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Abstract: The observed super-massive black hole SMBH mass - galaxy velocitydispersion $M { m bh} - \sigma$ correlation may be established whenwinds-outflows from the SMBH drive gas out of the potential wells of classicalbulges. Here we present numerical simulations of this process in a staticisothermal potential. Simple spherically symmetric models of SMBH feedback atthe Eddington luminosity can successfully explain the $M { m bh} - \sigma$ andnuclear cluster mass $M { m NC}-\sigma$ correlations, as well as why largerbulges host SMBHs while smaller ones host nuclear star clusters. However thesemodels do not specify how SMBHs feed on infalling gas whilst simultaneouslyproducing feedback that drives gas out of the galaxy.More complex models with rotation and-or anisotropic feedback allow SMBHs tofeed via a disc or regions not exposed to SMBH winds, but in these morerealistic cases it is not clear why a robust $M { m bh} - \sigma$ relationshould be established. In fact, some of the model predictions contradictobservations. For example, an isotropic SMBH wind impacting on a disc ratherthan a shell of aspect ratio $H-R \ll 1$ requires the SMBH mass to be largerby a factor $\sim R-H$, which is opposite to what is observed. We conclude thatunderstanding how a SMBH feeds is as important a piece of the puzzle asunderstanding how its feedback affects its host galaxy.Finally, we note that in aspherical cases the SMBH outflows inducedifferential motions in the bulge. This may pump turbulence that is known tohinder star formation in star forming regions. SMBH feedback thus may not onlydrive gas out of the bulge but also reduce the fraction of gas turned intostars.

Author: Sergei Nayakshin, Chris Power Leicester


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