MIGHTEE/COSMOS-3D: the discovery of three spectroscopically confirmed radio-selected star-forming galaxies at z = 4.9–5.6

Journal article

Radio observations offer a dust-independent probe of star formation and active galactic nucleus (AGN) activity, but sufficiently deep data are required to access the cross-over luminosity between these processes at high redshift (). We present three spectroscopically confirmed high-redshift radio sources (HzRSs) detected at 1.3 GHz at –5.6, with radio luminosities spanning –. These sources were first identified as high-redshift candidates through spectral energy distribution (SED) fitting of archival Hubble, James Webb Space Telescope (JWST) NIRCam + MIRI, and ground-based photometry, and then spectroscopically confirmed via the emission line using wide-field slitless spectroscopy from JWST COSMOS-3D. The star formation rates (SFRs) measured from SED fitting, the flux, and the 1.3 GHz luminosity, span –, demonstrating broad agreement between these SFR tracers. We find that these three sources lie either on or 0.5–1.0 dex above the star-forming main sequence at –6 and have undergone a recent burst of star formation. The sources have extended rest-ultraviolet (UV)/optical morphologies with no evidence for a dominant point source component, indicating that an AGN is unlikely to dominate their rest-UV and optical emission. Two of the sources have complex, multicomponent rest-frame UV/optical morphologies, suggesting that their starbursts may be triggered by merging activity. These HzRSs open up a new window towards probing radio emission powered by star formation alone at , representing a remarkable opportunity to begin tracing star formation, independent of dust, in the early Universe.

Authors: Varadaraj, RG; Saxena, A; Fakiolas, S; Whittam, IH; Jarvis, MJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 547
• Issue: 4
• Pages: stag473
• Article number: stag473
• Publication date: 2026-03-10
• Acceptance date: 2026-02-27
• DOI: 10.1093/mnras/stag473
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: radio continuum: galaxies; galaxies: evolution; galaxies: high-redshift