EPOCH OF GALAXY FORMATION

There are two distinct phases related to the formation epoch of galaxi es. In an expanding universe, a galaxy's birth would mark the time whe n a system turned around under its own self gravity and acquired a sep arate dynamical status. A second stage more amenable to searches for y oung galaxies marks the epoch when such a system undergoes its first p rimary episode of star formation. On the basis of cooling arguments an d dynamical timescales, it is usual to assume that the former phase pr ecedes the latter i.e. majority of stars form within a self-gravitatin g gaseous 'protogalaxy'. In this paper I illustrate how the pre-existe nce of a central black hole and its activity influences the protogalac tic environment to initiate large scale star formation.