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Abstract: Chandra and XMM-Newton observations of the Cartwheel galaxy show ~17 brightX-ray sources >~5x10^38 erg s^-1, all within the gas-rich outer ring. Weexplore the hypothesis that these X-ray sources are powered byintermediate-mass black holes IMBHs accreting gas or undergoing mass transferfrom a stellar companion. To this purpose, we run N-body-SPH simulations of thegalaxy interaction which might have led to the formation of Cartwheel, trackingthe 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 themcross the outer ring. Instead, more than half of the disc IMBHs are pulled inthe outer ring as a consequence of the galaxy collision. However, also in thecase of disc IMBHs, accretion from surrounding gas clouds cannot account forthe high luminosities of the observed sources. Finally, more than 500 discIMBHs are required to produce <~15 X-ray sources via mass transfer from veryyoung stellar companions. Such number of IMBHs is very large and impliesextreme assumptions. Thus, the hypothesis that all the observed X-ray sourcesin Cartwheel are associated with IMBHs is hardly consistent with oursimulations, even if it is still possible that IMBHs account for the few<~1-5 brightest ultraluminous X-ray sources ULXs.



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

Fuente: https://arxiv.org/







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