The Evolution of the Ultraviolet Background

Details The Evolution of the Ultraviolet Background The Evolution of the Ultraviolet Background

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003assl..281..125s&link_type=abstract

The IGM/Galaxy Connection: The Distribution of Baryons at z=0, ASSL Conference Proceedings Vol. 281. Edited by Jessica L. Rosenb

Physics

1

Scientific paper

Knowledge of photoionization rates in intergalactic gas is important for modeling the growth of structure and the formation of galaxies. We present measurements of these rates using the proximity effect in a sample of over 200 ground-based and HST/FOS quasar spectra covering 0.03 < z < 3.8. These measurements confirm the evolution in the ultraviolet background (UVB) from z ~ 2 to the present that is expected due to the decline in the quasar space density. The measured HI ionization rate is a factor of ~10 lower at z ~ 0.5 than at z ~ 2-3. The integrated UV emission from quasars can account for the observed UVB at z <~ 4 given the measurement uncertainties.
We present simulated Ly-alpha forest spectra created using the log-normal approximation to the linear and mildly non-linear evolution of the density and velocity fields. The photoionization effects of quasars placed in the simulated density fields on the surrounding intergalactic medium (IGM) are incorporated into the synthetic spectra. We find that maximum likelihood methods reliably estimate the metagalactic HI ionization rate from the proximity effect if quasars do not preferentially occupy regions of significant overdensity, and that the clustering of mass around quasars will bias the measurement of GammaHI upward by a factor of ~3.

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