Galaxy quenching time-scales from a forensic reconstruction of their colour evolution

Abstract

The time-scales on which galaxies move out of the blue cloud to the red sequence (τQ ) provide insight into the mechanisms driving quenching. Here, we build upon previous work, where we showcased a method to reconstruct the colour evolution of observed low-redshift galaxies from the Galaxy And Mass Assembly (GAMA) survey based on spectral energy distribution (SED) fitting with PROSPECT, together with a statistically driven definition for the blue and red populations. We also use the predicted colour evolution from the SHARK semi-analytic model, combined with SED fits of our simulated galaxy sample, to study the accuracy of the measured τQ and gain physical insight into the colour evolution of galaxies. In this work, we measure τQ in a consistent approach for both observations and simulations. After accounting for selection bias, we find evidence for an increase in τQ in GAMA as a function of cosmic time (from τQ ∼ 1 Gyr to τQ ∼ 2 Gyr in the lapse of ∼4 Gyr), but not in SHARK (τQ ≲ 1 Gyr). Our observations and simulations disagree on the effect of stellar mass, with GAMA showing massive galaxies transitioning faster, but is the opposite in SHARK. We find that environment only impacts galaxies below ∼1010 M☉ in GAMA, with satellites having shorter τQ than centrals by ∼0.4 Gyr, with SHARK only in qualitative agreement. Finally, we compare to previous literature, finding consistency with time-scales in the order of couple Gyr, but with several differences that we discuss.