Simulating the Carbon Footprint of Galactic Halos

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.Comment: 18 pages, 15 figures, published in MNRAS. Results tables adde