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Massissilia L. Hamadouche

Publications and source records attributed to Massissilia L. Hamadouche.

4 recordsLinked to original sources
arXiv2026

DeepDive: Simultaneous Formation of Massive Quiescent Galaxies in High-Redshift Galaxy Overdensities

We report on the spectroscopic confirmation of overdense regions of massive quiescent galaxies (QGs) in the early Universe with JWST/NIRSpec. Based on data from the DeepDive NIRSpec program and archival data from the Dawn JWST Archive, we confirm three QGs in the vicinity of Jekyll & Hyde, a pair of massive QG and a dusty star-forming galaxy, at $z=3.71$ and two QGs around SXDS-27434 at $z=4.01$. According to the analysis of galaxy number density with photometric redshifts, Jekyll & Hyde (SXDS-27434) are in an overdense region, where the number density of galaxies is three (four) times higher than the average in the COSMOS (SXDS) field. SED fitting suggests that most of the QGs follow similar star formation histories and have consistent formation and quenching epochs. The same trend is observed in other proto-clusters hosting QGs that were already identified by ground-based telescopes, indicating that the large-scale environment plays an important role in the formation of QGs. In addition, JWST spectra reveal a broad H$α$ emission line from SXDS-27434 and faint emission lines from other three QGs, which are identified as AGN-driven based on their emission line ratios. The overdensity is also reproduced by the Illustris TNG300 simulation at $z=3.71$, in which the member QGs also have similar quenching epochs. These results are consistent with a scenario in which the large-scale structure enhances merger activity and/or gas accretion and triggers AGN feedback, thereby driving simultaneous formation and quenching of QGs in the overdensity.

astro-ph.GA↗
arXiv2026

MAGAZ3NE: Spatially Resolved Ages and Chemical Abundances of Ultra-Massive Quiescent Galaxies at z $\sim$ 3.5 using JWST/NIRSpec IFU

We present spatially-resolved measurements of stellar age, [Fe/H], and [$α$/Fe] in three ultra-massive ($\rm{log(M_{\ast}/M_{\odot})>11}$), compact ($\rm{R_e} \lesssim 2$ kpc) quiescent galaxies at $z\sim3.5$ using JWST/NIRSpec IFU spectroscopy. These observations provide the first spatially-resolved constraints on $α$-enhancement at this epoch, enabling a direct test of quenching mechanisms before late-time assembly processes such as mergers can erase chemical signatures. The central regions of all three galaxies show both uniformly young ages ($\approx0.6-0.7$ Gyr) and elevated [$α$/Fe] ($\approx0.2-0.5$), indicating rapid, enhanced star formation shortly before recent quenching. Beyond the cores, two galaxies display positive age gradients and negative [$α$/Fe] gradients, consistent with rapid merger-driven quenching, while the third shows a flat age profile indicative of uniform quenching. The [Fe/H] gradients are also consistent with these trends, though we note that the metallicities reported by codes using $α$-enhanced models differ significantly ($\approx0.2-0.4$ dex) from those reported using solar-scaled templates. These data demonstrate that quenching pathways are diverse by $z\sim3.5$, with rapid, merger-driven quenching already operating in a subset of massive quiescent galaxies in the first two billion years of cosmic time. Furthermore, these results establish that explicit treatment of $α$-enhancement is essential for interpreting the star-formation histories of the earliest quenched systems.

astro-ph.GA↗
arXiv2026

A Spectral Atlas for Quiescent Galaxies

Key absorption features in the spectra of massive quiescent galaxies reveal a wealth of information about their stellar populations and, in some cases, the properties of gas within and around them. With the spectroscopic capabilities of \textit{JWST}, we are now able to probe deeper and farther into the near-infrared than ever before. It is therefore crucial that we fully understand the origins of observed spectral absorption and emission features. The goal of this document is to collate important rest-frame optical to near-infrared (NIR) spectral features of quiescent galaxies in the context of their physical origin (e.g., stellar photospheres, the interstellar medium, or a combination thereof). We present a look-up table summarizing key information, including a ``diagnostic'' column indicating whether lines are most sensitive to age, metallicity, surface gravity (IMF sensitivity), $α$-enhancement, electron temperature or gas density. This compilation is intended to serve as a practical reference for interpreting rest-optical-NIR spectral features in quiescent galaxies, particularly as \textit{JWST} spectroscopy enables increasingly detailed studies of their stellar populations and surrounding gas.

astro-ph.GA↗