Revisiting the role of the Thermally-Pulsating Asymptotic Giant Branch phase in high-redshift galaxies

TL;DR

This study evaluates the impact of thermally pulsing asymptotic giant branch (TP-AGB) stars on the spectral energy distributions of high-redshift galaxies, finding that models with significant TP-AGB contribution fit observations better, especially without dust reddening.

Contribution

It provides the largest spectroscopic sample to date testing different TP-AGB stellar population models against observed galaxy SEDs at high redshift.

Findings

TP-AGB-strong models fit observed SEDs better without reddening.

Low dust attenuation ($E(B-V) c 0.05$) is preferred for passive galaxies.

TP-AGB-light models yield systematically older galaxy ages.

Abstract

We study the debated contribution from thermally pulsing asymptotic giant branch (TP-AGB) stars in evolutionary population synthesis models. We investigate the Spectral Energy Distributions (SEDs) of a sample of 51 spectroscopically confirmed, high-z ($1.3<z_{\rm spec}<2.7$), galaxies using three evolutionary population synthesis models with strong, mild and light TP-AGB. Our sample is the largest of spectroscopically confirmed galaxies on which such models are tested so far. Galaxies were selected as passive, but we model them using a variety of star formation histories in order not to be dependent on this pre-selection. We find that the observed SEDs are best fitted with a significant contribution of TP-AGB stars or with substantial dust attenuation. Without including reddening, TP-AGB-strong models perform better and deliver solutions consistent within $1\sigma$ from the best-fit ones in the vast majority of cases. Including reddening, all models perform similarly. Using independent constraints from observations in the mid- and far-IR, we show that low/negligible dust attenuation, i.e. $E(B-V)\lesssim 0.05$ , should be preferred for the SEDs of passively-selected galaxies. Given that TP-AGB-light models give systematically older ages for passive galaxies, we suggest number counts of passive galaxies at higher redshifts as a further test to discriminate among stellar population models.