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arXiv · 2511.11805

LEGA-C stellar populations scaling relations. II: Dissecting mass-complete archaeological trends and their evolution since z~0.7 with LEGA-C and SDSS

Anna R. Gallazzi·Stefano Zibetti·Arjen van der Wel·Angelos Nersesian·Yasha Kaushal·Rachel Bezanson·Daniele Mattolini·Eric F. Bell·Laura Scholz-Diaz·Joel Leja·Francesco D'Eugenio·Po-Feng Wu·Camilla Pacifici·Michael Maseda
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Abstract

With a sample of 552 galaxies at z~0.7 from the LEGA-C survey, we investigate how current star formation influences light-weighted mean stellar ages and metallicities, and their median trends with stellar mass or velocity dispersion. The bimodality in the global age-mass relation stems from the different age distributions in the quiescent (Q) and star-forming (SF) populations. A bimodality is not observed in the stellar metallicity-mass relation, although Q and SF galaxies have different distributions in this parameter space. We identify a high-metallicity sequence populated by both Q and weakly SF galaxies. At masses below logM/Msun=10.8 the median stellar metallicity-mass relation of SF galaxies steepens, as a consequence of increasing scatter toward lower stellar metallicities for galaxies with increasing specific star formation rate at fixed mass. With a consistent analysis of SDSS DR7 spectra, accounting for aperture corrections, we quantify the evolution of the stellar age and stellar metallicity scaling relations between z=0.7 and the present. We find negligible evolution in the stellar metallicity-mass relation of Q galaxies and for logM/Msun>11 galaxies in general. Lower mass SF galaxies, instead, have typically lower metallicities than their local counterparts, indicating significant enrichment since z~0.7 in the low-mass regime. The median of the stellar ages of both the general population and Q galaxies has changed by only 2 Gyr between z=0.7 and z=0.1, less than expected from cosmic aging. Some Q galaxies must evolve passively to reach the old boundary of the local population. However, in order to explain the evolution of the median trends, both individual evolution, through rejuvenation and/or minor merging impacting the outer galaxy regions, and population evolution, through quenching of massive, metal-rich star-forming galaxies, are required. (Abridged)

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Anna R. Gallazzi, Stefano Zibetti, Arjen van der Wel, Angelos Nersesian, Yasha Kaushal, Rachel Bezanson, Daniele Mattolini, Eric F. Bell, Laura Scholz-Diaz, Joel Leja, Francesco D'Eugenio, Po-Feng Wu, Camilla Pacifici, Michael Maseda. 2025-11-14. LEGA-C stellar populations scaling relations. II: Dissecting mass-complete archaeological trends and their evolution since z~0.7 with LEGA-C and SDSS. https://doi.org/10.1051/0004-6361%2F202554981

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