The CDM model predicts the existence of lots of dark halos without star formation. These are halos which did not attract enough baryons in order to set some kind of gravitational instability, which could lead to the further collapse of the baryons and to star formation (see, e.g. http://arxiv.org/abs/astro-ph/0502312). On the other hand, mergers of halos and galaxies are still ongoing within galaxy clusters. I assume that collisions of halos may lead, in some cases, to some kind of energy loss or dissipation (e.g. angular momentum loss or shocks) of the baryonic gas, inducing a gravitational instability (fragmentation) and perhaps leading to a first star formation. If we consider that the birth of a galaxy is the formation of it’s first stars, this would mean that galaxy formation is a process which is currently onging. However, it is usually claimed that galaxy formation does not take place currently, or, at least, that it would be surprinsing to find newly formed galaxies in the neighborhood, see e.g. http://hubblesite.org/newscenter/newsdesk/archive/releases/2002/16/text/ So, what about my assumption above?