FM14.1.04 —  Effects of the Central Density Profile and the Stellar Mass Function of Merging Galaxies on Eccentricities and Coalescence Times of Supermassive Black Hole Binaries

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Aug 12th at 11:55 AM until 12:15 PM

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Author(s): Fazeel Mahmood Khan2, Peter Berczik1, Andreas Just1

Institution(s): 1. Astronomisches Rechen-Institut, Zentrum fur Astronomie, University of Heidelberg, 2. Institute of Space Technology, Islamabad


If able to coalesce in a Hubble time, Supermassive Black hole (SMBH) binaries are very promising sources of gravitational waves (GW). Our earlier studies have shown that SMBH binaries evolve at a constant rate in post-merger galactic nuclei having triaxial or axisymmetric geometry. Furthermore the extrapolation to the GW regime using this constant rate and estimating coalescence times based on the post Newtonian (PN) approximation leads to coalescence times of a few billion years. In this study, we model the complete evolution of SMBH binaries formed as a result of galaxy mergers having central density profiles that vary from shallow to very steep including a stellar mass function. Energy and angular momentum loss due to GW emission is taken into account using PN corrections in the equation of motion of the SMBH binaries. We carry out ten such simulations for each central density profile. For SMBH binaries evolving in merger remnant formed by shallow cusp galaxies, eccentricities remain very high ~ 0.8-0.99 and coalescence times ranges from 1 to 1.5 Gyr. For steeper profiles, eccentricities range form 0.5-0.8 and the coalescence time is ~ 0.6-0.8 Gyr. Low eccentricity values of SMBH binaries 0.4-0.6 and short coalescence time ~ 0.4 Gyr are recorded for very steep profile galaxy mergers. Typical coalescence times less than a Gyr strengthen our expectation that SMBH binaries should be very promising sources of GW radiation over a wide redshift range.