ALMA view of the Galactic super star cluster RCW 38 at 270 au resolution

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 ${0{^{\prime \prime }_{.}}17}\times {0{^{\prime \prime }_{.}}15}$ (≃ 289 au × 255 au). The C¹⁸O image reveals 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, H₂ column densities of 10²³-10²⁴ cm^-2, and H₂ masses of 10-130 M_⊙. 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 C¹⁸O condensation, whereas no counterpart is seen for Source B. The masses of Source A and Source B are estimated as 13 and 3 M_⊙ at the optically thin limit, respectively. The C¹⁸O 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_⊙ or infall motion of gas. Further, the ALMA ¹²CO data reveal that Source A and Source B are associated with molecular outflows exhibiting maximum velocities of ~30-70 km s^-1. The outflows have short dynamical timescales of <1000 yr and high-mass outflow rates of ~10^-4-10^-3 M_⊙ yr^-1. These observational signatures suggest an early evolutionary phase of the massive star formation in Source A and Source B.