The Radio-Infrared Nebula in II Zw 40: Clusters Forming in Colliding Elongated Clouds

TL;DR

This study investigates the complex structure and dynamics of the supernebula in II Zw 40, revealing it as a collision or merger of two star clusters associated with elongated molecular clouds, supported by multi-wavelength observations and simulations.

Contribution

It provides the first detailed multi-wavelength analysis of the supernebula in II Zw 40 and models it as a grazing collision of two star clusters, offering new insights into cluster formation in starburst regions.

Findings

Supernebula is likely a collision or merger of two star clusters.

The gas and stars show distorted structures consistent with a grazing collision.

Simulations match observed features, supporting the collision model.

Abstract

II Zw 40 is a starburst dwarf and merger product, and holds a radio-infrared supernebula excited by thousands of embedded OB stars. We present here observations of three aspects of the supernebula: maps of the K and KU radio continuum that trace dense ionized gas with spatial resolution $\sim0.1^{\prime\prime}$, a spectral data cube of the [S IV]$10.5\mu$m emission line that measures the kinematics of the ionized gas with velocity resolution $4.5$ km s$^{-1}$, and an ALMA spectral cube of the CO(3-2) line that probes the dense warm molecular gas with spatial and velocity resolution comparable to the ionized gas. The observations suggest that the supernebula is the overlap,collision or merger of two star clusters, each associated with an elongated molecular cloud. We accordingly modelled the supernebula with simulations of colliding clusters. The model that best agrees with the data is a grazing collision that has distorted the gas and stars to create the distinctive structures observed. These models may have wide applicability in the cluster-rich regions of young starbursts.