Journal Article

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

M. Mapelli, L. Zampieri and L. Mayer

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1309-1317
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1

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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.

Keywords: methods: numerical; galaxies: individual: ESO 243-49; galaxies: interactions; X-rays: individual: HLX-1

Journal Article.  7712 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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