Fragmentation and dynamics of dense gas structures in the proximity of massive young stellar object W42-MME

Abstract

We present an analysis of the dense gas structures in the immediate surroundings of the massive young stellar object (MYSO) W42-MME, using the high-resolution (0${}^{\prime \prime }$.31$\times$0${}^{\prime \prime }$.25) ALMA dust continuum and molecular line data. We performed a dendrogram analysis of H${}^{13}$CO${}^{+}$ (4-3) line data to study multi-scale structures and their spatio-kinematic properties, and analyzed the fragmentation and dynamics of dense structures down to $\sim$2000 AU scale. Our results reveal 19 dense gas structures, out of which 12 are leaves and 7 are branches in dendrogram terminology. These structures exhibit transonic-supersonic gas motions (1$<\mathcal{M}<5$) with overvirial states (${\alpha }_{\mathrm{vir}}\ge 2$). The non-thermal velocity dispersion-size relation (${\sigma }_{\mathrm{nt}}-L$) of dendrogram structures shows a weak negative correlation, while the velocity dispersion across the sky ($\delta V_{\mathrm{lsr}}$) correlates positively with structure size ($L$). Velocity structure function ($S_2(l{)}^{1/2}$) analysis of H${}^{13}$CO${}^{+}$ data reveals strong power-law dependencies with lag ($l$) up to a scale length of $\lesssim$ 6000 AU. The mass-size ($M-R$) relation of dendrogram structures shows a positive correlation with power-law index of 1.73$\pm$0.23, and the leaf L17 hosting W42-MME meets the mass-size conditions for massive star formation. Blue asymmetry is observed in the H${}^{12}$CO${}^{+}$ (4-3) line profiles of most of the leaves, indicating infall. Overall, our results observationally support the hierarchical and chaotic collapse scenario in the proximity of the MYSO W42-MME.

16 pages, 13 figures, 1 Table, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS) Journal