Populations of Globular Clusters in Merger Remnants

Previous abstract Next abstract

Session 52 -- Elliptical Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[52.08] Populations of Globular Clusters in Merger Remnants

M. Bolte, L. Hernquist, M.L. Weil (University of California, Santa Cruz)

The structure and kinematics of globular cluster systems (GCS) around elliptical galaxies may carry signatures which can distinguish between the two competeing theories for the formation of early-type galaxies -- collapse of a single large gas cloud or the merger of disk galaxies. We analyze the merger remnant of two spiral galaxies each consisting of a disk, a dark halo and a spherical population of globular clusters in the context of the remnant's cluster population characteristics. This simulation also allows an evaluation of the use of GCS for inferring the run of mass with radius in the parent galaxy. In addition, we consider the formation of young populations of globulars during mergers as a solution to the "specific frequency problem."

In these simulations, the mass ratios for the GCS:disk:halo components are .02:1:5.8. The initial globular cluster system in each progenitor galaxy is either diffuse, $R_e=7$ kpc, or compact, $R_e=3$ kpc and consists of 2500 members, a number which is larger than expected for late-type galaxies but which improves statistical analyses of the remnants. During the merger, the disks develop tidal tails which eventually collapse into irregular structure around the outer regions of an elliptical-like remnant. Because they are not rotationally supported, GCS do not exhibit similar tidal irregularities but merge into a single, spatially extended system whose surface brightness is described by an $R^{1/4}$ law. When the orbital angular momentum of each component is converted to spin during the merger, the GCS are ``spun up'' preferentially in the least tightly-bound outer regions. Estimated cumulative masses for samples of the remnant GCS are compared to the integrated total mass. The result indicates that mass estimators used to trace gravitational potential and the spatial extent of dark matter for real ellipticals are unreliable by factors of 2 or 3.

Several thousand globular clusters may be present in massive elliptical galaxies. One challenge to the merger hypothesis as a method for forming ellipticals from the coalescence of spiral galaxies is that ellipticals possess more globular clusters per unit luminosity than late-type galaxies. This problem may be mitigated by star formation induced during a merger.

Tuesday program listing