A New Sample of Low‐Mass Black Holes in Active Galaxies

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 broad-line active galaxies with masses = 1. 3 x 10⁶ Mₛun, 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, with soft X-ray luminosities in the range 10⁴0 to 7 x 10⁴3 ergs/sec. Much like the preliminary sample, these objects are predominantly radio-quiet (R = f₆cm/f₄400A =-19. 3 and = 0. 7 mag, the host galaxies are low-mass, late-type systems. At least 40% show disk-like morphologies, and the combination of host galaxy colors and higher-order Balmer absorption lines indicate intermediate-age stellar populations in a subset of the sample.