We introduce the galaxy intensity mapping cross-correlation estimator (GIMCO), which is a new tomographic estimator for the gravitational lensing potential, based on a combination of intensity ...mapping (IM) and galaxy number counts. The estimator can be written schematically as IM(z_{f})×galaxy(z_{b})-galaxy(z_{f})×IM(z_{b}) for a pair of distinct redshifts (z_{f},z_{b}); this combination allows to greatly reduce the contamination by density-density correlations, thus isolating the lensing signal. As an estimator constructed only from cross-correlations, it is additionally less susceptible to systematic effects. We show that the new estimator strongly suppresses cosmic variance and consequently improves the signal-to-noise ratio (SNR) for the detection of lensing, especially on linear scales and intermediate redshifts. For cosmic variance dominated surveys, the SNR of our estimator is a factor of 30 larger than the SNR obtained from the correlation of galaxy number counts only. Shot noise and interferometer noise reduce the SNR. For the specific example of the dark energy survey (DES) cross-correlated with the hydrogen intensity mapping and real time analysis experiment (HIRAX), the SNR is around four, whereas for Euclid cross-correlated with HIRAX it reaches 52. This corresponds to an improvement of a factor of 4-5 compared to the SNR from DES alone. For Euclid cross-correlated with HIRAX the improvement with respect to Euclid alone strongly depends on the redshift. We find that the improvement is particularly important for redshifts below 1.6, where it reaches a factor of 5. This makes our estimator especially valuable to test dark energy and modified gravity, that are expected to leave an impact at low and intermediate redshifts.
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 cosmological constraints from the combination of the full mission nine-year WMAP release and small-scale temperature data from the pre-Planck Atacama Cosmology Telescope (ACT) and South ...Pole Telescope (SPT) generation of instruments. This is an update of the analysis presented in Calabrese et al. Phys. Rev. D 87, 103012 (2013), and highlights the impact on ΛCDM cosmology of a 0.06 eV massive neutrino-which was assumed in the Planck analysis but not in the ACT/SPT analyses-and a Planck-cleaned measurement of the optical depth to reionization. We show that cosmological constraints are now strong enough that small differences in assumptions about reionization and neutrino mass give systematic differences which are clearly detectable in the data. We recommend that these updated results be used when comparing cosmological constraints from WMAP, ACT and SPT with other surveys or with current and future full-mission Planck cosmology. Cosmological parameter chains are publicly available on the NASA’s LAMBDA data archive.
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.
Abstract We present tomographic measurements of structure growth using cross-correlations of Atacama Cosmology Telescope (ACT) DR6 and Planck cosmic microwave background (CMB) lensing maps with the ...unWISE Blue and Green galaxy samples, which span the redshift ranges 0.2 ≲ z ≲ 1.1 and 0.3 ≲ z ≲ 1.8, respectively. We improve on prior unWISE cross-correlations not just by making use of the new, high-precision ACT DR6 lensing maps, but also by including additional spectroscopic data for redshift calibration and by analyzing our measurements with a more flexible theoretical model. We determine the amplitude of matter fluctuations at low redshifts ( z ≃ 0.2–1.6), finding S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 = 0.813 ± 0.021 using the ACT cross-correlation alone and S 8 = 0.810 ± 0.015 with a combination of Planck and ACT cross-correlations; these measurements are fully consistent with the predictions from primary CMB measurements assuming standard structure growth. The addition of baryon acoustic oscillation data breaks the degeneracy between σ 8 and Ω m , allowing us to measure σ 8 = 0.813 ± 0.020 from the cross-correlation of unWISE with ACT and σ 8 = 0.813 ± 0.015 from the combination of cross-correlations with ACT and Planck. These results also agree with the expectations from primary CMB extrapolations in ΛCDM cosmology; the consistency of σ 8 derived from our two redshift samples at z ∼ 0.6 and 1.1 provides a further check of our cosmological model. Our results suggest that structure formation on linear scales is well described by ΛCDM even down to low redshifts z ≲ 1.
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.
We present the optical and X-ray properties of 68 galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect at 148 GHz by the Atacama Cosmology Telescope (ACT). Our sample, from an area of 504 ...degsup 2 centered on the celestial equator, is divided into two regions. The main region uses 270 degsup 2 of the ACT survey that overlaps with the co-added ugriz imaging from the Sloan Digital Sky Survey (SDSS) over Stripe 82 plus additional near-infrared pointed observations with the Apache Point Observatory 3.5 m telescope. We confirm a total of 49 clusters to z approximate 1.3, of which 22 are new discoveries. We present the optical richness, photometric redshifts, and separation between the SZ position and the brightest cluster galaxy (BCG). We also present X-ray fluxes and luminosities from the ROSAT All Sky Survey which confirm that this is a massive sample.
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