Low-mass Active Galaxies in the SAMI Galaxy Survey with Spatially-resolved Spectroscopy

Abstract

The smallest supermassive black holes (BHs), which provide constraints on BH seeds, reside in low-mass galaxies. Here, we present a systematic analysis of 990 low-mass galaxies in the SAMI Galaxy Survey to identify emission from accreting BHs using integral field spectroscopy (IFS). Employing a novel automated scoring algorithm based on spatially resolved narrow emission-line diagnostics, we find signatures of active galactic nuclei (AGNs) in 41 galaxies, as well as an additional 46 less secure candidates. The galaxies have stellar masses in the range $10^{9.4} \lesssim M_\star/M_\odot \lesssim 10^{10}$ (down to $10^{8.5}$ including less secure candidates), redshifts $z \lesssim 0.06$, and morphologies ranging from early-type ellipticals to late-type spirals. Our AGN fraction of 4% (9% including the less secure candidates) is significantly higher than those reported by studies using single-fiber spectroscopy ($\lesssim 1$--2%). Indeed, our additional analysis of single-fiber spectra of the objects in our sample demonstrates that many of our AGN candidates detected via IFS are missed. This work highlights the advantages of IFS, particularly its ability to capture extended or off-nuclear emission from accreting BHs.