ngVLA Synthetic Observations of Ionized Gas in Massive Protostars

TL;DR

This paper demonstrates that the ngVLA will enable high-resolution observations of ionized gas in massive protostars, allowing detailed study of jets and disks at various distances, significantly advancing understanding of massive star formation.

Contribution

It presents synthetic ngVLA observations of ionized jets and disks around massive protostars, showing the array's capability to resolve structures down to a few astronomical units.

Findings

ngVLA can resolve ionized jets from 15 M_sun protostars at 700 pc

It can distinguish between jets and winds and measure their substructure

Detailed studies of disks around massive protostars up to 12 kpc are feasible

Abstract

Massive star formation involves significant ionization in the innermost regions near the central object, such as gravitationally trapped H II regions, jets, ionized disks, or winds. Resolved observations of the associated continuum and recombination line emission are crucial for guiding theory. The next-generation Very Large Array (ngVLA) will enable unprecedented observations of thermal emission with 1 mas resolution, providing a new perspective on massive star formation at scales down to a few astronomical units at kiloparsec distances. This work presents synthetic interferometric ngVLA observations of the free-free continuum (93-GHz band), $\mathrm{H41\alpha}$, and $\mathrm{H38\alpha}$ recombination lines from ionized jets and disks around massive protostars. Using the sf3dmodels Python package, we generate gas distributions based on analytical models, which are then processed through the RADMC-3D radiative transfer code. Our results indicate that the ngVLA can easily resolve, both spatially and spectrally, the ionized jet from a 15 $\mathrm{M_\odot}$ protostar at 700 pc, distinguishing between collimated jets and wide-angle winds, and resolving their launching radii, widths, and any substructure down to a few astronomical units. Detailed studies of radio jets launched by massive protostars will be feasible up to distances of $\sim 2$ kpc. Furthermore, ngVLA will be able to study in detail the ionized disks around massive ($> 10~\mathrm{M_\odot}$) protostars up to distances from 4 to 12 kpc, resolving their kinematics and enabling the measurement of their central masses across the Galaxy. These observations can be conducted with on-source integrations of only a few hours.