HI Spectroscopy of Reverberation-Mapped Active Galactic Nuclei

Abstract

We present HI 21 cm spectroscopy from the GBT for the host galaxies of 31 nearby AGNs with direct M$_{\textrm{BH}}$ measurements from reverberation mapping. These are the first published HI 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 HI mass, total gas mass, and redshifts. Combining M$_{\textrm{GAS}}$ with constraints on M$_{\textrm{STARS}}$ allows exploration of the baryonic content of these galaxies. We find a typical M$_{\textrm{GAS}}$/M$_{\textrm{STARS}}$ fraction of 10%, with a few reaching $\sim$30-50%. We also examined several relationships between M$_{\textrm{STARS}}$, M$_{\textrm{GAS}}$, M$_{\textrm{BH}}$, baryonic mass, and morphological type. We find a weak preference for galaxies with larger M$_{\textrm{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$_{\textrm{GAS}}$/M$_{\textrm{STARS}}$ with increasing M$_{\textrm{STARS}}$, with a slope suggesting the gas reservoirs have been replenished. Finally, we find a clear relationship for M$_{\textrm{BH}}$-M$_{\textrm{BARY}}$ with a similar slope as M$_{\textrm{BH}}$-M$_{\textrm{STARS}}$ reported by Bentz & Manne-Nicholas (2018). The dwarf Seyfert NGC 4395 appears to follow this relationship as well, even though it has a significantly higher gas fraction and smaller M$_{\textrm{BH}}$ than the remainder of our sample.