A new sample of low-mass black holes in active galaxies

Jenny E. Greene, Luis C. Ho

Research output: Contribution to journalArticlepeer-review

243 Scopus citations

Abstract

We present an expanded sample of low-mass black holes (BHs) found in galactic nuclei. Using standard virial mass techniques to estimate BH masses, we select from the Fourth Data Release of the Sloan Digital Sky Survey all broadline active galaxies with masses <2 x 106 M. BHs in this mass regime provide unique tests of the relationship between BHs and galaxies, since their late-type galaxy hosts do not necessarily contain classical bulges. Furthermore, they provide observational analogs of primordial seed BHs and are expected, when merging, to provide strong gravitational signals for future detectors such as LISA. From our preliminary sample of 19, we have increased the total sample by an order of magnitude to 174, as well as an additional 55 (less secure) candidates. The sample has a median BH mass of (MBH) = 1.3 x 106 M, and in general the objects are radiating at high fractions of their Eddington limits. We investigate the broad spectral properties of the sample; 55 are detected by ROSAT, with soft X-ray luminosities in the range 1040 to 7 x 10 43 ergs s_1. Much like the preliminary sample, these objects are predominantly radio-quiet (R ≡ f6cm/f 400Å < 10), but 11 objects are detected at 20 cm, with radio powers (1021-1023 W Hz-1) that may arise from either star formation or nuclear activity; only 1% of the sample is radio-loud. We further confirm that, with (M9) = -19.3 and (g -r) = 0.7 mag, the host galaxies are low-mass, late-type systems. At least 40% show disklike morphologies, and the combination of host galaxy colors and higher order Balmer absorption lines indicate intermediateage stellar populations in a subset of the sample.

Original languageEnglish (US)
Pages (from-to)92-104
Number of pages13
JournalAstrophysical Journal
Volume670
Issue number1
DOIs
StatePublished - Nov 20 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: Seyfert
  • Galaxies: active
  • Galaxies: nuclei

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