The OH Megamaser Luminosity Function

Abstract

We present the 1667 MHz OH megamaser luminosity function derived from a single flux-limited survey. The Arecibo Observatory OH megamaser (OHM) survey has doubled the number of known OH megamasers, and we list the complete catalog of OHMs detected by the survey here, including three redetections of known OHMs. OHMs are produced in major galaxy mergers which are (ultra)luminous in the far-infrared. The OH luminosity function follows a power law in integrated line luminosity, $Φ\propto L_{OH}^{-0.64}$ per Mpc^3 per dex, and is well-sampled for 10^{2.2} L(sun) < L_{OH} < 10^{3.8} L(sun). The OH luminosity function is incorporated into predictions of the detectability and areal density of OHMs in high redshift OH surveys for a variety of current and planned telescopes and merging evolution scenarios parameterized by (1+z)^m in the merger rate ranging from m=0 (no evolution) to m=8 (extreme evolution). Up to dozens of OHMs may be detected per square degree per 50 MHz by a survey reaching an rms noise of 100 microJy per 0.1 MHz channel. An adequately sensitive ``OH Deep Field'' would significantly constrain the evolution exponent m even if no detections are made. In addition to serving as luminous tracers of massive mergers, OHMs may also trace highly obscured nuclear starburst activity and the formation of binary supermassive black holes.