We present a study of the galaxy population predicted by hydrodynamical simulations of galaxy clusters .
These simulations , which are based on the GADGET-2 Tree+SPH code , include gas cooling , star formation , a detailed treatment of stellar evolution and chemical enrichment , as well as SN energy feedback in the form of galactic winds .
As such , they can be used to extract the spectro–photometric properties of the simulated galaxies , which are identified as clumps in the distribution of star particles .
Simulations have been carried out for a representative set of 19 cluster–sized halos , having mass M _ { 200 } in the range 5 \times 10 ^ { 13 } – 1.8 \times 10 ^ { 15 } h ^ { -1 } { M } _ { \odot } .
All simulations have been performed for two choices of the stellar initial mass function ( IMF ) , namely using a standard Salpeter IMF with power–law index x = 1.35 , and a top–heavy IMF with x = 0.95 .
In general , we find that several of the observational properties of the galaxy population in nearby clusters are reproduced fairly well by simulations .
A Salpeter IMF is successful in accounting for the slope and the normalization of the color–magnitude relation for the bulk of the galaxy population .
In contrast , the top–heavy IMF produces too red galaxies , as a consequence of their exceedingly large metallicity .
Simulated clusters have a relation between mass and optical luminosity which generally agrees with observations , both in normalization and slope .
Also in keeping with observational results , galaxies are generally bluer , younger and more star forming in the cluster outskirts .
However , we find that our simulated clusters have a total number of galaxies which is significantly smaller than the observed one , falling short by about a factor 2–3 .
We have verified that this problem does not have an obvious numerical origin , such as lack of mass and force resolution .
Finally , the brightest cluster galaxies are always predicted to be too massive and too blue , when compared to observations .
This is due to gas overcooling , which takes place in the core regions of simulated clusters , even in the presence of the rather efficient supernova feedback used in our simulations .