Oral Presentation

The Effect of Impact Parameter on the Formation of Supermassive Binary Black Holes in Galactic Mergers

Author(s): Yu-Heng Ho (National Tsing Hua University); Ing-Guey Jiang (National Tsing Hua University)

Presenter: Yu-Heng Ho (National Tsing Hua University)

Using N-body simulations, we've investigated the formation of supermassive binary black holes(SMBB) under different impact parameters. Tracing the individual supermassive black hole(SMBH) from an initial distance of 300 kpc until the separation where the SMBB becomes hard, the time scale of different stages has been estimated, and the relation between the orbital evolution and the properties of the stellar cores are discussed. We find that certain merger geometries of the galaxies do affect the lifetime of the SMBB significantly, and the time between SMBHs from entering the core of the merged galaxy and forming a hard SMBB can be as long as 1.5 Gyr. Furthermore, although triaxial systems are generally believed to be efficient towards driving the SMBB into coalescence at late stage, we find that this might not be the case at an earlier stage when dynamical friction still plays the dominant role of subtracting the SMBB orbital energy. We conclude that the geometry of the merger also plays an important role of determining the lifetime of the SMBB, the situation might be more complicated if, for example, multiple mergers or larger mass ratio between the SMBHs are considered.