eROSITA cluster cosmology forecasts: cluster temperature substructure bias

TL;DR

This paper investigates how unresolved temperature substructures in galaxy clusters observed by eROSITA bias temperature measurements low by about 5%, affecting cosmological parameter estimates from the survey.

Contribution

It quantifies the temperature bias caused by substructures in galaxy clusters and assesses its impact on cosmological constraints from eROSITA data.

Findings

Temperatures are biased low by about 5% due to unresolved substructures.

The bias significantly affects cosmological parameter estimation if uncorrected.

Simulations compare eROSITA observations with Chandra data to identify the bias.

Abstract

The eROSITA mission will provide the largest sample of galaxy clusters detected in X-ray to date (one hundred thousand expected). This sample will be used to constrain cosmological models by measuring cluster masses. An important mass proxy is the electron temperature of the hot plasma detected in X-rays. We want to understand the detection properties and possible bias in temperatures due to unresolved substructures in the cluster halos. We simulated a large number of galaxy cluster spectra with known temperature substructures and compared the results from analysing eROSITA simulated observations to earlier results from Chandra. We were able to constrain a bias in cluster temperatures and its impact on cluster masses as well as cosmological parameters derived from the survey. We found temperatures in the eROSITA survey to be biased low by about five per cent due to unresolved temperature substructures (compared to emission-weighted average temperatures from the Chandra maps). This bias would have a significant impact on the eROSITA cosmology constraints if not accounted for in the calibration. We isolated the bias effect that substructures in galaxy clusters have on temperature measurements and their impact on derived cosmological parameters in the eROSITA cluster survey.