The changing ISM of massive elliptical galaxies and cosmic evolution of
  radio galaxies and quasars
  The recently discovered apparent dramatic expansion in the effective radii of
massive elliptical galaxies from $z \simeq 2$ to $z \simeq 0.1$ has been
interpreted in terms of either galaxy mergers or the rapid loss of cold gas due
to AGN feedback. In examining the latter case we have quantified the extent of
the expansion, which is uncertain observationally, in terms of the star
formation parameters and time of the expulsion of the cold gas. In either case,
the large global decrease in stellar density should translate into a major drop
in the ISM density and pressure, and a much steeper radial decline in those
quantities with cosmic epoch. These cosmological changes are expected to have a
major influence on the gas accretion mode, which will shift from `cold' thin
disk accretion at high redshifts toward `hot' Bondi fed ADAF accretion at low
redshifts. The decline of angular momentum inflow would then lead to a spin
down of the black hole, for which we have calculated more precise time scales;
a value of about 0.2 Gyr is typical for a $10^9 M_\odot$ central black hole.
These results have implications for the different cosmological evolutionary
patterns found for the luminosity functions of powerful and weak radio
galaxies.
