Dynamical Evolution of Globular Clusters in Hierarchical Cosmology

We test the hypothesis that metal-poor globular clusters form within diskgalaxies at redshifts z>3. Numerical simulations demonstrate that giant gasclouds, which are cold and dense enough to produce massive star clusters,assemble naturally in hierarchical models of galaxy formation at high redshift.Do model clusters evolve into observed globular clusters or are they disruptedbefore present as a result of the dynamical evolution? To address thisquestion, we calculate the orbits of model clusters in the time-variablegravitational potential of a Milky Way-sized galaxy, using the outputs of acosmological N-body simulation. We find that at present the orbits areisotropic in the inner 50 kpc of the Galaxy and preferentially radial at largerdistances. All clusters located outside 10 kpc from the center formed insatellite galaxies, some of which are now tidally disrupted and some of whichsurvive as dwarf galaxies. The spatial distribution of model clusters isspheroidal and the fit to the density profile has a power-law slope of 2.7. Thecombination of two-body relaxation, tidal shocks, and stellar evolution drivesthe evolution of the cluster mass function from an initial power law to apeaked distribution, in agreement with observations. However, not all initialconditions and not all evolution scenarios are consistent with the observedmass function of the Galactic globular clusters. The successful models requirethe average cluster density to be constant initially for clusters of all massand to remain constant with time. Synchronous formation of all clusters at asingle epoch (z=4) and continuous formation over a span of 1.6 Gyr (between z=9and z=3) are both consistent with the data. For both formation scenarios, weprovide online catalogs of the main physical properties of model clusters.