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

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 $0^{\prime \prime }.17\times 0^{\prime \prime }.15$ ($\simeq 289\mathrm{AU}\times 255\mathrm{AU}$). 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 $\sim 10^{-4}$-$10^{-3}$ $M_{\odot }$ yr${}^{-1}$. These observational signatures suggest an early evolutionary phase of the massive star formation in Source A and Source B.

28 pages, 7 figures, 6 tables, accepted for publication in PASJ

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Cited by in corpus (3)

• An ALMA study of the massive molecular clump N159W-North in the Large Magellanic Cloud: A possible gas flow penetrating one of the most massive protocluster systems in the Local Group
• Observations of the [CI] (${}^3{P}_1$-${}^3{P}_0$) emission toward the massive star-forming region RCW38: further evidence for highly-clumped density distribution of the molecular gas
• A Low Frequency Pilot Survey of Southern HII Regions in the Vela Constellation