Kumar

    2014-01-01

    If you are an AngularJS developer who wants to learn about responsive web application development, this book is ideal for you. Responsive Web Design with AngularJS is intended for web developers or designers with a basic knowledge of HTML, CSS, and JavaScript.

  16. Quantum Correlation Coefficients for Angular Coherent States

    Institute of Scientific and Technical Information of China (English)

    CHEN Wei; HE Yan; GUO Hao

    2009-01-01

    Quantum covariance and correlation coefficients of angular or SU(2) coherent states are directly calculated for all irreducible unitary representations.These results explicitly verify that the angular coherent states minimize the Robertson-Schrodinger uncertainty relation for all spins, which means that they are the so-called intelligent states.The same results can be obtained by the Schwinger representation approach.

  17. Accelerated rotation with orbital angular momentum modes

    CSIR Research Space (South Africa)

    Schulze, C

    2015-04-01

    Full Text Available A 91, 043821 (2015) Accelerated rotation with orbital angular momentum modes Christian Schulze, Filippus S. Roux, Angela Dudley, Ronald Rop, Michael Duparr´e, and Andrew Forbes Abstract: We introduce a class of light field that angularly...

  18. The Orbital Angular Momentum Sum Rule

    Science.gov (United States)

    Aslan, Fatma; Burkardt, Matthias

    2015-10-01

    As an alternative to the Ji sum rule for the quark angular momentum, a sum rule for the quark orbital angular momentum, based on a twist-3 generalized parton distribution, has been suggested. We study the validity of this sum rule in the context of scalar Yukawa interactions as well as in QED for an electron.

  19. Angular Momentum Eigenstates for Equivalent Electrons.

    Science.gov (United States)

    Tuttle, E. R.; Calvert, J. B.

    1981-01-01

    Simple and efficient methods for adding angular momenta and for finding angular momentum eigenstates for systems of equivalent electrons are developed. Several different common representations are used in specific examples. The material is suitable for a graduate course in quantum mechanics. (SK)

  20. Physical Angular Momentum Separation for QED

    CERN Document Server

    Sun, Weimin

    2016-01-01

    We study the non-uniqueness problem of the gauge-invariant angular momentum separation for the case of QED, which stems from the recent controversy concerning the proper definitions of the orbital angular momentum and spin operator of the individual parts of a gauge field system. For the free quantum electrodynamics without matter, we show that the basic requirement of Euclidean symmetry selects a unique physical angular momentum separation scheme from the multitude of the possible angular momentum separation schemes constructed using the various Gauge Invariant Extentions. Based on these results, we propose a set of natural angular momentum separation schemes for the case of interacting QED by invoking the formalism of asymptotic fields. Some perspectives on such a problem for the case of QCD are briefly discussed.

  1. Does high harmonic generation conserve angular momentum?

    CERN Document Server

    Fleischer, Avner; Diskin, Tzvi; Sidorenko, Pavel; Cohen, Oren

    2013-01-01

    High harmonic generation (HHG) is a unique and useful process in which infrared or visible radiation is frequency up converted into the extreme ultraviolet and x ray spectral regions. As a parametric process, high harmonic generation should conserve the radiation energy, momentum and angular momentum. Indeed, conservation of energy and momentum have been demonstrated. Angular momentum of optical beams can be divided into two components: orbital and spin (polarization). Orbital angular momentum is assumed to be conserved and recently observed deviations were attributed to propagation effects. On the other hand, conservation of spin angular momentum has thus far never been studied, neither experimentally nor theoretically. Here, we present the first study on the role of spin angular momentum in extreme nonlinear optics by experimentally generating high harmonics of bi chromatic elliptically polarized pump beams that interact with isotropic media. While observing that the selection rules qualitatively correspond...

  2. Measurement of polarization with the Degree Angular Scale Interferometer.

    Science.gov (United States)

    Leitch, E M; Kovac, J M; Pryke, C; Carlstrom, J E; Halverson, N W; Holzapfel, W L; Dragovan, M; Reddall, B; Sandberg, E S

    Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision the conditions of the Universe when it was approximately 400,000 years old. The three most fundamental properties of the CMB are its frequency spectrum (which determines the temperature), and the fluctuations in both the temperature and polarization across a range of angular scales. The frequency spectrum has been well determined, and considerable progress has been made in measuring the power spectrum of the temperature fluctuations. But despite many efforts to measure the polarization, detection of this property of the CMB has hitherto been beyond the reach of even the most sensitive observations. Here we describe the Degree Angular Scale Interferometer (DASI), an array of radio telescopes, which for the past two years has conducted polarization-sensitive observations of the CMB from the Amundsen-Scott South Pole research station.

  3. Angular dependent light emission from planar waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Peter, Jaison, E-mail: jaison.peter@gmail.com [International School of Photonics, Cochin University of Science and Technology, Cochin 682022 (India); CRE" +E, IDEAS Research Institute, Robert Gordon University, Aberdeen AB10 7GJ (United Kingdom); Prabhu, Radhakrishna [CRE" +E, IDEAS Research Institute, Robert Gordon University, Aberdeen AB10 7GJ (United Kingdom); Radhakrishnan, P.; Vallabhan, C. P. G.; Nampoori, V. P. N.; Kailasnath, M. [International School of Photonics, Cochin University of Science and Technology, Cochin 682022 (India)

    2015-01-07

    We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (θ) from the plane parallel to film. From the detailed examination of the output emission spectra, as +θ increases from 0° there has been an initial decrease in output intensity, but at a particular angle ≈10° an increase in output intensity was observed. This additional peak in output intensity as +θ is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (∼50 μm thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM <0.2 nm was observed at 578 nm.

  4. Angular Rate Sensor Joint Kinematics Applications

    Directory of Open Access Journals (Sweden)

    Gregory W. Hall

    1997-01-01

    Full Text Available High speed rotary motion of complex joints were quantified with triaxial angular rate sensors. Angular rate sensors were mounted to rigid links on either side of a joint to measure angular velocities about three orthogonal sensor axes. After collecting the data, the angular velocity vector of each sensor was transformed to local link axes and integrated to obtain the incremental change in angular position for each time step. Using the angular position time histories, a transformation matrix between the reference frame of each link was calculated. Incremental Eulerian rotations from the transformation matrix were calculated using an axis system defined for the joint. Summation of the incremental Eulerian rotations produced the angular position of the joint in terms of the standard axes. This procedure is illustrated by applying it to joint motion of the ankle, the spine, and the neck of crash dummies during impact tests. The methodology exhibited an accuracy of less than 5% error, improved flexibility over photographic techniques, and the ability to examine 3-dimensional motion.

  5. Novel Detection of Optical Orbital Angular Momentum

    Science.gov (United States)

    2014-11-16

    Spreeuw, J. P . Woerdman, “ Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes,” Phys. Rev. A, 45(11), 8185-8189...AFRL-RD-PS- AFRL-RD-PS TR-2014-0045 TR-2014-0045 Novel Detection of Optical Orbital Angular Momentum David Voelz Klipsch... Orbital Angular Momentum FA9451-13-1-0261 GR0004113 David Voelz Klipsch School of ECE New Mexico State University MSC 3-O, PO Box 30001 Las Cruces, NM

  6. Angular Fock coefficients. Fixing the errors, and further development

    CERN Document Server

    Liverts, Evgeny Z

    2015-01-01

    The angular coefficients $\\psi_{k,p}(\\alpha,\\theta)$ of the Fock expansion characterizing the S-state wave function of the two-electron atomic system, are calculated in hyperspherical angular coordinates $\\alpha$ and $\\theta$. To solve the problem the Fock recurrence relations separated into the independent individual equations associated with definite power $j$ of the nucleus charge $Z$, are applied. The "pure" $j$-components of the angular Fock coefficients, orthogonal to of the hyperspherical harmonics $Y_{kl}$, are found for even values of $k$. To this end, the specific coupling equation is proposed and applied. Effective techniques for solving the individual equations with simplest nonseparable and separable right-hand sides are proposed. Some mistakes/misprints made earlier in representations of $\\psi_{2,0}$, were noted and corrected. All $j$-components of $\\psi_{4,1}$ and the majority of components and subcomponents of $\\psi_{3,0}$ are calculated and presented for the first time. All calculations were ...

  7. Angular dependence of primordial trispectra and CMB spectral distortions

    Science.gov (United States)

    Shiraishi, Maresuke; Bartolo, Nicola; Liguori, Michele

    2016-10-01

    Under the presence of anisotropic sources in the inflationary era, the trispectrum of the primordial curvature perturbation has a very specific angular dependence between each wavevector that is distinguishable from the one encountered when only scalar fields are present, characterized by an angular dependence described by Legendre polynomials. We examine the imprints left by curvature trispectra on the TTμ bispectrum, generated by the correlation between temperature anisotropies (T) and chemical potential spectral distortions (μ) of the Cosmic Microwave Background (CMB). Due to the angular dependence of the primordial signal, the corresponding TTμ bispectrum strongly differs in shape from TTμ sourced by the usual gNL or τNL local trispectra, enabling us to obtain an unbiased estimation. From a Fisher matrix analysis, we find that, in a cosmic-variance-limited (CVL) survey of TTμ, a minimum detectable value of the quadrupolar Legendre coefficient is d2 ~ 0.01, which is 4 orders of magnitude better than the best value attainable from the TTTT CMB trispectrum. In the case of an anisotropic inflationary model with a f(phi)F2 interaction (coupling the inflaton field phi with a vector kinetic term F2), the size of the curvature trispectrum is related to that of quadrupolar power spectrum asymmetry, g*. In this case, a CVL measurement of TTμ makes it possible to measure g* down to 10‑3.

  8. Gravitational waves carrying orbital angular momentum

    CERN Document Server

    Bialynicki-Birula, Iwo

    2015-01-01

    Spinorial formalism is used to map every electromagnetic wave into the gravitational wave (within the linearized gravity). In this way we can obtain the gravitational counterparts of Bessel, Laguerre-Gauss, and other light beams carrying orbital angular momentum.

  9. Radiofrequency encoded angular-resolved light scattering

    DEFF Research Database (Denmark)

    Buckley, Brandon W.; Akbari, Najva; Diebold, Eric D.

    2015-01-01

    The sensitive, specific, and label-free classification of microscopic cells and organisms is one of the outstanding problems in biology. Today, instruments such as the flow cytometer use a combination of light scatter measurements at two distinct angles to infer the size and internal complexity...... of cells at rates of more than 10,000 per second. However, by examining the entire angular light scattering spectrum it is possible to classify cells with higher resolution and specificity. Current approaches to performing these angular spectrum measurements all have significant throughput limitations...... Encoded Angular-resolved Light Scattering (REALS), this technique multiplexes angular light scattering in the radiofrequency domain, such that a single photodetector captures the entire scattering spectrum from a particle over approximately 100 discrete incident angles on a single shot basis. As a proof...

  10. Amplitude damping channel for orbital angular momentum

    CSIR Research Space (South Africa)

    Dudley, Angela L

    2010-03-01

    Full Text Available Since the pioneering work on the entanglement of the orbital angular momentum (OAM) states of light, much attention has been devoted to the subject, with particular attention into the quantum aspects of information processing using OAM. Furthermore...

  11. The Relationship between Pedal Force and Crank Angular Velocity in Sprint Cycling.

    Science.gov (United States)

    Bobbert, Maarten Frank; Casius, L J Richard; Van Soest, Arthur J

    2016-05-01

    Relationships between tangential pedal force and crank angular velocity in sprint cycling tend to be linear. We set out to understand why they are not hyperbolic, like the intrinsic force-velocity relationship of muscles. We simulated isokinetic sprint cycling at crank angular velocities ranging from 30 to 150 rpm with a forward dynamic model of the human musculoskeletal system actuated by eight lower extremity muscle groups. The input of the model was muscle stimulation over time, which we optimized to maximize average power output over a cycle. Peak tangential pedal force was found to drop more with crank angular velocity than expected based on intrinsic muscle properties. This linearizing effect was not due to segmental dynamics but rather due to active state dynamics. Maximizing average power in cycling requires muscles to bring their active state from as high as possible during shortening to as low as possible during lengthening. Reducing the active state is a relatively slow process, and hence must be initiated a certain amount of time before lengthening starts. As crank angular velocity goes up, this amount of time corresponds to a greater angular displacement, so the instant of switching off extensor muscle stimulation must occur earlier relative to the angle at which pedal force was extracted for the force-velocity relationship. Relationships between pedal force and crank angular velocity in sprint cycling do not reflect solely the intrinsic force-velocity relationship of muscles but also the consequences of activation dynamics.

  12. Mastering AngularJD for .NET developers

    CERN Document Server

    Majid, Mohammad Wadood

    2015-01-01

    This book is envisioned for traditional developers and programmers who want to develop client-side applications using the AngularJS framework and ASP.NET Web API 2 with Visual Studio. .NET developers who have already built web applications or web services and who have a fundamental knowledge of HTML, JavaScript, and CSS and want to explore single-page applications will also find this guide useful. Basic knowledge of AngularJS would be helpful.

  13. Generalized Uncertainty Principle and Angular Momentum

    CERN Document Server

    Bosso, Pasquale

    2016-01-01

    Various models of quantum gravity suggest a modification of the Heisenberg's Uncertainty Principle, to the so-called Generalized Uncertainty Principle, between position and momentum. In this work we show how this modification influences the theory of angular momentum in Quantum Mechanics. In particular, we compute Planck scale corrections to angular momentum eigenvalues, the Hydrogen atom spectrum, the Stern-Gerlach experiment and the Clebsch-Gordan coefficients. We also examine effects of the Generalized Uncertainty Principle on multi-particle systems.

  14. Angular distribution in complex oscillation theory

    Institute of Scientific and Technical Information of China (English)

    WU Shengjian

    2005-01-01

    Let f1 and f2 be two linearly independent solutions of the differential equation f" + Af =0,where A is an entire function.Set E-f1f2.In this paper,we shall study the angular distribution of E and establish a relation between zero accumulation rays and Borel directions of E.Consequently we can obtain some results in the complex differential equation by using known results in angular distribution theory of meromorphic functions.

  15. Geometric absorption of electromagnetic angular momentum

    Science.gov (United States)

    Konz, C.; Benford, Gregory

    2003-10-01

    Circularly polarized electromagnetic fields carry both energy and angular momentum. We investigate the conditions under which a circularly polarized wave field transfers angular momentum to a perfectly conducting macroscopic object, using exact electromagnetic wave theory in a steady-state calculation. We find that axisymmetric perfect conductors cannot absorb or radiate angular momentum when illuminated. However, any asymmetry allows absorption. A rigorous, steady-state solution of the boundary value problem for the reflection from a perfectly conducting infinite wedge shows that waves convey angular momentum at the edges of asymmetries. Conductors can also radiate angular momentum, so their geometric absorption coefficient for angular momentum can be negative. Such absorption or radiation depends solely on the specific geometry of the conductor. The geometric absorption coefficient can be as high as 0.8, and the coefficient for radiation can be -0.4, larger than typical material absorption coefficients. We apply the results to recent experiments which spun roof-shaped aluminum sheets with polarized microwave beams. Applications of geometric, instead of material, absorption can be quite varied. Though experiments testing these ideas will be simpler at microwavelengths, the ideas work for optical ones as well.

  16. Partial angular coherence and the angular Schmidt spectrum of entangled two-photon fields

    Energy Technology Data Exchange (ETDEWEB)

    Jha, Anand Kumar; Boyd, Robert W. [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Agarwal, Girish S. [Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)

    2011-12-15

    We study partially coherent fields that have a coherent-mode representation in the orbital-angular-momentum-mode basis. For such fields, we introduce the concepts of the angular coherence function and the coherence angle. Such fields are naturally produced by the process of parametric down-conversion--a second-order nonlinear optical process in which a pump photon breaks up into two entangled photons, known as the signal and idler photons. We show that the angular coherence functions of the signal and idler fields are directly related to the angular Schmidt (spiral) spectrum of the down-converted two-photon field and thus that the angular Schmidt spectrum can be measured directly by measuring the angular coherence function of either the signal or the idler field, without requiring coincidence detection.

  17. Characterization of the Bell-Shaped Vibratory Angular Rate Gyro

    Directory of Open Access Journals (Sweden)

    Junfang Fan

    2013-08-01

    Full Text Available The bell-shaped vibratory angular rate gyro (abbreviated as BVG is a novel shell vibratory gyroscope, which is inspired by the Chinese traditional bell. It sensitizes angular velocity through the standing wave precession effect. The bell-shaped resonator is a core component of the BVG and looks like the millimeter-grade Chinese traditional bell, such as QianLong Bell and Yongle Bell. It is made of Ni43CrTi, which is a constant modulus alloy. The exciting element, control element and detection element are uniformly distributed and attached to the resonator, respectively. This work presents the design, analysis and experimentation on the BVG. It is most important to analyze the vibratory character of the bell-shaped resonator. The strain equation, internal force and the resonator's equilibrium differential equation are derived in the orthogonal curvilinear coordinate system. When the input angular velocity is existent on the sensitive axis, an analysis of the vibratory character is performed using the theory of thin shells. On this basis, the mode shape function and the simplified second order normal vibration mode dynamical equation are obtained. The coriolis coupling relationship about the primary mode and secondary mode is established. The methods of the signal processing and control loop are presented. Analyzing the impact resistance property of the bell-shaped resonator, which is compared with other shell resonators using the Finite Element Method, demonstrates that BVG has the advantage of a better impact resistance property. A reasonable means of installation and a prototypal gyro are designed. The gyroscopic effect of the BVG is characterized through experiments. Experimental results show that the BVG has not only the advantages of low cost, low power, long work life, high sensitivity, and so on, but, also, of a simple structure and a better impact resistance property for low and medium angular velocity measurements.

  18. Angular-resolution and material-characterization measurements for a dual-particle imaging system with mixed-oxide fuel

    Energy Technology Data Exchange (ETDEWEB)

    Poitrasson-Rivière, Alexis, E-mail: alexispr@umich.edu [Department of Nuclear Engineering & Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Polack, J. Kyle; Hamel, Michael C.; Klemm, Dietrich D.; Ito, Kai; McSpaden, Alexander T.; Flaska, Marek; Clarke, Shaun D.; Pozzi, Sara A. [Department of Nuclear Engineering & Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Tomanin, Alice [Lainsa-Italia S.R.L., Via E. Fermi 2749, 21027 Ispra, VA (Italy); Peerani, Paolo [European Commission, Joint Research Centre, Institute for Transuranium Elements, 21027 Ispra, VA (Italy)

    2015-10-11

    A dual-particle imaging (DPI) system, capable of simultaneously imaging fast neutrons and gamma rays, has been operated in the presence of mixed-oxide (MOX) fuel to assess the system's angular resolution and material-characterization capabilities. The detection principle is based on the scattering physics of neutrons (elastic scattering) and gamma rays (Compton scattering) in organic and inorganic scintillators. The detection system is designed as a combination of a two-plane Compton camera and a neutron-scatter camera. The front plane consists of EJ-309 liquid scintillators and the back plane consists of interleaved EJ-309 and NaI(Tl) scintillators. MCNPX-PoliMi was used to optimize the geometry of the system and the resulting prototype was built and tested using a Cf-252 source as an SNM surrogate. A software package was developed to acquire and process data in real time. The software was used for a measurement campaign to assess the angular resolution of the imaging system with MOX samples. Measurements of two MOX canisters of similar isotopics and intensity were performed for 6 different canister separations (from 5° to 30°, corresponding to distances of 21 cm and 131 cm, respectively). The measurements yielded a minimum separation of 20° at 2.5 m (86-cm separation) required to see 2 separate hot spots. Additionally, the results displayed good agreement with MCNPX-PoliMi simulations. These results indicate an angular resolution between 15° and 20°, given the 5° step. Coupled with its large field of view, and its capability to differentiate between spontaneous fission and (α,n) sources, the DPI system shows its potential for nuclear-nonproliferation applications.

  19. Angular-resolution and material-characterization measurements for a dual-particle imaging system with mixed-oxide fuel

    Science.gov (United States)

    Poitrasson-Rivière, Alexis; Polack, J. Kyle; Hamel, Michael C.; Klemm, Dietrich D.; Ito, Kai; McSpaden, Alexander T.; Flaska, Marek; Clarke, Shaun D.; Pozzi, Sara A.; Tomanin, Alice; Peerani, Paolo

    2015-10-01

    A dual-particle imaging (DPI) system, capable of simultaneously imaging fast neutrons and gamma rays, has been operated in the presence of mixed-oxide (MOX) fuel to assess the system's angular resolution and material-characterization capabilities. The detection principle is based on the scattering physics of neutrons (elastic scattering) and gamma rays (Compton scattering) in organic and inorganic scintillators. The detection system is designed as a combination of a two-plane Compton camera and a neutron-scatter camera. The front plane consists of EJ-309 liquid scintillators and the back plane consists of interleaved EJ-309 and NaI(Tl) scintillators. MCNPX-PoliMi was used to optimize the geometry of the system and the resulting prototype was built and tested using a Cf-252 source as an SNM surrogate. A software package was developed to acquire and process data in real time. The software was used for a measurement campaign to assess the angular resolution of the imaging system with MOX samples. Measurements of two MOX canisters of similar isotopics and intensity were performed for 6 different canister separations (from 5° to 30°, corresponding to distances of 21 cm and 131 cm, respectively). The measurements yielded a minimum separation of 20° at 2.5 m (86-cm separation) required to see 2 separate hot spots. Additionally, the results displayed good agreement with MCNPX-PoliMi simulations. These results indicate an angular resolution between 15° and 20°, given the 5° step. Coupled with its large field of view, and its capability to differentiate between spontaneous fission and (α,n) sources, the DPI system shows its potential for nuclear-nonproliferation applications.

  20. Ultrafast angular momentum transfer in multisublattice ferrimagnets.

    Science.gov (United States)

    Bergeard, N; López-Flores, V; Halté, V; Hehn, M; Stamm, C; Pontius, N; Beaurepaire, E; Boeglin, C

    2014-03-11

    Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by ~150 fs.

  1. An orbital angular momentum spectrometer for electrons

    Science.gov (United States)

    Harvey, Tyler; Grillo, Vincenzo; McMorran, Benjamin

    2016-05-01

    With the advent of techniques for preparation of free-electron and neutron orbital angular momentum (OAM) states, a basic follow-up question emerges: how do we measure the orbital angular momentum state distribution in matter waves? Control of both the energy and helicity of light has produced a range of spectroscopic applications, including molecular fingerprinting and magnetization mapping. Realization of an analogous dual energy-OAM spectroscopy with matter waves demands control of both initial and final energy and orbital angular momentum states: unlike for photons, final state post-selection is necessary for particles that cannot be annihilated. We propose a magnetic field-based mechanism for quantum non-demolition measurement of electron OAM. We show that OAM-dependent lensing is produced by an operator of form U =exp iLzρ2/ℏb2 where ρ =√{x2 +y2 } is the radial position operator, Lz is the orbital angular momentum operator along z, and b is the OAM dispersion length. We can physically realize this operator as a term in the time evolution of an electron in magnetic round lens. We discuss prospects and practical challenges for implementation of a lensing orbital angular momentum measurement. This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under the Early Career Research Program Award # DE-SC0010466.

  2. Data-oriented development with AngularJS

    CERN Document Server

    Waikar, Manoj

    2015-01-01

    This book helps beginner-level AngularJS developers organize AngularJS applications by discussing important AngularJS concepts and best practices. If you are an experienced AngularJS developer but haven't written directives or haven't created custom HTML controls before, then this book is ideal for you.

  3. Energy and angular distributions of atmospheric muons at the Earth

    CERN Document Server

    Shukla, Prashant

    2016-01-01

    A fair knowledge of the atmospheric muon distributions at Earth is a prerequisite for the simulations of cosmic ray setups and rare event search detectors. A modified power law is proposed for atmospheric muon energy distribution which gives good description of the cosmic muon data in low as well as high energy regime. Using this distribution, analytical forms for zenith angle ($\\theta$) distribution are obtained. Assuming a flat Earth, it leads to the $\\cos^{n-1}\\theta$ form where it is shown that the parameter $n$ is nothing but the power of the energy distribution. A new analytical form for zenith angle distribution is obtained without assuming a flat Earth which gives an improved description of the data at all angles even above $70^o$. These distributions are tested with the available atmospheric muon data of energy and angular distributions. The parameters of these distributions can be used to characterize the cosmic muon data as a function of energy, angle and altitude.

  4. Angular momentum transfer in incomplete fusion

    Indian Academy of Sciences (India)

    B S Tomar; K Surendra Babu; K Sudarshan; R Tripathi; A Goswami

    2005-02-01

    Isomeric cross-section ratios of evaporation residues formed in 12C+93Nb and 16O + 89Y reactions were measured by recoil catcher technique followed by off-line -ray spectrometry in the beam energy range of 55.7-77.5 MeV for 12C and 68-81 MeV for 16O. The isomeric cross-section ratios were resolved into that for complete and incomplete fusion reactions. The angular momentum of the intermediate nucleus formed in incomplete fusion was deduced from the isomeric cross-section ratio by considering the statistical de-excitation of the incompletely fused composite nucleus. The data show that incomplete fusion is associated with angular momenta slightly smaller than critical angular momentum for complete fusion, indicating the deeper interpenetration of projectile and target nuclei than that in peripheral collisions.

  5. Surface angular momentum of light beams.

    Science.gov (United States)

    Ornigotti, Marco; Aiello, Andrea

    2014-03-24

    Traditionally, the angular momentum of light is calculated for "bullet-like" electromagnetic wave packets, although in actual optical experiments "pencil-like" beams of light are more commonly used. The fact that a wave packet is bounded transversely and longitudinally while a beam has, in principle, an infinite extent along the direction of propagation, renders incomplete the textbook calculation of the spin/orbital separation of the angular momentum of a light beam. In this work we demonstrate that a novel, extra surface part must be added in order to preserve the gauge invariance of the optical angular momentum per unit length. The impact of this extra term is quantified by means of two examples: a Laguerre-Gaussian and a Bessel beam, both circularly polarized.

  6. Localizing the Angular Momentum of Linear Gravity

    CERN Document Server

    Butcher, Luke M; Hobson, Michael; 10.1103/PhysRevD.86.084012

    2012-01-01

    In a previous article [Phys. Rev. D 82 104040 (2010)], we derived an energy-momentum tensor for linear gravity that exhibited positive energy density and causal energy flux. Here we extend this framework by localizing the angular momentum of the linearized gravitational field, deriving a gravitational spin tensor which possesses similarly desirable properties. By examining the local exchange of angular momentum (between matter and gravity) we find that gravitational intrinsic spin is localized, separately from orbital angular momentum, in terms of a gravitational spin tensor. This spin tensor is then uniquely determined by requiring that it obey two simple physically motivated algebraic conditions. Firstly, the spin of an arbitrary (harmonic-gauge) gravitational plane wave is required to flow in the direction of propagation of the wave. Secondly, the spin tensor of any transverse-traceless gravitational field is required to be traceless. (The second condition ensures that local field redefinitions suffice to ...

  7. Chirality and angular momentum in optical radiation

    CERN Document Server

    Coles, Matt M

    2012-01-01

    This paper develops, in precise quantum electrodynamic terms, photonic attributes of the "optical chirality density", one of several measures long known to be conserved quantities for a vacuum electromagnetic field. The analysis lends insights into some recent interpretations of chiroptical experiments, in which this measure, and an associated chirality flux, have been treated as representing physically distinctive "superchiral" phenomena. In the fully quantized formalism the chirality density is promoted to operator status, whose exploration with reference to an arbitrary polarization basis reveals relationships to optical angular momentum and helicity operators. Analyzing multi-mode beams with complex wave-front structures, notably Laguerre-Gaussian modes, affords a deeper understanding of the interplay between optical chirality and optical angular momentum. By developing theory with due cognizance of the photonic character of light, it emerges that only the spin angular momentum of light is engaged in such...

  8. Physics from Angular Projection of Rectangular Grids

    CERN Document Server

    Singh, Ashmeet

    2015-01-01

    In this paper, we present a mathematical model for the angular projection of a rectangular arrangement of points in a grid. This simple, yet interesting problem, has both a scholarly value and applications for data extraction techniques to study the physics of various systems. Our work can interest undergraduate students to understand subtle points in the angular projection of a grid and describes various quantities of interest in the projection with completeness and sufficient rigour. We show that for certain angular ranges, the projection has non-distinctness, and calculate the details of such angles, and correspondingly, the number of distinct points and the total projected length. We focus on interesting trends obtained for the projected length of the grid elements and present a simple application of the model to determine the geometry of an unknown grid whose spatial extensions are known, using measurement of the grid projection at two angles only. Towards the end, our model is shown to have potential ap...

  9. Angular momentum transport in protostellar discs

    CERN Document Server

    Salmeron, Roberto Aureliano; Wardle, M; Salmeron, Raquel; Konigl, Arieh; Wardle, Mark

    2006-01-01

    Angular momentum transport in protostellar discs can take place either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large-scale magnetic field that threads the disc. Using semi-analytic and numerical results, we construct a model of steady-state discs that includes vertical transport by a centrifugally driven wind as well as MRI-induced turbulence. We present approximate criteria for the occurrence of either one of these mechanisms in an ambipolar diffusion-dominated disc. We derive ``strong field'' solutions in which the angular momentum transport is purely vertical and ``weak field'' solutions that are the stratified-disc analogues of the previously studied MRI channel modes; the latter are transformed into accretion solutions with predominantly radial angular-momentum transport when we implement a turbulent-stress prescription based on published results of numerical simulations. We also analyze ``intermediate field strength'...

  10. Ghost Imaging Using Orbital Angular Momentum

    Institute of Scientific and Technical Information of China (English)

    赵生妹; 丁建; 董小亮; 郑宝玉

    2011-01-01

    We present a novel encoding scheme in a ghost-imaging system using orbital angular momentum. In the signal arm, object spatial information is encoded as a phase matrix. For an N-grey-scale object, different phase matrices, varying from 0 to K with increment n/N, are used for different greyscales, and then they are modulated to a signal beam by a spatial light modulator. According to the conservation of the orbital angular momentum in the ghost imaging system, these changes will give different coincidence rates in measurement, and hence the object information can be extracted in the idler arm. By simulations and experiments, the results show that our scheme can improve the resolution of the image effectively. Compared with another encoding method using orbital angular momentum, our scheme has a better performance for both characters and the image object.%We present a novel encoding scheme in a ghost-imaging system using orbital angular momentum.In the signal arm,object spatial information is encoded as a phase matrix.For an N-grey-scale object,different phase matrices,varying from 0 to π with increment π/N,are used for different greyscales,and then they are modulated to a signal beam by a spatial light modulator.According to the conservation of the orbital angular momentum in the ghost imaging system,these changes will give different coincidence rates in measurement,and hence the object information can be extracted in the idler arm.By simulations and experiments,the results show that our scheme can improve the resolution of the image effectively.Compared with another encoding method using orbital angular momentum,our scheme has a better performance for both characters and the image object.

  11. Simulation and experimental studies of a double-fiber angular displacement sensor

    Science.gov (United States)

    Zhu, Ruixue; Jing, Ruiping; Cheng, Yongjin

    2017-03-01

    A novel optical fiber angular displacement sensor is reported in this study. It gets the rotating angle of an object by means of the intensity modulation of a reflected light. The sensor probe, which is composed of an emitting fiber and a receiving fiber that are aligned along the vertical direction closely, is fixed directly on the rotating object. The measurements for axial displacement and angular displacement were operated separately. In particular, measurements for angular displacement were performed when the reflector is placed at different distances from the sensor probe separately. There is an excellent linearity between the angular displacement and the sensor output power. The results indicate that the larger the distance between the sensor probe and the reflector, the higher sensitivity the angular displacement sensor has. A theoretical model of the sensor is also developed and the simulate computation demonstrates that the theoretical results are in accordance with the experimental ones. The linear sensing range is ±7.2°, and the maximum sensitivity is 13.71%/deg. Furthermore, the hysteresis and the reproducibility of the measurement of the sensor are investigated. The designed sensor provides a kind of simple and effective method for measuring the angular displacement of a shaft system in practice due to its small size, light weight, good linearity and reproducibility.

  12. Orbital angular momentum in the nucleons

    CERN Document Server

    Lorcé, Cédric

    2014-01-01

    In the last decade, it has been realized that the orbital angular momentum of partons inside the nucleon plays a major role. It contributes significantly to nucleon properties and is at the origin of many asymmetries observed in spin physics. It is therefore of paramount importance to determine this quantity if we want to understand the nucleon internal structure and experimental observables. This triggered numerous discussions and controversies about the proper definition of orbital angular momentum and its extraction from experimental data. We summarize the present situation and discuss recent developments in this field.

  13. Concepts of radial and angular kinetic energies

    DEFF Research Database (Denmark)

    Dahl, Jens Peder; Schleich, W.P.

    2002-01-01

    We consider a general central-field system in D dimensions and show that the division of the kinetic energy into radial and angular parts proceeds differently in the wave-function picture and the Weyl-Wigner phase-space picture, Thus, the radial and angular kinetic energies are different quantiti...... in the two pictures, containing different physical information, but the relation between them is well defined. We discuss this relation and illustrate its nature by examples referring to a free particle and to a ground-state hydrogen atom....

  14. Angular momentum and the electromagnetic top

    Indian Academy of Sciences (India)

    GIANFRANCO SPAVIERI; GEORGE T GILLIES

    2016-08-01

    The electric charge–magnetic dipole interaction is considered. If $\\Gamma_{\\rm em}$ is the electromagnetic and $\\Gamma_{\\rm mech}$ the mechanical angular momentum, the conservation law for the total angular momentum $\\Gamma_{\\rm tot}$ holds: $\\Gamma_{\\rm tot}$ =$\\Gamma_{\\rm em}$ + $\\Gamma_{\\rm mech}$ = ${\\rm const.}$, but when the dipole moment varies with time, $\\Gamma_{\\rm mech}$ is not conserved. We show that the non-conserved $\\Gamma_{\\rm mech}$ of such a macroscopic isolated system might be experimentally observable. With advanced technology, the strength of the interaction hints to the possibility of novel applications for gyroscopes, such as the electromagnetic top.

  15. On the vector model of angular momentum

    Science.gov (United States)

    Saari, Peeter

    2016-09-01

    Instead of (or in addition to) the common vector diagram with cones, we propose to visualize the peculiarities of quantum mechanical angular momentum by a completely quantized 3D model. It spotlights the discrete eigenvalues and noncommutativity of components of angular momentum and corresponds to outcomes of measurements—real or computer-simulated. The latter can be easily realized by an interactive worksheet of a suitable program package of algebraic calculations. The proposed complementary method of visualization helps undergraduate students to better understand the counterintuitive properties of this quantum mechanical observable.

  16. Angular gyrus syndrome mimicking depressive pseudodementia.

    Science.gov (United States)

    Nagaratnam, Nages; Phan, Tai Anh; Barnett, Claire; Ibrahim, Neamat

    2002-09-01

    A 67-year-old left-handed woman with a diagnosis of pseudodementia was being treated for depression with little benefit. Neuropsychological evaluations revealed features of angular gyrus syndrome, namely, agraphia, alexia, Gerstmann's syndrome and behavioural manifestations such as depression, poor memory, frustration and irritability. A computed tomographic scan showed a right occipito-temporal infarction, which had occurred 18 months earlier. The patient demonstrated aspects of language dysfunction associated with the syndrome and showed reversed lateralization of cerebral functions. Recognizing and distinguishing between angular gyrus syndrome and depression is important because the appropriate therapies differ. The use of the term pseudodementia can be misleading.

  17. A new method for angular displacement measurement

    Institute of Scientific and Technical Information of China (English)

    Caini Zhang(张彩妮); Xiangzhao Wang(王向朝)

    2003-01-01

    We describe a new method for angular displacement measurements that is based on a Fabry-Perot inter-ferometer. A measurement accuracy of 10-s rad is obtained by use of the sinusoidal phase modulatinginterferometry. Another Fabry-Perot interferometer is used to obtain the key initial angle of incidence.

  18. Optical angular momentum conversion in a nanoslit

    NARCIS (Netherlands)

    Chimento, P.F.; Alkemade, P.F.A.; T Hooft, G.W.; Eliel, E.R.

    2012-01-01

    We demonstrate partial conversion of circularly polarized light into orbital angular momentum-carrying vortex light with opposite-handed circular polarization. This conversion is accomplished in a novel manner using the birefringent properties of a circular subwavelength slit in a thin metal film. O

  19. Wigner Functions and Quark Orbital Angular Momentum

    Directory of Open Access Journals (Sweden)

    Mukherjee Asmita

    2015-01-01

    Full Text Available Wigner distributions contain combined position and momentum space information of the quark distributions and are related to both generalized parton distributions (GPDs and transverse momentum dependent parton distributions (TMDs. We report on a recent model calculation of the Wigner distributions for the quark and their relation to the orbital angular momentum.

  20. Critical gravitational collapse with angular momentum

    CERN Document Server

    Gundlach, Carsten

    2016-01-01

    We derive a theoretical model of mass and angular momentum scaling in type-II critical collapse with rotation. We focus on the case where the critical solution has precisely one, spherically symmetric, unstable mode. We demonstrate excellent agreement with numerical results for critical collapse of a rotating radiation fluid, which falls into this case.

  1. ANGULAR MOMENTUM ACQUISITION IN GALAXY HALOS

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Kyle R. [Department of Natural and Mathematical Sciences, California Baptist University, 8432 Magnolia Ave., Riverside, CA 92504 (United States); Brooks, Alyson M. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States); Bullock, James S. [Center for Cosmology, Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697 (United States); Maller, Ariyeh H. [Department of Physics, New York City College of Technology, 300 Jay St., Brooklyn, NY 11201 (United States); Diemand, Juerg [Institute for Theoretical Physics, University of Zurich, 8057, Zurich (Switzerland); Wadsley, James [Department of Physics and Astronomy, McMaster University, Main Street West, Hamilton L85 4M1 (Canada); Moustakas, Leonidas A. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2013-05-20

    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 {approx}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 {lambda} {approx} 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.

  2. On the quantisation of the angular momentum

    CERN Document Server

    Ho, V B

    1994-01-01

    When a hydrogen-like atom is treated as a two dimensional system whose configuration space is multiply connected, then in order to obtain the same energy spectrum as in the Bohr model the angular momentum must be half-integral.

  3. Angular and linear momentum of excited ferromagnets

    NARCIS (Netherlands)

    Yan, P.; Kamra, A.; Cao, Y.; Bauer, G.E.W.

    2013-01-01

    The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist i

  4. Angular-momentum-bearing modes in fission

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Peaslee, G.F.; Wozniak, G.J.

    1989-03-01

    The angular-momentum-bearing degrees of freedom involved in the fission process are identified and their influence on experimental observables is discussed. The excitation of these modes is treated in the ''thermal'' limit, and the resulting distributions of observables are calculated. Experiments demonstrating the role of these modes are presented and discussed. 61 refs., 12 figs.

  5. A Novel Permanent Magnetic Angular Acceleration Sensor

    Directory of Open Access Journals (Sweden)

    Hao Zhao

    2015-07-01

    Full Text Available Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it has a relatively small rotational inertia. Due to the unique mechanical structure of the sensor, the output signal of the sensor can be directed without a slip ring, which avoids signal weakening effect. In this paper, the operating principle of the sensor is described, and simulated using finite element method. The sensitivity of the sensor is calibrated by torsional pendulum and angle sensor, yielding an experimental result of about 0.88 mV/(rad·s−2. Finally, the angular acceleration of the actual rotating system has been tested, using both a single-phase asynchronous motor and a step motor. Experimental result confirms the operating principle of the sensor and indicates that the sensor has good practicability.

  6. A Novel Permanent Magnetic Angular Acceleration Sensor.

    Science.gov (United States)

    Zhao, Hao; Feng, Hao

    2015-07-03

    Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it has a relatively small rotational inertia. Due to the unique mechanical structure of the sensor, the output signal of the sensor can be directed without a slip ring, which avoids signal weakening effect. In this paper, the operating principle of the sensor is described, and simulated using finite element method. The sensitivity of the sensor is calibrated by torsional pendulum and angle sensor, yielding an experimental result of about 0.88 mV/(rad·s(-2)). Finally, the angular acceleration of the actual rotating system has been tested, using both a single-phase asynchronous motor and a step motor. Experimental result confirms the operating principle of the sensor and indicates that the sensor has good practicability.

  7. Measuring angular diameters of extended sources

    NARCIS (Netherlands)

    van Hoof, PAM

    2000-01-01

    When measuring diameters of partially resolved sources like planetary nebulae, H II regions or galaxies, often a technique called Gaussian deconvolution is used. This technique yields a Gaussian diameter, which subsequently has to be multiplied by a conversion factor to obtain the true angular

  8. Oral medicine in practice: angular cheilitis.

    Science.gov (United States)

    Lamey, P J; Lewis, M A

    1989-07-08

    In a series of twelve articles the authors aim to cover the more common oral medicine problems likely to be encountered in dental practice. Whenever possible, clinical photographs have been used to illustrate important points, and the text is deliberately succinct and without references. In the first article, the pathogenesis, investigation and management of angular cheilitis is reviewed.

  9. Angular vibration measurement using grating and laser interferometer

    Science.gov (United States)

    Zhang, Li; Peng, Jun

    2006-06-01

    Primary angular acceleration calibration standard is developed by CIMM to generate standard rotational angle, angular velocity and angular acceleration, which are traceable to the International System of Units (SI). It can be used to calibrate angular transducers, i.e. angular accelerometer, angular velocity transducer, and rotational angle transducer to obtain amplitude sensitivity and phase shift by sinusoidal vibration. The measurement systems based on grating and laser interferometers are introduced in this paper. The measurement system based on PXI bus instrument is used to control the angular exciter, measure the output signal of the laser interferometers and the transducer to be calibrated synchronously. The methods for calculating the amplitude and phase of sinusoidal angular movement are investigated and high performance has been achieved. It shows the standard can be used in angular movement calibration in the frequency range from 0.1Hz to 200Hz.

  10. Beam Positioning Error Budget of Angular Multiplexing Excimer Master Osillator Power-Amplifier Laser System%角多路准分子激光主振荡器功率放大系统光束定位误差分配

    Institute of Scientific and Technical Information of China (English)

    王大辉; 赵军; 赵学庆; 黄珂; 孙昱薇; 张永生; 郑国鑫; 胡云

    2011-01-01

    Angular multiplexing excimer master oscillator power-amplifier laser (MOPA) system is simplified by object-image conjugate structure. Relations between the drifts of optical components and the deviation of corresponding imaging plane are derived by transfer matrix and ray tracing. The index weight is determined by improved analytic hierarchy process according to nine scale evaluation matrix, and the beam positioning stability requirement of optical components which affects system stability is acquired. Results show that the error budget values of optical components is related to the focus of image-relaying and the distance from object plane. The values change conversely with the focuses. The optical components stability in laboratory environment is measured and compared with those of error budget.%对角多路准分子激光主振荡器功率放大(MOPA)系统进行物像共轭结构简化.利用传输矩阵和光线追迹,推导出了像传递光路中光学元件扰动与相应像面光束定位误差之间关系式.根据九标度赋值矩阵,采用改进层次分析法确定指标权重系数,得到了影响系统稳定性的光学元件光束定位指标要求.结果表明,光学元件分配指标大小和像传递结构焦距、光学元件(反射镜)距离像传递结构物面距离有关,焦距越大指标越小,距离越远指标越大.测量了实验室环境下光学元件的稳定性,对测量结果和定位误差进行了分析,并在此基础上提出了光路设计和光路优化的建议.

  11. Measuring angular diameter distances of strong gravitational lenses

    CERN Document Server

    Jee, Inh; Suyu, Sherry H

    2014-01-01

    The distance-redshift relation plays a fundamental role in constraining cosmological models. In this paper, we show that measurements of positions and time delays of strongly lensed images of a background galaxy, as well as those of the velocity dispersion and mass profile of a lens galaxy, can be combined to extract the angular diameter distance of the lens galaxy. Physically, as the velocity dispersion and the time delay give a gravitational potential ($GM/r$) and a mass ($GM$) of the lens, respectively, dividing them gives a physical size ($r$) of the lens. Comparing the physical size with the image positions of a lensed galaxy gives the angular diameter distance to the lens. A mismatch between the exact locations at which these measurements are made can be corrected by measuring a local slope of the mass profile. We expand on the original idea put forward by Paraficz and Hjorth, who analyzed singular isothermal lenses, by allowing for an arbitrary slope of a power-law spherical mass density profile, an ex...

  12. Strong Clustering of Faint Galaxies at Small Angular Scales

    CERN Document Server

    Infante, L; Menanteau, F

    1996-01-01

    The 2-point angular correlation function of galaxies, \\wt, has been computed on equatorial fields observed with the CTIO 4m prime focus, within a total area of 2.31 deg$^2$. In the magnitude range $19\\le m_R \\le 21.5$, corresponding to $\\approx 0.35$, we find an excess of power in \\wt at scales $2''\\le\\theta larger $\\theta$. The significance of this excess is $\\approx 5\\sigma$. At larger scales, $6''< \\theta \\le 24''$, the amplitude of \\wt is 1.6 times smaller than the standard no evolutionary model. At these scales there is remarkable agreement between the present data and Infante \\& Pritchet (1995). At large angular scales ($6''< \\theta \\le 24''$) the data is best described by a model where clustering evolution in $\\xi(r,z)$ has taken place. Strong luminosity evolution cannot be ruled out with the present data. At smaller scales, $2''\\le \\theta \\le 6''$, our data are formally fit by models where $(Ømega=0.2, \\epsilon=0)$. If the mean redshift of our sample is 0.35 then our data show a clear detec...

  13. A detection system with broad angular acceptance for particle identification and angular distribution measurements

    Energy Technology Data Exchange (ETDEWEB)

    Carnelli, P.F.F., E-mail: carnelli@tandar.cnea.gov.ar [Laboratorio TANDAR, Comisión Nacional de Energía Atómica, Av. Gral. Paz 1499, B1650KNA, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033AAJ, Buenos Aires (Argentina); Universidad Nacional de San Martín, Campus Miguelete, B1650BWA, San Martín, Buenos Aires (Argentina); Arazi, A. [Laboratorio TANDAR, Comisión Nacional de Energía Atómica, Av. Gral. Paz 1499, B1650KNA, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033AAJ, Buenos Aires (Argentina); Fernández Niello, J.O. [Laboratorio TANDAR, Comisión Nacional de Energía Atómica, Av. Gral. Paz 1499, B1650KNA, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033AAJ, Buenos Aires (Argentina); Universidad Nacional de San Martín, Campus Miguelete, B1650BWA, San Martín, Buenos Aires (Argentina); Capurro, O.A. [Laboratorio TANDAR, Comisión Nacional de Energía Atómica, Av. Gral. Paz 1499, B1650KNA, San Martín, Buenos Aires (Argentina); and others

    2013-10-21

    A new detection system for time-optimized heavy-ion angular distribution measurements has been designed and constructed. This device is composed by an ionization chamber with a segmented-grid anode and three position-sensitive silicon detectors. This particular arrangement allows identifying reaction products emitted within a 30° wide angular range with better than 1° angular resolution. As a demonstration of its capabilities, angular distributions of the elastic scattering cross-section and the production of alpha particles in the {sup 7}Li+{sup 27}Al system, at an energy above the Coulomb barrier, are presented. -- Highlights: • We constructed a detection system for time-optimized heavy-ion angular distribution measurements. • We characterized this device and obtained an energy resolution of 3% and an angular resolution of 1°. • We measured elastic scattering cross-sections in {sup 7}Li+{sup 27}Al finding good agreement with previous data. • The performed tests included the measurement of alpha particle production cross-sections in {sup 7}Li+{sup 27}Al.

  14. Ultra-sensitive and super-resolving angular rotation measurement based on photon orbital angular momentum using parity measurement.

    Science.gov (United States)

    Zhang, Zijing; Qiao, Tianyuan; Ma, Kun; Cen, Longzhu; Zhang, Jiandong; Wang, Feng; Zhao, Yuan

    2016-08-15

    Photon orbital angular momentum has led to many novel insights and applications in quantum measurement. Photon orbital angular momentum can increase the resolution and sensitivity of angular rotation measurement. However, quantum measurement strategy can further surpass this limit and improve the resolution of angular rotation measurement. This Letter proposes and demonstrates a parity measurement method in angular rotation measurement scheme for the first time. Parity measurement can make the resolution superior to the limit of the existing method. The sensitivity can be improved with higher orbital angular momentum photons. Moreover, this Letter gives a detailed discussion of the change of resolution and sensitivity in the presence of photon loss.

  15. Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-delay Polarization Modulators

    CERN Document Server

    Miller, N J; Marriage, T A; Wollack, E J; Appel, J W; Bennett, C L; Eimer, J; Essinger-Hileman, T; Fixsen, D J; Harrington, K; Moseley, S H; Rostem, K; Switzer, E R; Watts, D J

    2015-01-01

    Polarimetric surveys of the microwave sky at large angular scales are crucial in testing cosmic inflation, as inflation predicts a divergence-free $B$-mode angular power spectrum that extends to the largest scales on the sky. A promising technique for realizing such large surveys is through the use of rapid polarization modulation to mitigate variations in the atmosphere, coupling to the environment, and drifts in instrumental response. VPMs change the state of polarization by introducing a controlled, adjustable delay between orthogonal linear polarizations resulting in transformations between linear and circular polarization states. VPMs are currently being implemented in experiments designed to measure the polarization of the cosmic microwave background on large angular scales because of their capability for providing rapid, front-end polarization modulation and control over systematic errors. Despite the advantages provided by the VPM, it is important to identify and mitigate any time-varying effects that...

  16. Bell inequalities with continuous angular variables

    CERN Document Server

    Borges, Carolina V S; Keller, Arne

    2011-01-01

    We consider bipartite quantum systems characterized by a continuous angular variable \\theta \\in [-\\pi, \\pi[, representing, for instance, the position of a particle on a circle. We show how to reveal non-locality on this type of system using inequalities similar to CHSH ones, originally derived for bipartite spin 1/2 like systems. Such inequalities involve correlated measurement of continuous angular functions and are equivalent to the continuous superposition of CHSH inequalities acting on bidimensional subspaces of the infinite dimensional Hilbert space. As an example, we discuss in detail one application of our results, and we derive inequalities based on orientation correlation measurements. The introduced Bell-type inequalities open the perspective of new and simpler experiments to test non locality on a variety of quantum systems described by continuous variables.

  17. Angular momentum in cluster Spherical Collapse Model

    CERN Document Server

    Cupani, Guido; Mardirossian, Fabio

    2011-01-01

    Our new formulation of the Spherical Collapse Model (SCM-L) takes into account the presence of angular momentum associated with the motion of galaxy groups infalling towards the centre of galaxy clusters. The angular momentum is responsible for an additional term in the dynamical equation which is useful to describe the evolution of the clusters in the non-equilibrium region which is investigated in the present paper. Our SCM-L can be used to predict the profiles of several strategic dynamical quantities as the radial and tangential velocities of member galaxies, and the total cluster mass. A good understanding of the non-equilibrium region is important since it is the natural scenario where to study the infall in galaxy clusters and the accretion phenomena present in these objects. Our results corroborate previous estimates and are in very good agreement with the analysis of recent observations and of simulated clusters.

  18. Quantum Entanglement of Very High Angular Momenta

    CERN Document Server

    Fickler, Robert; Plick, William N; Krenn, Mario; Schaeff, Christoph; Ramelow, Sven; Zeilinger, Anton

    2012-01-01

    Single photons with helical phase structure may carry a quantized amount of orbital angular momentum (OAM) and are of great interest in quantum information science and fundamental tests of quantum theory. Since there is no theoretical upper limit on how many quanta of OAM a single photon can carry, those systems offer the possibility to create superpositions for one particle and entanglement between two particles with an arbitrary high difference in the quantum number. By transferring polarization entanglement to the OAM degree-of-freedom with an interferometric scheme, we created and observed entanglement up to $600\\bar{h}$ difference in the orbital angular momentum. To our knowledge, we have thus demonstrated entanglement of the highest quantum number in any experiment so far. The only restrictive factor towards even higher numbers arises due to current technical limitations. Furthermore, we show experimentally that the entanglement of very high OAM can be used to improve applications, like the sensitivity ...

  19. Angular MET sensor for precise azimuth determination

    Science.gov (United States)

    Zaitsev, Dmitry; Antonov, Alexander; Krishtop, Vladimir

    2016-12-01

    This paper describes using a MET-based low-noise angular motion sensor to precisely determine azimuth direction in a dynamic-scheme method of measuring Earth's rotation velocity vector. The scheme includes installing a sensor on a rotating platform so that it could scan a space and seek for the position of highest Earth's rotation vector projection on its axis. This method is very efficient provided a low-noise sensor is used. We take a low-cost angular sensor based on MET (molecular electronic transduction) technology. Sensors of this kind were originally developed for the seismic activity monitoring and are well-known for very good noise performance and high sensitivity. This approach, combined with use of special signal processing algorithms, allowed for reaching the accuracy of 0.07° for a measurement time of 200 seconds.

  20. CMB Anisotropies Total Angular Momentum Method

    CERN Document Server

    Hu, W; Hu, Wayne; White, Martin

    1997-01-01

    A total angular momentum representation simplifies the radiation transport problem for temperature and polarization anisotropy in the CMB. Scattering terms couple only the quadrupole moments of the distributions and each moment corresponds directly to the observable angular pattern on the sky. We develop and employ these techniques to study the general properties of anisotropy generation from scalar, vector and tensor perturbations to the metric and the matter, both in the cosmological fluids and from any seed perturbations (e.g.~defects) that may be present. The simpler, more transparent form and derivation of the Boltzmann equations brings out the geometric and model-independent aspects of temperature and polarization anisotropy formation. Large angle scalar polarization provides a robust means to distinguish between isocurvature and adiabatic models for structure formation in principle. Vector modes have the unique property that the CMB polarization is dominated by magnetic type parity at small angles and ...

  1. The Cosmology Large Angular Scale Surveyor

    Science.gov (United States)

    Marriage, Tobias; Ali, A.; Amiri, M.; Appel, J. W.; Araujo, D.; Bennett, C. L.; Boone, F.; Chan, M.; Cho, H.; Chuss, D. T.; Colazo, F.; Crowe, E.; Denis, K.; Dünner, R.; Eimer, J.; Essinger-Hileman, T.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G. F.; Huang, C.; Irwin, K.; Jones, G.; Karakla, J.; Kogut, A. J.; Larson, D.; Limon, M.; Lowry, L.; Mehrle, N.; Miller, A. D.; Miller, N.; Moseley, S. H.; Novak, G.; Reintsema, C.; Rostem, K.; Stevenson, T.; Towner, D.; U-Yen, K.; Wagner, E.; Watts, D.; Wollack, E.; Xu, Z.; Zeng, L.

    2014-01-01

    Some of the most compelling inflation models predict a background of primordial gravitational waves (PGW) detectable by their imprint of a curl-like "B-mode" pattern in the polarization of the Cosmic Microwave Background (CMB). The Cosmology Large Angular Scale Surveyor (CLASS) is a novel array of telescopes to measure the B-mode signature of the PGW. By targeting the largest angular scales (>2°) with a multifrequency array, novel polarization modulation and detectors optimized for both control of systematics and sensitivity, CLASS sets itself apart in the field of CMB polarization surveys and opens an exciting new discovery space for the PGW and inflation. This poster presents an overview of the CLASS project.

  2. Mass and Angular Momentum in General Relativity

    CERN Document Server

    Jaramillo, J L

    2010-01-01

    We present an introduction to mass and angular momentum in General Relativity. After briefly reviewing energy-momentum for matter fields, first in the flat Minkowski case (Special Relativity) and then in curved spacetimes with or without symmetries, we focus on the discussion of energy-momentum for the gravitational field. We illustrate the difficulties rooted in the Equivalence Principle for defining a local energy-momentum density for the gravitational field. This leads to the understanding of gravitational energy-momentum and angular momentum as non-local observables that make sense, at best, for extended domains of spacetime. After introducing Komar quantities associated with spacetime symmetries, it is shown how total energy-momentum can be unambiguously defined for isolated systems, providing fundamental tests for the internal consistency of General Relativity as well as setting the conceptual basis for the understanding of energy loss by gravitational radiation. Finally, several attempts to formulate q...

  3. Angular resolution of stacked resistive plate chambers

    CERN Document Server

    Samuel, Deepak; Murgod, Lakshmi P

    2016-01-01

    We present here detailed derivations of mathematical expressions for the angular resolution of a set of stacked resistive plate chambers (RPCs). The expressions are validated against experimental results using data collected from the prototype detectors (without magnet) of the upcoming India-based Neutrino Observatory (INO). In principle, these expressions can be used for any other detector with an architecture similar to that of RPCs.

  4. Coherent Control of Photoelectron Wavepacket Angular Interferograms

    OpenAIRE

    Hockett, Paul; Wollenhaupt, Matthias; Baumert, Thomas

    2015-01-01

    Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the cohere...

  5. Angular Momentum Sharing in Dissipative Collisions

    Science.gov (United States)

    Casini, G.; Poggi, G.; Bini, M.; Calamai, S.; Maurenzig, P. R.; Olmi, A.; Pasquali, G.; Stefanini, A. A.; Taccetti, N.; Steckmeyer, J. C.; Laforest, R.; Saint-Laurent, F.

    1999-09-01

    Light charged particles emitted by the projectilelike fragment were measured in the direct and reverse collision of 93Nb and 116Sn at 25A MeV. The experimental multiplicities of hydrogen and helium particles as a function of the primary mass of the emitting fragment show evidence for a correlation with net mass transfer. The ratio of hydrogen and helium multiplicities points to a dependence of the angular momentum sharing on the net mass transfer.

  6. Angular momentum sharing in dissipative collisions

    CERN Document Server

    Casini, G; Bini, M; Calamai, S; Maurenzig, P R; Olmi, A; Pasquali, G; Stefanini, A A; Taccetti, N; Steckmeyer, J C; Laforest, R; Saint-Laurent, F

    1999-01-01

    Light charged particles emitted by the projectile-like fragment were measured in the direct and reverse collision of $^{93}$Nb and $^{116}$Sn at 25 AMeV. The experimental multiplicities of Hydrogen and Helium particles as a function of the primary mass of the emitting fragment show evidence for a correlation with net mass transfer. The ratio of Hydrogen and Helium multiplicities points to a dependence of the angular momentum sharing on the net mass transfer.

  7. Angular quadratures for improved transport computations

    Energy Technology Data Exchange (ETDEWEB)

    Abu-Shumays, I.K.

    1999-07-22

    This paper introduces new octant-range, composite-type Gauss and mid-point rule angular quadrature formulas for neutron and photon transport computations. A generalization to octant-range quadratures is also introduced in order to allow for discontinuities at material interfaces for two- and three-dimensional transport problems which can be modeled with 60-degree triangular or hexagonal mesh subdivisions in the x-y plane.

  8. Coherent Control of Photoelectron Wavepacket Angular Interferograms

    OpenAIRE

    Hockett, Paul; Wollenhaupt, Matthias; Baumert, Thomas

    2015-01-01

    Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the cohere...

  9. Angular cheilitis, part 1: local etiologies.

    Science.gov (United States)

    Park, Kelly K; Brodell, Robert T; Helms, Stephen E

    2011-06-01

    Angular cheilitis (AC) is a common condition characterized by erythema, moist maceration, ulceration, and crusting at the corners of the mouth. This article focuses on the common local factors that act alone and in combination to produce AC. These factors are categorized as irritant, allergic, and infectious causes. Identifying the underlying etiology of AC is a critical step in developing an effective treatment plan for this condition.

  10. Symmetries in the angular distribution of exclusive semileptonic B decays

    CERN Document Server

    Egede, Ulrik; Matias, Joaquim; Ramon, Marc; Reece, Will

    2010-01-01

    We discuss a method to construct observables protected against QCD uncertainties based on the angular distribution of the exclusive Bd -> K(*0}(-> Kpi) l+ l- decay. We focus on the identification and the interpretation of all the symmetries of the distribution. They constitute a key ingredient to construct a set of so-called transverse observables. We work in the framework of QCD factorization at NLO supplemented by an estimate of power-suppressed Lambda/mb corrections. A discussion of the new physics properties of two of the transverse asymmetries, AT^{(2)} and AT^{(5)}, is presented. A comparison between the transverse asymmetry AT^{(2)} and the forward-backward asymmetry shows that AT^{(2)} emerges as an improved version of it.

  11. Symmetries in the angular distribution of exclusive semileptonic B decays

    CERN Document Server

    Egede, Ulrik; Matias, Joaquim; Ramon, Marc; Reece, Will

    2010-01-01

    We discuss a method to construct observables protected against QCD uncertainties based on the angular distribution of the exclusive Bd -> K(*0}(-> Kpi) l+ l- decay. We focus on the identification and the interpretation of all the symmetries of the distribution. They constitute a key ingredient to construct a set of so-called transverse observables. We work in the framework of QCD factorization at NLO supplemented by an estimate of power-suppressed Lambda/mb corrections. A discussion of the new physics properties of two of the transverse asymmetries, AT^{(2)} and AT^{(5)}, is presented. A comparison between the transverse asymmetry AT^{(2)} and the forward-backward asymmetry shows that AT^{(2)} emerges as an improved version of it.

  12. Sorting and quantifying orbital angular momentum of laser beams

    CSIR Research Space (South Africa)

    Schulze, C

    2013-10-01

    Full Text Available We present a novel tool for sorting the orbital angular momentum and to determine the orbital angular momentum density of laser beams, which is based on the use of correlation filters....

  13. A neural circuit for angular velocity computation

    Directory of Open Access Journals (Sweden)

    Samuel B Snider

    2010-12-01

    Full Text Available In one of the most remarkable feats of motor control in the animal world, some Diptera, such as the housefly, can accurately execute corrective flight maneuvers in tens of milliseconds. These reflexive movements are achieved by the halteres, gyroscopic force sensors, in conjunction with rapidly-tunable wing-steering muscles. Specifically, the mechanosensory campaniform sensilla located at the base of the halteres transduce and transform rotation-induced gyroscopic forces into information about the angular velocity of the fly's body. But how exactly does the fly's neural architecture generate the angular velocity from the lateral strain forces on the left and right halteres? To explore potential algorithms, we built a neuro-mechanical model of the rotation detection circuit. We propose a neurobiologically plausible method by which the fly could accurately separate and measure the three-dimensional components of an imposed angular velocity. Our model assumes a single sign-inverting synapse and formally resembles some models of directional selectivity by the retina. Using multidimensional error analysis, we demonstrate the robustness of our model under a variety of input conditions. Our analysis reveals the maximum information available to the fly given its physical architecture and the mathematics governing the rotation-induced forces at the haltere's end knob.

  14. The Cosmology Large Angular Scale Surveyor

    CERN Document Server

    Harrington, Kathleen; Ali, Aamir; Appel, John W; Bennett, Charles L; Boone, Fletcher; Brewer, Michael; Chan, Manwei; Chuss, David T; Colazo, Felipe; Dahal, Sumit; Denis, Kevin; Dünner, Rolando; Eimer, Joseph; Essinger-Hileman, Thomas; Fluxa, Pedro; Halpern, Mark; Hilton, Gene; Hinshaw, Gary F; Hubmayr, Johannes; Iuliano, Jeffery; Karakla, John; McMahon, Jeff; Miller, Nathan T; Moseley, Samuel H; Palma, Gonzalo; Parker, Lucas; Petroff, Matthew; Pradenas, Bastián; Rostem, Karwan; Sagliocca, Marco; Valle, Deniz; Watts, Duncan; Wollack, Edward; Xu, Zhilei; Zeng, Lingzhen

    2016-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to characterize relic primordial gravitational waves from inflation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on the largest angular scales. The frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one dichroic system at 145/217 GHz, are chosen to avoid spectral regions of high atmospheric emission and span the minimum of the polarized Galactic foregrounds: synchrotron emission at lower frequencies and dust emission at higher frequencies. Low-noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique combination of high sensitivity, stability, and control of systematics. The CLASS site, at 5200 m in the Chilean Atacama desert, allows for daily mapping of up to 70\\% of the sky and enables the characterization of CMB polarization at the largest angular scales. Using this combination of a broad f...

  15. Angular cheilitis: a clinical and microbial study.

    Science.gov (United States)

    Ohman, S C; Dahlén, G; Möller, A; Ohman, A

    1986-04-01

    The purpose of this prospective study was to re-examine the relative importance of various factors in the pathogenesis of angular cheilitis. Sixty-four patients with cheilitis were examined clinically and microbiologically. In addition, a subsample of 23 patients was examined for serum iron and transferrin. The clinical appearance of the lip lesions fell into 4 categories. A ground rhagad at the corner of the mouth involving adjacent skin, was the most frequent type among dentate patients, whereas among denture wearers a deep lesion following the labial marginal sulcus was frequently observed. Dentate patients and denture wearers with cheilitis often had atopic constitution or cutaneous diseases. Pathogenic microorganisms were cultured from the lesions in all 64 patients; Staphylococcus aureus in 40 patients and Candida albicans in 45. The results of this study indicate a correlation between angular cheilitis and pathogenic microorganisms. Furthermore, among dentate patients, a correlation exists between cutaneous discomfort and angular cheilitis. Other etiological factors suggested for this disorder were found to be of subordinate importance.

  16. Angular momentum flux of nonparaxial acoustic vortex beams and torques on axisymmetric objects.

    Science.gov (United States)

    Zhang, Likun; Marston, Philip L

    2011-12-01

    An acoustic vortex in an inviscid fluid and its radiation torque on an axisymmetric absorbing object are analyzed beyond the paraxial approximation to clarify an analogy with an optical vortex. The angular momentum flux density tensor from the conservation of angular momentum is used as an efficient description of the transport of angular momentum. Analysis of a monochromatic nonparaxial acoustic vortex beam indicates that the local ratio of the axial (or radial) flux density of axial angular momentum to the axial (or radial) flux density of energy is exactly equal to the ratio of the beam's topological charge l to the acoustic frequency ω. The axial radiation torque exerted by the beam on an axisymmetric object centered on the beam's axis due to the transfer of angular momentum is proportional to the power absorbed by the object with a factor l/ω, which can be understood as a result of phonon absorption from the beam. Depending on the vortex's helicity, the torque is parallel or antiparallel to the beam's axis.

  17. Localization of angular momentum in optical waves propagating through turbulence.

    Science.gov (United States)

    Sanchez, Darryl J; Oesch, Denis W

    2011-12-01

    This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence.

  18. Study of the Angular Distribution of Scintillation Photons

    CERN Document Server

    Fornaro, Giulia Alice; Ghezzi, Alessio; Knapitsch, Arno; Modrzynski, Pawel; Pizzichemi, Marco; Lecoq, Paul; Auffray, Etiennette

    2014-01-01

    This paper presents a characterization method to experimentally determine the angular distribution of scintillation light. By exciting LYSO crystals with a radioactive source, we measured the light angular profiles obtained with samples of different geometries in different conditions of wrapping. We also measured the angular distribution of light emitting in glue and compared it with the one emitting in air. Angular distribution of light output of photonic crystals is also provided. Consistency of the measurements is verified with conventional light output measurements.

  19. Angular momentum of a brane-world model

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In this paper we discuss the properties of the general covariant angular momentum of a fivedimensional brane-world model. Through calculating the total angular momentum of this model, we are able to analyze the properties of the total angular momentum in the inflationary RS model. We show that the space-like components of the total angular momentum of the inflationary RS model are all zero while the others are non-zero, which agrees with the results from ordinary RS model.

  20. Angular Momentum of a Brane-world Model

    CERN Document Server

    Jia, Bei; Zhang, Peng-Ming

    2008-01-01

    In this paper we discuss the properties of the general covariant angular momentum of a five-dimensional brane-world model. Through calculating the total angular momentum of this model, we are able to analyze the properties of the total angular momentum in the inflationary RS model. We show that the space-like components of the total angular momentum of are all zero while the others are non-zero, which agrees with the results from ordinary RS model.