Hydroxyl Masers From Andromeda To The Peak Of Cosmic Star Formation
OH masers are naturally-occurring phenomena powered by stimulated emission, existing in a variety of astrophysical environments. The presence of powerful OH megamasers (OHMs) is associated with merging galaxies and extreme star formation, while the high luminosities and narrow beams of masers make them powerful probes of local physical conditions. I present research on three projects concentrating on observations of extragalactic OH masers. The first project analyzes mid-infrared spectroscopy
... ared spectroscopy of OHM host galaxies with data from the Spitzer Space Telescope. I identify several mid-infrared spectral features that signal the presence of an OHM, including deep silicate absorption and steep continuum emission, indicating the presence of large amounts of warm dust. Mid-infrared data are also used to test new OH pumping models, demonstrating that OHM hosts favor a smooth, highly embedded dust geometry. Secondly, I describe results of a radio-wavelength survey using the Green Bank Telescope for new OHMs at redshift z ~ 1. Detections of two new OHMs are included, while statistics of galaxies in which OH was not detected constrain the OHM fraction and overall galaxy merger rate. Finally, I present data from the first OH survey of M31 (the Andromeda galaxy) using the Very Large Array. We found no OH masers above a 5σ = 10 mJy limit in the galaxy. I discuss our results in the context of ongoing efforts to use masers as tools for measuring M31's proper motion with respect to the Milky Way.