Apertif view of the OH Megamaser IRAS 10597+5926: OH 18 cm satellite lines in wide-area HI surveys

TL;DR

This paper reports the discovery of a highly luminous OH megamaser in a merging galaxy, including satellite line measurements that offer new constraints on maser pumping models, within the context of wide-area HI surveys.

Contribution

First detection of OH satellite lines in a megamaser within a large survey, providing new data to test maser pumping theories and expanding knowledge of OHM host galaxy properties.

Findings

IRAS 10597+5926 is the fourth brightest OH megamaser known.

Measured a very high 1667/1612 ratio > 45.9.

Galaxy is a ULIRG undergoing a starburst with SFR ~179 M_sun/yr.

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 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_Sun) = 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 R_1612 > 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 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(L_TIR/L_Sun) = 12.24, undergoing a star burst with an estimated star formation rate of 179 +/- 40 M_Sun/yr. 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.