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    An X-Ray-Selected Sample of Candidate Black Holes in Dwarf Galaxies

    251730.pdf (844.8Kb)
    Access Status
    Open access
    Authors
    Lemons, S.
    Reines, A.
    Plotkin, Richard
    Gallo, E.
    Greene, J.
    Date
    2015
    Collection
    • Curtin Research Publications
    Type
    Journal Article
    Metadata
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    Abstract

    We present a sample of hard X-ray-selected candidate black holes (BHs) in 19 dwarf galaxies. BH candidates are identified by cross-matching a parent sample of ~44,000 local dwarf galaxies (M* = 3 × 10 9 M☉, z < 0.055) with the Chandra Source Catalog and subsequently analyzing the original X-ray data products for matched sources. Of the 19 dwarf galaxies in our sample, eight have X-ray detections reported here for the first time. We find a total of 43 point-like hard X-ray sources with individual luminosities L2-10 keV ~ 10 37 - 10 40 erg s-1. Hard X-ray luminosities in this range can be attained by stellar-mass X-ray binaries (XRBs) and by massive BHs accreting at low Eddington ratio. We place an upper limit of 53% (10/19) on the fraction of galaxies in our sample hosting a detectable hard X-ray source consistent with the optical nucleus, although the galaxy center is poorly defined in many of our objects. We also find that 42% (8/19) of the galaxies in our sample exhibit statistically significant enhanced hard X-ray emission relative to the expected galaxy-wide contribution from low-mass and high-mass XRBs, based on the [data] star formation rate relation defined by more massive and luminous systems. For the majority of these X-ray-enhanced dwarf galaxies, the excess emission is consistent with (but not necessarily due to) a nuclear X-ray source. Follow-up observations are necessary to distinguish between stellar-mass XRBs and active galactic nuclei powered by more massive BHs. In any case, our results support the notion that X-ray-emitting BHs in low-mass dwarf galaxies may have had an appreciable impact on reionization in the early universe.

    Citation
    Lemons, S. and Reines, A. and Plotkin, R. and Gallo, E. and Greene, J. 2015. An X-Ray-Selected Sample of Candidate Black Holes in Dwarf Galaxies. Astrophysical Journal. 805: 12.
    Source Title
    Astrophysical Journal
    URI
    http://hdl.handle.net/20.500.11937/52411
    DOI
    10.1088/0004-637X/805/1/12
    Department
    Department of Physics and Astronomy
    Remarks

    Copyright © 2015 The American Astronomical Society. All rights reserved.

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