Cosmic evolution of the CIV in high-resolution hydrodynamic simulations
  We investigate the properties of triply ionized Carbon (CIV) in the
Intergalactic Medium using a set of high-resolution and large box-size
cosmological hydrodynamic simulations of a $\Lambda$CDM model. We rely on a
modification of the GADGET-2 code that self-consistently follows the metal
enrichment mechanism by means of a detailed chemical evolution model. We focus
on several numerical implementations of galactic feedback: galactic winds in
the energy driven and momentum driven prescriptions and Active Galactic Nuclei
(AGN) powered by gas accretion onto massive black holes. We extract mock IGM
transmission spectra in neutral hydrogen (HI) and CIV and perform Voigt profile
fitting. The results are then compared with high-resolution quasar (QSO)
spectra obtained with the UVES spectrograph at the VLT and the HIRES
spectrograph at Keck. We find that feedback has little impact on statistics
related to the neutral hydrogen, while CIV is more affected by galactic winds
and/or AGN feedback. When the same analysis is performed over observed and
simulated CIV lines, we find reasonables good agreement between data and
simulations over the column density range $N_{\rm
  CIV}=10^{12.5-15}$ cm$^{-2}$. Also the CIV line-widths distribution appears
to be in agreement with the observed values, while the HI Doppler parameters,
$b_{\rm HI}$, are in general too large showing that the diffuse cosmic web is
heated more than what is inferred by observations. The simulation without
feedback fails in reproducing the CIV systems at high column densities at all
redshift, while the AGN feedback case agrees with observations only at $z<3$,
when this form of feedback is particularly effective. We also present scatter
plots in the $b-N$ and in the $N_{\rm CIV}-N_{\rm HI}$ planes, showing that
there is rough agreement between observations and simulations only when
feedback is taken into account.
