Abstract
Context: The LOFAR Twometre Sky Survey (LoTSS) will eventually map the complete Northern sky and provide an excellent opportunity to study the distribution and evolution of the largescale structure of the Universe.
Aims: We test the quality of LoTSS observations through a statistical comparison of the LoTSS first data release (DR1) catalogues to expectations from the established cosmological model of a statistically isotropic and homogeneous Universe.
Methods: We study the pointsource completeness and define several quality cuts, in order to determine the countincell statistics and differential source count statistics, and measure the angular twopoint correlation function. We use the photometric redshift estimates, which are available for about half of the LoTSSDR1 radio sources, to compare the clustering throughout the history of the Universe.
Results: For the masked LoTSSDR1 valueadded source catalogue, we find a pointsource completeness of 99% above flux densities of 0.8 mJy. The countsincell statistic reveals that the distribution of radio sources cannot be described by a spatial Poisson process. Instead, a good fit is provided by a compound Poisson distribution. The differential source counts are in good agreement with previous findings in deep fields at low radio frequencies and with simulated catalogues from the SKA Design Study and the Tiered Radio Extragalactic Continuum Simulation. Restricting the value added source catalogue to lownoise regions and applying a flux density threshold of 2 mJy provides our most reliable estimate of the angular twopoint correlation. Based on the distribution of photometric redshifts and the Planck 2018 bestfit cosmological model, the theoretically predicted angular twopoint correlation between 0.1 deg and 6 deg agrees reasonably well with the measured clustering for the subsample of radio sources with redshift information.
Conclusions: The deviation from a Poissonian distribution might be a consequence of the multicomponent nature of a large number of resolved radio sources and/or of uncertainties on the flux density calibration. The angular twopoint correlation function is < 10^{2} at angular scales > 1 deg and up to the largest scales probed. At a 2 mJy flux density threshold and at a pivot angle of 1 deg, we find a clustering amplitude of A = (5.1 ± 0.6) × 10^{3} with a slope parameter of γ = 0.74 ± 0.16. For smaller flux density thresholds, systematic issues are identified, which are most likely related to the flux density calibration of the individual pointings. We conclude that we find agreement with the expectation of largescale statistical isotropy of the radio sky at the per cent level. The angular twopoint correlation agrees well with the expectation of the cosmological standard model.
Original language  English 

Article number  A100 
Number of pages  30 
Journal  Astronomy and Astrophysics 
Volume  643 
DOIs  
Publication status  Published  10 Nov 2020 
Keywords
 Cosmology: observations
 Galaxies: statistics
 Largescale structure of Universe
 Radio continuum: galaxies
 RCUK
 STFC
 ST/N504233/1
 ST/N000668/1
 ST/R000905/1
 ST/R000972/1
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Siewert, T. M. (Creator), Hale, C. (Creator), Bhardwaj, N. (Creator), Biermann, M. (Creator), Bacon, D. (Creator), Jarvis, M. (Creator), Röttgering, H. J. A. (Creator), Schwarz, D. J. (Creator), Shimwell, T. W. (Creator), Best, P. N. (Creator), Keppie, J. D. (Creator), Hardcastle, M. J. (Creator), Sabater, J. (Creator), Tasse, C. (Creator), White, G. J. (Creator) & Williams, W. L. (Creator), IOP Publishing, 10 Nov 2020
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