Cosmological hydrodynamical simulations of galaxy clusters: X-ray
  scaling relations and their evolution
  We analyse cosmological hydrodynamical simulations of galaxy clusters to
study the X-ray scaling relations between total masses and observable
quantities such as X-ray luminosity, gas mass, X-ray temperature, and $Y_{X}$.
Three sets of simulations are performed with an improved version of the
smoothed particle hydrodynamics GADGET-3 code. These consider the following:
non-radiative gas, star formation and stellar feedback, and the addition of
feedback by active galactic nuclei (AGN). We select clusters with $M_{500} >
10^{14} M_{\odot} E(z)^{-1}$, mimicking the typical selection of
Sunyaev-Zeldovich samples. This permits to have a mass range large enough to
enable robust fitting of the relations even at $z \sim 2$. The results of the
analysis show a general agreement with observations. The values of the slope of
the mass-gas mass and mass-temperature relations at $z=2$ are 10 per cent lower
with respect to $z=0$ due to the applied mass selection, in the former case,
and to the effect of early merger in the latter. We investigate the impact of
the slope variation on the study of the evolution of the normalization. We
conclude that cosmological studies through scaling relations should be limited
to the redshift range $z=0-1$, where we find that the slope, the scatter, and
the covariance matrix of the relations are stable. The scaling between mass and
$Y_X$ is confirmed to be the most robust relation, being almost independent of
the gas physics. At higher redshifts, the scaling relations are sensitive to
the inclusion of AGNs which influences low-mass systems. The detailed study of
these objects will be crucial to evaluate the AGN effect on the ICM.
