H i Spectroscopy of Reverberation-mapped Active Galactic Nuclei

Abstract

We present H i 21 cm spectroscopy from the Robert C. Byrd Green Bank Telescope for the host galaxies of 31 nearby active galactic nuclei with direct M BH measurements from reverberation mapping. These are the first published H i detections for 12 galaxies, and the spectral quality is generally an improvement over archival data for the remainder of the sample. We present measurements of emission-line fluxes, velocity widths, and recessional velocities from which we derive H i mass, total gas mass, and redshifts. Combining M GAS with constraints on M STARS allows exploration of the baryonic content of these galaxies. We find a typical M GAS / M STARS fraction of 10%, with a few reaching ∼30%–50%. We also examine several relationships between M STARS , M GAS , M BH , baryonic mass, and morphological type. We find a weak preference for galaxies with larger M GAS to host more massive black holes. We also find gas-to-stellar fractions to weakly correlate with later types in unbarred spirals, with an approximately constant fraction for barred spirals. Consistent with previous studies, we find declining M GAS / M STARS with increasing M stars , with a slope suggesting the gas reservoirs have been replenished. Finally, we find a clear relationship for M BH – M BARY with a similar slope as M BH – M STARS reported by Bentz & Manne-Nicholas. The dwarf Seyfert NGC 4395 appears to follow this relationship as well, even though it has a significantly higher gas fraction and smaller M BH than the remainder of our sample.