CII fine-structure line observations of the Sagittarius C Region in the Galaxy's Central Molecular Zone

TL;DR

This study maps and analyzes the [CII] 158 micron emission in the Sagittarius C region of the Galactic Center, revealing complex gas dynamics, an expanding shell likely driven by a supernova, and triggered star formation.

Contribution

It provides the first detailed spatial and velocity-resolved [CII] observations of Sgr C, identifying an expanding shell and its potential role in star formation.

Findings

[CII] emission shows complex morphology and widespread distribution.

An expanding shell with a velocity of 23 km/s and age of 0.13 Myr was identified.

The shell's expansion may be driven by a buried supernova, triggering star formation.

Abstract

Context. Sagittarius C (Sgr C) is a massive, relatively quiescent complex at the western edge of the Galaxy's Central Molecular Zone (CMZ). While the Sgr B2 region has been extensively studied, Sgr C has received comparatively less attention. Aims. We aim to characterize the kinematics and physical state of the gas in Sgr C using spatially and velocity-resolved [CII] 158 microns emission. This line traces the multi-phase interstellar medium, providing a crucial complement to molecular, infrared, and radio observations. Methods. We present a fully sampled 74x47 pc map of the [CII] line toward Sgr C, observed with SOFIA. The data feature a 0.55 pc spatial and 1 km/s spectral resolution. These observations are analyzed in conjunction with ancillary maps of the CO(2-1) transition and its isotopologues from the APEX telescope. Results. [CII] emission is widespread, showing a continuous structure extending from Sgr A to Sgr C with complex morphology. The bulk emission arises at negative radial velocities, consistent with Galactic rotation. The most prominent feature is the giant Sgr C HII region, where [CII] reveals an expanding, ring-like shell interpreted as a photo-dissociation region (PDR). Kinematic modelling yields an expansion velocity of 23 km/s and a dynamical age of about 0.13 Myr. Our analysis suggests that stellar winds from known massive stars are insufficient to power the observed expansion, pointing toward alternative drivers like a buried supernova. Finally, we find a striking spatial association between this shell and a non-thermal radio filament, indicating that the shell's expansion has triggered high-mass star formation at its edge.