A FLASH on blazars

Capturing the radio realm of 4FGL blazars with SKA Observatory pathfinders

¹ Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, 34136 Trieste, Italy
² INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
³ IFPU – Institute for fundamental physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
⁴ ATNF, CSIRO Space and Astronomy, PO Box 76 Epping, NSW 1710, Australia
⁵ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia
⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁷ INAF-OAS Bologna, via Gobetti 101, I-40129 Bologna, Italy
⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
⁹ INFN, Sezione di Trieste, via Valerio 2, Trieste I-34127, Italy
¹⁰ INAF, Istituto di Radioastronomia, Italian ARC, Via Piero Gobetti 101, I-40129 Bologna, Italy

^⋆ Corresponding author: mbehiri@sissa.it

Received: 13 March 2025
Accepted: 6 August 2025

Abstract

This work investigates the multi-wavelength properties of 165 sources from the Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL), with the aim of identifying counterparts in the Australian SKA Pathfinder (ASKAP) First Large Absorption Survey in the HI (FLASH) continuum. Using high-resolution data from FLASH, complementary radio datasets, and archival ALMA observations, we performed detailed spectral energy distribution (SED) analyses across centimetre to millimetre wavelengths. Our findings reveal that most blazars exhibit re-triggered peaked spectra, which are indicative of emission dominated by a single emitting region. Additionally, we identify strong correlations between radio and gamma-ray luminosities, highlighting the significant role of relativistic jets in these active galactic nuclei. The inclusion of spectroscopic redshifts from the Sloan Digital Sky Survey and Gaia enabled a comprehensive analysis of the evolutionary trends and physical characteristics of the sources to be performed. Furthermore, we report a tight radio–X-ray correlation for flat spectrum radio quasars, thus contrasting with the more scattered behaviour observed in BL Lacertae objects and reflecting the distinct accretion and jet-driving mechanisms of the two populations. These results provide critical insights into the physics of blazars and their environments, paving the way for future studies with next-generation facilities such as the SKA Observatory for radio observations and the Cherenkov Telescope Array for gamma-ray studies.