X-ray properties of million solar mass black holes

Journal Article · Sun Jul 10 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/825/2/139· OSTI ID:22868908

Plotkin, Richard M.; Gallo, Elena; Reines, Amy E.; Wu, Jianfeng ^[1]; Haardt, Francesco ^[2]; Miller, Brendan P. ^[3]; Wood, Callum J. L. ^[4]

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1. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
2. DiSAT, Università dell’Insubria, via Valleggio 11, I-22100 Como (Italy)
3. Department of Chemistry and Physical Sciences, The College of St. Scholastica, Duluth, MN 55811 (United States)
4. International Centre for Radio Astronomy Research (ICRAR), Curtin University, G.P.O. Box U1987, Perth, WA 6845 (Australia)

We present new Chandra X-ray observations of seven low-mass black holes (M{sub BH}≈10{sup 6} M{sub ⊙}) accreting at low-bolometric Eddington ratios between −2.0≲logL{sub bol}/L{sub Edd}≲−1.5. We compare the X-ray properties of these seven low-mass active galactic nuclei (AGNs) to a total of 73 other low-mass AGNs in the literature with published Chandra observations (with Eddington ratios extending from −2.0≲logL{sub bol}/L{sub Edd}≲−0.1). We do not find any statistical differences between the low and high Eddington ratio low-mass AGNs in the distributions of their X-ray to ultraviolet luminosity ratios (α{sub ox}), or in their X-ray spectral shapes. Furthermore, the α{sub ox} distribution of low-L{sub bol}/L{sub Edd} AGNs displays an X-ray weak tail that is also observed within high-L{sub bol}/L{sub Edd} objects. Our results indicate that between −2≲logL{sub bol}/L{sub Edd}≲−0.1, there is no systematic change in the structure of the accretion flow for active galaxies hosting 10{sup 6} M{sub ⊙} black holes. We examine the accuracy of current bolometric luminosity estimates for our low-L{sub bol}/L{sub Edd} objects with new Chandra observations, and it is plausible that their Eddington ratios could be underestimated by up to an order of magnitude. If so, then in analogy with weak emission line quasars, we suggest that accretion from a geometrically thick, radiatively inefficient “slim disk” could explain their diverse properties in α{sub ox}. Alternatively, if current Eddington ratios are correct (or overestimated), then the X-ray weak tail would imply that there is diversity in disk/corona couplings among individual low-mass objects. Finally, we conclude by noting that the α{sub ox} distribution for low-mass black holes may have favorable consequences for the epoch of cosmic reionization being driven by AGN.

• OSTI ID: 22868908
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 825; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ACCURACY
BLACK HOLES
BOLOMETERS
COMPARATIVE EVALUATIONS
DISTRIBUTION
EMISSION
GALAXY NUCLEI
LUMINOSITY
MASS
QUASARS
ULTRAVIOLET RADIATION
X RADIATION
X-RAY GALAXIES