A luminous OH megamaser at z > 0.5

In the local Universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a frequency that increases with IR luminosity, suggesting that they are associated with gas-rich galaxy mergers. Owing to the similar rest frequencies of OH and neutral atomic hydrogen (HI), radio surveys designed to probe the cosmic evolution of HI in galaxies also enable the use of OHMs to probe the cosmic history of gas-rich mergers. Early observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep HI survey have yielded the first untargeted detection of an OHM at z > 0.5, in an infrared-luminous radio galaxy whose previously measured optical redshift confirms the detection as OH rather than HI. The system is among the most luminous OHMs known, with an OH/far-IR luminosity ratio that is similar to those for lower-redshift OHMs; an offset between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step towards a systematic exploitation of OHMs as a tracer of the growth of galaxies at high redshift.

This work has been supported by National Science Foundation grant AST-1814421.