Title:

Hydrodynamic Simulations of the Intergalactic Medium: A
Concordance Model and Beyond



Mike Norman
Dept. of Physics & CASS
UC San Diego



Abstract:

Hydrodynamic cosmological simulations of the Lyman alpha forest
have been remarkably successful at explaining its observed
properties over the redshift interval 0 < z < 6. The absorbers
are understood to correspond to a cosmic web of highly
photoionized gas tracing the large scale distribution of cold
dark matter.  As data and simulations are compared to higher
levels of precision, though, small discrepancies appear which
may require additional physical effects to model.  These include
inhomogeneous radiation backgrounds, late reionization of
helium, and feedback from galaxies. In addition, there is the
question of the chemical enrichment of the IGM, for which there
are observational hints but no coherent simulational models. In
this talk I report on our concordance model of the Lyman alpha
forest using standard assumptions, as well as preliminary
results of simulations with a self-consistent treatment of late
helium reionization due to quasars modeled as point sources. The
associated additional photoheating in the redshift range 2 < z <
4 is found to be sufficient to account for the extra heating
required by observations of the HI line width distribution of
the Lyman alpha forest.