期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 430, 期 3, 页码 2067-2081出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stt031
关键词
intergalactic medium; quasars: absorption lines; cosmology: observations; large-scale structure of Universe
资金
- Kavli Foundation
- STFC
- NSF CAREER grant [AST-0548180]
- NSF [AST-0908910]
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- American Museum of Natural History
- Astrophysical Institute Potsdam
- University of Basel
- University of Cambridge
- Case Western Reserve University
- University of Chicago
- Drexel University
- Fermilab
- Institute for Advanced Study
- Japan Participation Group
- Johns Hopkins University
- Joint Institute for Nuclear Astrophysics
- Kavli Institute for Particle Astrophysics and Cosmology
- Korean Scientist Group
- Chinese Academy of Sciences (LAMOST)
- Los Alamos National Laboratory
- Max-Planck-Institute for Astronomy (MPIA)
- Max-Planck-Institute for Astrophysics (MPA)
- New Mexico State University
- Ohio State University
- University of Pittsburgh
- University of Portsmouth
- Princeton University
- United States Naval Observatory
- University of Washington
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [908910] Funding Source: National Science Foundation
- Science and Technology Facilities Council [ST/K000985/1, ST/J001538/1, ST/H00243X/1, ST/J000647/1] Funding Source: researchfish
- STFC [ST/J000647/1, ST/J001538/1, ST/K000985/1] Funding Source: UKRI
We present new measurements of the mean transmitted flux in the Ly alpha forest over 2 < z < 5 made using 6065 quasar spectra from the Sloan Digital Sky Survey data release 7 (SDSS DR7). We exploit the general lack of evolution in the mean quasar continuum to avoid the bias introduced by continuum fitting over the Ly alpha forest at high redshifts, which has been the primary systematic uncertainty in previous measurements of the mean Ly alpha transmission. The individual spectra are first combined into 26 composites with mean redshifts spanning 2.25 <= z(comp) <= 5.08. The flux ratios of separate composites at the same rest wavelength are then used, without continuum fitting, to infer the mean transmitted flux, F(z), as a fraction of its value at z similar to 2. Absolute values for F(z) are found by scaling our relative values to measurements made from high-resolution data by Faucher-Giguere et al. at z <= 2.5, where continuum uncertainties are minimal. We find that F(z) evolves smoothly with redshift, with no evidence of a previously reported feature at z similar or equal to 3.2. This trend is consistent with a gradual evolution of the ionization and thermal state of the intergalactic medium over 2 < z < 5. Our results generally agree with the most careful measurements to date made from high-resolution data, but offer much greater precision and extend to higher redshifts. This work also improves upon previous efforts using SDSS spectra by significantly reducing the level of systematic errors.
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