Galaxy shapes are subject to distortions due to the tidal field of the Universe. The cross-correlation of galaxy lensing with the lensing of the cosmic microwave background (CMB) cannot easily be ...separated from the cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work suggested that the intrinsic alignment contamination can be 15 per cent of this cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope surveys. Here we re-examine these estimates using up-to-date observational constraints of intrinsic alignments at a redshift more similar to that of CS82 galaxies. We find an ≈10 per cent contamination of the cross-spectrum from red galaxies, with ≈3 per cent uncertainty due to uncertainties in the redshift distribution of source galaxies and the modelling of the spectral energy distribution. Blue galaxies are consistent with being unaligned, but could contaminate the cross-spectrum by an additional 9.5 per cent within current 95 per cent confidence levels. While our fiducial estimate of alignment contamination is similar to previous work, our work suggests that the relevance of alignments for CMB lensing–galaxy lensing cross-correlation remains largely unconstrained. Little information is currently available about alignments at z > 1.2. We consider the upper limiting case where all z > 1.2 galaxies are aligned with the same strength as low-redshift luminous red galaxies, finding as much as ≈60 per cent contamination.
We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915, likely the most massive, hottest, most X-ray luminous and brightest ...Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102-4915 as the most significant SZ decrement in a sky survey area of 755 deg super(2). Our Very Large Telescope (VLT)/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, sigma sub(gal) = 1321 + or - 106 km s super(-1). Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T sub(X) = 14.5 + or - 0.1 keV and 0.5-2.0 keV band luminosity of L sub(X) = (2.19 + or - 0.11) x 10 super(45) h super(-2) sub(70) erg s super(-1). We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y sub(X), and integrated SZ distortion, we estimate a cluster mass of M sub(200)a = (2.16 + or - 0.32) x 10 super(15) h super(-1) sub(70) M sub(middot in circle). We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102-4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6 + or - 0.7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22 + or - 6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other. Archival radio data at 843 MHz reveal diffuse radio emission that, if associated with the cluster, indicates the presence of an intense double radio relic, hosted by the highest redshift cluster yet. ACT-CL J0102-4915 is possibly a high-redshift analog of the famous Bullet cluster. Such a massive cluster at this redshift is rare, although consistent with the standard LambdaCDM cosmology in the lower part of its allowed mass range. Massive, high-redshift mergers like ACT-CL J0102-4915 are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.
We present efficient algorithms for cosmic microwave background (CMB) lensing simulation and power spectrum estimation for flat-sky CMB polarization maps. We build a pure B-mode estimator to remedy E ...to B leakage due to partial sky coverage. We show that our estimators are unbiased, and consistent with the projected errors. We demonstrate our algorithm using simulated observations of small sky patches with realistic noise and weights for upcoming CMB polarization experiments.
We present the first dynamical mass estimates and scaling relations for a sample of Sunyaev-Zel'dovich effect (SZE) selected galaxy clusters. The sample consists of 16 massive clusters detected with ...the Atacama Cosmology Telescope (ACT) over a 455 deg super(2) area of the southern sky. The dynamical masses M sub(200)c of the clusters have been calculated using simulation-based scaling relations between velocity dispersion and mass. These masses are compared to the ACT SZE properties of the sample, specifically, the match-filtered central SZE amplitude y sub(0), the central Compton parameter y sub(0), and the integrated Compton signal Y sub(200)c, which we use to derive SZE-mass scaling relations. All SZE estimators correlate with dynamical mass with low intrinsic scatter (lap20%), in agreement with numerical simulations. There are hints that disturbed systems might bias the scaling relations, but given the current sample sizes, these differences are not significant; further studies including more clusters are required to assess the impact of these clusters on the scaling relations.
Markov chain Monte Carlo (MCMC) techniques are now widely used for cosmological parameter estimation. Chains are generated to sample the posterior probability distribution obtained following the ...Bayesian approach. An important issue is how to optimize the efficiency of such sampling and how to diagnose whether a finite-length chain has adequately sampled the underlying posterior probability distribution. We show how the power spectrum of a single such finite chain may be used as a convergence diagnostic by means of a fitting function, and discuss strategies for optimizing the distribution for the proposed steps. The methods developed are applied to current cosmic microwave background and large-scale structure data interpreted using both a pure adiabatic cosmological model and a mixed adiabatic/isocurvature cosmological model including possible correlations between modes. For the latter application, because of the increased dimensionality and the presence of degeneracies, the need for tuning MCMC methods for maximum efficiency becomes particularly acute.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We describe the measurement of the beam profiles and window functions for the Atacama Cosmology Telescope (ACT), which operated from ...2007 to 2010 with kilopixel bolometer arrays centered at 148, 218, and 277 GHz. Maps of Saturn are used to measure the beam shape in each array and for each season of observations. Radial profiles are transformed to Fourier space in a way that preserves the spatial correlations in the beam uncertainty to derive window functions relevant for angular power spectrum analysis. Several corrections are applied to the resulting beam transforms, including an empirical correction measured from the final cosmic microwave background (CMB) survey maps to account for the effects of mild pointing variation and alignment errors. Observations of Uranus made regularly throughout each observing season are used to measure the effects of atmospheric opacity and to monitor deviations in telescope focus over the season. Using the WMAP-based calibration of the ACT maps to the CMB blackbody, we obtain precise measurements of the brightness temperatures of the Uranus and Saturn disks at effective frequencies of 149 and 219 GHz. For Uranus we obtain thermodynamic brightness temperatures ... = 106.7 + or - 2.2 K and ... = 100.1+ or -3.1 K. For Saturn, we model the effects of the ring opacity and emission using a simple model and obtain resulting (unobscured) disk temperatures of ... = 137.3 + or - 3.2 K and ... = 137.3 + or - 4.7 K.
The posterior probability distribution for a set of model parameters encodes all that the data have to tell us in the context of a given model; it is the fundamental quantity for Bayesian parameter ...estimation. In order to infer the posterior probability distribution we have to decide how to explore parameter space. Here we compare three prescriptions for how parameter space is navigated, discussing their relative merits. We consider Metropolis-Hasting sampling, nested sampling and affine-invariant ensemble Markov chain Monte Carlo (MCMC) sampling. We focus on their performance on toy-model Gaussian likelihoods and on a real-world cosmological data set. We outline the sampling algorithms themselves and elaborate on performance diagnostics such as convergence time, scope for parallelization, dimensional scaling, requisite tunings and suitability for non-Gaussian distributions. We find that nested sampling delivers high-fidelity estimates for posterior statistics at low computational cost, and should be adopted in favour of Metropolis-Hastings in many cases. Affine-invariant MCMC is competitive when computing clusters can be utilized for massive parallelization. Affine-invariant MCMC and existing extensions to nested sampling naturally probe multimodal and curving distributions.
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