Hierarchical models of high redshift galaxies with thermally pulsing asymptotic giant branch stars: comparison with observations

TL;DR

This paper demonstrates that incorporating the TP-AGB phase into semi-analytic galaxy formation models significantly improves the match with observed high-redshift galaxy colours and luminosities, challenging previous interpretations of red galaxies.

Contribution

The study introduces a fully implemented TP-AGB phase into semi-analytic models and shows its crucial role in reproducing high-redshift galaxy observations.

Findings

TP-AGB improves model's colour-magnitude relations at z ~ 2

Red V-K colours in star-forming galaxies explained by TP-AGB

Without TP-AGB, models fail to match observed colours, unaffected by dust reddening

Abstract

In a recent paper we presented the first semi-analytic model of galaxy formation in which the Thermally-Pulsing Asymptotic Giant Branch phase of stellar evolution has been fully implemented. Here we address the comparison with observations, and show how the TP-AGB recipe affects the performance of the model in reproducing the colours and near-IR luminosities of high-redshift galaxies. We find that the semi-analytic model with the TP-AGB better matches the colour-magnitude and colour-colour relations at z ~ 2, both for nearly-passive and for star-forming galaxies. The model with TP-AGB produces star-forming galaxies with red V-K colours, thus revising the unique interpretation of high-redshift red objects as 'red & dead'. We also show that without the TP-AGB the semi-analytic model fails at reproducing the observed colours, a situation that cannot be corrected by dust reddening. We also explore the effect of nebular emission on the predicted colour-magnitude relation of star-forming galaxies, to conclude that it does not play a significant role in reddening their colours, at least in the range of star-formation rates covered by the model. Finally, the rest-frame K-band luminosity function at z ~ 2.5 is more luminous by almost 1 magnitude. This indicates that the AGN feedback recipe that is adopted to regulate the high-mass end of the luminosity function should be sophisticated to take the effect of the stellar populations into account at high redshifts.