Looking at the Distant Universe with the MeerKAT Array: Discovery of a Luminous OH Megamaser at z > 0.5

Abstract

In the local universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (H i), radio surveys to probe the cosmic evolution of H i in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep H i survey, we report the first untargeted detection of an OHM at z > 0.5, LADUMA J033046.20−275518.1 (nicknamed “Nkalakatha”). The host system, WISEA J033046.26−275518.3, is an infrared-luminous radio galaxy whose optical redshift z ≈ 0.52 confirms the MeerKAT emission-line detection as OH at a redshift z OH = 0.5225 ± 0.0001 rather than H i at lower redshift. The detected spectral line has 18.4σ peak significance, a width of 459 ± 59 km s−1, and an integrated luminosity of (6.31 ± 0.18 [statistical] ± 0.31 [systematic]) × 103 L ⊙, placing it among the most luminous OHMs known. The galaxy’s far-infrared luminosity L FIR = (1.576 ±0.013) × 1012 L ⊙ marks it as an ultraluminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step toward a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts.

Maser Science with the African VLBI Network and MeerKAT

“…The MeerKAT debuted its maser science with the discovery of "Nkalakatha", a luminous OH megamaser at z >0.5 (Glowacki et al 2022). The MeerKAT Galactic Plane Legacy Survey (MGPLS) conducted in L-band focuses on continuum imaging, however, the coarse spectral resolution of the MGPLS data could still be used for OH maser detection and could be useful for mapping the most complete distribution of the OH maser in the Milky Way yet.…”

The Past, Present, and Groundbreaking Future of OH Megamaser Discoveries

“…This detection presents one of the most luminous OHMs ever found and places an upper limit on the 1612 MHz OH satellite line, making it only the fourth OHM with such a measurement. In addition, the record for highest-redshift OHM was recently shattered with the discovery of an OHM at a redshift of z = 0.52 with LADUMA (Looking at the Distant Universe with the MeerKAT Array; Glowacki et al 2022). However, these two detections are just a small glimpse as the future.…”

“…Even in the most conservative estimates, the next two decades of OHM detections will dominate those from the past four decades. In addition to the volume of detections, the quality and diversity of those discoveries will be unmatched, as demonstrated by the recent detections from APERTIF (Hess et al 2021) and LADUMA (Glowacki et al 2022). In addition, the tools necessary for identifying interloping OHMs, such as those presented in Roberts et al (2021), are currently being tested and will be imperative for ushering in this exciting future of OHM science.…”