Probing the dynamical state, baryon content, and multiphase nature of galaxy clusters with bright background QSOs

TL;DR

This study uses X-ray and UV spectroscopy to analyze the physical, dynamical, and baryonic properties of galaxy clusters and their gaseous halos, revealing disturbed states and baryon deficits.

Contribution

It provides new insights into the dynamical states, baryon content, and multiphase gas in galaxy clusters through combined X-ray and UV observations.

Findings

Most clusters are dynamically disturbed.

Baryon content in hot gas and stars is lower than expected.

UV spectroscopy indicates the presence of warm-hot gas phases.

Abstract

We have initiated a programme to study the physical/dynamical state of gas in galaxy clusters and the impact of the cluster environment on gaseous halos of individual galaxies using X-ray imaging and UV absorption line spectroscopy of background QSOs. Here we report results from the analysis Chandra and XMM-Newton archival data of five galaxy clusters with such QSOs, one of which has an archival UV spectrum. We characterize the gravitational masses and dynamical states, as well as the hot intracluster medium (ICM) properties of these clusters. Most clusters are dynamically disturbed clusters based on the X-ray morphology parameters, the X-ray temperature profiles, the large offset between X-ray peak and brightest cluster galaxy (BCG). The baryon contents in the hot ICM and stars of these clusters within $r_{500}$ are lower than the values expected from the gravitational masses, according to the standard cosmology. We also estimate column densities of the hot ICM along the sightlines toward the background QSOs as well as place upper limits on the warm-hot phase for the one sightline with existing UV observations. These column densities, compared with those of the warm and warm-hot ICM to be measured with UV absorption line spectroscopy, will enable us to probe the relationship among various gaseous phases and their connection to the heating/cooling and dynamical processes of the clusters. Furthermore, our analysis of the archival QSO spectrum probing one cluster underscores the need for high quality, targeted UV observations to robustly constrain the 10$^{5-6}$ K gas phase.