Ionized Gas Kinematics and Morphology in Sgr B2 Main on 1000 AU Scales

TL;DR

This study uses high-resolution radio observations to analyze the ionized gas dynamics and morphology in Sgr B2 Main, revealing complex kinematic behaviors and the influence of pressure broadening and gas motions in ultracompact HII regions.

Contribution

First detailed high-resolution imaging of ionized gas in Sgr B2 Main at 1000 AU scales, combining multiple radio recombination lines to analyze broadening mechanisms.

Findings

Detection of H52α emission in 12 UC and HC HII regions.

Identification of pressure broadening and gas motions as contributors to line widths.

Evidence of complex gas kinematics including turbulence, accretion, or outflows.

Abstract

We have imaged the Sgr B2 Main region with the Very Large Array in the BnA configuration ($\theta_{beam}$ = 0\farcs13) in both the H52$\alpha$ (45.453 GHz) radio recombination line (RRL) and 7 mm continuum emission. At a distance of 8500 pc, this spatial resolution corresponds to a physical scale of 0.005 pc ($\sim$1100 AU). The current observations detect H52$\alpha$ emission in 12 individual ultracompact (UC) and hypercompact (HC) HII regions. Two of the sources with detected H52 $\alpha$ emission have broad ($\Delta$V$_{FWHM}\sim$50 \kms) recombination lines, and two of the sources show lines with peaks at more than one velocity. We use line parameters from the H52$\alpha$ lines and our previous H66$\alpha$ line observations to determine the relative contribution of thermal, pressure and kinematic broadening, and electron density. These new observations suggest that pressure broadening can account for the broad lines in some of the sources, but that gas motions (e.g. turbulence, accretion or outflow) contribute significantly to the broad lines in at least one of the sources (Sgr B2 F3).