On the Effects of Subvirial Initial Conditions and the Birth Temperature of R136

Abstract

We investigate the effect of different initial virial temperatures, Q, on the dynamics of star clusters. We find that the virial temperature has a strong effect on many aspects of the resulting system, including among others: the fraction of bodies escaping from the system, the depth of the collapse of the system, and the strength of the mass segregation. These differences deem the practice of using "cold" initial conditions no longer a simple choice of convenience. The choice of initial virial temperature must be carefully considered as its impact on the remainder of the simulation can be profound. We discuss the pitfalls and aim to describe the general behavior of the collapse and the resultant system as a function of the virial temperature so that a well reasoned choice of initial virial temperature can be made. We make a correction to the previous theoretical estimate for the minimum radius, $R_{min}$, of the cluster at the deepest moment of collapse to include a Q dependency, $R_{min}\approx Q+N^{(-1/3)}$, where $N$ is the number of particles. We use our numerical results to infer more about the initial conditions of the young cluster R136. Based on our analysis, we find that R136 was likely formed with a rather cool, but not cold, initial virial temperature ($Q\approx 0.13$). Using the same analysis method, we examined 15 other young clusters and found the most common initial virial temperature to be between 0.18 and 0.25.

Accepted for publication in MNRAS

References in corpus (5)

• Dynamical mass segregation on a very short timescale
• Before the first supernova: combined effects of HII regions and winds on molecular clouds
• Using the minimum spanning tree to trace mass segregation
• Performance Analysis of Direct N-Body Algorithms on Special-Purpose Supercomputers
• The distinction between star clusters and associations

Cited by in corpus (2)

• Hierarchical formation of Westerlund 1: a collapsing cluster with no primordial mass segregation?
• Which young clusters/associations are we missing today?