Faint Blue Galaxies and Merging: the Evolution of the Luminosity Function

Abstract

We probe to what extent not only the counts of the faint blue galaxies and their redshift distribution but also their z-resolved luminosity functions can be explained in terms of binary merging (aggregations). We present a dynamical theory of such interactions. On this basis we find that ``minimal aggregations'' taking place within large scale structures and triggering starbusts yield rates and timing such as to explain the observations of the local, flat luminosity function and of its progressive rising and steepening for redshifts out to $z\approx 1$. Correspondingly, we predictfaint blue counts still rising up to $m_B\sim 28 -29$, redshift distributions shifting toward larger z with increasing $m_B$; in addition, we predict an upturn of the faint end of the luminosity function more pronounced in clusters than in the field. We propose that our picture provides the differential dynamics missing in the canonical hierarchical theories. This reconciles with the observations the steep luminosity functions predicted at high z by such theories.