Massive Protostars in a Protocluster -- A Multi-Scale ALMA View of G35.20-0.74N

TL;DR

This study uses high-resolution ALMA observations to reveal the complex structure, kinematics, and star formation activity within the massive protocluster G35.20-0.74N, including multiple young stars, disks, and outflows.

Contribution

It provides the first detailed multi-scale ALMA view of G35.20-0.74N, identifying multiple protostars, disks, and outflows, and suggests dynamical interactions and mass segregation in the cluster.

Findings

Detection of 22 compact sources with associated ionized regions.

Identification of spiral structures in the disks via SO2 emission.

Observation of complex outflow structures and potential disk disruption.

Abstract

We present a detailed study of the massive star-forming region G35.2-0.74N with ALMA 1.3 mm multi-configuration observations. At 0.2" (440 au) resolution, the continuum emission reveals several dense cores along a filamentary structure, consistent with previous ALMA 0.85 mm observations. At 0.03" (66 au) resolution, we detect 22 compact sources, most of which are associated with the filament. Four of the sources are associated with compact centimeter continuum emission, and two of these are associated with H30{\alpha} recombination line emission. The H30{\alpha} line kinematics show ordered motion of the ionized gas, consistent with disk rotation and/or outflow expansion. We construct models of photoionized regions to simultaneously fit the multi-wavelength free-free fluxes and the H30{\alpha} total fluxes. The derived properties suggest the presence of at least three massive young stars with nascent hypercompact Hii regions. Two of these ionized regions are surrounded by a large rotating structure that feeds two individual disks, revealed by dense gas tracers, such as SO2, H2CO, and CH3OH. In particular, the SO2 emission highlights two spiral structures in one of the disks and probes the faster-rotating inner disks. The 12CO emission from the general region reveals a complex outflow structure, with at least four outflows identified. The remaining 18 compact sources are expected to be associated with lower-mass protostars forming in the vicinity of the massive stars. We find potential evidence for disk disruption due to dynamical interactions in the inner region of this protocluster. The spatial distribution of the sources suggests a smooth overall radial density gradient without subclustering, but with tentative evidence of primordial mass segregation.