A flat photoionization rate at 2 ≤ z ≤ 4.2: Evidence for a stellar-dominated uv background and against a decline of cosmic star formation beyond z ∼ 3

Claude André Faucher-Giguère*, Adam Lidz, Lars Hernquist, Matias Zaldarriaga

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

69 Scopus citations

Abstract

We investigate the implications of our measurement of the Lya forest opacity at redshifts 2 ≤ z ≤ 4.2 from a sample of 86 high-resolution quasar spectra for the evolution of the cosmic ultraviolet luminosity density and its sources. The derived hydrogen photoionization rate G is remarkably flat over this redshift range, implying an increasing comoving ionizing emissivity with redshift. Because the quasar luminosity function is strongly peaked near z ∼ 2, star-forming galaxies likely dominate the ionizing emissivity atz ≳ 3. Our measurement argues against a star formation rate density declining beyondz ∼ 3, in contrast to existing state-of-the-art determinations of the cosmic star formation history from direct galaxy counts. Stellar emission from galaxies therefore likely reionized the universe.

Original languageEnglish (US)
Pages (from-to)L9-L12
JournalAstrophysical Journal
Volume682
Issue number1 PART 2
DOIs
StatePublished - 2008

Keywords

  • Diffuse radiation
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Methods: data analysis
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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