2018ApJS..235...20H

We present a catalog of 182 galaxy clusters detected through the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope in a contiguous 987.5 deg² field. The clusters were detected as SZ decrements by applying a matched filter to 148 GHz maps that combine the original ACT equatorial survey with data from the first two observing seasons using the ACTPol receiver. Optical/IR confirmation and redshift measurements come from a combination of large public surveys and our own follow-up observations. Where necessary, we measured photometric redshifts for clusters using a pipeline that achieves accuracy Δz/(1 + z) = 0.015 when tested on Sloan Digital Sky Survey data. Under the assumption that clusters can be described by the so-called universal pressure profile (UPP) and its associated mass scaling law, the full signal-to-noise ratio > 4 sample spans the mass range 1.6< M_500c^UPP/10¹⁴M_☉< 9.1, with median M_500c^UPP=3.1×10¹⁴M_☉. The sample covers the redshift range 0.1 < z < 1.4 (median z = 0.49), and 28 clusters are new discoveries (median z = 0.80). We compare our catalog with other overlapping cluster samples selected using the SZ, optical, and X-ray wavelengths. We find that the ratio of the UPP-based SZ mass to richness-based weak-lensing mass is <M_500c^UPP>/<M_500c^λWL^>=0.68±0.11. After applying this calibration, the mass distribution for clusters with M_500c > 4 x 10¹⁴ M_☉ is consistent with the number of such clusters found in the South Pole Telescope SZ survey.