# An ALMA view of the Galactic super star cluster RCW38 at 270-AU resolution

## TL;DR

This study uses high-resolution ALMA observations to reveal the detailed structure, kinematics, and early star formation activity within the Galactic super star cluster RCW 38, highlighting massive condensations, potential disk rotation, and molecular outflows.

## Contribution

First high-resolution ALMA imaging of RCW 38 revealing detailed condensations, outflows, and potential disk rotation in a super star cluster.

## Key findings

- Massive condensations embedded in filamentary structures.
- Detection of molecular outflows with high velocities.
- Evidence of early-stage massive star formation.

## Abstract

We report millimeter/submillimeter continuum and molecular line observations of the Galactic super star cluster RCW 38, obtained from the Atacama Large Millimeter/Submillimeter Array with a minimum angular resolution of $0''.17\times0''.15$ ($\simeq289\,{\rm AU}\times255\,{\rm AU}$). The C$^{18}$O image reveal many massive condensations embedded within filamentary structures extending along the northwest-southeast direction in the center of cluster. The condensations have sizes of 0.01-0.02 pc, H$_2$ column densities of $10^{23}$-$10^{24}$ cm$^{-2}$, and H$_2$ masses of 10-130 $M_\odot$. In addition, the 233-GHz continuum image reveals two dense, small millimeter-sources with radii of 460 and 200 AU (Source A and Source B). Source A is embedded within the most massive C$^{18}$O condensation, whereas no counterpart is seen for Source B. The masses of Source A and Source B are estimated as 13 and 3 $M_\odot$ at the optically-thin limit, respectively. The C$^{18}$O emission shows a velocity gradient of 2 km s$^{-1}$ at the central 2000 AU of Source A, which could be interpreted as a Keplerian rotation with a central mass of a few $M_\odot$ or infall motion of gas. Further, the ALMA $^{12}$CO data reveal that Source A and Source B are associated with molecular outflows exhibiting maximum velocities of $\sim$30-70 km s$^{-1}$. The outflows have short dynamical timescales of $<$1000 yr and high mass outflow rates of $\sim10^{-4}$-$10^{-3}$ $M_\odot$ yr$^{-1}$. These observational signatures suggest an early evolutionary phase of the massive star formation in Source A and Source B.