The Atacama Cosmology Telescope: Cosmology from galaxy clusters detected via the Sunyaev-Zel'dovich effect
Astrophysical Journal 732:1 (2011)
Abstract:
We present constraints on cosmological parameters based on a sample of Sunyaev-Zel'dovich-selected (SZ-selected) galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of nine optically confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 deg2 of sky surveyed during 2008 at 148 GHz. We focus on the most massive systems to reduce the degeneracy between unknown cluster astrophysics and cosmology derived from SZ surveys. We describe the scaling relation between cluster mass and SZ signal with a four-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives σ8 = 0.851 ± 0.115 and w = -1.14 ± 0.35 for a spatially flat wCDM cosmological model with Wilkinson Microwave Anisotropy Probe (WMAP) seven-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP seven-year constraints alone. Fixing the scaling relation between the cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by X-ray observations, we find σ8 = 0.821 ± 0.044 and w = -1.05 ± 0.20. These results are consistent with constraints from WMAP7 plus baryon acoustic oscillations plus Type Ia supernova which give σ8 = 0.802 ± 0.038 and w = -0.98 ± 0.053. A stacking analysis of the clusters in this sample compared to clusters simulated assuming the fiducial model also shows good agreement. These results suggest that, given the sample of clusters used here, both the astrophysics of massive clusters and the cosmological parameters derived from them are broadly consistent with current models. © 2011. The American Astronomical Society. All rights reserved.The Atacama Cosmology Telescope: Extragalactic sources at 148GHz in the 2008 survey
Astrophysical Journal 731:2 (2011)
Abstract:
We report on extragalactic sources detected in a 455 deg2 map of the southern sky made with data at a frequency of 148GHz from the Atacama Cosmology Telescope (ACT) 2008 observing season. We provide a catalog of 157 sources with flux densities spanning two orders of magnitude: from 15 mJy to 1500 mJy. Comparison to other catalogs shows that 98% of the ACT detections correspond to sources detected at lower radio frequencies. Three of the sources appear to be associated with the brightest cluster galaxies of low-redshift X-ray-selected galaxy clusters. Estimates of the radio to millimeter-wave spectral indices and differential counts of the sources further bolster the hypothesis that they are nearly all radio sources, and that their emission is not dominated by re-emission from warm dust. In a bright (>50 mJy) 148GHz selected sample with complete cross-identifications from the Australia Telescope 20GHz survey, we observe an average steepening of the spectra between 5, 20, and 148GHz with median spectral indices of α5-20 = -0.07 ± 0.06, α20-148 = -0.39 ± 0.04, and α5-148 = -0.20 ± 0.03. When the measured spectral indices are taken into account, the 148GHz differential source counts are consistent with previous measurements at 30 GHz in the context of a source count model dominated by radio sources. Extrapolating with an appropriately rescaled model for the radio source counts, the Poisson contribution to the spatial power spectrum from synchrotron-dominated sources with flux density less than 20 mJy is C Sync = (2.8 ± 0.3) × 10-6μK 2.Large-Scale Polarized Foreground Component Separation for Planck
ArXiv 1103.2554 (2011)
Abstract:
We use Bayesian component estimation methods to examine the prospects for large-scale polarized map and cosmological parameter estimation with simulated Planck data assuming simplified white noise properties. The sky signal is parametrized as the sum of the CMB, synchrotron emission, and thermal dust emission. The synchrotron and dust components are modelled as power-laws, with a spatially varying spectral index for synchrotron and a uniform index for dust. Using the Gibbs sampling technique, we estimate the linear polarisation Q and U posterior amplitudes of the CMB, synchrotron and dust maps as well as the two spectral indices in ~4 degree pixels. We use the recovered CMB map and its covariance in an exact pixel likelihood algorithm to estimate the optical depth to reionization tau, the tensor-to-scalar ratio r, and to construct conditional likelihood slices for the EE and BB spectra. Given our foreground model, we find sigma(tau)~0.004 for tau=0.1, sigma(r)~0.03 for a model with r=0.1, and a 95% upper limit of r<0.02 for r=0.0.The atacama cosmology telescope: A measurement of the cosmic microwave background power spectrum at 148 and 218 ghz from the 2008 southern survey
Astrophysical Journal 729:1 (2011)
Abstract:
We present measurements of the cosmic microwave background (CMB) power spectrum made by the Atacama Cosmology Telescope at 148GHz and 218GHz, as well as the cross-frequency spectrum between the two channels. Our results clearly show the second through the seventh acoustic peaks in the CMB power spectrum. The measurements of these higher-order peaks provide an additional test of the ΛCDM cosmological model. At ℓ>3000, we detect power in excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 < ℓ < 3000, we find evidence for gravitational lensing of the CMB in the power spectrum at the 2.8σ level. We also detect a low level of Galactic dust in our maps, which demonstrates that we can recover known faint, diffuse signals. © 2011. The American Astronomical Society. All rights reserved.COrE (Cosmic Origins Explorer) A White Paper
ArXiv 1102.2181 (2011)