5. AGN OUTFLOWS

We discuss two types of outflows from AGN: jets and winds-like outflows. There is much observational evidence for AGN jets interacting with the ICM - not only radio jets but also cavities in the ICM found in X-rays (e.g. Blanton et al. 2001, McNamara et al. 2001, Schindler et al. 2001, Heinz et al. 2002, Choi et al. 2004, Fabian et al. 2006, McNamara & Nulsen 2007), in which the pressure of the relativistic particles of the jet has pushed away the ICM. The jets consisting of relativistic particles can entrain some of the surrounding metal-rich gas (De Young 1986).

As the jet-ICM interaction can have an effect on both the energetics and the metal enrichment of the ICM, several groups have calculated this process. Many simulations for the energy transfer have been performed (Zhang et al. 1999, Churazov et al. 2001, Brüggen et al. 2002, Nulsen et al. 2002, Krause & Camenzind 2003, Heinz 2003, Beall et al. 2004, Beall et al. 2006, Dalla Vecchia et al. 2004, Zanni et al. 2005, Sijacki & Springel 2006, Heinz et al. 2006) while only few have attempted to calculate the metal enrichment due to the entrainment by jets (Heath et al. 2007, Moll et al. 2007). These simulations found that jets can both heat and enrich the ICM considerably. Another type of simulations calculated the metallicity distribution due to bubble-induced motions coming from a single AGN in the cluster centre (Roediger et al. 2007a). It was found that in this case the metallicity distribution is very elongated along the direction of the motion of the bubbles.

Also for wind-like outflows there is some observational evidence. Blue-shifted absorption lines have been observed in UV and X-rays (Crenshaw et al. 2003). Also from X-ray imaging evidence for nuclear outflows has been found (Machacek et al. 2006b). There are hints for a high metallicity of a few times solar (Hamann et al. 2001, Hasinger et al. 2002), for high velocities of several thousands or several ten thousands of km s^-1 (Chartas et al. 2002, Chartas et al. 2003, Pounds et al. 2003a, Pounds et al. 2003b, Reeves et al. 2003, O'Brian et al. 2005, Dasgupta et al. 2005, Gabel et al. 2006) and for considerable mass outflow rates (Crenshaw et al. 2003, Veilleux et al. 2005). The outflows can be quite strong, e.g. several 10⁹ M with kinetic energies around 10⁶⁰ erg expelled over the AGN live time of 10⁷ years as estimated from spectroscopic studies (Nesvadba et al. 2006).

In some galaxies the winds are not only driven by repeated supernova explosions but also the AGN are contributing to the energy necessary for the wind (see Sect. 3).