Imprints of recoiling massive black holes on the hot gas of early-type galaxies |
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| Authors: | B Devecchi E Rasia † M Dotti M Volonteri M Colpi |
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| Institution: | Dipartimento di Fisica G. Occhialini, Universitàdegli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy;Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA;Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA |
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| Abstract: | Anisotropic gravitational radiation from a coalescing black hole (BH) binary is known to impart recoil velocities of up to ～1000 km s?1 to the remnant BH. In this context, we study the motion of a recoiling BH inside a galaxy modelled as a Hernquist sphere, and the signature that the hole imprints on the hot gas, using N -body/smoothed particle hydrodynamics simulations. Ejection of the BH results in a sudden expansion of the gas ending with the formation of a gaseous core, similarly to what is seen for the stars. A cometary tail of particles bound to the BH is initially released along its trail. As the BH moves on a return orbit, a nearly spherical swarm of hot gaseous particles forms at every apocentre: this feature can live up to ≈108 years. If the recoil velocity exceeds the sound speed initially, the BH shocks the gas in the form of a Mach cone in density near each supersonic pericentric passage. We find that the X-ray fingerprint of a recoiling BH can be detected in Chandra X-ray maps out to a distance of Virgo. For exceptionally massive BHs, the Mach cone and the wakes can be observed out to a few hundred of milliparsec. The detection of the Mach cone is of twofold importance as it can be a probe of high-velocity recoils, and an assessment of the scatter of the M BH? M bulge relation at large BH masses. |
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| Keywords: | black hole physics gravitational waves hydrodynamics methods: numerical galaxies: nuclei X-rays: galaxies |
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