A disrupted bulgeless satellite galaxy as counterpart of the
  ultraluminous X-ray source ESO 243-49 HLX-1
  The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is one
the strongest intermediate-mass black hole candidates, but the nature of its
counterpart is still puzzling. By means of N-body/smoothed particle
hydrodynamics simulations, we investigate the hypothesis that the HLX-1
counterpart is the nucleus of a bulgeless satellite galaxy, which undergoes a
minor merger with the S0 galaxy. We derive synthetic surface brightness
profiles for the simulated counterpart of HLX-1 in six Hubble Space Telescope
(HST) filters, ranging from far ultraviolet (FUV) to infrared wavelengths, and
we compare them with the observed profiles. Our model matches the emission
associated with the HLX-1 counterpart in all considered filters, including the
bluer ones, even without requiring the contribution of an irradiated disc. The
simulation can also account for an extended FUV emission, of which there are
some hints from the analysis of the F140LP HST filter. This matching is
impossible to achieve by assuming either a bulgy satellite, or a young star
cluster, or an irradiated disc component.
