  We have performed cosmological simulations in a $\Lambda$CDM cosmology with
and without radiative cooling, in order to study the effect of cooling on the
cluster scaling relations. Our simulations consist of 4.1 million particles
each of gas and dark matter within a box-size of 100 $h^{-1}$ Mpc and the run
with cooling is the largest of its kind to have been evolved to $z=0$. Our
cluster catalogues both consist of over 400 objects and are complete in mass
down to $\sim 10^{13} h^{-1} {\rm M_{\odot}}$. We contrast the
emission-weighted temperature-mass ($T_{\rm ew}-M$) and bolometric
luminosity-temperature ($L_{\rm bol}-T_{\rm ew}$) relations for the simulations
at $z=0$. We find that radiative cooling \emph{increases} the temperature of
intracluster gas and \emph{decreases} its total luminosity, in agreement with
the results of Pearce et al. Furthermore, the temperature dependence of these
effects flattens the slope of the $T_{\rm ew}-M$ relation and steepens the
slope of the $L_{\rm bol}-T_{\rm ew}$ relation. Inclusion of radiative cooling
in the simulations is sufficient to reproduce the observed X-ray scaling
relations without requiring excessive non-gravitational energy injection.

Astrophysics