Simulating the Carbon Footprint of Galactic Halos

TL;DR

This paper compares cosmological simulations with observations of CIV and CII absorption at high redshift, evaluating feedback models and their effectiveness in enriching galactic halos with metals.

Contribution

It introduces improved wind feedback models with higher velocities and thermal energy to better match observed metal absorption features around galaxies.

Findings

Energetic wind models better reproduce CIV absorption around halos.

Simulations match CII covering fractions around DLAs.

CIV in simulations is mainly photoionized.

Abstract

We compare simulations, including the Illustris simulations, to observations of CIV and CII absorption at z=2-4. These are the CIV column density distribution function in the column density range $10^{12} - 10^{15}$ cm$^{-2}$, the CIV equivalent width distribution at 0.1 - 2 \AA, and the covering fractions and equivalent widths of CIV 1548 and CII 1337 around DLAs. In the context of the feedback models we investigate, all CIV observations favour the use of more energetic wind models, which are better able to enrich the gas surrounding halos. We propose two ways to achieve this; an increased wind velocity and an increase in wind thermal energy. However, even our most energetic wind models do not produce enough absorbers with CIV equivalent width > 0.6 \AA, which in our simulations are associated with the most massive haloes. All simulations are in reasonable agreement with the CII covering fraction and equivalent widths around Damped Lyman-$\alpha$ absorbers, although there is a moderate deficit in one bin 10 - 100 kpc from the DLA. Finally, we show that the CIV in our simulations is predominantly photoionized.