Pure Luminosity Evolution models for faint field galaxy samples

We have examined a set of pure luminosity evolution (PLE) models in order to explore up to what extent the rapidly increasing observational constraints from faint galaxy samples can be understood in this simple framework. We find that a PLE model, in which galaxies evolve mildly in time even in the rest frame UV, can reproduce most of the observed properties of faint galaxies assuming an open ($\Omega\sim0$) universe. In particular, such a model is able to fit reasonably well the number counts in the $U,~b_j,~r_f,~I$, and $K$ bands, as well as the colour and redshift distributions derived from most of the existing samples. The most significant discrepancy between the predictions of this model and the data is the $z$ distribution of faint $K$-selected galaxies. Significantly worse fits are obtained with PLE models for the theoretically attractive value of $\Omega = 1$, although a simple number luminosity evolution model with a significant amount of merger events fits the data also in this cosmology.Comment: 15 pages, plain tex (insert encapsulated postscript figures), plus an extra figure Fig3c.ps and the tex-macro mn.tex uuencoded, gzipp'ed tar file -- accepted by MNRA

A Radio View of the Sky: the Cosmic History of Star-Forming and AGN Galaxies

We explore the cosmic evolution of radio detected star forming (SF) galaxies and active galactic nuclei (AGN), drawn from the VLA-COSMOS survey, out to z = 1.3. We present the 20 cm radio luminosity function for these populations, and find that SF galaxies evolve much more rapidly than low-power radio AGN. Our results imply that weak radio AGN (L_(1.4GHz) ≤ 5×10^(25) WHz^(−1)) occur in the most massive galaxies already at z ~ 1. They may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the ‘radio mode’ AGN feedback in cosmological models

A substructure analysis of the A3558 cluster complex

The "algorithm driven by the density estimate for the identification of clusters" (DEDICA, Pisani 1993, 1996) is applied to the A3558 cluster complex in order to find substructures. This complex, located at the center of the Shapley Concentration supercluster, is a chain formed by the ACO clusters A3556, A3558 and A3562 and the two poor clusters SC 1327-312 and SC 1329-313. We find a large number of clumps, indicating that strong dynamical processes are active. In particular, it is necessary to use a fully three-dimensional sample(i.e. using the galaxy velocity as third coordinate) in order to recover also the clumps superimposed along the line of sight. Even if a great number of detected substructures were already found in a previous analysis (Bardelli et al. 1998), this method is more efficient and faster when compared with the use of a wide battery of tests and permits the direct estimate of the detection significance. Almost all subclusters previously detected by the wavelet analyses found in the literature are recognized by DEDICA. On the basis of the substructure analysis, we also briefly discuss the origin of the A3558 complex by comparing two hypotheses: 1) the structure is a cluster-cluster collision seen just after the first core-core encounter; 2) this complex is the result of a series of incoherent group-group and cluster-group mergings, focused in that region by the presence of the surrounding supercluster. We studied the fraction of blue galaxies in the detected substructures and found that the bluest groups reside between A3562 and A3558, i.e. in the expected position in the scenario of the cluster-cluster collision.Comment: 10 pages with 12 encapsulated figures; MNRAS in pres