Simulating the kinematics of damped Lyman alpha systems

Abstract

We investigate the kinematic properties of simulated DLA systems at redshift z=3 via associated low ionization metal absorption. These multiple-component optical depth profiles provide a direct measure of the dynamical motion of the underlying neutral gas. In particular we focus on the velocity width (extent) of these systems along 1D lines of sight using the v90 statistic. We utilize a large set of cosmological, hydrodynamical simulations sourced from the OWLS project, post-processed for radiative transfer using the 3D reverse ray tracing code URCHIN. We succeed in generating complex and high velocity width systems up to ~1000km/s. However we also produce a persistent overabundance of low velocity width (v90<30km/s) systems. We investigate the dependencies of the DLA VWD and quantify the physical origin of sightline kinematics using a novel approach. We uncover a slight bias against low velocity width measurements due to intrinsic
saturation of unresolved absorbers, potentially weakening the observed v90 - metallicity correlation.
We find that sightline kinematics are highly stochastic even for isolated host halo systems, reflecting the diverse configurations of neutral gas that may be probed by an unassociated background quasar.