LADUMA: Discovery of a luminous OH megamaser at $z &gt; 0.5$
Creators: name: Glowacki, Marcin
name: Collier, Jordan D.
name: Kazemi-Moridani, Amir
name: Frank, Bradley
name: Roberts, Hayley
name: Darling, Jeremy
name: Klöckner, Hans-Rainer
name: Adams, Nathan
name: Baker, Andrew J.
name: Bershady, Matthew
name: Blecher, Tariq
name: Blyth, Sarah-Louise
name: Bowler, Rebecca
name: Catinella, Barbara
name: Chemin, Laurent
name: Crawford, Steven M.
name: Cress, Catherine
name: Davé, Romeel
name: Deane, Roger
name: de Blok, Erwin
name: Delhaize, Jacinta
name: Duncan, Kenneth
name: Elson, Ed
name: February, Sean
name: Gawiser, Eric
name: Hatfield, Peter
name: Healy, Julia
name: Henning, Patricia
name: Hess, Kelley M.
name: Heywood, Ian
name: Holwerda, Benne W.
name: Hoosain, Munira
name: Hughes, John P.
name: Hutchens, Zackary L.
name: Jarvis, Matt
name: Kannappan, Sheila
name: Katz, Neal
name: Kereš, Dušan
name: Korsaga, Marie
name: Kraan-Korteweg, Renée C.
name: Lah, Philip
name: Lochner, Michelle
name: Maddox, Natasha
name: Makhathini, Sphesihle
name: Meurer, Gerhardt R.
name: Meyer, Martin
name: Obreschkow, Danail
name: Oh, Se-Heon
name: Oosterloo, Tom
name: Oppor, Joshua
name: Pan, Hengxing
name: Pisano, D. J.
name: Randriamiarinarivo, Nandrianina
name: Ravindranath, Swara
name: Schröder, Anja C.
name: Skelton, Rosalind
name: Smirnov, Oleg
name: Smith, Mathew
name: Somerville, Rachel S.
name: Srianand, Raghunathan
name: Staveley-Smith, Lister
name: Tanaka, Masayuki
name: Vaccari, Mattia
name: van Driel, Wim
name: Verheijen, Marc
name: Walter, Fabian
name: Wu, John F.
name: Zwaan, Martin A.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 (HI), radio surveys to probe the cosmic evolution of HI 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 HI survey, we report the first untargeted detection of an OHM at $z &gt; 0.5$, LADUMA J033046.20$-$275518.1 (nicknamed "Nkalakatha"). The host system, WISEA J033046.26$-$275518.3, is an infrared-luminous radio galaxy whose optical redshift $z \approx 0.52$ confirms the MeerKAT emission line detection as OH at a redshift $z_{\rm OH} = 0.5225 \pm 0.0001$ rather than HI at lower redshift. The detected spectral line has 18.4$σ$ peak significance, a width of $459 \pm 59\,{\rm km\,s^{-1}}$, and an integrated luminosity of $(6.31 \pm 0.18\,{\rm [statistical]}\,\pm 0.31\,{\rm [systematic]}) \times 10^3\,L_\odot$, placing it among the most luminous OHMs known. The galaxy's far-infrared luminosity $L_{\rm FIR} = (1.576 \pm 0.013) \times 10^{12}\,L_\odot$ marks it as an ultra-luminous 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 towards a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts.
description: 10 pages, 4 figures. Accepted to ApJ Letters