Intermediate-mass black holes in galactic nuclei

We present the first homogeneous sample of ntermediate-mass black hole candidates in active galactic nuclei. Starting with broad-line active nuclei from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling relation to select a sample of 19 galaxies in the mass range M_(BH) ≈ 8 × 10^4 – 10^6M_⊙. In contrast to the local active galaxy population, the host galaxies are ~ 1 mag fainter than M∗ and thus are probably late-type systems. The active nuclei are also faint, with M_g ≈ −15 to −18 mag, while the bolometric luminosities are close to the Eddington limit. The spectral properties of the sample are compared to the related class of objects known as narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as observational analogues of primordial black holes, contributors to the integrated signal for future gravitational wave experiments, and as a valuable tool in the calibration of the M_(BH)−σ_* relation