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Abstract
We present a new zoom-in hydrodynamical simulation, "Erisbh", which follows the cosmological evolution and feedback effects of a supermassive black hole at the center of a Milky Way-type galaxy. ErisBH shares the same initial conditions, resolution, recipes of gas cooling, star formation and feedback, as the close Milky Way-analog "Eris", but it also includes prescriptions for the formation, growth and feedback of supermassive black holes. We find that the galaxy's central black hole grows mainly through mergers with other black holes coming from infalling satellite galaxies. The growth by gas accretion is minimal because very little gas reaches the sub-kiloparsec scales. The final black hole is, at z=0, about 2.6 million solar masses and it sits closely to the position of SgrA* on the MBH-MBulge and MBH-sigma planes, in a location consistent with what observed for pseudobulges. Given the limited growth due to gas accretion, we argue that the mass of the central black hole should be above 10^5 solar masses already at z~8. The effect of AGN feedback on the host galaxy is limited to the very central few hundreds of parsecs. Despite being weak, AGN feedback seems to be responsible for the limited growth of the central bulge with respect to the original Eris, which results in a significantly flatter rotation curve in the inner few kiloparsecs. Moreover, the disk of ErisBH is more prone to instabilities, as its bulge is smaller and its disk larger then Eris. As a result, the disk of ErisBH undergoes a stronger dynamical evolution relative to Eris and around z=0.3 a weak bar grows into a strong bar of a few disk scale lengths in size. The bar triggers a burst of star formation in the inner few hundred parsecs, provides a modest amount of new fuel to the central black hole, and causes the bulge of ErisBH to have, by z=0, a box/peanut morphology.(Abridged)
Highlights
Present in most spheroids (e.g. Kormendy 2004), and being the engines powering active galactic nuclei (AGN), supermassive black holes seem to be an integral component of massive spheroidal galaxies
At z = 0, the main galaxy of ErisBH hosts a central black hole of 2.6 × 106 M⊙, which correlates to the bulge mass and the galaxy’s central velocity dispersion to what is observed in the Milky Way and in pseudobulges
5 SUMMARY AND CONCLUSIONS In this paper we presented ErisBH, a new zoom-in cosmological simulation where we followed the evolution of a Milky Way-size dark matter halo with its baryon content from z ∼ 90 to the present time
Summary
Present in most spheroids (e.g. Kormendy 2004), and being the engines powering active galactic nuclei (AGN), supermassive black holes ( black holes, from here onwards) seem to be an integral component of massive spheroidal galaxies. Navarro & Benz (1991) found that the baryonic component of galaxies evolving in hierarchically growing haloes was not able to retain enough angular momentum to feature a cold disc and flat rotation curves as in realistic spirals Those authors suggested that a proper treatment of supernova feedback (or some other form of heating) at early times would be necessary to prevent gas to lose angular momentum and catastrophically cool during galaxy interactions.
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