The PARADIGM Project II: characterizing nuclear and diffuse radio components in local U/LIRGs
Journal article, 2026
Disentangling SF and AGN emission is essential for understanding galaxy evolution, yet remains challenging in merging systems where both processes are enhanced and spatially intertwined. Galaxy mergers drive gas inflows that simultaneously fuel nuclear starbursts and black hole accretion, shaping morphology from nuclear (less than or similar to 250 pc) to largescale (>= 500 pc) regions. Radio interferometry provides an unobscured view, but separating compact nuclear starbursts, AGN, and diffuse star formation requires multiscale, multifrequency observations. We present a systematic method to characterize multiscale radio properties in 15 local ( z less than or similar to 0.1) luminous and ultraluminous infrared galaxies (U/LIRGs) (L-IR > 10(11) L-(R)). Using e-MERLIN and VLA at 1.4, 6.0, and 33.0 GHz, we probe physical scales from similar to 10-250 pc to similar to 0.5-3.0 kpc. We decompose radio emission into nuclear (compact cores and nuclear extended) and large-scale (total and diffuse) components, comparing morphological properties (emission fractions, sizes, luminosities, surface densities) and investigating correlations with source classes, merger stages, and infrared luminosities. We find: (i) nuclear emission contributes similar to 50 per cent of total radio emission on average; (ii) total multiscale diffuse emission (SF-related) contributes similar to 80 per cent to total power; (iii) nuclear emission components act together to correlate with total radio and infrared luminosities, which increase with merger stage, whilst diffuse emission at larger scales shows no clear dependence on nuclear processes; (iv) sources with radio excess (lower qIR) show lower nuclear luminosity ratios L-N (R,33)/L-R, 6(N), indicating a deficit of high-frequency radio emission; since 33.0 GHz traces recent star formation, this suggests the radio excess is dominated by non-thermal emission at lower frequencies, likely AGN-related, rather than enhanced star formation.
techniques: image processing
techniques: interferometric
galaxies: starburst
galaxies: interaction
radio continuum: galaxies
galaxies: nuclei
Author
Geferson Lucatelli
University of Manchester
Spanish National Research Council (CSIC)
Rob J. Beswick
University of Manchester
Javier Moldon
University of Manchester
Spanish National Research Council (CSIC)
Antxon Alberdi
Spanish National Research Council (CSIC)
Miguel A. Perez-Torres
Spanish National Research Council (CSIC)
European University Cyprus
University of Zaragoza
Santiago Del Palacio
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Kelvin Wandia
University of Manchester
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
John Conway
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Loreto Barcos-Munoz
University of Virginia
National Radio Astronomy Observatory
David Williams-Baldwin
University of Manchester
Cristina Romero-Canizales
Academia Sinica
Eskil Varenius
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Hans-Rainer Klockner
Max Planck Society
Simon T. Garrington
University of Manchester
Willem A. Baan
Chinese Academy of Sciences
Netherlands Institute for Radio Astronomy (ASTRON)
Ylva M. Pihlstrom
University of New Mexico
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 549 2 1-18 stag929Opticon RadioNet Pilot (ORP)
European Commission (EC) (EC/H2020/101004719), 2021-03-01 -- 2025-02-28.
Exploring the Hidden Dusty Nuclei of Galaxies (HIDDeN)
European Research Council (ERC) (789410), 2018-10-01 -- 2023-09-30.
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
Subatomic Physics
DOI
10.1093/mnras/stag929