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J. K. Darling, R. Giovanelli (Cornell University)
We present the current results of a survey for OH megamasers (OHMs) underway at the Arecibo Observatory. The survey is 2/3 complete and has produced a high OHM detection rate (1 in 6) from a redshift-selected sample of IRAS galaxies, identifying 35 new OHMs in luminous infrared galaxies to add to the sample of 55 found in the literature. The OHM fraction in luminous infrared galaxies shows a strong bias for the most FIR-luminous hosts, indicating that OHMs can be used to measure the high luminosity tail of the luminous IR galaxy luminosity function for redshifts spanning the epoch of major galaxy mergers (0.5 < z < 5). This survey will provide a low-redshift (0.1 < z < 0.3) calibration of the OHM luminosity function to the galaxy merger rate which can be applied to blind OHM surveys in order to measure the galaxy merger rate as a function of cosmic time.
The survey has also made the first detection of strong variability in OHMs. The variability appears over time scales of months in individual spectral features rather than in broad-band modulation which could be attributed to antenna calibration or pointing errors. Variability in OHMs constrains the sizes of the variable and quiescent spectral features, regardless of the source of modulation (intrinsic to the source or due to propagation effects). Variability in OHMs, particularly those with 0.1 < z < 1.0, will provide a powerful tool for understanding the small-scale physical settings and mechanisms of these masers which can be observed at cosmological distances.
The author(s) of this abstract have provided an email address for comments about the abstract: darling@astrosun.tn.cornell.edu