# Absorption systems at $z\sim 2$ as a probe of the circum galactic medium: a probabilistic approach

## TL;DR

This study uses hydrodynamical simulations to analyze the properties of the intergalactic medium around galaxies at redshift 2, focusing on metal absorption systems and their relation to galaxy proximity, comparing results with observational data.

## Contribution

It introduces a probabilistic method to analyze absorber properties around galaxies in simulations, comparing two feedback models and matching observational data.

## Key findings

- Simulated absorber properties are similar across models, with minor differences at certain impact parameters.
- Metal absorption systems are most likely within 150-400 kpc of galaxies.
- C IV covering fractions agree with observational measurements.

## Abstract

We characterize the properties of the intergalactic medium (IGM) around a sample of galaxies extracted from state-of-the-art hydrodynamical simulations of structure formation in a cosmological volume of 25 Mpc comoving at $z\sim 2$. The simulations are based on two different subresolution schemes for star formation and supernova feedback: the MUlti-Phase Particle Integrator (MUPPI) scheme and the Effective Model. We develop a quantitative and probabilistic analysis based on the apparent optical depth method of the properties of the absorbers as a function of impact parameter from their nearby galaxies: in such a way we probe different environments from circumgalactic medium to low-density filaments. Absorbers' properties are then compared with a spectroscopic observational data set obtained from high-resolution quasar spectra. Our main focus is on the N$_{\rm{ CIV}}$-N$_{\rm { HI}}$ relation around simulated galaxies: the results obtained with MUPPI and the Effective model are remarkably similar, with small differences only confined to regions at impact parameters $b = [1-3] \times r_{\rm {vir}}$. Using $\mbox{C IV}$ as a tracer of the metallicity, we obtain evidence that the observed metal absorption systems have the highest probability to be confined in a region of 150-400 kpc around galaxies. Near-filament environments have instead metallicities too low to be probed by present-day telescopes, but could be probed by future spectroscopical studies. Finally we compute $\mbox{C IV}$ covering fractions which are in agreement with observational data.