GMC Collisions As Triggers of Star Formation. VIII. The Core Mass Function

TL;DR

This study uses simulations to explore how giant molecular cloud collisions influence the formation and properties of prestellar cores, revealing a top-heavy core mass function and differences in core characteristics between colliding and non-colliding clouds.

Contribution

It provides new insights into the core mass function resulting from GMC collisions and compares simulated core properties with observational data.

Findings

GMC collisions produce a top-heavy core mass function with a power-law slope of ~0.7.

Cores from colliding clouds are generally warmer and more kinematically disturbed.

The dynamical state of cores in collisions can appear supervirial due to observational effects.

Abstract

Compression in giant molecular cloud (GMC) collisions is a promising mechanism to trigger formation of massive star clusters and OB associations. We simulate colliding and non-colliding magnetised GMCs and examine the properties of prestellar cores, selected from projected mass surface density maps, including after synthetic {\it ALMA} observations. We then examine core properties, including mass, size, density, velocity, velocity dispersion, temperature and magnetic field strength. After four Myr, $\sim1,000$ cores have formed in the GMC collision and the high-mass end of the core mass function (CMF) can be fit by a power law $dN/d{\rm{log}}M\propto{M}^{-\alpha}$ with $\alpha\simeq0.7$, i.e., relatively top-heavy compared to a Salpeter mass function. Depending on how cores are identified, a break in the power law can appear around a few $\times10\:M_\odot$. The non-colliding GMCs form fewer cores with a CMF with $\alpha\simeq0.8$ to 1.2, i.e., closer to the Salpeter index. We compare the properties of these CMFs to those of several observed samples of cores. Considering other properties, cores formed from colliding clouds are typically warmer, have more disturbed internal kinematics and are more likely to be gravitational unbound, than cores formed from non-colliding GMCs. The dynamical state of the protocluster of cores formed in the GMC-GMC collision is intrinsically subvirial, but can appear to be supervirial if the total mass measurement is affected by observations that miss mass on large scales or at low densities.