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 frequencies just above 1420 MHz , sensitive sky surveys might detect OH masers , which could be mistaken for a population of “ infalling , compact High Velocity Clouds ” but would ultimately be traced to luminous FIR background galaxies at z \approx 0.17 once optical and IR follow-up has been performed .