al 1997). The comoving number density of bright QSOs ($M_B<-24.5$ $+5\log(h)$) increases as $(1+z)^{6}$ from $z=0$ to 2 (Hewett et al 1993), and, if the QSO phenomenon is tied to galaxy interactions, this steep evolution could point to a steep rise in the interaction rate.

Surveys in the range 400 to 1000 MHz may provide an independent measure of the merging rate by determining the density of merging galaxies as a function of redshift. Since some of the currently most viable models of galaxy formation require the bulk of the construction of the larger galaxies to occur by merging throughout this range of redshift ($z \approx 0.5$ to 3), surveys for OH masers will form an important test of the principal processes of galaxy formation.

Detection rate of cosmologically distant OH Masers
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The detection rate for OH megamasers can be estimated by combining 1) knowledge of the density of prospective FIR luminous host galaxies, 2) the probability that galaxies of each luminosity will be seen as megamaser emitters, 3) the dependence of megamaser strength on FIR luminosity, and 4) the sensitivity of radio telescope receiving systems. The steps in the estimation of the detection rate are outlined in the 