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Title: Chandra and MMT observations of low-mass black hole active galactic nuclei accreting at low rates in dwarf galaxies

We report on Chandra X-ray observations of four candidate low-mass black hole (M {sub bh} ≲ 10{sup 6} M {sub ☉}) active galactic nuclei (AGNs) that have the estimated Eddington ratios among the lowest (∼10{sup –2}) found for this class. The aims are to validate the nature of their AGNs and to confirm the low Eddington ratios that are derived from the broad Hα line, and to explore this poorly studied regime in the AGN parameter space. Among them, two objects with the lowest significance of the broad lines are also observed with the Multi-Mirror Telescope, and the high-quality optical spectra taken confirm them as Seyfert 1 AGNs and as having small black hole masses. X-ray emission is detected from the nuclei of two of the galaxies, which is variable on timescales of ∼10{sup 3} s, whereas no significant (or only marginal at best) detection is found for the remaining two. The X-ray luminosities are on the order of 10{sup 41} erg s{sup –1} or even lower, on the order of 10{sup 40} erg s{sup –1} for non-detections, which are among the lowest regimes ever probed for Seyfert galaxies. The low X-ray luminosities, compared to their black hole masses derivedmore » from Hα, confirm their low accretion rates assuming typical bolometric corrections. Our results hint at the existence of a possibly large population of under-luminous low-mass black holes in the local universe. An off-nucleus ultra-luminous X-ray source in one of the dwarf galaxies is detected serendipitously, with a luminosity (6-9)× 10{sup 39} erg s{sup –1} in 2-10 keV.« less
Authors:
 [1] ; ; ; ;  [2] ;  [3]
  1. National Astronomical Observatories, Space Science Division, Chinese Academy of Sciences, Beijing 100012 (China)
  2. Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, The University of Sciences and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)
  3. Steward Observatory, The University of Arizona, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22348027
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 782; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; BOLOMETERS; DETECTION; EMISSION; GALAXY NUCLEI; KEV RANGE; LUMINOSITY; MASS; SEYFERT GALAXIES; SPACE; SPECTRA; UNIVERSE; X RADIATION; X-RAY GALAXIES; X-RAY SOURCES