Populating the low-mass end of the $M_{\rm BH}-\sigma_{\ast}$ relation

We present high resolution spectroscopy taken with the Keck Echellete Spectrograph and Imager to measure stellar velocity dispersions for eight active dwarf galaxies ($M_{\ast}<3\times10^{9}~M_{\odot}$) with virial black hole masses. We double the number of systems in this stellar mass regime with measurements of both black hole mass ($M_{\rm BH}$) and stellar velocity dispersion ($\sigma_{\ast}$), and place them on the $M_{\rm BH}-\sigma_{\ast}$ relation. The tight relation between $M_{\rm BH}$ and $\sigma_{\ast}$ for higher mass galaxies is a strong piece of evidence for the co-evolution of BHs and their host galaxies, but it has been unclear whether this relation holds in the dwarf galaxy regime. Our sample is in good agreement with the extrapolation of the $M_{\rm BH}-\sigma_{\ast}$ relation to low BH/galaxy masses, suggesting that the processes which produce $M_{\rm BH}-\sigma_{\ast}$ can also operate in dwarf galaxies. These results provide important constraints for massive black hole seed formation models and models exploring the impact of AGN feedback in dwarf galaxies.