On the role of the environments and star formation for quasar activity
  We investigate the host galaxy and environment properties of a sample of 400
low z (<0.5) quasars that were imaged in the SDSS Stripe82. We can detect and
study the properties of the host galaxy for more than 75% of the data sample.
We discover that quasar are mainly hosted in luminous galaxies of absolute
magnitude M* -3 < M(R) < M* and that in the quasar environments the galaxy
number density is comparable to that of inactive galaxies of similar
luminosities. For these quasars we undertake also a study in u,g,r,i and z SDSS
bands and again we discover that the mean colours of the quasar host galaxy it
is not very different with respect to the values of the sample of inactive
galaxies. For a subsample of low z sources the imaging study is complemented by
spectroscopy of quasar hosts and of close companion galaxies. This study
suggests that the supply and cause of the nuclear activity depends only weakly
on the local environment of quasars. Contrary to past suggestions, for low
redshift quasar there is a very modest connection between recent star formation
and the nuclear activity.
