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abstract: |
    Bright OH megamaser galaxies, radiating 1667/1665 MHz lines, could be detected at redshifts from $z \approx 1$ to 3 in moderate integration times with existing radio telescopes. The superluminous FIR galaxies that host the megamasers are relatively rare at $z\approx 0$, but they may have been more common at high redshift, if the galaxy merger rate increases steeply with redshift. Therefore, blind radio spectroscopic surveys at frequencies of 400 to 1000 Mhz can form an independent test of the galaxy merger rate as a function of time over the redshift interval $z =$ 4 to 0.7.

    The redshift range $z = 0.17$ to ${\sim}0.4$ will be difficult to survey for OH masers, since spectroscopic survey signals will be confused with HI emission from normal galaxies at redshifts less than 0.3. In fact, the signals from OH masers are likely to dominate over 21cm line emission from normal galaxies at frequencies below 1200 MHz (i.e. large redshifts $z_{HI} > 0.18 $ and $z_{OH} > 0.4$). Surveyors of nearby galaxies in the 21cm line may find that OH masers form a contaminant to deep, blind HI surveys for redshift velocities less than a few hundred kilometers per second. At 