Molecular Gas in the Andromeda Galaxy

We present results from an Andromeda Galaxy (M31) survey of star-forming regions based on 24 $\mu$m luminosity for H$_{2}$O masers, NH$_{3}$ (1,1) and NH$_{3}$ (2,2) lines, and Hydrogen recombination lines (H66$\alpha$). Although five H$_{2}$O masers were detected in the initial survey of 206 regions towards M31, we do not detect additional masers in a follow up survey of 300 similar compact 24 $\mu$m regions. We do not detect NH$_{3}$ (1,1), NH$_{3}$ (2,2), or H66$\alpha $ lines in any of the 506 regions. The typical rms noise for 3.3 km s$^{-1}$ channels in individual spectra is 2.5 mJy. Additionally, averaging all 506 spectra, shifted to the correct radial velocity, yields no detection for H$_{2}$O, NH$_{3}$ (1,1), NH$_{3}$ (2,2), or H66$\alpha $. The typical rms noise for 3.3 km s$^{-1}$ channels in stacked spectra is 0.13 mJy. The non-detection of NH$_{3}$ provides an upper limit on NH$_{3}$ column density and corresponding dense gas fraction. In calculating this upper limit, we use both Herschel infrared continuum data and CO integrated line data to independently determine the mean molecular gas mass of each region and corresponding upper limits on the dense gas fraction.