The dustier early-type galaxies deviate from late-type galaxies' scaling relations

TL;DR

This study investigates early-type galaxies (ETGs) and finds they deviate from typical star formation and dust-gas relations observed in late-type galaxies, showing more dust at a given SFR and lower specific SFR.

Contribution

The paper provides a detailed analysis of ETGs' interstellar medium properties, revealing deviations from established galaxy scaling relations and highlighting their unique star formation characteristics.

Findings

ETGs have more dust at the same SFR compared to late-type galaxies.

ETGs exhibit lower specific SFR than normal star-forming galaxies.

Using the Schmidt-Kennicutt law underestimates gas mass in ETGs.

Abstract

Several dedicated surveys focusing on early-type galaxies (ETGs) reveal that significant fractions of them are detectable in all interstellar medium phases studied to date. We select ETGs from the Herschel Reference Survey that have both far-infrared Herschel and either HI or CO detection (or both). We derive their star formation rates (SFR), stellar masses and dust masses via modelling their spectral energy distributions. We combine these with literature information on their atomic and molecular gas properties, in order to relate their star formation, total gas mass and dust mass on global scales. The ETGs deviate from the dust mass-SFR relation and the Schmidt-Kennicutt relation that SDSS star forming galaxies define: compared to SDSS galaxies, ETGs have more dust at the same SFR, or less SFR at the same dust mass. When placing them in the M*-SFR plane, ETGs show a much lower specific SFR as compared to normal star-forming galaxies. ETGs show a large scatter compared to the Schmidt-Kennicutt relation found locally within our Galaxy, extending to lower SFRs and gas mass surface densities. Using an ETG's SFR and the Schmidt-Kennicutt law to predict its gas mass leads to an underestimate. ETGs have similar observed-gas-to-modelled-dust mass ratios to star forming-galaxies of the same stellar mass, as well as they exhibit a similar scatter.