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Robert Suhada, 04/23/2013 06:55 AM

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A comprehensive picture of baryons in groups and clusters of galaxies

T. F. Lagana, N. Martinet, F. Durret, G. B. Lima Neto, B. Maughan, Y.-Y. Zhang
(Submitted on 22 Apr 2013)
(Abridged) Based on XMM-Newton, Chandra and SDSS data, we investigate the baryon distribution in groups and clusters and its use as a cosmological constraint. For this, we considered a sample of 123 systems, with total masses in the mass range M500 = ~ 10^13 - 4 x 10^15 h_70^-1 Msun.
The gas masses and total masses are derived from X-ray data under the assumption of hydrostatic equilibrium and spherical symmetry. The stellar masses are based on SDSS-DR8 data. For the 37 systems out of 123 that had both optical and X-ray data available, we investigated the gas, stellar and total baryon mass fractions inside r2500 and r500, and the differential gas mass fraction within the spherical annulus between r2500 and r500, as a function of total mass. For the other objects, we investigated the gas mass fraction only. We find that the gas mass fraction inside r2500 and r500 depends on the total mass.
However, the differential gas mass fraction does not show any dependence on total mass for systems with M500 > 10^14 Msun. We find that the total baryonic content increases with cluster mass. This led us to investigate the contribution of the ICL to the total baryon budget for lower mass systems, but we find that it cannot account for the difference observed. The gas mass fraction dependence on total mass observed for groups and clusters could be due to the difficulty of low-mass systems to retain gas inside the inner region. Due to their shallower potential well, non-thermal processes are more effective in expelling the gas from their central regions outwards. Since the differential gas mass fraction is nearly constant it provides better constraints for cosmology.
Using our total f_b estimates, our results imply 0.17 < Omega_m < 0.55.

http://arXiv.org/abs/1304.6061

Votes: 0

The synergy between the Dark Energy Survey and the South Pole Telescope

Alberto Vallinotto
(Submitted on 11 Apr 2013)
The Dark Energy Survey (DES) has recently completed the Science Verification phase (SV), collecting data over 150 sq. deg. of sky. In this work we analyze to what extent it is beneficial to supplement the analysis of DES data with CMB lensing data. We provide forecasts for both DES-SV and for the full survey covering 5000 sq. deg. We show that data presently available from DES-SV and SPT-SZ would allow a ~8% measurement of the linear galaxy bias in four redshift bins. We further show that a joint analysis of cosmic shear, galaxy density and CMB lensing data allows to self calibrate the shear multiplicative bias and the linear galaxy bias to the percent or sub-percent level, depending on the quality of available data, fraction of overlap of the footprints and priors included in the analysis.

http://arXiv.org/abs/1304.3474

Votes: 0

X-ray Cluster Constraints on Non-Gaussianity

Sarah Shandera,a Adam Mantz,b David Rapetti,c Steven W. Allend,e

- see email by Adam Mantz

Votes: 0

Measuring Gravitational Redshifts in Galaxy Clusters

Nick Kaiser
(Submitted on 15 Mar 2013)
Wojtak {\it et al} have stacked 7,800 clusters from the SDSS survey in redshift space. They find a small net blue-shift for the cluster galaxies relative to the brightest cluster galaxies, which agrees quite well with the gravitational redshift from GR. Zhao {\it et al.} have pointed out that, in addition to the gravitational redshift, one would expect to see transverse Doppler (TD) redshifts, and that these two effects are generally of the same order. Here we show that there are other corrections that are also of the same order of magnitude. The fact that we observe galaxies on our past light cone results in a bias such that more of the galaxies observed are moving away from us in the frame of the cluster than are moving towards us. This causes the observed average redshift to be $\langle \delta z \rangle = -\langle \Phi \rangle + \langle \beta^2 \rangle / 2 + \langle \beta_x^2 \rangle$, with $\beta_x$ is the line of sight velocity. That is if we average over galaxies with equal weight. If the galaxies in each cluster are weighted by their fluence, or equivalently if we do not resolve the moving sources, and make an average of the mean redshift giving equal weight per photon, the observed redshift is then opposite to the usual transverse Doppler effect. In the WHH experiment, the weighting is a step-function because of the flux-limit for inclusion in the spectroscopic sample and the result is different again, and depends on the details of the luminosity function and the SEDs of the galaxies. Including these effects substantially modifies the blue-shift profile. We identify some potential biases in the dynamical analysis of stacked clusters. We show that in-fall and out-flow have very small effect over the relevant range of impact parameters.

http://arXiv.org/abs/1303.3663

Votes: 0

Probing dark energy with cluster counts and cosmic shear power spectra: including the full covariance

Masahiro Takada (Tohoku Univ., Japan), Sarah Bridle (University College London)
(Submitted on 2 May 2007 (v1), last revised 22 Sep 2007 (this version, v2))
(Abridged) Combining cosmic shear power spectra and cluster counts is powerful to improve cosmological parameter constraints and/or test inherent systematics. However they probe the same cosmic mass density field, if the two are drawn from the same survey region, and therefore the combination may be less powerful than first thought. We investigate the cross-covariance between the cosmic shear power spectra and the cluster counts based on the halo model approach, where the cross-covariance arises from the three-point correlations of the underlying mass density field. Fully taking into account the cross-covariance as well as non-Gaussian errors on the lensing power spectrum covariance, we find a significant cross-correlation between the lensing power spectrum signals at multipoles l~10^3 and the cluster counts containing halos with masses M>10^{14}Msun. Including the cross-covariance for the combined measurement degrades and in some cases improves the total signal-to-noise ratios up to plus or minus 20% relative to when the two are independent. For cosmological parameter determination, the cross-covariance has a smaller effect as a result of working in a multi-dimensional parameter space, implying that the two observables can be considered independent to a good approximation. We also discuss that cluster count experiments using lensing-selected mass peaks could be more complementary to cosmic shear tomography than mass-selected cluster counts of the corresponding mass threshold. Using lensing selected clusters with a realistic usable detection threshold (S/N~6 for a ground-based survey), the uncertainty on each dark energy parameter may be roughly halved by the combined experiments, relative to using the power spectra alone.

http://arXiv.org/abs/0705.0163

Votes: 0

ALMA Observations of SPT-Discovered, Strongly Lensed, Dusty, Star-Forming Galaxies

Y. D. Hezaveh, D. P. Marrone, C. D. Fassnacht, J. S. Spilker, J. D. Vieira, J. E. Aguirre, K. A. Aird, M. Aravena, M. L. N. Ashby, M. Bayliss, B. A. Benson, L. E. Bleem, M. Bothwell, M. Brodwin, J. E. Carlstrom, C. L. Chang, S. C. Chapman, T. M. Crawford, A. T. Crites, C. De Breuck, T. de Haan, M. A. Dobbs, E. B. Fomalont, E. M. George, M. D. Gladders, A. H. Gonzalez, T. R. Greve, N. W. Halverson, F. W. High, G. P. Holder, W. L. Holzapfel, S. Hoover, J. D. Hrubes, K. Husband, T. R. Hunter, R. Keisler, A. T. Lee, E. M. Leitch, M. Lueker, D. Luong-Van, M. Malkan, V. McIntyre, J. J. McMahon, J. Mehl, K. M. Menten, S. S. Meyer, L. M. Mocanu, E. J. Murphy, T. Natoli, S. Padin, T. Plagge, C. L. Reichardt, A. Rest, J. Ruel, J. E. Ruhl, K. Sharon, K. K. Schaffer, L. Shaw, E. Shirokoff, B. Stalder, et al. (7 additional authors not shown)
(Submitted on 11 Mar 2013)
We present Atacama Large Millimeter/submillimeter Array (ALMA) 860 micrometer imaging of four high-redshift (z=2.8-5.7) dusty sources that were detected using the South Pole Telescope (SPT) at 1.4 mm and are not seen in existing radio to far-infrared catalogs. At 1.5 arcsec resolution, the ALMA data reveal multiple images of each submillimeter source, separated by 1-3 arcsec, consistent with strong lensing by intervening galaxies visible in near-IR imaging of these sources. We describe a gravitational lens modeling procedure that operates on the measured visibilities and incorporates self-calibration-like antenna phase corrections as part of the model optimization, which we use to interpret the source structure. Lens models indicate that SPT0346-52, located at z=5.7, is one of the most luminous and intensely star-forming sources in the universe with a lensing corrected FIR luminosity of 3.7 X 10^13 L_sun and star formation surface density of 4200 M_sun yr^-1 kpc^-2. We find magnification factors of 5 to 22, with lens Einstein radii of 1.1-2.0 arcsec and Einstein enclosed masses of 1.6-7.2x10^11 M_sun. These observations confirm the lensing origin of these objects, allow us to measure the their intrinsic sizes and luminosities, and demonstrate the important role that ALMA will play in the interpretation of lensed submillimeter sources.

http://arXiv.org/abs/1303.2722

Votes: 0

Cluster Cosmology at a Crossroads: Neutrino Masses

Eduardo Rozo, Eli S. Rykoff, James G. Bartlett, August E. Evrard
(Submitted on 20 Feb 2013)
Galaxy clusters --- in combination with CMB and BAO data --- can provide precise constraints on the sum of neutrino masses. However, these constraints depend on the calibration of the mass--observable relation. For instance, the mass calibration employed in Planck Collaboration (2011a,b) rules out the minimal 6-parameter \Lambda CDM model at 3.7\sigma, and implies a sum of neutrino masses \sum m_\nu = 0.39 \pm 0.10. By contrast, the mass calibration favored by Rozo et al. (2012b) from a self-consistent analysis of X-ray, SZ, and optical scaling relations is consistent with a minimal flat \Lambda CDM model with no massive neutrinos (1.7\sigma), and is a better fit to additional data (e.g. H0). We discuss these results in light of the recent SPT and ACT analysis, noting that the Rozo et al. (2012b) model suggests the current mild "tension" (<2\sigma) between CMB and BAO+$H_0$ data will decrease as the uncertainties in these measurements decrease.

http://arXiv.org/abs/1302.5086

Votes: 0

Combining Probes of Large-Scale Structure

Tim Eifler, Elisabeth Krause, Peter Schneider, Klaus Honscheid
(Submitted on 11 Feb 2013)
Developing accurate analysis techniques to combine various probes of cosmology is essential to tighten constraints on cosmological parameters and to check for inconsistencies in our model of the Universe. In this paper we develop a joint analysis framework for six different second-order statistics of tracers of the dark matter density field, namely galaxy position, shear, and magnification. We extend a data compression scheme developed in the context of shear-shear statistics (the so-called COSEBIs) to the other five second-order statistics, thereby significantly reducing the number of data points in the joint data vector. We simulate a likelihood analysis for the Dark Energy Survey (DES) in a five dimensional cosmological parameter space (plus basic parametrization for bias and correlation parameter) comparing the information content of the individual probes to several combined probes (CP) data vectors. Given the significant correlations of these second-order statistics we model all cross terms in the covariance matrix; furthermore we go beyond the Gaussian covariance approximation and use the halo model to include higher order correlations of the density field. We find that modeling both, Non-Gaussianity and cross terms, is essential for accurate likelihood contours from the CP data vector; assuming Gaussian errors or uncorrelated probes impacts the contours at a similar level as assuming perfect knowledge of galaxy bias. We also identify several nulltests based on the degeneracy of magnification and shear statistics which can be used to quantify the contamination of data sets by astrophysical systematics and/or calibration issues.
http://arxiv.org/abs/1302.2401

The Contribution of Radio Galaxy Contamination to Measurements of the Sunyaev-Zel'dovich Decrement in Massive Galaxy Clusters at 140 GHz with Bolocam

Jack Sayers, Tony Mroczkowski, Nicole G. Czakon, Sunil R. Golwala, Adam Mantz, Silvia Ameglio, Tom P. Downes, Patrick M. Koch, Kai-Yang Lin, Sandor M. Molnar, Stephen J. C. Muchovej, Elena Pierpaoli, Jennifer A. Shitanishi, Seth Siegel, Keiichi Umetsu
(Submitted on 23 Sep 2012)
We describe in detail our characterization of the compact radio source population in 140 GHz Bolocam observations of a set of 45 massive galaxy clusters. We use a combination of 1.4 and 30 GHz data to select a total of 28 probable cluster member radio galaxies and also to predict their 140 GHz flux densities. All of these galaxies are steep-spectrum radio sources and they are found preferentially in the cool-core clusters within our sample. In particular, 11 of the 12 brightest cluster member radio sources are associated with cool-core systems. Although none of the individual galaxies are robustly detected in the Bolocam data, the ensemble-average flux density at 140 GHz is consistent with, but slightly lower than, the extrapolation from lower frequencies assuming a constant spectral index. Specifically, we find a multiplicative factor of 0.85 +- 0.16 between the flux densities observed at 140 GHz and those predicted from a power-law extrapolation. In addition, our data indicate an intrinsic scatter of 30 percent around the power-law extrapolated flux densities at 140 GHz, although our data do not tightly constrain this scatter. For our cluster sample, which is composed of high mass and moderate redshift systems, we find that the maximum fractional change in the Sunyaev-Zel'dovich signal integrated over any single cluster due to the presence of these radio sources is 20 percent, and only 1/4 of the clusters show a fractional change of more than 1 percent. The amount of contamination is strongly dependent on cluster morphology, and nearly all of the clusters with more than 1 percent contamination are cool-core systems. This result indicates that radio contamination is not significant compared to current noise levels in 140 GHz images of massive clusters and is in good agreement with the level of radio contamination found in previous results based on lower frequency data or simulations.

http://arxiv.org/abs/1209.5129v1

Votes: 0

Mind the Gap: Tightening the Mass-Richness Relation with Magnitude Gaps

Andrew P. Hearin, Andrew R. Zentner, Jeffrey A. Newman, Andreas A. Berlind
(Submitted on 4 Jul 2012 (v1), last revised 7 Jan 2013 (this version, v2))
We investigate the potential to improve optical tracers of cluster mass by exploiting measurements of the magnitude gap, m12, defined as the difference between the r-band absolute magnitude of the two brightest cluster members. We find that in a mock sample of galaxy groups and clusters constructed from the Bolshoi simulation, the scatter about the mass-richness relation decreases by 15-20% when magnitude gap information is included. A similar trend is evident in a volume-limited, spectroscopic sample of galaxy groups observed in the Sloan Digital Sky Survey (SDSS). We find that SDSS groups with small magnitude gaps are richer than large-gap groups at fixed values of the one-dimensional velocity dispersion among group members sigma_v, which we use as a mass proxy. We demonstrate explicitly that m12 contains information about cluster mass that supplements the information provided by group richness and the luminosity of the brightest cluster galaxy, L_bcg. In so doing, we show that the luminosities of the members of a group with richness N are inconsistent with the distribution of luminosities that results from N random draws from the global galaxy luminosity function. As the cosmological constraining power of galaxy clusters is limited by the precision in cluster mass determination, our findings suggest a new way to improve the cosmological constraints derived from galaxy clusters.

http://arXiv.org/abs/1207.1074

Notes:
- recommended by Ben Hoyle

Votes: 1

The Atacama Cosmology Telescope: the stellar content of galaxy clusters selected using the Sunyaev-Zel'dovich effect

Matt Hilton, Matthew Hasselfield, Cristóbal Sifón, Andrew J. Baker, L. Felipe Barrientos, Nicholas Battaglia, J. Richard Bond, Devin Crichton, Sudeep Das, Mark J. Devlin, Megan Gralla, Amir Hajian, Adam D. Hincks, John P. Hughes, Leopoldo Infante, Kent D. Irwin, Arthur Kosowsky, Yen-Ting Lin, Tobias A. Marriage, Danica Marsden, Felipe Menanteau, Kavilan Moodley, Michael D. Niemack, Mike R. Nolta, Lyman A. Page, Erik D. Reese, Jon Sievers, David N. Spergel, Edward J. Wollack
(Submitted on 4 Jan 2013)
We present a first measurement of the stellar mass component of galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect, using 3.6 um and 4.5 um photometry from the Spitzer Space Telescope. Our sample consists of 14 clusters detected by the Atacama Cosmology Telescope (ACT), which span the redshift range 0.27 < z < 1.07 (median z = 0.50), and have dynamical mass measurements, accurate to about 30 per cent, with median M500 = 6.9 x 10^{14} MSun. We measure the 3.6 um and 4.5 um galaxy luminosity functions, finding the characteristic magnitude (m*) and faint-end slope (alpha) to be similar to those for IR-selected cluster samples. We perform the first measurements of the scaling of SZ-observables (Y500 and y0) with both brightest cluster galaxy (BCG) stellar mass and total cluster stellar mass (M500star). We find a significant correlation between BCG stellar mass and Y500 (E(z)^{-2/3} DA^2 Y500 ~ M*^{1.2 +/- 0.6}), although we are not able to obtain a strong constraint on the slope of the relation due to the small sample size. Additionally, we obtain E(z)^{-2/3} DA^2 Y500 ~ M500star^{1.0 +/- 0.6} for the scaling with total stellar mass. The mass fraction in stars spans the range 0.006-0.034, with the second ranked cluster in terms of dynamical mass (ACT-CL J0237-4939) having an unusually low total stellar mass and the lowest stellar mass fraction. For the five clusters with gas mass measurements available in the literature, we see no evidence for a shortfall of baryons relative to the cosmic mean value.

http://arXiv.org/abs/1301.0780

Votes: 0

The Atacama Cosmology Telescope: likelihood for small-scale CMB data

J. Dunkley, E. Calabrese, J. Sievers, G. E. Addison, N. Battaglia, E. S. Battistelli, J. R. Bond, S. Das, M. J. Devlin, R. Dunner, J. W. Fowler, M. Gralla, A. Hajian, M. Halpern, M. Hasselfield, A. D. Hincks, R. Hlozek, J. P. Hughes, K. D. Irwin, A. Kosowsky, T. Louis, T. A. Marriage, D. Marsden, F. Menanteau, K. Moodley, M. Niemack, M. R. Nolta, L. A. Page, B. Partridge, N. Sehgal, D. N. Spergel, S. T. Staggs, E. R. Switzer, H. Trac, E. Wollack
(Submitted on 4 Jan 2013)
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 nine-parameter model describing these secondary effects, including the thermal and kinematic Sunyaev-Zel'dovich (tSZ and kSZ) power; the clustered and Poisson-like power from Cosmic Infrared Background (CIB) sources, and their frequency scaling; the tSZ-CIB 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 multi-frequency 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 multi-frequency likelihood to estimate the CMB power spectrum from ACT in bandpowers, marginalizing over the secondary parameters. This provides a simplified `CMB-only' likelihood in the range 500<ell<3500 for use in cosmological parameter estimation.

http://arXiv.org/abs/1301.0776

Votes: 0

Planck Intermediate Results. XI: The gas content of dark matter halos: the Sunyaev-Zeldovich-stellar mass relation for locally brightest galaxies

We present the scaling relation between Sunyaev-Zeldovich (SZ) signal and stellar mass for almost 260,000 locally brightest galaxies (LBGs) selected from the Sloan Digital Sky Survey (SDSS). These are predominantly the central galaxies of their dark matter halos. We calibrate the stellar-to-halo mass conversion using realistic mock catalogues based on the Millennium Simulation. Applying a multi-frequency matched filter to the Planck data for each LBG, and averaging the results in bins of stellar mass, we measure the mean SZ signal down to $M_\ast\sim 2\times 10^{11} \Msolar$, with a clear indication of signal at even lower stellar mass. We derive the scaling relation between SZ signal and halo mass by assigning halo properties from our mock catalogues to the real LBGs and simulating the Planck observation process. This relation shows no evidence for deviation from a power law over a halo mass range extending from rich clusters down to $M_{500}\sim 2\times 10^{13} \Msolar$, and there is a clear indication of signal down to $M_{500}\sim 4\times 10^{12} \Msolar$. Planck's SZ detections in such low-mass halos imply that about a quarter of all baryons have now been seen in the form of hot halo gas, and that this gas must be less concentrated than the dark matter in such halos in order to remain consistent with X-ray observations. At the high-mass end, the measured SZ signal is 20% lower than found from observations of X-ray clusters, a difference consistent with Malmquist bias effects in the X-ray sample.

http://arxiv.org/abs/1212.4131
Votes : 1

The Planck Sunyaev-Zel'dovich vs. the X-ray View of the Coma Cluster

R. Fusco-Femiano (1), A. Lapi (2,3), A. Cavaliere (2,4) (1-IAPS/INAF Roma, Italy, 2-Univ. 'Tor Vergata', Rome, Italy, 3-SISSA, Trieste, Italy, 4-OAR/INAF, Rome, Italy)
(Submitted on 13 Dec 2012)
The Planck collaboration has recently published precise and resolved measurements of the Sunyaev-Zel'dovich effect in Abell 1656 (the Coma cluster of galaxies), so directly gauging the electron pressure profile in the intracluster plasma. On the other hand, such a quantity may be also derived from combining the density and temperature provided by X-ray observations of the thermal bremsstrahlung radiation emitted by the plasma. We find a model-independent tension between the SZ and the X-ray pressure, with the SZ one being definitely lower by 15-20%. We propose that such a challenging tension can be resolved in terms of an additional, non-thermal support to the gravitational equilibrium of the intracluster plasma. This can be straightforwardly included in our Supermodel, so as to fit in detail the Planck SZ profile while being consistent with the X-ray observables. Possible origins of the nonthermal component include cosmic-ray protons, ongoing turbulence, and relativistic electrons; given the existing observational constraints on the first two options, here we focus on the third. For this to be effective, we find that the electron population must include not only an energetic tail accelerated to gamma> 10^3 responsible for the Coma radiohalo, but also many more, lower energy electrons. The electron acceleration is to be started by merging events similar to those which provided the very high central entropy of the thermal intracluster plasma in Coma.

http://arxiv.org/abs/1212.3082

Votes : 0

The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) III. Construction of the first flux-limited supercluster sample

Gayoung Chon, Hans Boehringer, Nina Nowak
(Submitted on 7 Dec 2012)
We present the first supercluster catalogue constructed with the extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster survey (REFLEX II) data, which comprises 919 X-ray selected galaxy clusters. Based on this cluster catalogue we construct a supercluster catalogue using a friends-of-friends algorithm with a linking length depending on the local cluster density. The resulting catalogue comprises 164 superclusters at redshift z<=0.4. We study the properties of different catalogues such as the distributions of the redshift, extent and multiplicity by varying the choice of parameters. In addition to the main catalogue we compile a large volume-limited cluster sample to investigate the statistics of the superclusters. We also compare the X-ray luminosity function for the clusters in superclusters with that for the field clusters with the flux- and volume-limited catalogues. The results mildly support the theoretical suggestion of a top-heavy X-ray luminosity function of galaxy clusters in regions of high cluster density.

http://arxiv.org/abs/1212.1597

Votes : 0

An HST/WFC3-UVIS View of the Starburst in the Cool Core of the Phoenix Cluster

Michael McDonald, Bradford Benson, Sylvain Veilleux, Marshall W. Bautz, Christian L. Reichardt
(Submitted on 29 Nov 2012)
We present the results of Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix Cluster (SPT-CLJ2344-4243) in five broadband filters spanning rest-frame 1000-5500A. These observations reveal complex, filamentary blue emission, extending for >40 kpc from the brightest cluster galaxy. We observe an underlying, diffuse population of old stars, following an r^1/4 distribution, confirming that this system is somewhat relaxed. The spectral energy distribution in the inner part of the galaxy, as well as along the extended filaments, is a smooth continuum and is consistent with that of a star-forming galaxy, suggesting that the extended, filamentary emission is not due to a large-scale highly-ionized outflow from the central AGN, but rather a massive population of young stars. We estimate an extinction-corrected star formation rate of 798 +/- 42 Msun/yr, consistent with our earlier work based on low spatial resolution ultraviolet, optical, and infrared imaging. We argue that such a high star formation rate is not the result of a merger, as it would require >10 mergers with gas-rich galaxies and there is no evidence for such multiple merger events. Instead, we propose that the high X-ray cooling rate of ~2850 Msun/yr is the origin of the cold gas reservoir. The combination of such a high cooling rate and the relatively weak radio source in the cluster core suggests that feedback has been unable to halt runaway cooling in this system, leading to this tremendous burst of star formation.

http://arxiv.org/abs/1211.7058

Votes: 0

Reconstructing three-dimensional parameters of galaxy clusters via multifrequency SZ observations

Andrea Morandi, Daisuke Nagai, Wei Cui
(Submitted on 29 Nov 2012)
The Sunyaev-Zeldovich (SZ) effect is a promising tool to study physical properties of the hot X-ray emitting intracluster medium (ICM) in galaxy clusters. To date, most SZ observations have been interpreted in combination with X-ray follow-up measurements in order to determine the ICM temperature and estimate the cluster mass. Future high-resolution, multifrequency SZ observations promise to enable detailed studies of the ICM structures, by measuring the ICM temperature through the temperature-dependent relativistic corrections. In this work we develop a non-parametric method to derive three-dimensional physical quantities, including temperature, pressure, total mass, and peculiar velocities, of galaxy clusters from SZ observations alone. We test the performance of this method using hydrodynamical simulations of galaxy clusters, in order to assess systematic uncertainties in the reconstructed physical parameters. In particular, we analyze mock Cerro Chajnantor Atacama Telescope (CCAT) SZ observations, taking into account various sources of systematic uncertainties associated with instrumental effects and astrophysical foregrounds. We show that our method enables accurate reconstruction of the three-dimensional ICM profiles, while retaining full information about the gas distribution. We discuss the application of this technique for ongoing and future multifrequency SZ observations.

http://arxiv.org/abs/1211.7096

Votes: 0

Quenching star formation in cluster galaxies

Dan S. Taranu, Michael J. Hudson, Michael L. Balogh, Russell J. Smith, Chris Power, Brad Krane
(Submitted on 14 Nov 2012)
In order to understand the processes that quench star formation within rich clusters, we construct a library of subhalo orbits drawn from lambdaCDM cosmological N-body simulations of four rich clusters. The orbits are combined with models of star formation followed by quenching in the cluster environment to predict colours and spectroscopic line indices of satellite galaxies. Simple models with only halo mass-dependent quenching and without environmental (i.e. cluster-dependent) quenching fail to reproduce the observed cluster-centric colour and absorption linestrength gradients. Models in which star formation is instantly quenched at the virial radius also fail to match the observations. Better matches to the data are achieved by more complicated bulge-disc models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc quenching depends on the cluster environment. In the most successful models quenching begins at pericentre, operating on an exponential timescale of 2 -- 3 Gyr, with the shorter timescale being a better match to disc colours as a function of cluster-centric radius and the longer being a better fit to the radial dependence of stellar absorption line indices. The models thus imply that the environments of rich clusters must impact star formation rates of infalling galaxies on relatively long timescales - several times longer than a typical halo spends within the virial radius of a cluster. This scenario favours gentler quenching mechanisms such as slow "strangulation" over more rapid ram-pressure stripping.

http://arxiv.org/abs/1211.3411

Votes: 0

Sunyaev-Zel'dovich-Measured Pressure Profiles from the Bolocam X-ray/SZ Galaxy Cluster Sample

Jack Sayers, Nicole G. Czakon, Adam Mantz, Sunil R. Golwala, Silvia Ameglio, Tom P. Downes, Patrick M. Koch, Kai-Yang Lin, Ben J. Maughan, Sandor M. Molnar, Leonidas Moustakas, Tony Mroczkowski, Elena Pierpaoli, Jennifer A. Shitanishi, Seth Siegel, Keiichi Umetsu, Nina Van der Pyl
(Submitted on 7 Nov 2012)
We describe Sunyaev-Zel'dovich (SZ) effect measurements and analysis of the intracluster medium (ICM) pressure profiles of a set of 45 massive galaxy clusters imaged using Bolocam at the Caltech Submillimeter Observatory. We have used masses determined from Chandra X-ray observations to scale each cluster's profile by the overdensity radius R500 and the mass-and-redshift-dependent normalization factor P500. We deproject the average pressure profile of our sample into 13 logarithmically spaced radial bins between 0.07R500 and 3.5R500. We find that a generalized Navarro, Frenk, and White (gNFW) profile describes our data with sufficient goodness-of-fit and best-fit parameters (C500, alpha, beta, gamma, P0 = 1.18, 0.86, 3.67, 0.67, 4.29). We also use the X-ray data to define cool-core and disturbed subsamples of clusters, and we constrain the average pressure profiles of each of these subsamples. We find that given the precision of our data the average pressure profiles of disturbed and cool-core clusters are consistent with one another at R>~0.15R500, with cool-core systems showing indications of higher pressure at R<~0.15R500. In addition, for the first time, we place simultaneous constraints on the mass scaling of cluster pressure profiles, their ensemble mean profile, and their radius-dependent intrinsic scatter between 0.1R500 and 2.0R500. The scatter among profiles is minimized at radii between ~0.2R500 and ~0.5R500, with a value of ~20%. The best-fit mass scaling has a power-law slope of 0.49, which is shallower than the nominal prediction of 2/3 from self-similar hydrostatic equilibrium models. These results for the intrinsic scatter and mass scaling are largely consistent with previous analyses, most of which have relied heavily on X-ray derived pressures of clusters at significantly lower masses and redshifts compared to our sample.

http://arxiv.org/abs/1211.1632

Votes: 0

The Sloan Bright Arcs Survey: Ten Strong Gravitational Lensing Clusters and Evidence of Overconcentration

Matthew P. Wiesner, Huan Lin, Sahar S. Allam, James Annis, Elizabeth J. Buckley-Geer, H. Thomas Diehl, Donna Kubik, Jeffrey M. Kubo, Douglas Tucker
(Submitted on 6 Nov 2012)
We describe ten strong lensing galaxy clusters of redshift 0.26-0.56 that were found in the Sloan Digital Sky Survey. We present measurements of richness, mass and velocity dispersion for the clusters. We find that in order to use the mass-richness relation from Johnston et al. (2007), which was established at mean redshift of 0.25, it is necessary to scale measured richness values up by 1.47. We also present measurements of Einstein radius, mass and velocity dispersion for the lensing systems. The Einstein radii are all relatively small, between 5.4-13 arcseconds. Finally we consider if there is evidence that our clusters are more concentrated than standard cosmology would predict. We find that six of our clusters do not show evidence of overconcentration, while four of our clusters do. We note a correlation between overconcentration and mass, as the four clusters showing evidence of overconcentration are all lower-mass clusters.

http://arxiv.org/abs/1211.1421

Votes: 0

A low-scatter survey-based mass proxy for clusters of galaxies

S. Andreon (INAF-OABrera)
(Submitted on 5 Nov 2012)
Estimates of cosmological parameters using galaxy clusters have the scatter in the observable at a given mass as a fundamental parameter. This work computes the amplitude of the scatter for a newly introduced mass proxy, the product of the cluster total luminosity times the mass-to-light ratio, usually referred as stellar mass. The analysis of 12 galaxy clusters with excellent total masses shows a tight correlation between the stellar mass, or stellar fraction, and total mass within r500 with negligible intrinsic scatter: the 90% upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is similar to the one of best-determined mass proxies, such as Yx, i.e. the product of X-ray temperature and gas mass. The size of the cluster sample used to determine the intrinsic scatter is small, as in previous works proposing low-scatter proxies because very accurate masses are needed to infer very small values of intrinsic scatter. Three-quarters of the studied clusters have lgM <~14 Msol, which is advantageous from a cosmological perspective because these clusters are far more abundant than more massive clusters. At the difference of other mass proxies such as Yx, stellar mass can be determined with survey data up to at least z=0.9 using upcoming optical near-infrared surveys, such as DES and Euclid, or even with currently available surveys, covering however smaller solid angles. On the other end, the uncertainty about the predicted mass of a single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This is largely because the proxy itself has 0.10 dex errors for clusters of lgM< 14 Msol mass.

http://arxiv.org/abs/1211.0790

Votes: 1

Notes
  • controversial?

CALCLENS: Weak Lensing Simulations for Large-area Sky Surveys and Second-order Effects in Cosmic Shear Power Spectra

Matthew R. Becker (UChicago/KICP)
(Submitted on 10 Oct 2012 (v1), last revised 12 Oct 2012 (this version, v2))
I present a new algorithm, CALCLENS, for efficiently computing weak gravitational lensing shear signals from large N-body light cone simulations over a curved sky. This new algorithm properly accounts for the sky curvature and boundary conditions, is able to produce redshift-dependent shear signals including corrections to the Born approximation by using multiple-plane ray tracing, and properly computes the lensed images of source galaxies in the light cone. The key feature of this algorithm is a new, computationally efficient Poisson solver for the sphere that combines spherical harmonic transform and multgrid methods. As a result, large areas of sky (~10, 000 square degrees) can be ray traced efficiently at high-resolution using only a few hundred cores on widely available machines. Using this new algorithm and curved-sky calculations that only use a slower but more accurate spherical harmonic transform Poisson solver, I study the shear B-mode and rotation mode power spectra. Employing full-sky E/B-mode decompositions, I confirm that the shear B-mode and rotation mode power spectra are equal at high accuracy (~1%), as expected from perturbation theory up to second order. Coupled with realistic galaxy populations placed in large N-body light cone simulations, this new algorithm is ideally suited for the construction of synthetic weak lensing shear catalogs to be used to test for systematic effects in data analysis procedures for upcoming large-area sky surveys. The implementation presented in this work, written in C and employing widely available software libraries to maintain portability, is publicly available at this http URL

http://arxiv.org/abs/1210.3069

Votes: 1

Dark matter mass profiles in the Milky Way and in galaxy clusters support a prior claim of 4.0 eV and 21.4 eV sterile neutrinos

Man Ho Chan, Robert Ehrlich

In several recent papers it was claimed that SN 1987A data supports the existence of 4.0 eV and 21.4 eV active neutrino mass eigenstates, and it was shown that such large masses could be made consistent with existing constraints including neutrino oscillation data and upper limits on the neutrino flavor state masses, provided that there also exist a pair of sterile neutrino mass states whose masses are nearly degenerate with the active ones, plus a third active-sterile doublet that is tachyonic ($m^2 <0$). Here, independent evidence is presented for the existence of sterile neutrinos with the previously claimed masses based on fits to the dark matter distributions in the Milky Way galaxy and four clusters of galaxies. The fits are in excellent agreement with observations. In addition, sterile neutrinos having the suggested masses address the "cusp" problem and the missing satellites problem, as well as that of the "top down" scenario of structure formation -- previously a chief drawback of HDM particles. Nevertheless, the highly controversial nature of the claim, and the need for two free parameters in the dark matter fits, additional confirming evidence will be required before it can be considered proven.

http://arxiv.org/abs/1301.6640

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