325 research outputs found
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
First results of the XI Groups Project: Studying an unbiased sample of galaxy groups
X-ray observations of hot, intergalactic gas in galaxy groups provide a
useful means of characterizing the global properties of groups. However, X-ray
studies of large group samples have typically involved very shallow X-ray
exposures or have been based on rather heterogeneous samples. Here we present
the first results of the XI (XMM/IMACS) Groups Project, a study targeting, for
the first time, a redshift-selected, statistically unbiased sample of galaxy
groups using deep X-ray data. Combining this with radio observations of cold
gas and optical imaging and spectroscopy of the galaxy population, the project
aims to advance the understanding of how the properties and dynamics of group
galaxies relate to global group properties. Here, X-ray and optical data of the
first four galaxy groups observed as part of the project are presented. In two
of the groups we detect diffuse emission with a luminosity of L_X ~ 10^41
erg/s, among the lowest found for any X-ray detected group thus far, with a
comparable upper limit for the other two. Compared to typical X-ray selected
groups of similar velocity dispersion, these four systems are all surprisingly
X-ray faint. We discuss possible explanations for the lack of significant X-ray
emission in the groups, concluding that these systems are most likely
collapsing for the first time. Our results strongly suggest that, unlike our
current optically selected sample, previous X-ray selected group samples
represented a biased picture of the group population. This underlines the
necessity of a study of this kind, if one is to reach an unbiased census of the
properties of galaxy groups and the distribution of baryons in the Universe.Comment: 14 pages, 8 figures, accepted for publication in MNRA
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