Joint signal extraction from galaxy clusters in X-ray and SZ surveys: A matched-filter approach

TL;DR

This paper introduces a joint X-ray and SZ matched-filter method to improve galaxy cluster detection, achieving higher signal-to-noise ratios and better photometry by combining complementary data sources from ROSAT and Planck surveys.

Contribution

The paper develops a novel joint matched-filter algorithm that combines X-ray and SZ data, enhancing detection sensitivity and accuracy over single-probe methods.

Findings

Joint filter improves detection rate of galaxy clusters.

Method provides accurate photometry when cluster relations are known.

Enhanced signal-to-noise ratio compared to single-map extractions.

Abstract

The hot ionized gas of the intra-cluster medium emits thermal radiation in the X-ray band and also distorts the cosmic microwave radiation through the Sunyaev-Zel'dovich (SZ) effect. Combining these two complementary sources of information through innovative techniques can therefore potentially improve the cluster detection rate when compared to using only one of the probes. Our aim is to build such a joint X-ray-SZ analysis tool, which will allow us to detect fainter or more distant clusters while maintaining high catalogue purity. We present a method based on matched multifrequency filters (MMF) for extracting cluster catalogues from SZ and X-ray surveys. We first designed an X-ray matched-filter method, analogous to the classical MMF developed for SZ observations. Then, we built our joint X-ray-SZ algorithm by combining our X-ray matched filter with the classical SZ-MMF, for which we used the physical relation between SZ and X-ray observations. We show that the proposed X-ray matched filter provides correct photometry results, and that the joint matched filter also provides correct photometry when the $F_{\rm X}/Y_{500}$ relation of the clusters is known. Moreover, the proposed joint algorithm provides a better signal-to-noise ratio than single-map extractions, which improves the detection rate even if we do not exactly know the $F_{\rm X}/Y_{500}$ relation. The proposed methods were tested using data from the ROSAT all-sky survey and from the Planck survey.