Can gravitational infall energy lead to the observed velocity dispersion in DLAs?

TL;DR

This study investigates whether gravitational infall energy can explain the observed velocity dispersion in damped Ly-alpha systems, finding it insufficient without additional feedback mechanisms like galactic winds.

Contribution

It demonstrates through simulations that gravitational infall alone cannot account for the observed velocity widths in DLAs, emphasizing the need for explicit feedback processes.

Findings

Gravitational infall energy alone is insufficient to produce observed velocity dispersions.

Current simulations lack high-velocity neutral gas absorbers seen in observations.

Galactic winds are necessary to match the observed velocity widths in DLAs.

Abstract

The median observed velocity width v_90 of low-ionization species in damped Ly-alpha systems is close to 90 km/s, with approximately 10% of all systems showing v_90 > 210 km/s at z=3. We show that a relative shortage of such high-velocity neutral gas absorbers in state-of-the-art galaxy formation models is a fundamental problem, present both in grid-based and particle-based numerical simulations. Using a series of numerical simulations of varying resolution and box size to cover a wide range of halo masses, we demonstrate that energy from gravitational infall alone is insufficient to produce the velocity dispersion observed in damped Ly-alpha systems, nor does this dispersion arise from an implementation of star formation and feedback in our highest resolution (~ 45 pc) models, if we do not put any galactic winds into our models by hand. We argue that these numerical experiments highlight the need to separate dynamics of different components of the multiphase interstellar medium at z=3.