Shedding light on the nature of ESO 243-49 HLX-1
  The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is one
of the strongest intermediate-mass black hole candidates. We discuss the
hypothesis that ESO 243-49 is undergoing a minor merger with a gas-rich disc
galaxy. We propose that the counterpart of HLX-1 coincides with the nucleus of
the secondary galaxy. We re-analyze the available photometric HST data, and we
compare them with the results of N-body/smoothed particle hydrodynamics
simulations. In particular, we derive synthetic surface brightness profiles for
the simulated counterpart of HLX-1 in six HST filters, ranging from far
ultraviolet (FUV) to infrared wavelengths. Such synthetic profiles include a
contribution from the stellar population associated with the simulated
disrupted satellite and a contribution from an irradiated disc model. These are
in agreement with the observed surface brightness profiles of the HLX-1
counterpart, provided that the merger is at sufficiently late stage (>~2.5 Gyr
since the first pericentre passage). The main difference between models and
observations is in the FUV band, where the HST image shows a fuzzy and extended
emission.
