A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1

The point-like X-ray source HLX-1 is the brightest known ultraluminous X-ray source and likely the strongest intermediate-mass black hole candidate. HLX-1 is hosted in the S0 galaxy ESO 243-49, but offset with respect to the nucleus, and its optical counterpart was identified with a massive star cluster. In this paper, we study, through N-body/smoothed particle hydrodynamics simulations, the scenario where ESO 243-49 is undergoing (or just underwent) a minor merger with a gas-rich low-mass late-type galaxy. The simulations suggest that the observed star formation rate (SFR) in ESO 243-49 is a consequence of the interaction and that the companion galaxy already underwent the second pericentre passage. We propose that the counterpart of HLX-1 coincides with the nucleus (and possibly with the nuclear star cluster) of the secondary galaxy. We estimate that, if the minor merger scenario is correct, the number density of X-ray sources similar to HLX-1 is �10-6 Mpc-3. DOI: https://doi.org/10.1111/j.1365-2966.2012.20955.x Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-70257 Originally published at: Mapelli, M; Zampieri, L; Mayer, L (2012). A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1. Monthly Notices of the Royal Astronomical Society, 423(2):1309-1317. DOI: https://doi.org/10.1111/j.1365-2966.2012.20955.x ar X iv :1 20 3. 42 37 v2 [ as tr oph .H E ] 2 9 A pr 2 01 2 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 1 May 2012 (MN LTEX style file v2.2) A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1 M. Mapelli, L. Zampieri, L. Mayer INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I–35122, Padova, Italy, [email protected] Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH–8057, Zürich, Switzerland