Direct Constraints on the Impact of TP-AGB Stars on the SED of Galaxies from Near-Infrared Spectroscopy

TL;DR

This study uses near-infrared spectroscopy of post-starburst galaxies to test models predicting strong TP-AGB star features, finding no such features and supporting earlier models with lower TP-AGB impact.

Contribution

The paper provides observational evidence challenging recent models that predict strong TP-AGB star features in galaxy spectra.

Findings

No strong carbon features of TP-AGB stars detected

NIR fluxes align with older stellar population models

Supports models with lower TP-AGB impact

Abstract

We present new spectro-photometric NIR observations of 16 post-starburst galaxies especially designed to test for the presence of strong carbon features of thermally pulsing AGB (TP-AGB) stars, as predicted by recent models of stellar population synthesis. Selection based on clear spectroscopic optical features indicating the strong predominance of stellar populations with ages between 0.5 and 1.5 Gyr and redshift around 0.2 allows us to probe the spectral region that is most affected by the carbon features of TP-AGB stars (unaccessible from the ground for z~0 galaxies) in the evolutionary phase when their impact on the IR luminosity is maximum. Nevertheless, none of the observed galaxies display such features. Moreover the NIR fluxes relative to optical are consistent with those predicted by the original Bruzual & Charlot (2003) models, where the impact of TP-AGB stars is much lower than has been recently advocated.