Water Masers in the Andromeda Galaxy: I. A Survey for Water Masers,
  Ammonia, and Hydrogen Recombination Lines
  We report the results of a Green Bank Telescope survey for water masers,
ammonia (1,1) and (2,2), and the H66-alpha recombination line toward 506
luminous compact 24 micron-emitting regions in the Andromeda Galaxy (M31). We
include the 206 sources observed in the Darling (2011) water maser survey for
completeness. The survey was sensitive enough to detect any maser useful for
~10 microarcsecond/yr astrometry. No new water masers, ammonia lines, or
H66-alpha recombination lines were detected individually or in spectral stacks
reaching rms noise levels of ~3 mJy and ~0.2 mJy, respectively, in 3.1-3.3 km/s
channels. The lack of detections in individual spectra and in the spectral
stacks is consistent with Galactic extrapolations. Contrary to previous
assertions, there do not seem to be additional bright water masers to be found
in M31. The strong variability of water masers may enable new maser detections
in the future, but variability may also limit the astrometric utility of known
(or future) masers since flaring masers must also fade.
