Low-luminosity Active Galaxies and their Central Black Holes

Abstract

Central black hole masses for 118 spiral galaxies representing morphological stages S0/a through Sc and taken from the large spectroscopic survey of Ho, Filippenko & Sargent (1997) are derived using 2MASS Ks data. Black hole (BH) masses are found using a calibrated black-hole - Ks bulge luminosity relation, while bulge luminosities are measured using GALFIT, a two-dimensional bulge/disk decomposition routine. The BH masses are correlated against a variety of nuclear and host-galaxy properties. Nuclear properties such as line width and line ratios show a very high degree of correlation with BH mass. The excellent correlation with line-width supports the view that the emission-line gas is in virial equilibrium with either the BH or bulge potential. The very good emission-line ratio correlations may indicate a change in ionizing continuum shape with BH mass in the sense that more massive BHs generate harder spectra. Apart from the inclination-corrected rotational velocity, no excellent correlations are found between BH mass and host-galaxy properties. Significant differences are found between the distributions of BH masses in early-, mid- and later-type spiral galaxies in the sense that early-type galaxies have preferentially larger central BHs. The line-width distributions show a marked difference among the subsamples in the sense that earlier-type galaxies have larger line widths. There are also clear differences in line ratios between subsamples likely related to the level of ionization in the gas. Finally, a Ks-band Simien & de Vaucouleurs diagram shows excellent agreement with the original B-band relation.