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تسجيل مستخدم جديدWhy do Black Holes Trace Bulges (& Central Surface Densities), Instead of Galaxies as a Whole?
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Philip F. Hopkins
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Previous studies of fueling black holes (BHs) in galactic nuclei have argued (on scales ~0.01-1000pc) accretion is dynamical with inflow rates $dot{M}simeta,M_{rm gas}/t_{rm dyn}$ in terms of gas mass $M_{rm gas}$, dynamical time $t_{rm dyn}$, and some $eta$. But these models generally neglected expulsion of gas by stellar feedback, or considered extremely high densities where expulsion is inefficient. Studies of star formation, however, have shown on sub-kpc scales the expulsion efficiency $f_{rm wind}=M_{rm ejected}/M_{rm total}$ scales with the gravitational acceleration as $(1-f_{rm wind})/f_{rm wind}simbar{a}_{rm grav}/langledot{p}/m_{ast}ranglesim Sigma_{rm eff}/Sigma_{rm crit}$ where $bar{a}_{rm grav}equiv G,M_{rm tot}(<r)/r^{2}$ and $langledot{p}/m_{ast}rangle$ is the momentum injection rate from young stars. Adopting this as the simplest correction for stellar feedback, $eta rightarrow eta,(1-f_{rm wind})$, we show this provides a more accurate description of simulations with stellar feedback at low densities. This has immediate consequences, predicting e.g. the slope and normalization of the $M-sigma$ and $M-M_{rm bulge}$ relation, $L_{rm AGN}-$SFR relations, and explanations for outliers in compact Es. Most strikingly, because star formation simulations show expulsion is efficient ($f_{rm wind}sim1$) below total-mass surface density $M_{rm tot}/pi,r^{2}<Sigma_{rm crit}sim3times10^{9},M_{odot},{rm kpc^{-2}}$ (where $Sigma_{rm crit}=langledot{p}/m_{ast}rangle/(pi,G)$), BH mass is predicted to specifically trace host galaxy properties above a critical surface brightness $Sigma_{rm crit}$ (B-band $mu_{rm B}^{rm crit}sim 19,{rm mag,arcsec^{-2}}$). This naturally explains why BH masses preferentially reflect bulge properties or central surface-densities ($Sigma_{1,{rm kpc}}$), not total galaxy properties.
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