Constraining the giant radio galaxy population with machine learning and Bayesian inference

Abstract

Large-scale sky surveys at low frequencies, like the LOFAR Two-metre Sky Survey (LoTSS), allow for the detection and characterisation of unprecedented numbers of giant radio galaxies (GRGs, or 'giants'). In this work, by automating the creation of radio--optical catalogues, we aim to significantly expand the census of known giants. We then combine this sample with a forward model to constrain GRG properties of cosmological interest. In particular, we automate radio source component association through machine learning and optical host identification for resolved radio sources. We create a radio--optical catalogue for the full LoTSS Data Release 2 (DR2) and select all possible giants. We combine our candidates with an existing catalogue of LoTSS DR2 crowd-sourced GRG candidates and visually confirm or reject them. To infer intrinsic GRG properties from GRG observations, we develop further a population-based forward model that takes into account selection effects and constrain its parameters using Bayesian inference. We confirm 5,647 previously unknown giants from the crowd-sourced catalogue and 2,597 previously unknown giants from the ML-driven catalogue. Our confirmations and discoveries bring the total number of known giants to at least 11,585. We predict a comoving GRG number density $n_{\mathrm{GRG}}=13\pm 10(100\mathrm{Mpc}{)}^{-3}$, close to a recent estimate of the number density of luminous non-giant radio galaxies. We derive a current-day GRG lobe volume-filling fraction $V_{\mathrm{GRG}-\mathrm{CW}}(z=0)=1.4\pm 1.1\cdot 10^{-5}$ in clusters and filaments of the Cosmic Web. Our analysis suggests that giants are more common than previously thought. Moreover, tentative results imply that it is possible that magnetic fields once contained in giants pervade a significant ($\gtrsim 10\%$) fraction of today's Cosmic Web.

25 pages, 15 figures, 3 tables, accepted for publication in Astronomy & Astrophysics

References in corpus (19)

• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• The LOFAR Two-metre Sky Survey -- V. Second data release
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• A radio ridge connecting two galaxy clusters in a filament of the cosmic web
• Simulations of extragalactic magnetic fields and of their observables
• The Energetics and Lifetimes of Local Radio Active Galactic Nuclei
• All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8
• The LOFAR Two-Metre Sky Survey (LoTSS): VI. Optical identifications for the second data release
• Magnetic field evolution in cosmic filaments with LOFAR data
• The discovery of a radio galaxy of at least 5 Mpc
• Black hole jets on the scale of the Cosmic Web
• MIGHTEE: Are giant radio galaxies more common than we thought?
• A survey of the thermal and non-thermal properties of cosmic filaments
• A Wide-area GMRT 610~MHz survey of ELAIS N1 field
• Giant radio galaxies in the LoTSS Boötes deep field
• A machine learning classifier for LOFAR radio galaxy cross-matching techniques
• Radio source-component association for the LOFAR Two-metre Sky Survey with region-based convolutional neural networks
• Luminous giants populate the dense Cosmic Web: The radio luminosity-environmental density relation for radio galaxies in action
• An intergalactic medium temperature from a giant radio galaxy

Cited by in corpus (2)

• Black hole jets on the scale of the Cosmic Web
• Luminous giants populate the dense Cosmic Web: The radio luminosity-environmental density relation for radio galaxies in action