A Search for 6.7 Ghz Methanol Masers in Oh Megamaser Galaxies

We report the results of a search for 6.7 GHz methanol (CH3OH) maser emission in OH megamaser galaxies at 0.11 < z < 0.27. No detections were made in the 25 objects observed down to rms noise levels of roughly 0.6 mJy in 150 kHz channels. The OH megamaser sample includes OH emission of all observed types: narrow and broad, physically compact and extended, variable and quiescent, and from simple single lines to multi-component complexes to lines with high velocity wings. Our null result indicates, for the widest possible range of OH megamaser environments, that methanol masing does not scale with OH from Galactic masers to megamasers. These observations, however, are not sensitive enough to rule out methanol masing that scales with star formation from Galactic compact HII regions to starbursts associated with major mergers. This and previous work suggest that OH megamasers do not represent large ensembles of individual masers associated with star forming regions. Maser models combined with observational constraints on the physical settings of OH megamasers indicate that 6.7 GHz methanol megamasers will not be detected by this survey if Tdust < 100 K or if nCH3OH ≤ nOH . Subject headings: masers — galaxies: ISM — ISM: molecules — galaxies: starburst — radio lines: galaxies