Low-scatter galaxy cluster mass proxies for the eROSITA all-sky survey

TL;DR

This paper introduces a new method to accurately estimate low-scatter galaxy cluster mass proxies from low photon count X-ray data, enhancing cosmological parameter constraints from the eROSITA survey.

Contribution

The authors propose and validate a novel technique to reconstruct gas mass and core-excised luminosity from low-count data, reducing systematics in cosmological analyses.

Findings

Gas mass and core-excised luminosity can be recovered with 20-30% precision at ~50 counts.

The method significantly reduces systematics compared to using full X-ray luminosity.

Validation performed using extensive eROSITA-like simulations.

Abstract

The on-going X-ray all-sky survey with the eROSITA instrument will yield large galaxy cluster samples, which will bring strong constraints on cosmological parameters. In particular, the survey holds great promise to investigate the tension between CMB and low-redshift measurements. The current bottleneck preventing the full exploitation of the survey data is the systematics associated with the relation between survey observable and halo mass. Numerous recent studies have shown that gas mass and core-excised X-ray luminosity exhibit very low scatter at fixed mass. We propose a new method to reconstruct these quantities from low photon count data and validate the method using extensive eROSITA-like simulations. We find that even near the detection threshold of ~50 counts the core-excised luminosity and the gas mass can be recovered with 20-30% precision, which is substantially less than the scatter of the full integrated X-ray luminosity at fixed mass. When combined with an accurate calibration of the absolute mass scale (e.g. through weak gravitational lensing), our technique reduces the systematics on cosmological parameters induced by the mass calibration.