Early Evolution of Stellar Groups and Clusters: Environmental Effects on Forming Planetary Systems

This paper studies the dynamical evolution of young stellar clusters with $N$ = 100 - 1000 members. We use N-body simulations to explore how evolution depends on system size $N$ and the initial conditions. Motivated by recent observations of extremely young systems, this study compares subvirial and virial starting states. Multiple realizations of equivalent cases (100 simulations per case) are used to build up a robust statistical description of these systems, e.g., distributions of closest approaches, mass profiles, and distributions of radial locations. These results provide a framework from which to assess the effects of these clusters on star and planet formation. The distributions of radial positions are used in conjunction with distributions of FUV luminosities (also calculated here) to determine the radiation exposure of circumstellar disks. The distributions of closest approaches are used in conjunction with scattering cross sections (calculated here from $10^5$ scattering experiments) to determine the probability of solar system disruption. We also use the nearby cluster NGC 1333 as a test case. Our main conclusion is that clusters in this size range have only a modest effect on forming planetary systems: Interaction rates are low so that the typical solar system experiences a single encounter within 1000 AU. Radiation exposure is low, with median FUV flux $G_0$ = 900, so that photoevaporation of disks is only important beyond 30 AU. Given the low interaction rates and modest radiation levels, we suggest that solar system disruption is a rare event in these clusters.Comment: 54 pages; accepted to Ap