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A ULX and a giant cloud collision in M 99

Published online by Cambridge University Press:  01 August 2006

Roberto Soria  and
Diane Sonya Wong
Roberto Soria
Affiliation:
Harvard-Smithsonian CfA, 60 Garden st, Cambridge, MA 02138, USA email: rsoria@cfa.harvard.edu
Diane Sonya Wong
Affiliation:
Astronomy Dept, 601 Campbell Hall, Univ. of Cal. at Berkeley, CA 94720-3411, USA email: dianew@astron.berkeley.edu
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Abstract

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The Sc galaxy M 99 in the Virgo Cluster has been strongly affected by recent tidal interactions, responsible for an asymmetric spiral pattern and a high star formation rate (∼ 10 M⊙ yr−1). We studied the galaxy with XMM-Newton, Keck and the Very Large Array (VLA). The inner disk is dominated by hot plasma with a total X-ray luminosity ≈ 1041 erg s−1. 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 ≈ 2 × 1040 erg s−1 and a hard spectrum (power-law photon index Γ ≈ 1.7). This source is close to the location where a massive H I cloud appears to be falling onto the M 99 disk at a relative speed > 100 km s−1. The infalling gas may have been stripped from the nearby “dark galaxy” candidate VIRGOHI 21. We speculate there may be a relation between collisional events, infall of metal-poor gas clouds, and ULX formation.

Keywords

X-rays: galaxies – radio lines: galaxies – galaxies: individual (NGC 4254) – X-rays: binaries – black hole physics

References

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