期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 408, 期 1, 页码 234-253出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2010.17048.x
关键词
black hole physics; galaxies: starburst; X-rays: binaries; X-rays: galaxies
资金
- Swiss National Science Foundation [200020-109581/1]
- University of Zurich
- INAF [PRIN-2007-26]
- ASI INAF [ASI-INAF I/016/07/0]
- National Aeronautics and Space Administration
Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25 <= m(BH)/M-circle dot = 80, via direct collapse. We derive the number of massive BHs (N-BH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (N-ULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between N-ULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our results.
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