{"paper":{"title":"The Qz5 Survey (I): How the HI Mass Density of the Universe Evolves With Cosmic Time","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"","cross_cats":["astro-ph.CO"],"primary_cat":"astro-ph.GA","authors_text":"Fiona Ozyurt, George D. Becker, Grecco A. Oyarz\\'un, G. Worseck, J. Xavier Prochaska, Lise Christensen, Marcel Neeleman, Marc Rafelski, M.E. Wisz, Michele Fumagalli, Regina A. Jorgenson, Sebasti\\'an L\\'opez","submitted_at":"2025-02-07T19:00:01Z","abstract_excerpt":"We report that the neutral hydrogen (HI) mass density of the Universe ($\\rho_{HI}$) increases with cosmic time since $z \\sim 5$, peaks at $z \\sim 3$, and then decreases toward $z \\sim 0$. This is the first result of Qz5, our spectroscopic survey of 63 quasars at $z \\gtrsim 5$ with VLT/X-SHOOTER and Keck/ESI aimed at characterizing intervening HI gas absorbers at $z \\sim 5$. The main feature of Qz5 is the high resolution ($R \\sim 7000 - 9000$) of the spectra, which allows us to (1) accurately detect high column density HI gas absorbers in an increasingly neutral intergalactic medium at $z \\sim "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"2502.05261","kind":"arxiv","version":2},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2502.05261/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}