The Atacama Cosmology Telescope (ACT): Beam Profiles and First SZ Cluster Maps

TL;DR

This paper presents initial results from the Atacama Cosmology Telescope, including high-precision beam profiles and the first Sunyaev-Zel'dovich (SZ) cluster maps, demonstrating the telescope's capabilities in cosmic microwave background and galaxy cluster observations.

Contribution

The paper introduces a maximum-likelihood map-making method using B-splines for atmospheric signal removal and provides the first SZ cluster maps from ACT data.

Findings

High-precision beam maps and window functions determined.

Detection of the z=0.44 component of A3128 cluster.

Evidence of SZ effect's redshift-independent mass selection.

Abstract

The Atacama Cosmology Telescope (ACT) is currently observing the cosmic microwave background with arcminute resolution at 148 GHz, 218 GHz, and 277 GHz. In this paper, we present ACT's first results. Data have been analyzed using a maximum-likelihood map-making method which uses B-splines to model and remove the atmospheric signal. It has been used to make high-precision beam maps from which we determine the experiment's window functions. This beam information directly impacts all subsequent analyses of the data. We also used the method to map a sample of galaxy clusters via the Sunyaev-Zel'dovich (SZ) effect, and show five clusters previously detected with X-ray or SZ observations. We provide integrated Compton-y measurements for each cluster. Of particular interest is our detection of the z = 0.44 component of A3128 and our current non-detection of the low-redshift part, providing strong evidence that the further cluster is more massive as suggested by X-ray measurements. This is a compelling example of the redshift-independent mass selection of the SZ effect.