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Author(s): Lemons, Sean M; Reines, Amy E; Plotkin, Richard M; Gallo, Elena; Greene, Jenny E.

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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 similar to 44,000 local dwarf galaxies (M-star <= 3 x 10(9) M-circle dot, 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 L2-10keV similar to 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 L-2-10keV(XRB)-M-star-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.
Publication Date: 20-May-2015
Electronic Publication Date: 14-May-2015
Citation: Lemons, Sean M, Reines, Amy E, Plotkin, Richard M, Gallo, Elena, Greene, Jenny E. (2015). AN X-RAY-SELECTED SAMPLE OF CANDIDATE BLACK HOLES IN DWARF GALAXIES. ASTROPHYSICAL JOURNAL, 805 (10.1088/0004-637X/805/1/12
DOI: doi:10.1088/0004-637X/805/1/12
ISSN: 0004-637X
EISSN: 1538-4357
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Type of Material: Journal Article
Journal/Proceeding Title: ASTROPHYSICAL JOURNAL
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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