期刊
ASTROPHYSICAL JOURNAL
卷 721, 期 2, 页码 1448-1466出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/721/2/1448
关键词
cosmology: observations; early universe; galaxies: evolution; galaxies: formation; quasars: absorption lines
资金
- National Science Foundation [AST 06-07871]
We have measured the redshift evolution of the density of Lyman limit systems (LLSs) in the intergalactic medium over the redshift range 0 < z < 6. We have used two new quasar samples to (1) improve coverage at z similar to 1, with GALEX grism spectrograph observations of 50 quasars with 0.8 < z(em) < 1.3, and (2) extend coverage to z similar to 6, with Keck ESI spectra of 25 quasars with 4.17 < z(em) < 5.99. Using these samples together with published data, we find that the number density of LLS per unit redshift, n(z), can be well fit by a simple evolution of the form n(z) = n(3.5)[(1 + z)/ 4.5](gamma) with = n(3.5) = 2.80 +/- 0.33 and gamma = 1.94(-0.32)(+0.36) for the entire range 0 < z < 6. We have also reanalyzed the evolution of damped Lya systems (DLAs) in the redshift range 4 < z < 5 using our high-redshift quasar sample. We find a total of 17 DLAs and sub-DLAs, which we have analyzed in combination with published data. The DLAs with logHi column density > 20.3 show the same redshift evolution as the LLS. When combined with previous results, our DLA sample is also consistent with a constant Omega(DLA) = 9 x 10(-4) from z = 2 to z = 5. We have used the LLS number density evolution to compute the evolution in the mean free path (mfp) of ionizing photons. We find a smooth evolution to z similar to 6, very similar in shape to that of Madau et al. but about a factor of two higher. Recent theoretical models roughly match to the z < 6 data but diverge from the measured power law at z > 6 in different ways, cautioning against extrapolating the fit to the mfp outside the measured redshift range.
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