K Gabanyi, S Frey, L Gurvits, Z Paragi, K Perger, A. Saxena, R. Overzier, M Villar-Martín, V Reynaldi, G. Miley, H. J. A. Röttgering, A. Humphrey, G Mezo
Abstract
Context. High-redshift radio galaxies can provide important insights into structure formation and galaxy evolution during earlier cosmological epochs. TGSS J1530+1049 was selected as a candidate high-redshift radio galaxy based on its very steep radio spectrum. Subsequent observations with the James Webb Space Telescope (JWST) presented in a companion paper have shown that it is located at a redshift of z = 4.0. The JWST data furthermore showed that the radio source is part of one of the densest structures of galaxies and ionized gas known at these redshifts. The complex system qualitatively resembles a massive (cluster) galaxy that formed early through a rapid succession of mergers. Aims. TGSS J1530+1049 is an unresolved source down to an ∼0.6″ scale in multiple radio surveys. To reveal its high-resolution radio structure and allow for a detailed comparison with JWST observations, we studied its morphology at various angular scales with different radio interferometric instruments. Methods. We observed TGSS J1530+1049 at a milliarcsecond- (mas) scale angular resolution with the European VLBI Network (EVN), and at an ∼100-mas scale resolution with the enhanced Multi-Element Remotely Linked Interferometer Network (e-MERLIN). Results. We recovered a complex north─south oriented structure with steep-spectrum radio-emitting features, which are associated with the lobes and hot spots of a jetted active galactic nucleus. However, the centre of the radio galaxy proved to be too faint at centimetre wavelengths to be unambiguously detected in our observations. Nevertheless, its linear size (∼5.5 kpc) and radio power (L1.4 GHz ≍ 3 × 1027 W Hz−1) place it among the so-called medium-sized symmetric objects, which are a smaller and/or confined version of larger radio galaxies. A comparison between its radio morphology and that of the ionized gas as observed with the NIRSpec integral field unit on JWST shows that the two are closely aligned. However, the optical emission line gas extends out to ∼25 kpc, which is well beyond the detected radio structures.
Keywords
techniques: interferometric / galaxies: active / galaxies: high-redshift / galaxies: individual: TGSS J1530+1049 / galaxies: jets / radio continuum: galaxies
Astronomy & Astrophysics
Volume 710, Article Number A20, Number of pages 9
2026 May
