2009ApJ...699...89C

The importance of the radiative feedback from massive black holes 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 black hole is also expected to occur and has been included in the work of several investigators. In this paper, we improve and extend the accretion and feedback physics explored in our previous papers to include also a physically motivated model of mechanical feedback, in addition to radiative effects. In particular, we study the evolution of an isolated elliptical galaxy with the aid of a high-resolution one-dimensional 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 (in the form of nuclear winds). 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 adopted by some investigators, 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 supermassive black hole (SMBH) growth occurs. But models with low enough mechanical efficiency to accommodate 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. In a surprising conclusion, we find that both types of feedback are required. Radiative heating over the inner few kiloparsecs is needed to prevent calamitous cooling flows, and mechanical feedback from active galactic nucleus winds, which affects primarily the inner few hundred parsecs, is needed to moderate the luminosity and growth of the central SMBH. Models with combined feedback are explored in a forthcoming paper.