HI study of the environment around ESO 243-49, the host galaxy of an
  intermediate mass black hole
  The lenticular galaxy ESO 243-49 hosts the ultraluminous X-ray source HLX-1,
the best candidate intermediate mass black hole (IMBH) currently known. The
environments of IMBHs remain unknown, however the proposed candidates include
the nuclei of dwarf galaxies or globular clusters. Evidence at optical
wavelengths points at HLX-1 being the remnant of an accreted dwarf galaxy. Here
we report the Australia Telescope Compact Array radio observations of HI
emission in and around ESO 243-49 searching for signatures of a recent merger
event. No HI line emission is detected in ESO 243-49 with a 5$\sigma$ upper
limit on the HI gas mass of a few $10^8 M_{\odot}$. A likely reason for this
non-detection is the cluster environment depleting ESO 243-49's HI gas
reservoir. The upper limit is consistent with an interpretation of HLX-1 as a
dwarf satellite of ESO 243-49, however more sensitive observations are required
for a detection. We detect ~$5 \times 10^8 M_{\odot}$ of HI gas in the peculiar
spiral galaxy AM 0108-462, located at a projected distance of ~170 kpc from ESO
243-49. This amount of HI gas is ~10 times less than in spiral galaxies with
similar optical and near-infrared properties in the field, strengthening the
conclusion that the cluster environment indeed depletes the HI gas reservoir of
these two galaxies. Here we also report observations of AM 0108-462 in several
optical and near-infrared bands using the Magellan 6.5 m telescopes, and
archival X-ray and ultraviolet observations with XMM-Newton and Swift. These
data combined with the HI line data suggest it is likely that AM 0108-462 is
experiencing a merger event.
