Optical Properties of Host Galaxies of Extragalactic Nuclear Water
  Masers
  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.
