{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/towards-a-better-understanding-of-cosmic","title":"Toward a Better Understanding of Cosmic Chronometers: Stellar Population Properties of Passive Galaxies at Intermediate Redshift","arxiv_id":"2106.14894","date":"2021-06-28","proceeding":null,"authors":["Nicola Borghi","Michele Moresco","Andrea Cimatti","Alexandre Huchet","Salvatore Quai","Lucia Pozzetti"],"abstract":"We take advantage of the publicly available LEGA-C spectroscopic survey to measure the stellar population properties of 140 individual massive and passive galaxies at $z\\sim0.7$. We develop and publicly release PyLick, a flexible python code to measure UV to near-IR spectral indices. With PyLick we study the H/K ratio as a new diagnostic based on the pseudo-Lick CaII H and K indices, and find that a cut in ${\\rm H/K}<1.1$ can be used jointly with other criteria to select (or verify the purity of) samples of passive galaxies. By combining photometric and spectroscopic criteria, we select a reliable sample of passively evolving galaxies. We constrain single-burst stellar ages, metallicities $\\mathrm{[Z/H]}$, and $\\mathrm{[\\alpha/Fe]}$ with an optimized set of Lick indices, exploring in detail the robustness of our measurement against different combinations. Even without imposing cosmological priors, the derived ages follow a clear trend compatible with the expected cosmological aging of the Universe. We observe no significant redshift evolution for the metal abundance with respect to the values derived at $z=0$, with median $\\mathrm{[Z/H]}=0.08\\pm0.18$ and $\\mathrm{[\\alpha/Fe]}=0.13\\pm0.11$. Finally, we find positive correlations between $\\log\\mathrm{age}$, $\\mathrm{[Z/H]}$, $\\mathrm{[\\alpha/Fe]}$ and the stellar velocity dispersion, with slopes of ($0.48\\pm0.14$), ($0.26\\pm0.17$), and ($0.23\\pm0.11$), respectively; the small scatter of $<0.2$ dex points to rather homogeneous and short star formation histories. Overall, these results confirm and extend low-redshift findings of a mass-downsizing evolution. This work further strengthens the possibility of selecting pure samples of passive galaxies to be exploited reliably as cosmic chronometers to place independent cosmological constraints.","url_abs":"https://arxiv.org/abs/2106.14894v2","url_pdf":"https://arxiv.org/pdf/2106.14894v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"towards-a-better-understanding-of-cosmic","repo_url":"https://gitlab.com/mmoresco/pylick","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":1,"framework":"none","reach":null},{"paper_slug":"towards-a-better-understanding-of-cosmic","repo_url":"https://github.com/CosmoStatGW/CHIMERA","is_official":0,"mentioned_in_paper":0,"mentioned_in_github":1,"framework":"jax","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}