The Atacama Cosmology Telescope: High-Resolution Sunyaev-Zel'dovich Array Observations of ACT SZE-selected Clusters from the Equatorial Strip

TL;DR

This paper reports high-resolution Sunyaev-Zel'dovich Array observations of galaxy clusters from the ACT survey, providing improved mass estimates and insights into contamination effects, including a newly discovered high-redshift cluster.

Contribution

It introduces targeted SZA follow-up observations that enhance cluster mass estimation accuracy and investigates point source contamination in SZE measurements.

Findings

Detection of a new high-redshift, massive cluster ACT-CL J0022-0036.

Consistent mass estimates from SZE, X-ray, and optical data.

Point source contamination could affect SZE measurements by up to 20%.

Abstract

We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically-confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly-discovered, massive (10^15 Msun), high-redshift (z=0.81) cluster revealed by ACT through the Sunyaev-Zel'dovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as Abell 2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the <= 20% level for some fraction of clusters.