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

TL;DR

This study uses spatially-resolved spectroscopy to identify active galactic nuclei in low-mass galaxies, revealing a higher AGN fraction than previous single-fiber studies and demonstrating IFS's advantages.

Contribution

Introduces a novel automated scoring algorithm for detecting AGNs in low-mass galaxies using integral field spectroscopy, increasing detection sensitivity.

Findings

Detected AGNs in 41 galaxies, with 46 additional candidates.

Found an AGN fraction of 4%, higher than previous studies.

IFS captures extended or off-nuclear emission missed by single-fiber 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.