Looking for evidence of high-mass star formation at core scale in a massive molecular clump

Abstract

We present a comprehensive physical and chemical study of the fragmentation and star formation activity towards the massive clump AGAL G338.9188+0.5494 harbouring the extended green object EGO 338.92+0.55(b). The presence of an EGO embedded in a massive clump, suggests, at clump scale, that high-mass star formation is occurring. The main goal of this work is to find evidence of such high-mass star formation, but at core scale. Using mm observations of continuum and lines obtained from the ALMA database at Bands 6 and 7, we study the substructure of the massive clump. The angular resolution of the data is about 0.5'', which allow us to resolve structures of about 0.01pc ($\sim$ 2000 au) at the distance of 4.4 kpc. The continuum emission at 340 GHz reveals that the molecular clump is fragmented in five cores, labeled from C1 to C5. The $^{12}$CO J=3--2 emission shows the presence of molecular outflows related to three of them. The analysis of the CH$_3$CN and CH$_3$CCH emissions suggests temperatures of about 340 and 72~K, respectively, for C1, showing that the methyl cyanide would trace a gas layer closer to the protostar than the methyl acetylene. The obtained mass of core C1 ranges from 3 to 10 M$_{\odot}$. We found that the discovered molecular outflow arising from core C1 should be the main responsible for the 4.5 $\mu$m extended emission. The average mass and energy of such a molecular outflow is about 0.5 M$_{\odot}$~and $10^{46}$~erg, respectively, which suggest that 10 M$_{\odot}$ is the most likely mass value for core C1. Additionally we found that the region is chemically very rich with several complex molecular species. Particularly, from the analysis of the CN emission we found strong evidence that such a radical is indirectly tracing the molecular outflows, more precisely the border of the cavity walls carved out by such outflows.Comment: Accepted for publication in A&A (July 5, 2023