Publications (76)283.97 Total impact
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ABSTRACT: The Atacama Bmode Search (ABS) instrument, which began observation in February of 2012, is a crossedDragone telescope located at an elevation of 5,100 m in the Atacama Desert in Chile. The primary scientific goal of ABS is to measure the Bmode polarization spectrum of the Cosmic Microwave Background from multipole moments of about \(\ell \approx \) 50 to \(\ell \approx \) 500 (angular scales from \({\sim }0.4^\circ \) to \({\sim }4^\circ \) ), a range that includes the primordial Bmode peak from inflationary gravitational waves. The ABS focal plane array consists of 240 pixels designed for observation at 145 GHz by the TRUCE collaboration. Each pixel has its own individual, singlemoded feedhorn and contains two transitionedge sensor bolometers coupled to orthogonal polarizations that are read out using time domain multiplexing. We will report on the current status of ABS and discuss the time constants and optical efficiencies of the TRUCE detectors in the field.Journal of Low Temperature Physics 09/2014; 176(56). · 1.18 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Future arcminute resolution polarization data from groundbased Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near $\ell=1500$ in the small angularscale temperature measurements. Our projections are based on combining expected smallscale Emode polarization measurements from Advanced ACTPol in the range $300<\ell<3000$ with simulated temperature data from the full Planck mission in the low and intermediate $\ell$ region, $2<\ell<2000$. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than $1\%$ accuracy. Assuming an efficient cleaning from multifrequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic SunyaevZel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a $15 \sigma$ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at $\ell>1500$, leading to a measurement of the amplitude of matter density fluctuations, $\sigma_8$, at $1\%$ precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with $\sigma(z_{\rm re})=1.1$ and $\sigma(\Delta z_{\rm re})=0.2$. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminutescale resolution for future CMB surveys.Journal of Cosmology and Astroparticle Physics 06/2014; JCAP08(2014)010. · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Understanding the outskirts of galaxy clusters at the virial radius (R200) and beyond is critical for an accurate determination of cluster masses and to ensure unbiased cosmological parameter estimates from cluster surveys. This problem has drawn renewed interest due to recent determinations of gas mass fractions beyond R200, which appear to be considerably larger than the cosmic mean, and because the clusters' total SunyaevZel'dovich flux receives a significant contribution from these regions. Here, we use a large suite of cosmological hydrodynamical simulations to study the clumpiness of density and pressure and employ different variants of simulated physics, including radiative gas physics and thermal feedback by active galactic nuclei. We find that density and pressure clumping closely trace each other as a function of radius, but the bias on density remains on average < 20% within the virial radius R200. At larger radius, clumping increases steeply due to the continuous infall of coherent structures that have not yet passed the accretion shock. Density and pressure clumping increase with cluster mass and redshift, which probes on average dynamically younger objects that are still in the process of assembling. The angular power spectra of gas density and pressure show that the clumping signal is dominated by comparably large substructures with scales >R200/5, signaling the presence of gravitationallydriven "superclumping". In contrast, the angular power spectrum of the dark matter (DM) shows an almost uniform size distribution due to unimpeded subhalos. The quadrupolar anisotropy dominates the signal and correlates well across different radii as a result of the prolateness of the DM potential. We provide a synopsis of the radial dependence of the clusters' nonequilibrium measures (kinetic pressure support, ellipticity, and clumping) that all increase sharply beyond R200.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Understanding the outskirts of galaxy clusters at the virial radius (R200) and beyond is critical for an accurate determination of cluster masses and to ensure unbiased cosmological parameter estimates from cluster surveys. This problem has drawn renewed interest due to recent determinations of gas mass fractions beyond R200, which appear to be considerably larger than the cosmic mean, and because the clusters' total SunyaevZel'dovich flux receives a significant contribution from these regions. Here, we use a large suite of cosmological hydrodynamical simulations to study the clumpiness of density and pressure and employ different variants of simulated physics, including radiative gas physics and thermal feedback by active galactic nuclei. We find that density and pressure clumping closely trace each other as a function of radius, but the bias on density remains on average < 20% within the virial radius R200. At larger radius, clumping increases steeply due to the continuous infall of coherent structures that have not yet passed the accretion shock. Density and pressure clumping increase with cluster mass and redshift, which probes on average dynamically younger objects that are still in the process of assembling. The angular power spectra of gas density and pressure show that the clumping signal is dominated by comparably large substructures with scales >R200/5, signaling the presence of gravitationallydriven "superclumping". In contrast, the angular power spectrum of the dark matter (DM) shows an almost uniform size distribution due to unimpeded subhalos. The quadrupolar anisotropy dominates the signal and correlates well across different radii as a result of the prolateness of the DM potential. We provide a synopsis of the radial dependence of the clusters' nonequilibrium measures (kinetic pressure support, ellipticity, and clumping) that all increase sharply beyond R200.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the crossfrequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we crosscorrelate the ACT and the South Pole Telescope (SPT) maps and show they are consistent. The measurements of higherorder peaks in the CMB power spectrum provide an additional test of the Lambda CDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the SunyaevZel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing convergence power spectrum at 4.6sigma detection significance.Journal of Cosmology and Astroparticle Physics 04/2014; 2014(04):014. · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present the temperature power spectrum of the Cosmic Microwave Background obtained by crosscorrelating maps from the Atacama Cosmology Telescope (ACT) at 148 and 218 GHz with maps from the Planck satellite at 143 and 217 GHz, in two overlapping regions covering 592 square degrees. We find excellent agreement between the two datasets at both frequencies, quantified using the variance of the residuals between the ACT power spectra and the ACTxPlanck crossspectra. We use these crosscorrelations to calibrate the ACT data at 148 and 218 GHz, to 0.7% and 2% precision respectively. We find no evidence for anisotropy in the calibration parameter. We compare the Planck 353 GHz power spectrum with the measured amplitudes of dust and cosmic infrared background (CIB) of ACT data at 148 and 218 GHz. We also compare planet and point source measurements from the two experiments.Journal of Cosmology and Astroparticle Physics 03/2014; · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We evaluate the modulation of cosmic microwave background polarization using a rapidly rotating, halfwave plate (HWP) on the Atacama BMode Search. After demodulating the timeordereddata (TOD), we find a significant reduction of atmospheric fluctuations. The demodulated TOD is stable on time scales of 5001000 s, corresponding to frequencies of 12 mHz. This facilitates recovery of cosmological information at large angular scales, which are typically available only from balloonborne or satellite experiments. This technique also achieves a sensitive measurement of celestial polarization without differencing the TOD of paired detectors sensitive to two orthogonal linear polarizations. This is the first demonstration of the ability to remove atmospheric contamination at these levels from a groundbased platform using a rapidly rotating HWP.The Review of scientific instruments 02/2014; 85(2):024501. · 1.52 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Highresolution GBT+MUSTANG observations of the SunyaevZel'dovich Effect (SZE) at 90GHz have revealed complex substructure in the hot intracluster medium (ICM) of several massive galaxy clusters. The SZE is a nearly redshiftindependent, complementary probe of the ICM to Xray emission and combined analyses of both data sets provide a better understanding of astrophysical phenomena such as shocks, cold fronts, and sloshing of the gas within a cluster's dark matter potential. Understanding how substructure, especially in merging clusters, affects the scaling between SZE flux and total cluster mass is essential to placing tight constraints on cosmological parameters with SZE surveys. First, I will present recent results from MUSTANG observations of the SZE in MACS J0647.7+7015 and MACS J1206.20847. In order to better characterize the cluster dynamics, a number of models are jointly fit in the map domain using a least squares fitting routine. We compare our data to the bestfit generalized Navarro, Frenk, and White (gNFW) profiles from Bolocam and find evidence for a steeper central slope in both clusters than had previously been determined. Furthermore, MUSTANG detects significant features near the core of both clusters that are suggestive of substructure. Highresolution SZE measurements out to larger angular scales will be necessary to better understand the nature of features like these. With this in mind, we are building MUSTANG1.5, a new bolometer camera which offers many advantages over MUSTANG and unlocks SZE's true potential as an independent tool to understand the ICM on a broad range of angular scales and with a noise level better than any current instrument. I will present a status report on the progress of the receiver, which we aim to install on the Green Bank Telescope (GBT) for first light this season. The improvement in sensitivity and much larger fieldofview (3.5' compared to 35" for MUSTANG) will enable us to pursue a far more comprehensive observing program including the first ever detection of Xray cavities via the SZE and highresolution measurements of the ICM out to unprecedented radii.01/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We measure the crosscorrelation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the CanadaFranceHawaii Telescope Stripe 82 Survey. The CMBgalaxy lensing cross power spectrum is measured for the first time with a significance of 3.2{\sigma}, which corresponds to a 16% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: This is a report on the status and prospects of the quantification of neutrino properties through the cosmological neutrino background for the Cosmic Frontier of the Division of Particles and Fields Community Summer Study longterm planning exercise. Experiments planned and underway are prepared to study the cosmological neutrino background in detail via its influence on distanceredshift relations and the growth of structure. The program for the next decade described in this document, including upcoming spectroscopic galaxy surveys eBOSS and DESI and a new StageIV CMB polarization experiment CMBS4, will achieve sigma(sum m_nu) = 16 meV and sigma(N_eff) = 0.020. Such a mass measurement will produce a high significance detection of nonzero sum m_nu, whose lower bound derived from atmospheric and solar neutrino oscillation data is about 58 meV. If neutrinos have a minimal normal mass hierarchy, this measurement will definitively rule out the inverted neutrino mass hierarchy, shedding light on one of the most puzzling aspects of the Standard Model of particle physics  the origin of mass. This precise a measurement of N_eff will allow for high sensitivity to any light and dark degrees of freedom produced in the big bang and a precision test of the standard cosmological model prediction that N_eff = 3.046.Astroparticle Physics 09/2013; · 4.78 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Fluctuations in the intensity and polarization of the cosmic microwave background (CMB) and the largescale distribution of matter in the universe each contain clues about the nature of the earliest moments of time. The next generation of CMB and largescale structure (LSS) experiments are poised to test the leading paradigm for these earliest momentsthe theory of cosmic inflationand to detect the imprints of the inflationary epoch, thereby dramatically increasing our understanding of fundamental physics and the early universe. A future CMB experiment with sufficient angular resolution and frequency coverage that surveys at least 1% of the sky to a depth of 1 uKarcmin can deliver a constraint on the tensortoscalar ratio that will either result in a 5sigma measurement of the energy scale of inflation or rule out all largefield inflation models, even in the presence of foregrounds and the gravitational lensing Bmode signal. LSS experiments, particularly spectroscopic surveys such as the Dark Energy Spectroscopic Instrument, will complement the CMB effort by improving current constraints on running of the spectral index by up to a factor of four, improving constraints on curvature by a factor of ten, and providing nonGaussianity constraints that are competitive with the current CMB bounds.Astroparticle Physics 09/2013; · 4.78 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We measure a significant correlation between the thermal SunyaevZel'dovich effect in the Planck and WMAP maps and an Xray cluster map based on ROSAT. We use the 100, 143 and 343 GHz Planck maps and the WMAP 94 GHz map to obtain this cluster cross spectrum. We check our measurements for contamination from dusty galaxies using the cross correlations with the 220, 545 and 843 GHz maps from Planck. Our measurement yields a direct characterization of the cluster power spectrum over a wide range of angular scales that is consistent with large cosmological simulations. The amplitude of this signal depends on cosmological parameters that determine the growth of structure (\sigma_8 and \Omega_M) and scales as \sigma_8^7.4 and \Omega_M^1.9 around the multipole (ell) ~ 1000. We constrain \sigma_8 and \Omega_M from the crosspower spectrum to be \sigma_8 (\Omega_M/0.30)^0.26 = 0.8 +/ 0.02. Since this cross spectrum produces a tight constraint in the \sigma_8 and \Omega_M plane the errors on a \sigma_8 constraint will be mostly limited by the uncertainties from external constraints. Future cluster catalogs, like those from eRosita and LSST, and pointed multiwavelength observations of clusters will improve the constraining power of this cross spectrum measurement. In principle this analysis can be extended beyond \sigma_8 and \Omega_M to constrain dark energy or the sum of the neutrino masses.Journal of Cosmology and Astroparticle Physics 09/2013; · 6.04 Impact Factor 
Article: Determining the Hubble constant from gravitational wave observations of merging compact binaries
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ABSTRACT: Recent observations have accumulated compelling evidence that some short gammaray bursts (SGRBs) are associated with the mergers of neutron star (NS) binaries. This would indicate that the SGRB event is associated with a gravitationalwave (GW) signal corresponding to the final inspiral of the compact binary. In addition, the radioactive decay of elements produced in NS binary mergers may result in transients visible in the optical and infrared with peak luminosities on hoursdays timescales. Simultaneous observations of the inspiral GWs and signatures in the electromagnetic band may allow us to directly and independently determine both the luminosity distance and redshift to a binary. These standard sirens (the GW analog of standard candles) have the potential to provide an accurate measurement of the lowredshift Hubble flow. In addition, these systems are absolutely calibrated by general relativity, and therefore do not experience the same set of astrophysical systematics found in traditional standard candles, nor do the measurements rely on a distance ladder. We show that 15 observable GW and EM events should allow the Hubble constant to be measured with 5% precision using a network of detectors that includes advanced LIGO and Virgo. Measuring 30 beamed GWSGRB events could constrain H_0 to better than 1%. When comparing to standard Gaussian likelihood analysis, we find that each event's nonGaussian posterior in H_0 helps reduce the overall measurement errors in H_0 for an ensemble of NS binary mergers.07/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We present a catalog of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 GHz and/or 218 GHz in the 2008 Southern survey. Flux densities span 141700 mJy, and we use source spectral indices derived using ACTonly data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN), and 24 dusty starforming galaxies (DSFGs). We crossidentify 97% of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogs. When combined with flux densities from the Australian Telescope 20 GHz survey and followup observations with the Australia Telescope Compact Array, the synchrotrondominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dustdominated source population has a median spectral index of 3.7+0.620.86, and includes both local galaxies and sources with redshifts as great as 5.6. Dusty sources with no counterpart in existing catalogs likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.Monthly Notices of the Royal Astronomical Society 06/2013; · 4.90 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat LCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n_s = 0.9690 +/ 0.0089, is less than unity at the 3.6 sigma level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be N_eff = 3.28 +/ 0.40, in agreement with the standard model's three species of light neutrinos.Physical Review D 02/2013; 85:103012. · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The Atacama Cosmology Telescope has measured the angular power spectra of microwave fluctuations to arcminute scales at frequencies of 148 and 218 GHz, from three seasons of data. At small scales the fluctuations in the primordial Cosmic Microwave Background (CMB) become increasingly obscured by extragalactic foregounds and secondary CMB signals. We present results from a nineparameter model describing these secondary effects, including the thermal and kinematic SunyaevZel'dovich (tSZ and kSZ) power; the clustered and Poissonlike power from Cosmic Infrared Background (CIB) sources, and their frequency scaling; the tSZCIB correlation coefficient; the extragalactic radio source power; and thermal dust emission from Galactic cirrus in two different regions of the sky. In order to extract cosmological parameters, we describe a likelihood function for the ACT data, fitting this model to the multifrequency spectra in the multipole range 500<ell<10000. We extend the likelihood to include spectra from the South Pole Telescope at frequencies of 95, 150, and 220 GHz. Accounting for different radio source levels and Galactic cirrus emission, the same model provides an excellent fit to both datasets simultaneously, with chi2/dof= 675/697 for ACT, and 96/107 for SPT. We then use the multifrequency likelihood to estimate the CMB power spectrum from ACT in bandpowers, marginalizing over the secondary parameters. This provides a simplified `CMBonly' likelihood in the range 500<ell<3500 for use in cosmological parameter estimation.Journal of Cosmology and Astroparticle Physics 01/2013; 2013(07). · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present constraints on cosmological and astrophysical parameters from highresolution microwave background maps at 148 GHz and 218 GHz made by the Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to 2010. A model of primary cosmological and secondary foreground parameters is fit to the map power spectra and lensing deflection power spectrum, including contributions from both the thermal SunyaevZeldovich (tSZ) effect and the kinematic SunyaevZeldovich (kSZ) effect, Poisson and correlated anisotropy from unresolved infrared sources, radio sources, and the correlation between the tSZ effect and infrared sources. The power ell^2 C_ell/2pi of the thermal SZ power spectrum at 148 GHz is measured to be 3.4 +\ 1.4 muK^2 at ell=3000, while the corresponding amplitude of the kinematic SZ power spectrum has a 95% confidence level upper limit of 8.6 muK^2. Combining ACT power spectra with the WMAP 7year temperature and polarization power spectra, we find excellent consistency with the LCDM model. We constrain the number of effective relativistic degrees of freedom in the early universe to be Neff=2.79 +\ 0.56, in agreement with the canonical value of Neff=3.046 for three massless neutrinos. We constrain the sum of the neutrino masses to be Sigma m_nu < 0.39 eV at 95% confidence when combining ACT and WMAP 7year data with BAO and Hubble constant measurements. We constrain the amount of primordial helium to be Yp = 0.225 +\ 0.034, and measure no variation in the fine structure constant alpha since recombination, with alpha/alpha0 = 1.004 +/ 0.005. We also find no evidence for any running of the scalar spectral index, dns/dlnk = 0.004 +\ 0.012.Journal of Cosmology and Astroparticle Physics 01/2013; 2013(10):60. · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Secondary anisotropies in the cosmic microwave background are a treasuretrove of cosmological information. Interpreting current experiments probing them are limited by theoretical uncertainties rather than by measurement errors. Here we focus on the secondary anisotropies resulting from the thermal SunyaevZel'dovich (tSZ) effect; the amplitude of which depends critically on the average thermal pressure profile of galaxy groups and clusters. To this end, we use a suite of hydrodynamical TreePMSPH simulations that include radiative cooling, star formation, supernova feedback, and energetic feedback from active galactic nuclei. We examine in detail how the pressure profile depends on cluster radius, mass, and redshift and provide an empirical fitting function. We employ three different approaches for calculating the tSZ power spectrum: an analytical approach that uses our pressure profile fit, a semianalytical method of pasting our pressure fit onto simulated clusters, and a direct numerical integration of our simulated volumes. We demonstrate that the detailed structure of the intracluster medium and cosmic web affect the tSZ power spectrum. In particular, the substructure and asphericity of clusters increase the tSZ power spectrum by 10%20% at l {approx} 20008000, with most of the additional power being contributed by substructures. The contributions to the power spectrum from radii larger than R {sub 500} is {approx}20% at l = 3000, thus clusters interiors (r < R {sub 500}) dominate the power spectrum amplitude at these angular scales.The Astrophysical Journal 10/2012; 758(2). · 6.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The utility of large SunyaevZel'dovich (SZ) surveys for determining cosmological parameters from cluster abundances is limited by the theoretical uncertainties in the integrated SZfluxtomass relation, YM. We explore how nonthermal pressure and the anisotropic shape of the gas distribution of the intracluster medium (ICM) impacts YM scaling using a suite of smoothed particle hydrodynamic simulations of the cosmic web. We contrast results for models with different treatments of entropy injection and transport, varying radiative cooling, star formation and accompanying supernova feedback, cosmic rays, and energetic feedback from active galactic nuclei (AGNs). We find that the gas kinetictothermal pressure ratio, P {sub kin}/P {sub th}, from internal bulk motions depends on the cluster mass, and increases in the outercluster due to enhanced substructure, as does the asphericity of the ICM gas. With only a {approx}5%10% correction to projected (observable) ellipticities, we can infer the threedimensional ellipticities. Our simulated YM slope roughly follows the selfsimilar prediction, except for a steepening due to a deficit of gas in lower mass clusters at low redshift in our AGN feedback simulations. AGN feedback enhances the overall YM scatter, from {approx}11% to {approx}13% (z = 0) and to {approx}15% (z = 1), a reflection of the accretion history variations due to cluster merging. If we split the cluster system into lower, middle, and upper bands of both P {sub kin}/P {sub th} and longtoshort axis ratio, we find a {approx}10% effect on YM. Identifying observable second parameters related to internal bulk flows and anisotropy for cluster selection to minimize YM scatter in a 'fundamental plane' would allow tighter cosmological parameter constraints.The Astrophysical Journal 10/2012; 758(2). · 6.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Gas masses tightly correlate with the virial masses of galaxy clusters, allowing for a precise determination of cosmological parameters by means of largescale Xray surveys. However, according to recent Suzaku Xray measurements, gas mass fractions, f_gas, appear to be considerably larger than the cosmic mean at the virial radius, R_200, questioning the accuracy of the cosmological parameter estimations. Here, we use a large suite of cosmological hydrodynamical simulations to study measurement biases of f_gas. We employ different variants of simulated physics, including radiative gas physics, star formation, and thermal feedback by active galactic nuclei. Computing the mass profiles in 48 angular cones, whose footprints partition the sphere, we find anisotropic gas and total mass distributions that imply an angular variance of f_gas at the level of 30%. This anisotropic distribution originates from the recent formation epoch of clusters and from the strong internal baryontodarkmatter density bias. In the most extreme cones, f_gas can be biased high by a factor of two at R_200 in massive clusters, thereby providing a potential explanation for high f_gas measurements by Suzaku. While projection lowers this factor, there are other measurement biases that may (partially) compensate. We find that at R_200, f_gas is biased high by 20% when assuming hydrostatic equilibrium masses, i.e., neglecting the kinetic pressure, and by another ~1020% due to the presence of density clumping. At larger radii, both measurement biases increase dramatically. While the cluster sample variance of the true f_gas decreases to a level of 5% at R_200, the sample variance that includes both measurement biases remains fairly constant at the level of 1020%. The constant redshift evolution of f_gas within R_500 for massive clusters is encouraging for using gas masses to derive cosmological parameters.The Astrophysical Journal 09/2012; · 6.73 Impact Factor
Publication Stats
1k  Citations  
283.97  Total Impact Points  
Top Journals
Institutions

2013–2014

Princeton University
 Department of Astrophysical Sciences
Princeton, New Jersey, United States 
University of KwaZuluNatal
 School of Mathematics, Statistics and Computer Science
Port Natal, KwaZuluNatal, South Africa


2004–2012

University of Toronto
 Canadian Institute for Theoretical Astrophysics
Toronto, Ontario, Canada


2011

University of Nottingham
 School of Physics and Astronomy
Nottigham, England, United Kingdom


2002–2011

National Radio Astronomy Observatory
Charlottesville, Virginia, United States


2001–2011

California Institute of Technology
 Department of Astronomy
Pasadena, California, United States
