A ug 2 00 6 Mass functions in coupled Dark Energy models

We evaluate the mass function of virialized halos, by using Press & Schechter (PS) and/or Steth & Tormen (ST) expressions, for cosmologies where Dark Energy (DE) is due to a scalar self– interacting field, coupled with Dark Matter (DM). We keep to coupled DE (cDE) models known to fit linear observables. To implement the PS–ST approach, we start from reviewing and extending the results of a previous work on the growth of a spherical top–hat fluctuation in cDE models, confirming their most intriguing astrophysical feature, i.e. a significant baryon–DM segregation, occurring well before the onset of any hydrodynamical effect. Accordingly, the predicted mass function depends on how halo masses are measured. For any option, however, the coupling causes a distortion of the mass function, still at z = 0. Furthermore, the z–dependence of cDE mass functions is mostly displaced, in respect to ΛCDM, in the opposite way of uncoupled dynamical DE. This is an aspect of the basic underlying result, that even a little DM–DE coupling induces relevant modifications in the non–linear evolution. Therefore, without causing great shifts in linear astrophysical observables, the DM–baryon segregation induced by the coupling can have an impact on a number of cosmological problems, e.g., galaxy satellite abundance, spiral disk formation, apparent baryon shortage, entropy input in clusters, etc.. PACS numbers: 98.80.-k, 98.65.-r