Journal Article

Imprints of recoiling massive black holes on the hot gas of early-type galaxies

B. Devecchi, E. Rasia, M. Dotti, M. Volonteri and M. Colpi

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 2, pages 633-640
Published in print April 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14329.x
Imprints of recoiling massive black holes on the hot gas of early-type galaxies

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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 MBHMbulge relation at large BH masses.

Keywords: black hole physics; gravitational waves; hydrodynamics; methods: numerical; galaxies: nuclei; X-rays: galaxies

Journal Article.  6533 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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