The atacama cosmology telescope: Dynamical masses and scaling relations for A sample of massive Sunyaev-Zel'dovich effect selected galaxy clusters
Astrophysical Journal 772:1 (2013)
Abstract:
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 deg2 area of the southern sky. Deep multi-object spectroscopic observations were taken to secure intermediate-resolution (R ∼ 700-800) spectra and redshifts for 60 member galaxies on average per cluster. The dynamical masses M 200c of the clusters have been calculated using simulation-based scaling relations between velocity dispersion and mass. The sample has a median redshift z = 0.50 and a median mass with a lower limit , consistent with the expectations for the ACT southern sky survey. These masses are compared to the ACT SZE properties of the sample, specifically, the match-filtered central SZE amplitude , the central Compton parameter y 0, and the integrated Compton signal Y 200c , which we use to derive SZE-mass scaling relations. All SZE estimators correlate with dynamical mass with low intrinsic scatter (≲ 20%), in agreement with numerical simulations. We explore the effects of various systematic effects on these scaling relations, including the correlation between observables and the influence of dynamically disturbed clusters. Using the three-dimensional information available, we divide the sample into relaxed and disturbed clusters and find that ∼50% of the clusters are disturbed. 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. © 2013. The American Astronomical Society. All rights reserved.The Atacama Cosmology Telescope: Sunyaev-Zel'dovich selected galaxy clusters at 148 GHz from three seasons of data
Journal of Cosmology and Astroparticle Physics 2013:7 (2013)
Abstract:
We present a catalog of 68 galaxy clusters, of which 19 are new discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the Atacama Cosmology Telescope (ACT) survey on the celestial equator. With this addition, the ACT collaboration has reported a total of 91 optically confirmed, SZ detected clusters. The 504 square degree survey region includes 270 square degrees of overlap with SDSS Stripe 82, permitting the confirmation of SZ cluster candidates in deep archival optical data. The subsample of 48 clusters within Stripe 82 is estimated to be 90% complete for M500c > 4.5 × 1014M⊙ and redshifts 0.15 < z < 0.8. While a full suite of matched filters is used to detect the clusters, the sample is studied further through a "Profile Based Amplitude Analysis" using a statistic derived from a single filter at a fixed θ500 = 5'9 angular scale. This new approach incorporates the cluster redshift along with prior information on the cluster pressure profile to fix the relationship between the cluster characteristic size (R500) and the integrated Compton parameter (Y500). We adopt a one-parameter family of "Universal Pressure Profiles" (UPP) with associated scaling laws, derived from X-ray measurements of nearby clusters, as a baseline model. Three additional models of cluster physics are used to investigate a range of scaling relations beyond the UPP prescription. Assuming a concordance cosmology, the UPP scalings are found to be nearly identical to an adiabatic model, while a model incorporating non-thermal pressure better matches dynamical mass measurements and masses from the South Pole Telescope. A high signal to noise ratio subsample of 15 ACT clusters with complete optical follow-up is used to obtain cosmological constraints. We demonstrate, using fixed scaling relations, how the constraints depend on the assumed gas model if only SZ measurements are used, and show that constraints from SZ data are limited by uncertainty in the scaling relation parameters rather than sample size or measurement uncertainty. We next add in seven clusters from the ACT Southern survey, including their dynamical mass measurements, which are based on galaxy velocity dispersions and thus are independent of the gas physics. In combination with WMAP7 these data simultaneously constrain the scaling relation and cosmological parameters, yielding 68% confidence ranges described by σ8 = 0.829 ± 0.024 and Ωm = 0.292 ± 0.025. We consider these results in the context of constraints from CMB and other cluster studies. The constraints arise mainly due to the inclusion of the dynamical mass information and do not require strong priors on the SZ scaling relation parameters. The results include marginalization over a 15% bias in dynamical masses relative to the true halo mass. In an extension to ACDM that incorporates non-zero neutrino mass density, we combine our data with WMAP7, Baryon Acoustic Oscillation data, and Hubble constant measurements to constrain the sum of the neutrino mass species to be Σv mv < 0.29 eV (95% confidence limit). © 2013 IOP Publishing Ltd and Sissa Medialab srl.The Atacama Cosmology Telescope: Likelihood for small-scale CMB data
Journal of Cosmology and Astroparticle Physics 2013:7 (2013)
Abstract:
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 < l < 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 χ2/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 < l < 3500 for use in cosmological parameter estimation. © 2013 IOP Publishing Ltd and Sissa Medialab srl.Cosmological parameters from pre-planck cosmic microwave background measurements
Physical Review D - Particles, Fields, Gravitation and Cosmology 87:10 (2013)
Abstract:
Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat ΛCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n s=0.9690±0.0089, is less than unity at the 3.5σ level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be Neff=3.28±0.40, in agreement with the standard model's three species of light neutrinos. © 2013 American Physical Society.The atacama cosmology telescope: Relation between galaxy cluster optical richness and Sunyaev-Zel'dovich effect
Astrophysical Journal 767:1 (2013)