A Comprehensive Archival Chandra Search for X-ray Emission from Ultracompact Dwarf Galaxies
Viraj Pandya (Princeton), John Mulchaey (Carnegie Observatories),, Jenny E. Greene (Princeton)

TL;DR
This study systematically analyzes archival Chandra X-ray data for 578 ultracompact dwarf galaxies, finding that a small fraction host X-ray sources likely from low-mass X-ray binaries, with limited evidence for central black holes.
Contribution
It provides the first comprehensive X-ray survey of UCDs, assessing black hole presence and X-ray source properties across diverse environments.
Findings
3% of UCDs are X-ray detected.
X-ray sources are consistent with low-mass X-ray binaries.
Tentative correlation between X-ray detection and stellar velocity dispersion.
Abstract
We present the first comprehensive archival study of the X-ray properties of ultracompact dwarf (UCD) galaxies, with the goal of identifying weakly-accreting central black holes in UCDs. Our study spans 578 UCDs distributed across thirteen different host systems, including clusters, groups, fossil groups, and isolated galaxies. Of the 336 spectroscopically-confirmed UCDs with usable archival Chandra imaging observations, 21 are X-ray-detected. Imposing a completeness limit of erg s, the global X-ray detection fraction for the UCD population is . Of the 21 X-ray-detected UCDs, seven show evidence of long-term X-ray time variability on the order of months to years. X-ray-detected UCDs tend to be more compact than non-X-ray-detected UCDs, and we find tentative evidence that the X-ray detection fraction increases with surface luminosity density and…
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