Exploring Galaxy Cluster Signatures in the Cosmic Microwave Background with the Atacama Cosmology Telescope

Abstract

Studying the Cosmic Microwave Background at smaller and smaller scales has been a topic of great interest in astrophysics within the past decade. Moreover, due to their complex structure, understanding the physics of galaxy clusters can lead to significant progress in understanding the nature and structure of the Universe. In this paper, we analyze different properties of galaxy clusters using their signature in the CMB maps and cluster catalog provided by the Atacama Cosmology Telescope (ACT) Collaboration.

We analyze the cluster signature by performing a weighted inverse-variance stacking of cluster map patches and computing the average radial profiles at three different frequency bands: f090, f150 and f220. The first check involves fitting the Arnaud et al. profile on the cluster radial profiles to check if the data behaves according to the theoretical predictions. The second check represents a frequency consistency between the 96 GHz and the 148 GHz profile to obtain the expected map-independent ratio and check whether it confirms the theoretical expectations. We find that the experimental ratios are within 15% of the theoretical values for all mass and redshift bins tested. Last, we analyze the average radial profiles of the polarization and Stokes parameters and confirm that no signal is observed for any mass or redshift range.

The second goal of this paper is to identify the cluster lensing signal in the CMB maps. We look for the signal in both cluster simulations and the ACT data. We obtain a lensing signature of order 1 muK in the simulations, about 5 times smaller than the theoretical example given by Seljak and Zaldarriaga. Such a small magnitude would explain the lack of lensing in the ACT data due to its limited precision. However, Madhavacheril and others have detected the lensing signal at high significance in the ACT data using matched filter techniques and their findings agree with the theory. This could mean that either our technique is sub optimal and does not recover the signal from the background noise or that there is an error in the analysis that partly or totally removes the lensing signal from the maps.