{"paper":{"title":"The Spin-Resolved Atomic Velocity Distribution and 21-cm Line Profile of Dark-Age Gas","license":"","headline":"","cross_cats":[],"primary_cat":"astro-ph","authors_text":"Christopher M. Hirata, Kris Sigurdson (IAS)","submitted_at":"2006-05-02T20:00:03Z","abstract_excerpt":"The 21-cm hyperfine line of atomic hydrogen (HI) is a promising probe of the cosmic dark ages. In past treatments of 21-cm radiation it was assumed the hyperfine level populations of HI could be characterized by a velocity-independent ``spin temperature'' T_s determined by a competition between 21-cm radiative transitions, spin-changing collisions, and (at lower redshifts) Lyman-alpha scattering. However we show here that, if the collisional time is comparable to the radiative time, the spin temperature will depend on atomic velocity, T_s=T_s(v), and one must replace the usual hyperfine level "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"astro-ph/0605071","kind":"arxiv","version":1},"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/astro-ph/0605071/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"}