Fabio Ditrani | Searcharxiv

arXiv2025

Archaeological investigation of galaxies' evolutionary history in the cosmic middle ages

The cosmic Middle Ages, spanning the last 8-10 Gyr of the Universe, is a critical period in which massive early-formed systems coexist with global star formation quenching in less massive galaxies, yet galaxies experience further dynamical, morphological and chemical evolution. Understanding the relative role of internal drivers and of interaction with the evolving large-scale structures remains a highly complex and unsettled issue. To make transformative progress on these questions we must characterize the physical and kinematic properties (integrated and spatially resolved) of stellar populations in galaxies, fossil record of their past star formation and assembly histories, together with gas properties, across a wide range of masses and environmental scales, over this critical cosmic epoch. Volume-representative samples of 10^6 galaxies down to 10^9 solar masses are essential to fully trace the complex interplay between physical processes and to physically connect progenitor and descendant galaxy populations. This demands a deep and extensive survey with high signal-to-noise, medium-resolution, rest-frame optical spectroscopy. Current and planned facilities in the 2020-2030s cannot simultaneously achieve the required sample size, spectral quality, mass limit, and spatial coverage. A dedicated large-aperture spectroscopic facility with wide-area high-multiplex MOS and large field-of-view IFU is needed to provide transformative insights into the physical mechanisms regulating star formation and galaxy evolution.

astro-ph.GA↗

arXiv2025

TP-AGB stars and stellar population properties of a post-starburst galaxy at $z \sim 2$ through optical and NIR spectroscopy with JWST

We present a detailed optical and NIR spectral analysis of J-138717, a post-starburst galaxy at $z = 1.8845$ observed with JWST/NIRSpec, for which we derive a stellar mass of $3.5 \pm 0.2 \times 10^{10}$ M$_\odot$ and a stellar velocity dispersion of $198 \pm 10$ km s$^{-1}$. We estimate an age of $\sim0.9$ Gyr and a sub-solar metallicity (between $-0.4$ and $-0.2$ dex). We find generally consistent results when fitting the optical and NIR wavelength ranges separately or using different model libraries. The reconstruction of the star formation history indicates that the galaxy assembled most of its mass quickly and then rapidly quenched, $\sim0.4$ Gyr prior to observation. Line diagnostics suggest that the weak emission is probably powered by residual star formation (SFR$\sim0.2$M$_\odot$ yr$^{-1}$) or a low-luminosity AGN, with no strong evidence for outflows in ionized or neutral gas. We perform a detailed study of the NIR spectral indices by comparing observations with predictions of several state-of-the-art stellar population models. This is unprecedented at such a high redshift. In particular, the analysis of several CO and CN features argues against a heavy contribution of Thermally Pulsating (TP-)AGB stars. Observations align better with models that include a minimal contribution from TP-AGB stars, but they are also consistent with a mild contribution from TP-AGB stars, assuming a younger age (consistent with the fits). The analysis of other NIR spectral indices shows that current models struggle to reproduce observations. This highlights the need for improved stellar population models in the NIR, especially at young ages and low metallicities, which is most relevant for studying high redshift galaxies in the JWST era.

astro-ph.GA↗