Predicting CO and dust emission of star-forming galaxies

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.

Figures (15)

• Figure 1: Model TIR luminosity as a function of the observed TIR luminosity. The dotted lines show a factor two above and below the equality.
• Figure 2: Model CO luminosity as a function of the observed CO luminosity for the star-forming low-mass and dwarf galaxies. The dotted lines show a factor two above and below the equality.
• Figure 3: IR-radio correlations. Upper left: $70$$\mu$m - $1.4$ GHz correlation. Upper right: $100$$\mu$m - $1.4$ GHz correlation. Lower left: $160$$\mu$m - $1.4$ GHz correlation. Lower right: TIR - $1.4$ GHz correlation. The colored and black symbols show model galaxies. For clarity, the $z \sim 0.5$ LIRGs are shown as yellow diamonds in the lower right panel. The solid and dotted black lines mark the model linear regression. The gray dots show the observations.
• Figure 4: Left panels: TIR--$1.4$ GHz correlations. The symbols show the model galaxies. Black solid and dotted lines show the model linear regression. Upper panel: Gray solid and dashed lines show the observed linear regression (Basu et al. 2015). Lower panel: Orange error bars show data from Bell (2003). Gray solid and dashed lines mark the observed linear regression (Bell 2003). Upper right panel: SFR--$1.4$ GHz correlation. Lower right panel: SFR--$150$ MHz correlation. The colored lines show observed correlations of Wang et al. (2019), Smith et al. (2021), and Gürkan et al. (2018). The pluses mark the model galaxies. The dashed black lines in both panels correspond to outlier-resistant linear bisector fits.
• Figure 5: CO(1-0) conversion factor as a function of stellar mass. The solid line corresponds to an outlier-robust linear regression.