Probing ultradiffuse galaxies out to the virial radius of the Coma cluster with XMM–Newton

Abstract

ABSTRACT We probe the formation scenarios and the active galactic nucleus (AGN) occupation fraction of ultradiffuse galaxies (UDGs) in the nearby Coma cluster by utilizing XMM–Newton observations of 779 out of 854 UDG candidates identified by the Subaru survey. Their origin is probed by measuring the dark matter halo mass of the stacked sample of UDGs and the population of low-mass X-ray binaries residing in globular clusters. Our measurements suggest that the average UDG population does not have a substantial amount of hot gas or a large number of globular clusters. This supports the formation scenario, in which UDGs are puffed-up dwarf galaxies, agreeing with that obtained for 404 Coma cluster UDGs using Chandra. We also determine AGN occupation fraction of UDGs by cross-correlating the position of UDGs with the detected point sources in Coma. We detect three X-ray sources with detection significance σ ≥ 5 that could be off-centre AGNs within 5 arcsec from the centre of the UDG 317, UDG 432, and UDG 535. We identify an optical counterpart for the X-ray source associated with the UDG 317, suggesting that this source is more likely an off-centre AGN. Based on the current data, however, we cannot conclusively constrain whether the detected AGN is residing in the Coma cluster or not.