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.
Highlights
Understanding the nature of galactic feedback, the manner in which luminous objects such as stars and quasars affect the gas surrounding them, is one of the most significant open problems in galaxy formation
We have shown above that our simulations differ in the extent to which they expel metals into the circumgalactic medium, and Damped Lyman-α Systems (DLAs) are a tracer of the low-mass galaxy population at z = 2 − 4
We have compared our simulations to three different carbon absorber measurements at z = 2 − 4, with the aim of constraining a parameter of the Illustris feedback model
Summary
Understanding the nature of galactic feedback, the manner in which luminous objects such as stars and quasars affect the gas surrounding them, is one of the most significant open problems in galaxy formation. Neither individual supernovae nor black hole accretion discs are resolved in current cosmological simulations, and so they are included through approximate effective models for stellar and Active Galactic Nuclei (AGN) feedback These models are tuned to produce realistic low-redshift galaxies (e.g. Schaye et al 2010; Dave, Oppenheimer & Finlator 2011; Puchwein & Springel 2013; Vogelsberger et al 2013; Schaye et al 2015). We use the line density of strong CIV absorbers (equivalent width 0.3 − 1.2 ̊A) from Cooksey et al (2013), measured using a large spectral sample of absorbers from the Sloan Digital Sky Survey (SDSS; York et al 2000) These stronger absorbers allow us to extend the range of our comparison to gas at a density and enrichment found only around large haloes. Appendix A shows the convergence of our results with numerical resolution, and Appendix B reproduces in tabular form the results shown in some of our figures
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