Investigating dusty Red Supergiant outflows in Westerlund 1 with 3D Hydrodynamic simulations

Abstract

Recent JWST observations towards Westerlund 1 revealed extensive nebular emission associated with the cluster. Given the age of the region and proximity of that material to massive stars it cannot be primordial star forming gas and the origin is uncertain. We aim to determine whether the nebular emission in Westerlund 1 could be due to ablation flows from Red Supergiant (RSG) stars embedded in the cluster wind driven by the Wolf-Rayet stars in the cluster core. We also aim to explore the efficiency of mass-loading for the RSG wind in this scenario. We use 3D hydrodynamic simulations with the \textsc{pion} code to study the interaction between the cluster and RSG winds. We compare with the JWST observations by generating synthetic dust-emission maps. We find that the ablation flow morphology is consistent with the observations towards Westerlund 1, with clumps and instabilities. Synthetic observations at 11 $\mu$m predict fluxes in the ablation flow of $\sim 1000-6000$ MJy ster${}^{-1}$ which is consistent with the unsaturated components of the JWST F1130W observations in the vicinity of the red supergiants in the region. This good agreement is achieved without any consideration of polycyclic aromatic hydrocarbons (PAHs), which have a known 11.3 $\mu$m feature that appears in the F1130W band. This suggests that the ablation flow is PAH depleted. Ablation of RSG winds can explain the observed nebulosity in Westerlund 1, at least in the vicinity of the RSGs. Further observations are encouraged to enable detailed studies of these interactions.

12 pages, 13 figures. Published in Astronomy & Astrophysics, updated following comments from the referee

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