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Title: THE PHOTON UNDERPRODUCTION CRISIS

We examine the statistics of the low-redshift Lyα forest from smoothed particle hydrodynamic simulations in light of recent improvements in the estimated evolution of the cosmic ultraviolet background (UVB) and recent observations from the Cosmic Origins Spectrograph (COS). We find that the value of the metagalactic photoionization rate (Γ{sub HI}) required by our simulations to match the observed properties of the low-redshift Lyα forest is a factor of five larger than the value predicted by state-of-the art models for the evolution of this quantity. This mismatch in Γ{sub HI} results in the mean flux decrement of the Lyα forest being overpredicted by at least a factor of two (a 10σ discrepancy with observations) and a column density distribution of Lyα forest absorbers systematically and significantly elevated compared to observations over nearly two decades in column density. We examine potential resolutions to this mismatch and find that either conventional sources of ionizing photons (galaxies and quasars) must contribute considerably more than current observational estimates or our theoretical understanding of the low-redshift universe is in need of substantial revision.
Authors:
 [1] ; ;  [2] ; ;  [3] ;  [4] ; ;  [5] ;  [6] ;  [7] ;  [8] ;  [9]
  1. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  2. Astronomy Department and CCAPP, Ohio State University, Columbus, OH 43210 (United States)
  3. Astronomy Department, University of Colorado, Boulder, CO 80309 (United States)
  4. Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, Via Valleggio 11, I-22100 Como (Italy)
  5. Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)
  6. University of the Western Cape, Bellville, Cape Town 7535 (South Africa)
  7. Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
  8. Astronomy Department, University of Arizona, Tucson, AZ 85721 (United States)
  9. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22365629
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 789; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BACKGROUND RADIATION; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COSMIC PHOTONS; COSMOLOGY; DENSITY; GALAXIES; LYMAN LINES; PHOTOIONIZATION; POTENTIALS; QUASARS; RED SHIFT; RESOLUTION; STATISTICS; ULTRAVIOLET RADIATION; UNIVERSE; VISIBLE RADIATION