183 research outputs found
A Comprehensive Archival Chandra Search for X-ray Emission from Ultracompact Dwarf Galaxies
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 global stellar
velocity dispersion. The X-ray emission of UCDs is fully consistent with
arising from a population of low-mass X-ray binaries (LMXBs). In fact, there
are fewer X-ray sources than expected using a naive extrapolation from globular
clusters. Invoking the fundamental plane of black hole activity for SUCD1 near
the Sombrero galaxy, for which archival Jansky Very Large Array imaging at 5
GHz is publicly available, we set an upper limit on the mass of a hypothetical
central black hole in that UCD to be . While the
majority of our sources are likely LMXBs, we cannot rule out central black
holes in some UCDs based on X-rays alone, and so we address the utility of
follow-up radio observations to find weakly-accreting central black holes.Comment: 20 pages, 6 figures, re-submitted to ApJ after minor revision
Calcium-rich Gap Transients: Solving the Calcium Conundrum in the Intracluster Medium
X-ray measurements suggest the abundance of Calcium in the intracluster
medium is higher than can be explained using favored models for core-collapse
and Type Ia supernovae alone. We investigate whether the Calcium conundrum in
the intracluster medium can be alleviated by including a contribution from the
recently discovered subclass of supernovae known as Calcium-rich gap
transients. Although the Calcium-rich gap transients make up only a small
fraction of all supernovae events, we find that their high Calcium yields are
sufficient to reproduce the X-ray measurements found for nearby rich clusters.
We find the goodness-of-fit metric improves from 84 to 2 by
including this new class. Moreover, Calcium-rich supernovae preferentially
occur in the outskirts of galaxies making it easier for the nucleosynthesis
products of these events to be incorporated in the intracluster medium via
ram-pressure stripping. The discovery of a Calcium-rich gap transients in
clusters and groups far from any individual galaxy suggests supernovae
associated with intracluster stars may play an important role in enriching the
intracluster medium. Calcium-rich gap transients may also help explain
anomalous Calcium abundances in many other astrophysical systems including
individual stars in the Milky Way, the halos of nearby galaxies and the
circumgalactic medium. Our work highlights the importance of considering the
diversity of supernovae types and corresponding yields when modeling the
abundance of the intracluster medium and other gas reservoirs
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