The MeerKAT Absorption Line Survey Data Release 2: Wideband continuum catalogues and a measurement of the cosmic radio dipole^★

¹ Max-Planck Institut fur Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India
³ National Radio Astronomy Observatory, Socorro, NM 87801, USA
⁴ ThoughtWorks Technologies India Private Limited, Yerawada, Pune 411 006, India
⁵ Ioffe Institute, 26 Politeknicheskaya st., St. Petersburg, 194021, Russia
⁶ Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France
⁷ College de France, 11 Pl. Marcelin Berthelot, 75231 Paris, France
⁸ Observatoire de Paris, 61 avenue de l’Observatoire, 75014 Paris, France
⁹ Wits Centre for Astrophysics, School of Physics, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, South Africa
¹⁰ Astrophysics Research Centre, School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Durban 4041, South Africa
¹¹ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
¹² French-Chilean Laboratory for Astronomy, IRL 3386, CNRS and U. de Chile, Casilla 36-D, Santiago, Chile
¹³ Université Claude Bernard Lyon1, Centre de Recherche Astrophysique de Lyon, UMR5574, 9 av Charles André, 69230 Saint Genis Laval, France
¹⁴ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden

^★★ Corresponding author; wagenveld@mpifr-bonn.mpg.de

Received: 8 April 2024
Accepted: 8 August 2024

Abstract

We present the second data release of the MeerKAT Absorption Line Survey (MALS), consisting of wideband continuum catalogues of 391 pointings observed at L band. The full wideband catalogue covers 4344 deg² of sky, reaches a depth of 10 µJy beam⁻¹, and contains 971 980 sources. With its balance between survey depth and sky coverage, MALS DR2 covers five orders of magnitude of flux density, presenting a robust view of the extragalactic radio source population down to 200 µJy. Using this catalogue, we perform a measurement of the cosmic radio dipole, an anisotropy in the number counts of radio sources with respect to the cosmic background, analogous to the dipole found in the cosmic microwave background (CMB). For this measurement, we present the characterisation of completeness and noise properties of the catalogue, and show that a declination-dependent systematic affects the number density of faint sources. In the dipole measurement on the MALS catalogue, we recover reasonable dipole measurements once we model the declination systematic with a linear fit between the size of the major axis of the restoring beam and the amount of sources of each pointing. The final results are consistent with the CMB dipole in terms of direction and amplitude, unlike many recent measurements of the cosmic radio dipole made with other centimetre wavelength catalogues, which generally show a significantly larger amplitude. This result demonstrates the value of dipole measurements with deeper and more sparse radio surveys, as the population of faint sources probed may have had a significant impact on the measured dipole.