Predicting CO and dust emission of star-forming galaxies

Extension to star-forming low-mass and dwarf galaxies

¹ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
² Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allé Geoffroy Saint-Hilaire, 33615 Pessac, France
³ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 December 2025
Accepted: 31 March 2026

Abstract

In this work, we investigate whether dwarf galaxies differ from spirals and whether star formation produces radio and far-infrared (FIR) emission in the same way as it does for spiral galaxies. Radio, FIR, and CO emission depend on gas density, temperature, magnetic field strength, and metallicity. The radio-FIR correlation and Schmidt-Kennicutt relation characterize the links for Milky Way-like galaxies. However, in this work, we want to investigate whether they also hold for smaller objects with different morphologies. Here, we extend our previous work on the IR, line, and radio emission of local and high-z galaxies to local star-forming low-mass and dwarf galaxies. The calculation of the cosmic ray (CR) densities were improved compared to the previous version of the model. The CR ionization rate we found for the different galaxy samples is higher by a factor of 3 than the rate determined for the solar neighborhood. This means that the mean yield of low-energy CR particles is three times higher in external galaxies than what was observed by Voyager I. The dependence of the N(H₂)/I_CO factor on the metallicity and stellar mass are calculated by the model. The weaker CO emission from low-metallicity galaxies is due to the large amount of (CO-dark) H₂ surrounding the regions where CO is not photodissociated. Within our model framework, star-forming low-mass and dwarf galaxies follow the radio-IR correlation.