PKS 1830–211: OH and H I at z = 0.89 and the first MeerKAT UHF spectrum^⋆

¹ Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France
e-mail: francoise.combes@obspm.fr
² Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India
³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁴ Ioffe Institute, Polyteknicheskaya 26, 194021 Saint-Petersburg, Russia
⁵ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory 7925, South Africa
⁶ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
⁷ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁸ National Radio Astronomy Observatory, Socorro, NM 87801, USA
⁹ Institut d’Astrophysique de Paris, CNRS-SU, UMR 7095, 98bis Bd Arago, 75014 Paris, France
¹⁰ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019, USA
¹² Department of Astronomy & Astrophysics, The University of Chicago, 5640 S Ellis Ave., Chicago, IL 60637, USA
¹³ Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
¹⁴ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
¹⁵ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
¹⁶ ThoughtWorks Technologies India Private Limited, Yerawada, Pune 411 006, India
¹⁷ Astrophysics Research Centre and School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Durban 4041, South Africa
¹⁸ Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA
¹⁹ School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Durban 4041, South Africa
²⁰ The Inter-Univ. Institute for Data Intensive Astronomy (IDIA), Dep. of Astronomy, and Univ. of Cape Town, Private Bag X3, Rondebosch 7701, South Africa, and Univ. of the Western Cape, Dep. of Physics and Astronomy, Bellville 7535, South Africa

Received: 18 December 2020
Accepted: 25 February 2021

Abstract

The Large Survey Project (LSP) “MeerKAT Absorption Line Survey” (MALS) is a blind H I 21 cm and OH 18 cm absorption line survey in the L- and UHF-bands, primarily designed to better determine the occurrence of atomic and molecular gas in the circumgalactic and intergalactic medium, and its redshift evolution. Here we present the first results using the UHF band obtained towards the strongly lensed radio source PKS 1830−211, revealing the detection of absorption produced by the lensing galaxy. With merely 90 min of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known H I 21 cm and OH 18 cm main lines at z = 0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, in each 6 km s⁻¹ wide channel). For the first time we report the detection of OH satellite lines at z = 0.89, which until now have not been detected at z > 0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720 MHz lines are conjugate. The total OH 1720 MHz emission line luminosity is 6100 L_⊙. This is the most luminous known 1720 MHz maser line and is also among the most luminous of the OH main line megamasers. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20 years ago, and find no variation. We interpret the absorption spectra with the help of a lens galaxy model derived from an N-body hydrodynamical simulation, with a morphology similar to its optical HST image. The resulting absorption lines depend mainly on the background continuum and the radial distribution of the gas surface density for each atomic and molecular species. We show that it is possible to reproduce the observations assuming a realistic spiral galaxy disk without invoking any central gas outflows. However, there are distinct and faint high-velocity features in the ALMA millimeter absorption spectra that most likely originate from high-velocity clouds or tidal features. These clouds may contribute to broaden the H I and OH spectra.