The importance of the local density in shaping the galaxy stellar mass functions

Exploiting the capabilities of four different surveys - the Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby Galaxy-cluster Survey (WINGS), the IMACS (Inamori-Magellan Areal Camera and Spectrograph) Cluster Building Survey (ICBS) and the ESO (European Southern Observatory) Distant Cluster Survey (EDisCS) - we analyse the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low (z>0.04) to high (z<0.8) redshift. We find that at all redshifts and in all environments, local density plays a role in shaping the mass distribution. In the field, it regulates the shape of the mass function at any mass above the mass limits. In clusters, it seems to be important only at low masses, otherwise it seems not to influence the mass distribution. Putting together our results with those of Calvi et al. and Vulcani et al. for the global environment, we argue that at least at z~0.8 local density is more important than global environment in determining the galaxy stellar mass distribution, suggesting that galaxy properties are not much dependent on halo mass, but do depend on local scale processes. Within these groups a few very massive groups (?), comparable to clusters, are included (see Calvi et al. 2011). ? is defined as the radius delimiting a sphere with interior mean density 200 times the critical density of the Universe at that redshift and is commonly used as an approximation for the cluster virial radius. The ? values for our structures are computed from the velocity dispersions using the formula We remind the reader that the normalization adopted in displaying the mass functions does not influence the KS test and hence our results. For the sake of completeness, 'other galaxies' are also plotted; they include all galaxies that belong to groups but are outside each group radial limit or the redshift range for groups. From now on, when we change the mass limit, we always compute again the limits of the density bins: each time, above the adopted mass limit we subdivide galaxies so that in the two central bins galaxies are twice as numerous as galaxies in the outer bins. e remind the reader that the WINGS sample is not spectroscopically complete, so in all the following analyses, we always take into account WINGS' weights. The fact that at low and intermediate redshifts we find the same fraction of massive galaxies indicates that the evolution of the fraction is independent of environment.