Calibrating the role of TP-AGB stars in the cosmic matter cycle

TL;DR

This paper reviews recent efforts to accurately calibrate TP-AGB stars across various metallicities and ages, addressing their critical role in galaxy property estimation and resolving conflicting claims about their significance.

Contribution

It presents a new approach combining refined stellar models with high-quality data to calibrate TP-AGB stars across a wide metallicity range, identifying an 'island' of significant contribution.

Findings

Preliminary evidence of a 'TP-AGB island' in the age-metallicity plane.

Calibration suggests TP-AGB contribution peaks at intermediate ages and solar-like metallicities.

Highlights the need for improved calibration to resolve existing uncertainties.

Abstract

In the last ten years three main facts about the thermally pulsing asymptotic giant branch (TP-AGB) have become evident: 1) the modelling of the TP-AGB phase is critical for the derivation of basic galaxy properties (e.g. mass and age) up to high redshift, with consequent cosmological implications; 2) current TP-AGB calibrations based on Magellanic Cloud (MC) clusters come out not to work properly for other external galaxies, yielding a likely TP-AGB overestimation; 3) the significance of the TP-AGB contribution in galaxies, hence their derived properties, are strongly debated, with conflicting claims in favour of either a heavy or a light TP-AGB. The only way out of this condition of persisting uncertainty is to perform a reliable calibration of the TP-AGB phase as a function of the star's initial mass (hence age) over a wide range of metallicity, from very low to super-solar values. In this context, I will review recent advancements and ongoing efforts towards a physically-sound TP-AGB calibration that, moving beyond the classical use of the MC clusters, combines increasingly refined TP-AGB stellar models with exceptionally high-quality data for resolved TP-AGB stars in nearby galaxies. Preliminary results indicate that a sort of "TP-AGB island" emerges in the age-metallicity plane, where the contribution of these stars is especially developed, embracing preferentially solar- and MC-like metallicities, and intermediate ages (~ few Gyr).