h1metals

The metallicity distribution of HI systems in the EAGLE cosmological simulations

Alireza Rahmati¹, Benjamin D. Oppenheimer²

1 Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

2 CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309, USA

Abstract

The metallicity of strong HI systems, spanning from damped Lyman-α absorbers (DLAs) to Lyman-limit systems (LLSs) is explored between z = 5 → 0 using the EAGLE high-resolution cosmological hydrodynamic simulation of galaxy formation. The metallicities of LLSs and DLAs steadily increase with time in agreement with observations. DLAs are more metal rich than LLSs, although the metallicities in the LLS column density range (N_HI ≈ 10^17 −10^20 cm^−2) are relatively flat, evolving from a median HI-weighted metallicity of Z<∼10^−2 Z⊙ at z = 3 to ≈ 10^−0.5 Z⊙ by z = 0. The metal content of HI systems tracks the increasing stellar content of the Universe, holding ≈ 5% of the integrated total metals released from stars at z = 0. We also consider partial LLS (pLLS, NHI ≈ 10^16 − 10^17 cm−2) metallicities, and find good agreement with Wotta et al. (2016) for the fraction of systems above (40%) and below (60%) 0.1Z⊙. We also find a large dispersion of pLLS metallicities, although we do not reproduce the observed metallicity bimodality and instead we make the prediction that a larger sample will yield more pLLSs around 0.1Z⊙. We under-predict the median metallicity of strong LLSs, and predict a population of Z < 10^−3 Z⊙ DLAs at z > 3 that are not observed, which may indicate more widespread early enrichment in the real Universe compared to EAGLE.

Figures

Figure 1- Cumulative metallicity distribution functions for partial Lyman limit systems (pLLSs), LLSs, strong LLSs (SLLSs), and damped Lyman-alpha absorbers (DLAs) at 6 different redshifts between z=5->0.

Figure 2- Median metallicities of LLSs and DLAs at 6 different redshifts.  

Figure 3- Evolution of strong LLSs and DLAs compared to observations.  Medians along with 25-75% cuts, 15-85% cuts, and 5-95% cuts are displayed.  

Figure 4- Cosmic density of stars, HI, and metals in HI systems.  

Figure 5- Simulations of the Wotta et al. (2016) metallicity distribution of HI absorbers.

On-line Data

Data will be directly accessible here upon paper acceptance.  For now, please e-mail the 2nd author for this data.