PKS 1830-211: OH and HI at z = 0.89 and the first MeerKAT UHF spectrum
Artikel i vetenskaplig tidskrift, 2021

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.

Quasars: absorption lines

Galaxies: ISM

Quasars: individual: PKS 1830-211


F. Combes

Observatoire de Paris

N. Gupta

Inter-University Centre for Astronomy and Astrophysics

Sebastien Muller

Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium, Observationssupport

S. Balashev

Russian Academy of Sciences

G. I.G. Józsa

Rhodes University

Universität Bonn

South African Radio Astronomy Observatory (SARAO)

R. Srianand

Inter-University Centre for Astronomy and Astrophysics

E. Momjian

National Radio Astronomy Observatory Socorro

P. Noterdaeme

Centre national de la recherche scientifique (CNRS)

H. R. Klockner


A. J. Baker

Rutgers University

Erin Boettcher

University of Chicago

A. Bosma

Laboratoire d'Astrophysique de Marseille

H. W. Chen

University of Chicago

Rajeshwari Dutta

Durham University

P. Jagannathan

National Radio Astronomy Observatory Socorro

J. Jose

ThoughtWorks Technologies India

K. Knowles

University of KwaZulu-Natal

J. K. Krogager

Centre national de la recherche scientifique (CNRS)

V. P. Kulkarni

University of South Carolina

K. Moodley

University of KwaZulu-Natal

S. Pandey

ThoughtWorks Technologies India

P. Petitjean

Centre national de la recherche scientifique (CNRS)

S. Sekhar

National Radio Astronomy Observatory Socorro

University of the Western Cape

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 648 A116


Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

Annan fysik



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