Joint Astrophysical Colloquium
James Webb Space telescope detection of asymptotic giant branch stars’ spectral features in high-redshift galaxies: Impact on stellar and galaxy evolution
Claudia Maraston (University of Portsmouth)
Thursday 30/05/2024 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
Age-dating and weighting stellar populations in galaxies at various cosmic epochs are essential steps to study galaxy formation through cosmic times. Evolutionary population synthesis models with different input physics are used towards this aim. In particular, the contribution from the thermally pulsing asymptotic-giant-branch (TP-AGB) stellar phase, which peaks for intermediate-age 0.6–2 Gyr systems, has been debated upon for two decades, with different population synthesis models isplaying a wide range of predictions for this phase. Based on research made in Bologna 30 years ago, we forecasted a sizable effect of the TP-AGB on a galaxy spectrum, resulting in a series of Carbon-rich and Oxygen-rich broad spectral features, plus other rare absorptions (e.g. Zirconium and Vanadium), typical of the cold temperatures and unique Carbon species across this evolutionary phase. We also forecasted that the best place to look for these features - should they exist - is at high-redshift, in massive galaxies with short formation timescales, in which the luminous, yet short TP-AGB phase is emphasised without dilution from massive stars from recent bursts. High quality near-IR rest-frame spectra of distant (redshift 1-2) galaxies taken with the James Webb Space Telescope have recently confirmed this early prediction, revealing strong absorption features that can only be explained by a bright TP-AGB phase. Population synthesis models with significant TP-AGB contribution reproduce the observations considerably better than those with weak TP-AGB, which are those commonly used in the literature. These findings call for revisions of published stellar population fitting results, pointing to lower masses and younger ages, with additional implications on stellar evolution, cosmic dust production and chemical enrichment.