AGN Feedback in Galaxy Groups: the Delicate Touch of Self-Regulated Outflows

AGN heating, through massive subrelativistic outflows, might be the key to solve the long-lasting ‘cooling flow problem ’ in cosmological systems. In a previous paper, we showed that cold accretion feedback and, to a lesser degree, Bondi self-regulated models are in fact able to quench cooling rates for several Gyr, at the same time preserving the main cool core features, like observed density and temperature profiles. Is it true also for lighter systems, such as galaxy groups? The answer is globally yes, although with remarkable differences. Adopting a modified version of the AMR code FLASH 3.2, we found that successful 3D simulations with cold and Bondi models are almost convergent in the galaxy group environment, with mechanical efficiencies in the range 5×10−4−10−3 and 5×10−2−10−1, respectively. The evolutionary storyline of galaxy groups is dominated by a quasi-continuous gentle injection with sub-Eddington outflows (with mechanical power P ∼ 1044 erg s−1, v ∼ 104 km s−1). The cold and hybrid accretion models present, in addition, very short quiescence periods, followed by moderate outbursts (10 times the previous phase), which generate a series of 10−20 kp