The VLT LBG Redshift Survey - IV. Gas and galaxies at z ~ 3 in observations and simulations

TL;DR

This study combines observations and simulations to analyze the relationship between star-forming galaxies and the intergalactic medium at z~3, focusing on peculiar velocities, correlation functions, and feedback effects.

Contribution

It provides a detailed comparison of observed and simulated galaxy-IGM interactions at z~3, highlighting the impact of peculiar velocities and feedback on correlation functions.

Findings

Peculiar velocities are dominated by large-scale coherent motions.

Simulated galaxy correlation functions match observations when velocity errors are considered.

Reduced infall in simulations may be due to galaxy-wide outflows.

Abstract

We use observations and simulation to study the relationship between star-forming galaxies and the intergalactic medium at z~3. The observed galaxy sample is based on spectroscopic redshift data from a combination of the VLT LBG Redshift Survey and Keck observations in fields centred on bright z>3 QSOs, whilst the simulation data is taken from GIMIC. In the simulation, we find that the dominant peculiar velocities are in the form of large-scale coherent motions of gas and galaxies. Gravitational infall of galaxies towards one another is also seen. At smaller scales, the peculiar velocities in the simulation over-predict the difference between the simulated real- and z-space galaxy correlation functions. Peculiar velocity pairs separated by <1Mpc/h have a smaller dispersion and explain the z-space correlation function better. The Ly{\alpha} auto- and cross-correlation functions in the GIMIC simulation show infall smaller than implied by previous work. This reduced infall may be due to the galaxy wide outflows implemented in the simulation. The main challenge in comparing these simulated results with the observed correlation functions comes from the presence of velocity errors for the observed LBGs which dominate at ~1Mpc/h scales. When these are taken into account, the observed LBG correlation function is well matched by a simulated $M_*>10^9M_\odot$ galaxy sample. The simulated cross-correlation shows similar neutral gas densities around galaxies as are seen in the observations. The simulated and observed Ly{\alpha} z-space autocorrelation functions agree well with each other. Our overall conclusion is that gas and galaxy peculiar velocities are towards the low end of expectation. Finally, little direct evidence is seen in either simulation or observations for high transmission near galaxies due to feedback. (Abridged)