772 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
Gas stripping in galaxy groups - the case of the starburst spiral NGC 2276
Ram pressure stripping of galactic gas is generally assumed to be inefficient
in galaxy groups due to the relatively low density of the intragroup medium and
the small velocity dispersions of groups. To test this assumption, we obtained
Chandra X-ray data of the starbursting spiral NGC 2276 in the NGC 2300 group of
galaxies, a candidate for a strong galaxy interaction with hot intragroup gas.
The data reveal a shock-like feature along the western edge of the galaxy and a
low-surface-brightness tail extending to the east, similar to the morphology
seen in other wavebands. Spatially resolved spectroscopy shows that the data
are consistent with intragroup gas being pressurized at the leading western
edge of NGC 2276 due to the galaxy moving supersonically through the intragroup
medium at a velocity ~850 km/s. Detailed modelling of the gravitational
potential of NGC 2276 shows that the resulting ram-pressure could significantly
affect the morphology of the outer gas disc but is probably insufficient to
strip large amounts of cold gas from the disc. We estimate the mass loss rates
due to turbulent viscous stripping and starburst outflows being swept back by
ram pressure, showing that both mechanisms could plausibly explain the presence
of the X-ray tail. Comparison to existing HI measurements shows that most of
the gas escaping the galaxy is in a hot phase. With a total mass loss rate of
roughly 5 M_Sun/yr, the galaxy could be losing its entire present HI supply
within a Gyr. This demonstrates that the removal of galactic gas through
interactions with a hot intragroup medium can occur rapidly enough to transform
the morphology of galaxies in groups. Implications of this for galaxy evolution
in groups and clusters are briefly discussed.Comment: 16 pages, 8 figures, accepted for publication in MNRA
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