Feedback from central black holes in elliptical galaxies. III. Models with both radiative and mechanical feedback

Abstract

We find, from high-resolution hydro simulations, that winds from active galactic nuclei effectively heat the inner parts (≈ 100 pc) of elliptical galaxies, reducing infall to the central black hole; and radiative (photoionization and X-ray) heating reduces cooling flows at the kpc scale. Including both types of feedback with (peak) efficiencies of 3 × 10 -4 ≲ εw ≲ 10-3 and of εEM ≃ 10-1.3 respectively, produces systems having duty cycles, central black hole masses, X-ray luminosities, optical light profiles, and E+A spectra in accord with the broad suite of modern observations of massive elliptical systems. Our main conclusion is that mechanical feedback (including energy, momentum, and mass) is necessary but the efficiency, based on several independent arguments, must be a factor of 10 lower than is commonly assumed. Bursts are frequent at z > 1 and decline in frequency toward the present epoch as energy and metal-rich gas are expelled from the galaxies into the surrounding medium. For a representative galaxy of final stellar mass ≃3 × 1011 M ⊙, roughly 3 × 10 10 M ⊙ of recycled gas has been added to the interstellar medium (ISM) since z ≃ 2 and, of that, roughly 63% has been expelled from the galaxy, 19% has been converted into new metal-rich stars in the central few hundred parsecs, and 2% has been added to the central supermassive black hole (SMBH), with the remaining 16% in the form of hot X-ray emitting ISM. The bursts occupy a total time of ≃170 Myr, which is roughly 1.4% of the available time. Of this time, the central supermassive black hole would be seen as a UV or optical source for ≃45% and ≃71% of the time, respectively. Restricting to the last 8.5 Gyr, the bursts occupy ≃44 Myr, corresponding to a fiducial duty cycle of ≃5 × 10-3. © 2010. The American Astronomical Society. All rights reserved.