The molecular environment of the massive star forming region NGC 2024: Multi CO transition analysis

Abstract

Context. Sites of massive star formation have complex internal structures. Local heating by young stars and kinematic processes, such as outflows and stellar winds, generate large temperature and velocity gradients. Complex cloud structures lead to intricate emission line shapes. CO lines from high mass star forming regions are rarely Gaussian and show often multiple peaks. Furthermore, the line shapes vary significantly with the quantum number < cm < CO lines. Deep absorption notches indicate that very cold material (∼20 K) exists in front of the warm material, too.Conclusions. A temperature and column density structure consistent with those predicted by PDR models, combined with the velocity structure of a "Blister model", appropriately describes the observed emission line profiles of this massive star forming region. This case study of NGC 2024 shows that, with physical insights into these complex regions and careful modeling, multi-line observations of