Searching for new OH megamasers out to redshifts z>1

We have carried out a search for 18-cm OH megamaser (OHM) emission with the Green Bank Telescope. The targeted galaxies comprise a sample of 121 ULIRGs at 0.09<z<1.5, making this is the first large, systematic search for OHMs at z>0.25. Nine new detections of OHMs are reported, all at redshifts z<0.25. For the remainder of the galaxies, observations constrain the upper limit on OH emission; this rules out OHMs of moderate brightness (L_OH >10³ L⊙) for 26% of the sample, and extremely bright OHM emission (L_OH >10⁴ L⊙) for 73% of the sample. Losses from RFI result in the OHM detection fraction being significantly lower than expected for galaxies with L_IR >10¹² L_⊙. The new OHM detections are used to calculate an updated OH luminosity function, with Φ~ L_OH ^-0.66 this slope is in agreement with previous results. Non-detections of OHMs in the COSMOS field constrain the predicted sky density of OHMs; the results are consistent with a galaxy merger rate evolving as (1+z) ^m , where m<=6.