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Intermediate-mass black holes and ultraluminous X-ray sources in the Cartwheel ring galaxy

Mapelli, M. ; Moore, B. ; Giordano, L. ; Mayer, L. ; Colpi, M. ; Ripamonti, E. ; Callegari, S.

In: Monthly Notices of the Royal Astronomical Society, 2008, vol. 383, no. 1, p. 230-246

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    Title
    • Intermediate-mass black holes and ultraluminous X-ray sources in the Cartwheel ring galaxy
    Author
    • Mapelli, M.. Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • Moore, B.. Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • Giordano, L.. Università Milano Bicocca, Dipartimento di Fisica G. Occhialini, Piazza delle Scienze 3, I-20126 Milano, Italy
    • Mayer, L.. Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • Colpi, M.. Università Milano Bicocca, Dipartimento di Fisica G. Occhialini, Piazza delle Scienze 3, I-20126 Milano, Italy
    • Ripamonti, E.. Università Milano Bicocca, Dipartimento di Fisica G. Occhialini, Piazza delle Scienze 3, I-20126 Milano, Italy
    • Callegari, S.. Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:301370
    Summary
    Chandra and XMM-Newton observations of the Cartwheel galaxy show ∼17 bright X-ray sources (≳5 × 1038erg s−1), all within the gas-rich outer ring. We explore the hypothesis that these X-ray sources are powered by intermediate-mass black holes (IMBHs) accreting gas or undergoing mass transfer from a stellar companion. To this purpose, we run N-body/smoothed particle hydrodynamics simulations of the galaxy interaction which might have led to the formation of Cartwheel, tracking the dynamical evolution of two different IMBH populations: halo and disc IMBHs. Halo IMBHs cannot account for the observed X-ray sources, as only a few of them cross the outer ring. Instead, more than half of the disc IMBHs are pulled in the outer ring as a consequence of the galaxy collision. However, also in the case of disc IMBHs, accretion from surrounding gas clouds cannot account for the high luminosities of the observed sources. Finally, more than 500 disc IMBHs are required to produce ≲15 X-ray sources via mass transfer from very young stellar companions. Such number of IMBHs is very large and implies extreme assumptions. Thus, the hypothesis that all the observed X-ray sources in Cartwheel are associated with IMBHs is hardly consistent with our simulations, even if it is still possible that IMBHs account for the few (≲1-5) brightest ultraluminous X-ray sources