Predicting CO and dust emission of star-forming galaxies

TL;DR

This study models the IR, line, and radio emissions of local and high-redshift star-forming low-mass and dwarf galaxies, revealing higher cosmic ray ionization rates and the persistence of the radio-IR correlation in these galaxies.

Contribution

It extends previous models to include low-mass and dwarf galaxies, improving cosmic ray density calculations and analyzing CO-dark H2 effects related to metallicity.

Findings

Cosmic ray ionization rates are three times higher than in the solar neighborhood.

Weaker CO emission in low-metallicity galaxies is due to CO-dark H2 regions.

Star-forming low-mass and dwarf galaxies follow the radio-IR correlation.

Abstract

How do Dwarf Galaxies differ from spirals? Does star formation produce radio and far-infrared emission in the same way as in spiral galaxies? Radio, FarIR, and CO emission depend on gas density, temperature, magnetic field strength, and metallicity. The radio-FarIR correlation and Schmidt-Kennicutt relation characterize the links for Milky Way-like galaxies but do they 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 three than for the solar neighborhood. This means that the mean yield of low-energy CR particles three times higher in external galaxies than 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) H_2 surrounding the regions where CO is not photo-dissociated. Within our model framework, star-forming low-mass and dwarf galaxies follow the radio-IR correlation.