The photon underproduction crisis

Juna A. Kollmeier, David H. Weinberg, Benjamin D. Oppenheimer, Francesco Haardt, Neal Katz, Romeel Davé, Mark Fardal, Piero Madau, Charles Danforth, Amanda B. Ford, Molly S. Peeples, Joseph McEwen

Research output: Contribution to journalArticle

65 Scopus citations

Abstract

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 (ΓHI) 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 ΓHI 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.

Original languageEnglish (US)
Article numberL32
JournalAstrophysical Journal Letters
Volume789
Issue number2
DOIs
StatePublished - Jul 10 2014

Keywords

  • cosmology: theory
  • diffuse radiation
  • intergalactic medium
  • large-scale structure of universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Kollmeier, J. A., Weinberg, D. H., Oppenheimer, B. D., Haardt, F., Katz, N., Davé, R., Fardal, M., Madau, P., Danforth, C., Ford, A. B., Peeples, M. S., & McEwen, J. (2014). The photon underproduction crisis. Astrophysical Journal Letters, 789(2), [L32]. https://doi.org/10.1088/2041-8205/789/2/L32