Discovery of Infalling Motion with Rotation of the Cluster-Forming Clump S235AB and Its Implication to the Clump Structures

TL;DR

This paper reports the discovery of infalling and rotating motion in a massive cluster-forming clump, revealing its collapse dynamics and implications for core formation and star development.

Contribution

It presents the first evidence of infall with rotation in a cluster-forming clump and models its structure based on observational data.

Findings

Clump exhibits elliptical shape and symmetric PV peaks indicating collapse.

Inferred mass infall rate is approximately 10^-3 solar masses per year.

Formation of a compact core (~4 solar masses, <0.1 pc) at the center is observed.

Abstract

We report the discovery of infalling motion with rotation of S235AB the massive cluster-forming clump (~10^3 Mo) in the S235 region. Our C18O observations with the 45m telescope at the Nobeyama Radio Observatory have revealed the elliptical shape of the clump. Position-velocity (PV) diagram taken along its major axis exhibits two well-defined peaks symmetrically located with respect to the clump center, which is similar to that found for a dynamically infalling envelope with rotation around a single protostar modeled by N. Ohashi and his collaborators, indicating that the cluster-forming clump is also collapsing by the self-gravity toward the clump center. With analogue to Ohashi's model, we made a simple model of an infalling, rotating clump to fit the observed data. Based on the inferred model parameters as well as results of earlier observations and simulations in the literature, we discuss structures of the clump such as the relation among the global mass infall rate (~10^-3 Mo/yr), formation of a compact core (with a mass and size of ~4 Mo and < 0.1 pc) at the center, and a massive star (~11 Mo) forming in the core.