On Lyman-limit Systems and the Evolution of the Intergalactic Ionizing Background

Details On Lyman-limit Systems and the Evolution of the Intergalactic Ionizing Background On Lyman-limit Systems and the Evolution of the Intergalactic Ionizing Background

2011-01-10

arxiv.org/abs/1101.1964v2

Astrophys.J.743:82, 2011

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

10 pages, 5 figures, submitted to ApJ, added Fig. 2

Scientific paper

10.1088/0004-637X/743/1/82

We study the properties of self-shielding intergalactic absorption systems and their implications for the ionizing background. We find that cosmological simulations post-processed with detailed radiative transfer calculations generally are able to reproduce the observed abundance of Lyman-limit systems, and we highlight possible discrepancies between the observations and simulations. This comparison tests cosmological simulations at overdensities of ~100. Furthermore, we show that the properties of Lyman-limit systems in these simulations, in simple semi-analytic arguments, and as suggested by recent observations indicate that a small change in the ionizing emissivity of the sources would have resulted in a much larger change in the amplitude of the intergalactic HI-ionizing background (with this scaling strengthening with increasing redshift). This strong scaling could explain the rapid evolution in the Lyman-alpha forest transmission observed at z = 6. Our calculations agree with the suggestion of simpler models that the comoving ionizing emissivity was constant or even increasing from z = 3 to 6. Our calculations also provide a more rigorous estimate than in previous studies for the clumping factor of intergalactic gas after reionization, which we estimate was 2 - 3 at z = 6.

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