# Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with Clumpy Interstellar Medium

## TL;DR

This study uses 3D magnetohydrodynamic simulations to explore how jets interacting with clumpy interstellar medium can produce the peculiar shapes of molecular clouds observed near Westerlund 2, revealing the influence of HI clump distribution.

## Contribution

It introduces a novel simulation approach to explain the formation and morphology of molecular clouds via jet-ISM interactions considering HI clump filling factors.

## Key findings

- Arc-shaped clouds form with high HI clump filling factors.
- Molecular clouds align with jets at low HI clump filling factors.
- Jet propagation speed varies with HI clump distribution.

## Abstract

The formation mechanism of CO clouds observed with NANTEN2 and Mopra telescope toward the stellar cluster Westerlund 2 is studied by three-dimensional magnetohydrodynamic (MHD) simulations taking into account the interstellar cooling. These molecular clouds show a peculiar shape composing of an arc-shaped cloud in one side of a TeV-ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) in another side. We propose that these clouds are formed by the interaction of a jet with interstellar neutral hydrogen (HI) clumps. By studying the dependence of the shape of dense cold clouds formed by shock compression and cooling on the filling factor of HI clumps, we found that the density distribution of HI clumps determines the shape of molecular clouds formed by the jet-cloud interaction; arc-clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.