Optical Properties of Host Galaxies of Extragalactic Nuclear Water Masers

TL;DR

This study investigates the optical properties of galaxies hosting nuclear water masers, revealing correlations with black hole activity indicators and proposing a targeted survey strategy to enhance maser detection rates.

Contribution

It identifies key optical and AGN activity indicators linked to water maser detection, and suggests an optimized pre-selection method to improve detection efficiency.

Findings

Higher maser detection rates in galaxies with greater optical luminosity and velocity dispersion.

Strong correlation between maser luminosity and AGN activity indicators like [OIII]5007 luminosity.

Proposed ranking by extinction-corrected [OIII]5007 flux increases detection efficiency from 3% to 16%.

Abstract

We study the optical properties of the host galaxies of nuclear 22 GHz (lambda=1.35 cm) water masers. To do so, we cross-match the galaxy sample surveyed for water maser emission (123 detections and 3806 non-detections) with the SDSS low-redshift galaxy sample (z<0.05). Out of 1636 galaxies with SDSS photometry, we identify 48 detections; out of the 1063 galaxies that also have SDSS spectroscopy, we identify 33 detections. We find that maser detection rate is higher at higher optical luminosity (M_B), larger velocity dispersion ($\sigma$), and higher [OIII]5007 luminosity, with [OIII]5007 being the dominant factor. These detection rates are essentially the result of the correlations of isotropic maser luminosity with all three of these variables. These correlations are natural if maser strength increases with central black hole mass and the level of AGN activity. We also find that the detection rate is higher in galaxies with higher extinction. Based on these results, we propose that maser surveys seeking to efficiently find masers should rank AGN targets by extinction-corrected [OIII]5007 flux when available. This prioritization would improve maser detection efficiency, from an overall ~ 3% without pre-selection to ~ 16% for the strongest intrinsic [OIII]5007 emitters, by a factor of ~ 5.