A ultraluminous X-ray source associated with a cloud collision in M 99 |
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| Authors: | Roberto Soria Diane Sonya Wong |
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| Institution: | Harvard-Smithsonian Center for Astrophysics, 60 Garden st, Cambridge, MA 02138, USA;Mullard Space Science Laboratory (UCL), Holmbury St Mary, Dorking, Surrey RH5 6NT;Astronomy Department, 601 Campbell Hall, University of California at Berkeley, CA 94720-3411, USA |
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| Abstract: | The Sc galaxy M 99 in the Virgo Cluster has been strongly affected by tidal interactions and recent close encounters, responsible for an asymmetric spiral pattern and a high star formation rate. Our XMM–Newton study shows that the inner disc is dominated by hot plasma at kT ≈ 0.30 keV, with a total X-ray luminosity of ≈1041 erg s?1 in the 0.3–12 keV band. At the outskirts of the galaxy, away from the main star-forming regions, there is an ultraluminous X-ray source (ULX) with an X-ray luminosity of ≈2 × 1040 erg s?1 and a hard spectrum well fitted by a power law of photon index Γ≈ 1.7. This source is close to the location where a massive H i cloud appears to be falling on to the M 99 disc at a relative speed of >100 km s?1. We suggest that there may be a direct physical link between fast cloud collisions and the formation of bright ULXs, which may be powered by accreting black holes with masses ～100 M⊙. External collisions may trigger large-scale dynamical collapses of protoclusters, leading to the formation of very massive (?200 M⊙) stellar progenitors; we argue that such stars may later collapse into massive black holes if their metal abundance is sufficiently low. |
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| Keywords: | black hole physics galaxies: individual: NGC 4254 radio lines: galaxies X-rays: binaries X-rays: galaxies |
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