Cosmic Evolution of Size and Velocity Dispersion for Early Type Galaxies
  [abridged] Massive, passively evolving galaxies at redshifts z>1 exhibit on
the average physical sizes smaller by factors ~3 than local early type galaxies
(ETGs) endowed with the same stellar mass. Small sizes are in fact expected on
theoretical grounds, if dissipative collapse occurs. Recent results show that
the size evolution at z<1 is limited to less than 40%, while most of the
evolution occurs at z>1, where both compact and already extended galaxies are
observed and the scatter in size is remarkably larger than locally. The
presence at high z of a significant number of ETGs with the same size as their
local counterparts as well as of ETGs with quite small size, points to a
timescale to reach the new, expanded equilibrium configuration of less than the
Hubble time. We demonstrate that the projected mass of compact, high-z galaxies
and that of local ETGs within the *same physical radius*, the nominal
half-luminosity radius of high-z ETGs, differ substantially, in that the high-z
ETGs are on the average significantly denser. We propose that quasar activity,
which peaks at z~2, can remove large amounts of gas from central galaxy regions
on a timescale shorter than of the dynamical one, triggering a puffing up of
the stellar component at constant stellar mass; in this case the size increase
goes together with a decrease of the central mass. The size evolution is
expected to parallel that of the quasars and the inverse hierarchy, or
downsizing, seen in the quasar evolution is mirrored in the size evolution.
