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Energy input from quasars regulates the growth and activity of black holes and their host galaxies


In the early Universe, while galaxies were still forming, black holes as massive as a billion solar masses powered quasars. Supermassive black holes are found at the centres of most galaxies today1,2,3, where their masses are related to the velocity dispersions of stars in their host galaxies and hence to the mass of the central bulge of the galaxy4,5. This suggests a link between the growth of the black holes and their host galaxies6,7,8,9, which has indeed been assumed for a number of years. But the origin of the observed relation between black hole mass and stellar velocity dispersion, and its connection with the evolution of galaxies, have remained unclear. Here we report simulations that simultaneously follow star formation and the growth of black holes during galaxy–galaxy collisions. We find that, in addition to generating a burst of star formation10, a merger leads to strong inflows that feed gas to the supermassive black hole and thereby power the quasar. The energy released by the quasar expels enough gas to quench both star formation and further black hole growth. This determines the lifetime of the quasar phase (approaching 100 million years) and explains the relationship between the black hole mass and the stellar velocity dispersion.

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Figure 1: Snapshots of the simulated time evolution of mergers of two galaxies with and without black holes.
Figure 2: Black hole activity, star formation and black hole growth plotted as a function of time during a galaxy–galaxy merger.
Figure 3: The relation between the final black hole mass, MBH, and the velocity dispersion of stars, σ, of our galaxy merger simulations compared with observational measurements.

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The computations reported here were performed at the Center for Parallel Astrophysical Computing at the Harvard-Smithsonian Center for Astrophysics and at the Rechenzentrum der Max-Planck-Gesellschaft in Garching.

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Correspondence to Tiziana Di Matteo.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Methods

This document provides technical information about the simulation method and details the equations solved for describing the physics of star formation, black hole accretion and feedback processes. Where appropriate, references to relevant literature for the simulation methodology are included. (PDF 44 kb)

Supplementary Movie

This computer animation visualizes the time evolution of a merger simulation of two spiral galaxies that host supermassive black holes at their centres. Only the gas distribution is shown. Brightness represents gas density, whereas the colour hue indicates gas temperature. (AVI 10827 kb)

Supplementary Figure S1

Evolution of the gas density of two gas rich (80% gas) spiral galaxies with supermassive black holes. Colour indicates temperature, and brightness the gas density. After the merger and the formation of a large bulge, the remaining gas cools in the central regions and reassembles in a disk component. The black hole mass and the bulge velocity dispersion of this system are consistent with the M BM s relation. (PDF 77 kb)

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Di Matteo, T., Springel, V. & Hernquist, L. Energy input from quasars regulates the growth and activity of black holes and their host galaxies. Nature 433, 604–607 (2005).

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