The Role of a Massive Central Singularity in Galactic Mergers on the Survival of the Core Fundamental Plane

Abstract

In order for the core Fundamental Plane (cFP) to endure, small ellipticals must not survive mergers with giant ellipticals, despite the fact the small secondary galaxy can be as much as a million times more dense than the primary. However, our previous set of experiments has shown that, for purely stellar galaxies, the secondary does in fact survive mergers with primaries up to 100 times more massive. In this paper, we demonstrate the effect that a massive central black hole has on mergers of cFP galaxies. Our results indicate that the addition of a massive central singularity inside the primary galaxy provides strong enough tidal forces to destroy dense cFP companions when the secondary's orbital decay is sufficiently elongated. The destruction of the secondary acts to preserve the original low central density profile of the primary in the giant merger remnant, which allows the remnant to remain on the cFP. On more circular orbits, though, the secondary is only disrupted near the end of the merger, and the degree to which the secondary particles disperse depends on the amount of orbital energy left in the merger. Hence, there are some mergers for which the cFP is not preserved in our experiments. We find that if the secondary is not dispersed, it forms a spinning stellar disk with a central density that forces the merger remnant off the cFP.