The MeerKAT Absorption Line Survey: Homogeneous continuum catalogues towards a measurement of the cosmic radio dipole
Journal article, 2023
The number counts of homogeneous samples of radio sources are a tried and true method of probing the large-scale structure of the Universe, as most radio sources outside the Galactic plane are at cosmological distances. As such, they are expected to trace the cosmic radio dipole, an anisotropy analogous to the dipole seen in the cosmic microwave background (CMB). Results have shown that although the cosmic radio dipole matches the direction of the CMB dipole, it has a significantly larger amplitude. This unexplained result challenges our assumption of the Universe being isotropic, which can have large repercussions for the current cosmological paradigm. Though significant measurements have been made, sensitivity to the radio dipole is generally hampered by systematic effects that can cause large biases in the measurement. Here we assess these systematics with data from the MeerKAT Absorption Line Survey (MALS), a blind search for absorption lines with pointings centred on bright radio sources. With the sensitivity and field of view of MeerKAT, thousands of sources are observed in each pointing, allowing for the possibility of measuring the cosmic radio dipole given enough pointings. We present the analysis of ten MALS pointings, focusing on systematic effects that could lead to an inhomogeneous catalogue. We describe the calibration and creation of full band continuum images and catalogues, producing a combined catalogue containing 16 307 sources and covering 37.5 square degrees of sky down to a sensitivity of 10 μJy beam-1. We measure the completeness, purity, and flux recovery statistics for these catalogues using simulated data. We investigate different source populations in the catalogues by looking at flux densities and spectral indices and how they might influence source counts. Using the noise characteristics of the pointings, we find global measures that can be used to correct for the incompleteness of the catalogue, producing corrected number counts down to 100-200 μJy. We show that we can homogenise the catalogues and properly account for systematic effects. We determine that we can measure the dipole to 3significance with 100 MALS pointings.
Surveys
Galaxies: statistics
Radio continuum: galaxies
Author
Jonah D. Wagenveld
Max Planck Society
H. R. Klockner
Max Planck Society
N. Gupta
Inter-University Centre for Astronomy and Astrophysics
Partha P. Deka
Inter-University Centre for Astronomy and Astrophysics
P. Jagannathan
National Radio Astronomy Observatory Socorro
S. Sekhar
University of the Western Cape
National Radio Astronomy Observatory Socorro
S. Balashev
Russian Academy of Sciences
National Research University Higher School of Economics
Erin Boettcher
NASA Goddard Space Flight Center
University of Maryland
Françoise Combes
Paris Observatory
K.L. Emig
National Radio Astronomy Observatory
M. Hilton
University of KwaZulu-Natal
University of Witwatersrand
G. I.G. Józsa
Rhodes University
Max Planck Society
Peter Kamphuis
Ruhr-Universität Bochum
D. Klutse
University of KwaZulu-Natal
K. Knowles
Rhodes University
J. K. Krogager
Ruhr-Universität Bochum
Abhisek Mohapatra
Inter-University Centre for Astronomy and Astrophysics
E. Momjian
National Radio Astronomy Observatory Socorro
K. Moodley
University of KwaZulu-Natal
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Patrick Petitjean
Centre national de la recherche scientifique (CNRS)
P. Salas
Green Bank Observatory
S. Sikhosana
University of KwaZulu-Natal
R. Srianand
Inter-University Centre for Astronomy and Astrophysics
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 673 A113Subject Categories
Subatomic Physics
Astronomy, Astrophysics and Cosmology
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/202245477