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

TL;DR

This paper investigates how gravitational collapse influences Lyman Alpha forest absorption lines at high redshift, providing evidence of ongoing structure formation through analysis of line profiles and comparison with cosmological simulations.

Contribution

It demonstrates that gravitational effects cause observable deviations in absorption line profiles, linking these features to the process of structure formation at high redshift.

Findings

Observed line profile deviations indicate bulk motion and heating from gravitational collapse.

Correlation among components in velocity space supports ongoing structure formation.

Comparison with simulations confirms gravitational effects on intergalactic gas at high redshift.

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.