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The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is onethe strongest intermediate-mass black hole candidates, but the nature of itscounterpart is still puzzling. By means of N-body/smoothed particlehydrodynamics simulations, we investigate the hypothesis that the HLX-1counterpart is the nucleus of a bulgeless satellite galaxy, which undergoes aminor merger with the S0 galaxy. We derive synthetic surface brightnessprofiles for the simulated counterpart of HLX-1 in six Hubble Space Telescope(HST) filters, ranging from far ultraviolet (FUV) to infrared wavelengths, andwe compare them with the observed profiles. Our model matches the emissionassociated with the HLX-1 counterpart in all considered filters, including thebluer ones, even without requiring the contribution of an irradiated disc. Thesimulation can also account for an extended FUV emission, of which there aresome hints from the analysis of the F140LP HST filter. This matching isimpossible to achieve by assuming either a bulgy satellite, or a young starcluster, or an irradiated disc component.

A disrupted bulgeless satellite galaxy as counterpart of the ultraluminous X-ray source ESO 243-49 HLX-1