Feedback from central black holes in elliptical galaxies. I: models with
  either radiative or mechanical feedback but not both
  The importance of the radiative feedback from SMBHs at the centers of
elliptical galaxies is not in doubt, given the well established relations among
electromagnetic output, black hole mass and galaxy optical luminosity. In
addition, feedback due to mechanical and thermal deposition of energy from jets
and winds emitted by the accretion disk around the central SMBH is also
expected to occur. In this paper we improve and extend the accretion and
feedback physics explored in our previous papers to include also a physically
motivated mechanical feedback. We study the evolution of an isolated elliptical
galaxy with the aid of a high-resolution 1-D hydrodynamical code, where the
cooling and heating functions include photoionization and Compton effects, and
restricting to models which include only radiative or only mechanical feedback.
We confirm that for Eddington ratios above 0.01 both the accretion and
radiative output are forced by feedback effects to be in burst mode, so that
strong intermittencies are expected at early times, while at low redshift the
explored models are characterized by smooth, very sub-Eddington mass accretion
rates punctuated by rare outbursts. However, the explored models always fail
some observational tests. If we assume the high mechanical efficiency of
10^{-2.3}, we find that most of the gas is ejected from the galaxy, the
resulting X-ray luminosity is far less than is typically observed and little
SMBH growth occurs. But models with low enough mechanical efficiency to
accomodate satisfactory SMBH growth tend to allow too strong cooling flows and
leave galaxies at z=0 with E+A spectra more frequently than is observed. We
conclude that both types of feedback are required. Models with combined
feedback are explored in a forthcoming paper [abridged]
