The Nuclear Disk in the Dwarf Elliptical Galaxy NGC 4486A

Abstract

Many ellipticals contain nuclear disks of dust and gas. Some ellipticals contain nuclear disks of stars that are distinct from the rest of the galaxy. We show that the dwarf E2 galaxy NGC 4486A contains both—it is a "Rosetta stone" object that tells us how nuclear disks evolve. Its properties suggest that, as accreted gas dissipates and settles toward the center, it forms stars and builds a stellar disk. Secular growth may explain not only the most distinct nuclear disks such as the one in NGC 4486A but also some of the disky distortions that are commonly seen in elliptical galaxies. That is, density distributions may grow secularly cuspier. This would result in chaotic mixing of stellar orbits in phase space and would tend to make an elliptical galaxy evolve toward a more nearly axisymmetric shape.