The Qz5 Survey (II): Metallicity Evolution of Damped Lyα Systems Out to z$\sim$5

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Main Authors:	Wisz, Marie, Rafelski, Marc, Oyarzun, Grecco, Jorgenson, Regina, Fumagalli, Michele, Neeleman, Marcel, Prochaska, Xavier, Christensen, Lise, Fobbs, Eldon, Becker, George, Hennawi, Joseph, Worseck, Gabor, Lopez, Sebastian
Format:	Preprint
Published:	2026
Subjects:	Astrophysics of Galaxies
Online Access:	Acceder al recurso
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author	Wisz, Marie Rafelski, Marc Oyarzun, Grecco Jorgenson, Regina Fumagalli, Michele Neeleman, Marcel Prochaska, Xavier Christensen, Lise Fobbs, Eldon Becker, George Hennawi, Joseph Worseck, Gabor Lopez, Sebastian
author_facet	Wisz, Marie Rafelski, Marc Oyarzun, Grecco Jorgenson, Regina Fumagalli, Michele Neeleman, Marcel Prochaska, Xavier Christensen, Lise Fobbs, Eldon Becker, George Hennawi, Joseph Worseck, Gabor Lopez, Sebastian
contents	Damped Ly$α$ absorbers (DLAs) are the highest \HI\ column density (\NHI) absorption line systems detected in the spectra of background quasars. DLAs dominate the neutral gas content of the Universe ($Ω_{\rm HI}$) and are used to measure the metallicity evolution of \HI\ gas. In this work, we introduce a sample of five recently detected DLAs at $z > 4.7$, found in mid to high-resolution spectroscopy from VLT/X-shooter and Keck/HIRES. These DLAs were not pre-selected based on metallicity, enabling an unbiased study of the metallicity of HI gas at $z \sim 5$. We also search for DLAs unbiased in metallicity at $0<z<5.5$ from the literature, we apply a combined correction for dust depletion and $α$-enhancement (assuming no depletion of S, Si, and Zn) to Fe abundances, and we measure the cosmic metallicity evolution of $α$-elements using a linear fit with a slope of$-0.22 \pm 0.05$ dex per unit redshift. For the highest redshift bin, we find an \NHI weighted average of $\langle Z \rangle = -2.00$. This value is $4.4σ$ deviant from the trend recovered at $z < 4.7$ and a K-S test comparison gives a $2.4 σ$ difference. We conclude that the metallicity of HI gas sharply decreases at $z \sim 5$, in agreement with previous tentative evidence. This sharp decrease may be connected with the onset of the enrichment of galaxies' circumgalactic media or with the end of cosmic reionization, though we cannot exclude that it is driven by small sample statistics.
format	Preprint
id	arxiv_https___arxiv_org_abs_2604_16751
institution	arXiv
publishDate	2026
record_format	arxiv
spellingShingle	The Qz5 Survey (II): Metallicity Evolution of Damped Lyα Systems Out to z$\sim$5 Wisz, Marie Rafelski, Marc Oyarzun, Grecco Jorgenson, Regina Fumagalli, Michele Neeleman, Marcel Prochaska, Xavier Christensen, Lise Fobbs, Eldon Becker, George Hennawi, Joseph Worseck, Gabor Lopez, Sebastian Astrophysics of Galaxies Damped Ly$α$ absorbers (DLAs) are the highest \HI\ column density (\NHI) absorption line systems detected in the spectra of background quasars. DLAs dominate the neutral gas content of the Universe ($Ω_{\rm HI}$) and are used to measure the metallicity evolution of \HI\ gas. In this work, we introduce a sample of five recently detected DLAs at $z > 4.7$, found in mid to high-resolution spectroscopy from VLT/X-shooter and Keck/HIRES. These DLAs were not pre-selected based on metallicity, enabling an unbiased study of the metallicity of HI gas at $z \sim 5$. We also search for DLAs unbiased in metallicity at $0<z<5.5$ from the literature, we apply a combined correction for dust depletion and $α$-enhancement (assuming no depletion of S, Si, and Zn) to Fe abundances, and we measure the cosmic metallicity evolution of $α$-elements using a linear fit with a slope of$-0.22 \pm 0.05$ dex per unit redshift. For the highest redshift bin, we find an \NHI weighted average of $\langle Z \rangle = -2.00$. This value is $4.4σ$ deviant from the trend recovered at $z < 4.7$ and a K-S test comparison gives a $2.4 σ$ difference. We conclude that the metallicity of HI gas sharply decreases at $z \sim 5$, in agreement with previous tentative evidence. This sharp decrease may be connected with the onset of the enrichment of galaxies' circumgalactic media or with the end of cosmic reionization, though we cannot exclude that it is driven by small sample statistics.
title	The Qz5 Survey (II): Metallicity Evolution of Damped Lyα Systems Out to z$\sim$5
topic	Astrophysics of Galaxies
url	https://arxiv.org/abs/2604.16751

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