The Sagittarius C Complex in the Mid-Infrared with SOFIA/FORCAST

TL;DR

This study uses high-resolution mid-infrared data from SOFIA/FORCAST to analyze the Sagittarius C Complex, revealing dust properties, potential electron acceleration mechanisms, and the influence of massive stars in the region.

Contribution

It provides the first detailed dust temperature and optical depth analysis of Sgr C at 25 and 37 μm, and explores the role of a Wolf-Rayet star in electron acceleration and heating.

Findings

Sgr C HII region has an average dust temperature of 61 K.

High-density dust ridges may host relativistic electrons due to shock acceleration.

Unidentified massive stars likely contribute to the HII region's luminosity.

Abstract

We present an analysis of high-resolution mid-infrared observations at 25 and 37 $\mu m$ of the Sagittarius C Complex (Sgr C) in the Central Molecular Zone (CMZ), based on data from the SOFIA/FORCAST Galactic Center Legacy Survey. Enabled by the high bright-source limit of the FORCAST instrument, we perform a map-level dust temperature and optical depth analysis with a focus on the Sgr C HII region, which has an average dust temperature of 61 K and an average 37 $\mu m$ optical depth of 0.05. We find that the Sgr C HII region contains several high-density dust emission ridges, with lengths of up to several parsecs. Noting prior evidence for nonthermal radio emission from these density ridges, we postulate that there is an enhancement of relativistic electrons within them, possibly attributable to diffusive shock acceleration induced by the wind of a known nearby Wolf-Rayet (WR) star impacting the density ridges and the ambient gas in the surrounding photo-dissociation region. Additionally, the tangential magnetic field in the outskirts of the Sgr C HII region may serve to confine the electrons within this region. We examined the heating effect of the WR star by calculating its heating profile and performing a spectral energy distribution modelling of the HII region. We found an integrated MIR luminosity of $(1.40\pm0.19)\times10^{6} L_\odot$, which implies that presently unidentified massive stars must be present in the HII region in addition to the WR star. We also present a brief analysis of adjacent regions, such as a mid-infrared/radio source denoted "Source C" and the G359.43+0.02 young stellar object cluster near the northern end of the prominent Sgr C non-thermal filament (NTF).