Warm Gas at High Redshift - Clues to Gravitational Structure Formation from Optical Spectroscopy of Lyman Alpha Absorption Systems

Abstract

We discuss the effects of gravitational collapse on the shape of absorption line profiles for low column density (log N(HI) < 14) Lyman Alpha forest clouds and argue by comparison with cosmological simulations that Lyman alpha forest observations show the signs of ongoing gravitational structure formation at high redshift. The departures of observed line profiles from thermal Voigt profiles (caused by bulk motion of infalling gas and compressional heating) are evident from the results of profile fitting as a correlation in velocity space among pairs of components with discrepant Doppler parameters. This correlation also allows us to qualitatively understand the meaning of the Doppler parameter - column density (b vs. N(HI)) diagram for intergalactic gas.

6 pages, gzipped postscript file (figures included) To appear in the proceedings of the conference on "Cold Gas at High Redshift", August 28-30th, 1995, Hoogeveen, Holland

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• Strong Clustering of High-Redshift Lyman-alpha Forest Absorption Systems
• Non-Voigt Lyman-alpha absorption line profiles
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