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 M _ { 500 c } > 4.5 \times 10 ^ { 14 } \textrm { M } _ { \odot } 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 \theta _ { 500 } = 5 \farcm { 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 ( R _ { 500 } ) and the integrated Compton parameter ( Y _ { 500 } ) .
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 \sigma _ { 8 } = 0.829 \pm 0.024 and \Omega _ { m } = 0.292 \pm 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 \Lambda CDM 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 \sum _ { \nu } m _ { \nu } < 0.29 eV ( 95 % confidence limit ) .