Dust sub-millimetre emission in green valley galaxies

TL;DR

This study uses a semi-analytic galaxy evolution model to analyze dust emission in green valley galaxies, revealing that sub-millimetre emission does not always correlate directly with star formation activity during galaxy transitions.

Contribution

The paper introduces a detailed modeling approach linking dust evolution and galaxy transition states, highlighting the complex relationship between dust emission and star formation.

Findings

GV galaxies have about half the 250 μm luminosity of blue galaxies at fixed stellar mass.

Red galaxies show up to an order of magnitude lower 250 μm luminosity than GV galaxies.

Dust content remains high during the GV transition, affecting sub-millimetre emission independently of star formation.

Abstract

Context. Green valley (GV) galaxies are objects defined on a colour-magnitude diagram, or a colour-mass diagram, as being associated with a transition from a star-forming to a quiescent state (quenching), or vice versa (rejuvenation). Aims. We studied the sub-millimetre emission of galaxies in the GV and linked it with their physical evolutionary properties. Methods. We exploited a semi-analytic model (SAM) for galaxy evolution that includes a detailed treatment of dust production and evolution in galactic contexts. We modelled the observational properties of simulated galaxies by post-processing the SAM catalogues with the spectral synthesis and radiative transfer code GRASIL. Results. Our model produces a clear bimodality (and thus a GV) in the colour-mass diagram, although some tensions arise when compared to observations. After introducing a new criterion for identifying the GV in any dataset, we find that GV galaxies, at fixed stellar mass, have $250 \mu$m luminosities approximately half those of blue galaxies, while red galaxies exhibit luminosities of up to an order of magnitude lower. While specific star formation rates drop sharply during quenching, the dust content remains relatively high during the GV transition, powering sub-millimetre emission. Rejuvenating galaxies in the GV, which were previously red, have experienced a star formation burst that shifts their colour to green, but their $S_{250\, \mu \rm m}$ fluxes remain low due to their still low dust masses. Conclusions. Our galaxy evolution model highlights the delay between star formation and dust evolution, showing that sub-millimetre emission is not always a safe indicator of star formation activity, with quenching (rejuvenating) GV galaxies featuring relatively high (low) sub-millimetre emission.