Active Galaxies in the Sloan Digital Sky Survey II: galaxy and activity
  evolution
  In this second paper of a series of papers based on the FIRST and SDSS
surveys we investigate the evolution of galaxy morphology and nuclear activity
in the look-back time of the SDSS (~2 Gyrs) for a sample of ~150000 galaxies in
the local universe. We demonstrate an evolution in the strength of the radio
power and the spectroscopic emission-lines typical of AGN, as well as in the
morphology of their hosts. Such evolution appears more substantial for less
luminous systems, and is possibly the low-redshift tail of the downsizing in
star-formation, AGN activity and supermassive black hole build-up observed in
higher redshift surveys.This suggests that the differences in intrinsic
properties of galaxies along the Hubble Sequence may arise from the difference
in the depth of their potential wells which leads to different evolutionary
paths because of different timescales for gas infall. This primordial infall
and the following secular evolution mediated by bar and density wave
instabilities may bring galaxies of different mass to have the different
activity levels and morphological features in the local universe shown in this
study. In agreement with such a hypothesis, we find that star-formation as
traced by radio emission is progressively more centrally concentrated in more
evolved star-forming galaxies and we show that the environment in which a
galaxy resides plays a lesser role in shaping the features and activity for the
majority of systems.
