Apertif view of the OH megamaser IRAS 10597+5926: OH 18 cm satellite lines in wide-area H I surveys

Abstract

We present the serendipitous detection of the two main OH maser lines at 1667 and 1665 MHz associated with IRAS 10597+5926 at z⊙ = 0.19612 in the untargeted Apertif Wide-area Extragalactic imaging Survey (AWES), and the subsequent measurement of the OH 1612 MHz satellite line in the same source. With a total OH luminosity of log(L/L⊙) = 3.90 ± 0.03, IRAS 10597+5926 is the fourth brightest OH megamaser (OHM) known. We measure a lower limit for the 1667/1612 ratio of R1612 > 45.9, which is the highest limiting ratio measured for the 1612 MHz OH satellite line to date. OH satellite line measurements provide a potentially valuable constraint by which to compare detailed models of OH maser pumping mechanisms. Optical imaging shows that the galaxy is likely a late-stage merger. Based on published infrared and far ultraviolet fluxes, we find that the galaxy is an ultra-luminous infrared galaxy (ULIRG) with log(LTIR/L⊙) = 12.24 that is undergoing a starburst with an estimated star formation rate of 179 ± 40 M⊙ yr−1. These host galaxy properties are consistent with the physical conditions responsible for very bright OHM emission. Finally, we provide an update on the predicted number of OH masers that may be found in AWES and estimate the total number of OH masers that will be detected in each of the individual main and satellite OH 18 cm lines.