Evidence for inverse Compton scattering in high-redshift Lyman-break galaxies
ABSTRACT Radio continuum emission provides a unique opportunity to study star formation unbiased by dust obscuration. However, if radio observations are to be used to accurately trace star formation to high redshifts, it is crucial that the physical processes that affect the radio emission from star-forming galaxies are well understood. While inverse Compton (IC) losses from the cosmic microwave background (CMB) are negligible in the local universe, the rapid increase in the strength of the CMB energy density with redshift [$\sim (1+z)^4$] means that this effect becomes increasingly important at $z\gtrsim 3$. Using a sample of $\sim 200\,000$ high-redshift ($3 < z < 5$) Lyman-break galaxies selected in the rest-frame ultraviolet (UV), we have stacked radio observations from the MIGHTEE survey to estimate their 1.4-GHz flux densities. We find that for a given rest-frame UV magnitude, the 1.4-GHz flux density and luminosity decrease with redshift. We compare these results to the theoretical predicted effect of energy losses due to IC scattering off the CMB, and find that the observed decrease is consistent with this explanation. We discuss other possible causes for the observed decrease in radio flux density with redshift at a given UV magnitude, such as a top-heavy initial mass function at high redshift or an evolution of the dust properties, but suggest that IC scattering is the most compelling explanation.
Authors
- L. Marchetti (ORCID: https://orcid.org/0000-0003-3948-7621)
- F. S. Tabatabaei (ORCID: https://orcid.org/0000-0002-0377-0970)
- R G Varadaraj (ORCID: https://orcid.org/0009-0006-9953-6471)
- M. Vaccari (ORCID: https://orcid.org/0000-0002-6748-0577)
- Kenda Knowles (ORCID: https://orcid.org/0000-0002-8452-0825)
- E. J. Murphy (ORCID: https://orcid.org/0000-0001-7089-7325)
- Ian Heywood (ORCID: https://orcid.org/0000-0001-6864-5057)
- A. P. Matthews (ORCID: https://orcid.org/0000-0003-3981-1874)
- Nathan Adams (ORCID: https://orcid.org/0000-0003-4875-6272)
- N. Seymour (ORCID: https://orcid.org/0000-0003-3506-5536)
- R. A. A. Bowler (ORCID: https://orcid.org/0000-0003-3917-1678)
- Catherine Hale (ORCID: https://orcid.org/0000-0001-6279-4772)
- A. R. Taylor (ORCID: https://orcid.org/0000-0001-9885-0676)
- M. J. Jarvis (ORCID: https://orcid.org/0000-0001-7039-9078)
- I. H. Whittam (ORCID: https://orcid.org/0000-0003-2265-5983)
- A. Verma (ORCID: https://orcid.org/0000-0002-0730-0781)
Institutions
- University of Cape Town (ZA)
- Rhodes University (ZA)
- Curtin University (AU)
- National Radio Astronomy Observatory (US)
- University of Manchester (GB)
- University of Oxford (GB)
- Max Planck Institute for Astronomy (DE)
- Istituto di Radioastronomia di Bologna (IT)
- South African Radio Astronomy Observatory (ZA)
- Carnegie Observatories (US)
- Institute for Research in Fundamental Sciences (IR)
- Max Planck Institute for Radio Astronomy (DE)
- International Centre for Radio Astronomy Research (AU)
- University of the Western Cape (ZA)
- University of KwaZulu-Natal (ZA)
Publication Details
- Journal
- Monthly Notices of the Royal Astronomical Society
- Published
- 2025-09-09
- DOI
- https://doi.org/10.1093/mnras/staf1505
- Citations
- 2
- Primary Topic
- Astrophysics and Star Formation Studies
- Type
- article
- Field-Weighted Citation Impact
- 2.31
Funders
- UK Research and Innovation
- Department of Science and Innovation, South Africa
- National Research Foundation
- University of Pretoria
- University of the Western Cape
- University of Cape Town
- Science and Technology Facilities Council