Abstract
We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40$\alpha$, H42$\alpha$, and H50$\beta$ emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562$-$3959. The HRLs exhibit Voigt profiles, a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need a high-velocity component. The Lorentzian line wings imply electron densities of $5\times10^7$ cm$^{-3}$ on average. In addition, we detect SO and SO$_2$ emission arising from a compact ($\sim3000$ AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.
Highlights
Stars of all masses form by gravitational collapse within unstable regions of molecular clouds
We focus on results derived from the continuum, hydrogen recombination lines (HRLs), and sulfuretted molecular lines, and leave the analysis of other observed molecular tracers (e.g., SiO, CH3OH, and C2H) for upcoming publications
We detect spatially unresolved emission in the H40α, H42α, and H50β HRLs toward the collimated ionized wind source associated with G345.49+1.47
Summary
Stars of all masses form by gravitational collapse within unstable regions of molecular clouds. Low-mass star formation is characterized by the following interrelated phenomena: an infalling envelope, an accretion disk, and a highly collimated jet (Shu et al 1987; Li et al 2014). High-mass stars (M > 8 M ) form by accretion within massive (∼103 M ) and dense (104−5 cm−3) molecular clumps, with typical diameters of 1 pc and generally supported by turbulent motions (Garay 2005; Zinnecker & Yorke 2007; Tan et al 2014). These clumps harbor the luminous, embedded infrared sources known as high-mass young stellar objects (HMYSOs), which represent an early evolutionary stage of a single, high-mass star or a multiple stellar system. The following phenomena—analogous to the ones observed in low-mass star formation—are detected
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