Publications (8)41.77 Total impact
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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.  [Show abstract] [Hide abstract]
ABSTRACT: We present a description of the data reduction and mapmaking pipeline used for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from 2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hours of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hours of observation. From these, 1085 hours were devoted to a 850 deg^2 stripe (11.2 hours by 9.1 deg) centered on a declination of 52.7 deg, while 175 hours were devoted to a 280 deg^2 stripe (4.5 hours by 4.8 deg) centered at the celestial equator. We discuss sources of statistical and systematic noise, calibration, telescope pointing, and data selection. Out of 1260 survey hours and 1024 detectors per array, 816 hours and 593 effective detectors remain after data selection for this frequency band, yielding a 38% survey efficiency. The total sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in the timeordered data stream (TOD), is 32 microKelvin sqrt{s} in CMB units. Atmospheric brightness fluctuations constitute the main contaminant in the data and dominate the detector noise covariance at low frequencies in the TOD. The maps were made by solving the leastsquares problem using the Preconditioned Conjugate Gradient method, incorporating the details of the detector and noise correlations. Crosscorrelation with WMAP sky maps, as well as analysis from simulations, reveal that our maps are unbiased at multipoles ell > 300. This paper accompanies the public release of the 148 GHz southern stripe maps from 2008. The techniques described here will be applied to future maps and data releases.  [Show abstract] [Hide abstract]
ABSTRACT: We present a new calibration method based on crosscorrelations with the Wilkinson Microwave Anisotropy Probe (WMAP) and apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing strategy and mapmaking procedure allows an unbiased reconstruction of the modes in the maps over a wide range of multipoles. By directly matching the ACT maps to WMAP observations in the multipole range of 400 < l < 1000, we determine the absolute calibration with an uncertainty of 2% in temperature. The precise measurement of the calibration error directly impacts the uncertainties in the cosmological parameters estimated from the ACT power spectra. We also present a combined map based on ACT and WMAP data that has a high signaltonoise ratio over a wide range of multipoles.  [Show abstract] [Hide abstract]
ABSTRACT: We present constraints on cosmological parameters based on a sample of SunyaevZeldovichselected galaxy clusters detected in a millimeterwave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 opticallyconfirmed highmass clusters comprising the highsignificance end of the total cluster sample identified in 455 square degrees of sky surveyed during 2008 at 148GHz. 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 4parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives {sigma}{sub 8} = 0.851 {+} 0.115 and w = 1.14 {+} 0.35 for a spatiallyflat wCDM cosmological model with WMAP 7year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7year constraints alone. Fixing the scaling relation between cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by Xray observations, we find {sigma}{sub 8} = 0.821 {+} 0.044 and w = 1.05 {+} 0.20. These results are consistent with constraints from WMAP 7 plus baryon acoustic oscillations plus type Ia supernoava which give {sigma}{sub 8} = 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.  [Show abstract] [Hide abstract]
ABSTRACT: We present measurements of the cosmic microwave background (CMB) power spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as well as the crossfrequency 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 higherorder peaks provide an additional test of the {\Lambda}CDM 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 2.8{\sigma} level. We also detect a low level of Galactic dust in our maps, which demonstrates that we can recover known faint, diffuse signals.  [Show abstract] [Hide abstract]
ABSTRACT: We report on twentythree clusters detected blindly as SunyaevZel'dovich (SZ) decrements in a 148 GHz, 455 squaredegree map of the southern sky made with data from the Atacama Cosmology Telescope 2008 observing season. All SZ detections announced in this work have confirmed optical counterparts. Ten of the clusters are new discoveries. One newly discovered cluster, ACTCL J01024915, with a redshift of 0.75 (photometric), has an SZ decrement comparable to the most massive systems at lower redshifts. Simulations of the cluster recovery method reproduce the sample purity measured by optical followup. In particular, for clusters detected with a signaltonoise ratio greater than six, simulations are consistent with optical followup that demonstrated this subsample is 100% pure. The simulations further imply that the total sample is 80% complete for clusters with mass in excess of 6x10^14 solar masses referenced to the cluster volume characterized by five hundred times the critical density. The Compton y  Xray luminosity mass comparison for the eleven best detected clusters visually agrees with both selfsimilar and nonadiabatic, simulationderived scaling laws.  [Show abstract] [Hide abstract]
ABSTRACT: We present constraints on cosmological parameters based on a sample of SunyaevZel'dovichselected galaxy clusters detected in a millimeterwave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 opticallyconfirmed highmass clusters comprising the highsignificance end of the total cluster sample identified in 455 square degrees 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 4parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives sigma_8 = 0.851 +/ 0.115 and w = 1.14 +/ 0.35 for a spatiallyflat wCDM cosmological model with WMAP 7year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7year constraints alone. Fixing the scaling relation between cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by Xray observations, we find sigma_8 = 0.821 +/ 0.044 and w = 1.05 +/ 0.20. These results are consistent with constraints from WMAP 7 plus baryon acoustic oscillations plus type Ia supernoava which give sigma_8 = 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.  [Show abstract] [Hide abstract]
ABSTRACT: We report on extragalactic sources detected in a 455 deg2 map of the southern sky made with data at a frequency of 148 GHz 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 lowredshift Xrayselected galaxy clusters. Estimates of the radio to millimeterwave 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 reemission from warm dust. In a bright (>50 mJy) 148 GHz selected sample with complete crossidentifications from the Australia Telescope 20 GHz survey, we observe an average steepening of the spectra between 5, 20, and 148 GHz with median spectral indices of α520 = –0.07 ± 0.06, α20148 = –0.39 ± 0.04, and α5148 = –0.20 ± 0.03. When the measured spectral indices are taken into account, the 148 GHz 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 synchrotrondominated sources with flux density less than 20 mJy is C Sync = (2.8 ± 0.3) × 10–6μK2.
Publication Stats
450  Citations  
41.77  Total Impact Points  
Top Journals
Institutions

20102013

University of Pittsburgh
 Physics and Astronomy
Pittsburgh, Pennsylvania, United States


20112012

Pontifical Catholic University of Chile
 Facultad de Física
CiudadSantiago, Santiago Metropolitan, Chile
