The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray properties of Subaru optically-selected clusters

TL;DR

This study analyzes the X-ray properties of optically-selected galaxy clusters using joint eROSITA and Subaru HSC data, revealing a low fraction of relaxed clusters and shallow scaling relation slopes, highlighting differences from X-ray-selected samples.

Contribution

It provides the first systematic X-ray analysis of optically selected clusters in the eFEDS field, establishing their dynamical status and scaling relations, and comparing them with X-ray-selected samples.

Findings

Low fraction (<39%) of relaxed clusters among optically selected sample.

Shallow L-T slope of 2.1±0.5 consistent with self-similar models.

L-M slope of 1.5±0.3 aligns with theoretical predictions.

Abstract

We present the results of a systematic X-ray analysis of optically rich galaxy clusters detected by the Subaru HSC survey in the eROSITA eFEDS field. Through a joint analysis of SRG/eROSITA and Subaru/HSC surveys, we aim to study the dynamical status of the optically selected clusters and derive the cluster scaling relations. The sample consists of 43 optically selected galaxy clusters with a richness $>40$ in $0.16<z<0.89$. We systematically analyzed the X-ray images and spectra using the eROSITA data. We identified the BCG using the optical and far-infrared databases. We evaluated the cluster's dynamical status by measuring the offset between the X-ray peak and BCG position, the gas concentration, and the number of galaxy-density peaks. We studied the luminosity-temperature and mass-luminosity relations based on eROSITA X-ray spectra and HSC weak-lensing data analyses. Based on the these measurements, the fraction of relaxed clusters is $2(<39)$%, which is smaller than that of the X-ray-selected cluster samples. After correcting for a selection bias due to the richness cut, we obtained a shallow $L-T$ slope of $2.1\pm0.5$, which is consistent with the predictions of the self-similar model and the baseline model incorporating a mass-concentration relation. The $L-M$ slope of $1.5\pm0.3$ agrees with the above theoretical models and that of the shear-selected clusters in the eFEDs field. Our analysis of high-richness optical clusters yields a small fraction of relaxed clusters and a shallow slope for the luminosity-temperature relation. This suggests that the average X-ray properties of the optical clusters are likely to be different from those observed in the X-ray samples. Thus, the joint eROSITA and HSC observations are a powerful tool in extending the analysis to a larger sample and understanding the selection effect with a view to establish cluster scaling relations.