Signature of cool cores in SZ clusters: a multiwavelength approach

TL;DR

This study investigates how cool cores in galaxy clusters affect their Sunyaev-Zeldovich signals using multiwavelength data, revealing biases in cluster detection and proposing optical and UV indicators for cool core presence.

Contribution

The paper introduces a multiwavelength approach combining SZ, optical, and UV data to identify cool cores and assess their impact on cluster detection biases.

Findings

Cool cores influence the central Compton parameter y_0.

Presence of cool cores causes a bias in SZ cluster detection.

Optical and UV colours of BCGs can indicate cool core presence.

Abstract

We use the high quality pressure profiles of 239 galaxy clusters made available by the ACCEPT project (Cavagnolo et al. 2009) in order to derive the expected Sunyaev Zeldovich (SZ) signal in a variety of cases that hardly find a counterpart in the simulations. We made use of the Melin et al. (2006) cluster selection function for both the South Pole Telescope (SPT) and Planck instruments. We infer a clear effect of the cool core (CC) on the central Compton parameter y_0. We find that the presence of CCs introduces a small bias in cluster detection, especially around the mass at which the performance of the survey begins to decrease. If the CC were removed, a lower overall fraction of detected clusters would be expected. In order to estimate the presence of such a bias by means of SZ only surveys, we show that the ratio between y_0 and y_int anti-correlates with the cluster central cooling time. If multi-band optical cluster surveys are either available for a cross-match or a follow-up is planned, we suggest that likely CC clusters are those with a Brightest Cluster Galaxy (BCG) at least 0.3 magnitudes bluer than the average. A more robust estimate of the CC presence is given by UV-optical colours of the BCG, like the NUV-r, whose values can be 4 magnitudes off the NUV-r equivalent of the red sequence, in clusters with low excess entropy. We also find correlation of the y_0/y_int ratio with Halpha, IR and radio luminosities. We argue that the analysis of a combined SZ/optical/UV surveys can be also used to shed light on the suggested CC evolution with redshift. (abridged)