BASS. XXVI. DR2 Host Galaxy Stellar Velocity Dispersions

Abstract

We present new central stellar velocity dispersions for 484 Sy 1.9 and Sy 2 from the second data release of the Swift/BAT AGN Spectroscopic Survey (BASS DR2). This constitutes the largest study of velocity dispersion measurements in X-ray-selected obscured active galactic nuclei (AGN) with 956 independent measurements of the Ca ii H and K lambda 3969, 3934 and Mg I lambda 5175 region (3880-5550 angstrom) and the calcium triplet region (8350-8730 angstrom) from 642 spectra mainly from VLT/X-Shooter or Palomar/DoubleSpec. Our sample spans velocity dispersions of 40-360 km s(1), corresponding to 4-5 orders of magnitude in black hole mass (M (BH) = 10(5.5-9.6) M (circle dot)), bolometric luminosity (L (bol) similar to 10(42-46) erg s(-1)), and Eddington ratio (L/L (Edd) similar to 10(-5) to 2). For 281 AGN, our data and analysis provide the first published central velocity dispersions, including six AGN with low-mass black holes (M (BH) = 10(5.5-6.5) M (circle dot)), discovered thanks to high spectral resolution observations (sigma (inst) similar to 25 km s(-1)). The survey represents a significant advance with a nearly complete census of velocity dispersions of hard X-ray-selected obscured AGN with measurements for 99% of nearby AGN (z < 0.1) outside the Galactic plane ( divide b divide > 10 degrees). The BASS AGN have much higher velocity dispersions than the more numerous optically selected narrow-line AGN (i.e., similar to 150 versus similar to 100 km s(-1)) but are not biased toward the highest velocity dispersions of massive ellipticals (i.e., >250 km s(-1)). Despite sufficient spectral resolution to resolve the velocity dispersions associated with the bulges of small black holes (similar to 10(4-5) M (circle dot)), we do not find a significant population of super-Eddington AGN. Using estimates of the black hole sphere of influence from velocity dispersion, direct stellar and gas black hole mass measurements could be obtained with existing facilities for more than similar to 100 BASS AGN.