The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data (1301.0816v2)

Abstract: [Abridged] 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 of 504 square degrees on the celestial equator. A subsample of 48 clusters within the 270 square degree region overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14 Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters, the sample is studied further through a "Profile Based Amplitude Analysis" using a single filter at a fixed \theta_500 = 5.9' angular scale. This new approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the relationship between the cluster characteristic size (R_500) and the integrated Compton parameter (Y_500). 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 is used to obtain cosmological constraints. We first confirm 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 based on galaxy velocity dispersions. In combination with WMAP7 these data simultaneously constrain the scaling relation and cosmological parameters, yielding \sigma_8 = 0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include marginalization over a 15% bias in dynamical mass relative to the true halo mass. In an extension to LCDM that incorporates non-zero neutrino mass density, we combine our data with WMAP7+BAO+Hubble constant measurements to constrain \Sigma m_\nu < 0.29 eV (95% C. L.).

• The paper introduces a catalog of 68 SZ-selected galaxy clusters, including 19 new detections, based on 148 GHz ACT data.
• The paper employs a Profile Based Amplitude Analysis using fixed angular filters and a Universal Pressure Profile to extract SZ signals.
• The paper constrains key cosmological parameters like σ8 and Ωm and sets an upper limit on neutrino masses, enhancing our understanding of large-scale structure.

Overview of the ACT: SZ Selected Galaxy Clusters

The paper, "The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data," presents a comprehensive analysis of galaxy clusters identified via the Sunyaev-Zel'dovich effect (SZ) using data from the Atacama Cosmology Telescope (ACT). The paper introduces a catalog of 68 galaxy clusters, with 19 newly discovered, based on SZ selection at 148 GHz covering a survey region on the celestial equator. This catalog constitutes a significant dataset for probing galaxy cluster properties and cosmology.

Methodology

The detection method is rooted in using the SZ effect, exploiting the inverse Compton scattering of cosmic microwave background (CMB) photons by hot electrons in the intracluster medium. The survey focused on a 504 square degree area, overlapping with 270 square degrees of SDSS Stripe 82, which facilitated optical confirmations. The approach involves a comprehensive suite of matched spatial filters to detect the SZ signal amid a background of CMB fluctuations, astrophysical signal, and noise.

For analysis, a "Profile Based Amplitude Analysis" (PBAA) was implemented contrary to the traditional full-scale models, allowing for SZ signal quantification based on a fixed angular scale of 5.9'. This method leverages a "Universal Pressure Profile" (UPP) for the intracluster gas, incorporating redshift data and prior cluster pressure profiles to derive the characteristic size and integrated Compton parameters. The paper assessed three cluster physics models to explore SZ-mass scaling relations.

Key Results

The paper articulates several notable results from their cluster sample and models:

• The SZ sample was estimated to be 90% complete for $M_{500c} > 4.5 \times 10^{14} \textrm{M}_\odot$ between redshifts $0.15 < z < 0.8$.
• Cosmological parameters derived included $\sigma_8 = 0.829$ and $\Omega_m = 0.292$, assuming a concordance cosmology. The constraints primarily benefitted from calibration using dynamical masses.
• Further constraints were explored integrating WMAP7, Baryon Acoustic Oscillation data, and Hubble constant measurements, setting an upper limit on the sum of neutrino masses at $\sum_\nu m_\nu < 0.29$ eV (95% confidence level).

Implications and Future Directions

The implications of this research are substantial for understanding cosmic structure formation and development of cosmological models. The ACT's dataset enriches the existing databases of galaxy clusters, significantly contributing to the mapping of large-scale structures. The measurements, in tandem with complementary datasets (e.g., optical and X-ray observations), provide a multifaceted approach to understanding cluster physics and enhancing the precision in cosmological parameters.

The introduction of PBAA represents a methodological advancement, simplifying analysis by utilizing fixed filters specific to the survey's noise characteristics, thereby reducing inter-filter noise bias. This approach can serve as a framework for future SZ surveys, emphasizing the modular nature of the method adaptable to different modelling assumptions.

Future work will likely focus on refining scaling relations through extended analysis of halo masses using galaxy velocity dispersions, weak lensing, and X-ray observations. A challenge remains in minimizing the systematic biases in mass estimation which significantly affect cosmological parameter constraints. The ongoing developments in survey techniques and analysis similarly promise potential enhancements in the reliability and depth of cosmological inferences drawn from SZ-selected cluster samples.