Globular cluster ultraluminous X-ray sources in the furthest early-type galaxies

Abstract

Ultraluminous X-ray Sources (ULXs) in globular clusters are low mass X-ray binaries that achieve high X-ray luminosities through a currently uncertain accretion mechanism. Using archival Chandra and Hubble Space Telescope (HST) observations, we perform a volume-limited search (≲ 70 Mpc) of 21 of the most massive (>1011.5M⊙) early-type galaxies to identify ULXs hosted by globular cluster (GC) candidates. We find a total of 34 ULX candidates above the expected background within 5 times the effective radius of each galaxy, with 10 of these ($\sim 29.4\%$) potentially hosted by a GC. A comparison of the spatial and luminosity distributions of these new candidate GC ULXs with previously identified GC ULXs shows that they are similar: both samples peak at LX ∼ a few × 1039 erg/s and are typically located within a few effective radii of their host galaxies.