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OH megamasers (OHMs) are rare, luminous molecular masers that are typicallyobserved in (ultra) luminous infrared galaxies and serve as markers of majorgalaxy mergers. In blind emission line surveys such as the Arecibo Legacy FastArecibo L-Band Feed Array (ALFALFA) survey for neutral hydrogen (HI), OHMs atz~0.2 can mimic z~0.05 HI lines. We present the results of optical spectroscopyof ambiguous HI detections in the ALFALFA 40% data release detected by the WideField Infrared Survey Explorer (WISE) but with uncertain optical counterparts.The optical redshifts, obtained from observations at the Apache PointObservatory, revealed five new OHMs and identified 129 HI optical counterparts.Sixty candidates remain ambiguous. The new OHMs are the first detected in ablind spectral line survey.  The number of OHMs in ALFALFA is consistent with predictions from the OHluminosity function. Additionally, the mid-infrared magnitudes and colors ofthe OHM host galaxies found in a blind survey do not seem to differ from thosefound in previous targeted surveys. This validates the methods used in previousIR-selected OHM surveys and indicates there is no previously unknownOHM-producing population at z~0.2. We also provide a method for future surveysto separate OH megamasers from 99% of HI line emitters without opticalspectroscopy by using WISE infrared colors and magnitudes. Since the fractionof OHMs found in flux-limited HI surveys is expected to increase with thesurvey's redshift, this selection method can be applied to future flux-limitedhigh-redshift hydrogen surveys.

Identifying OH Imposters in the ALFALFA Neutral Hydrogen Survey