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