SOFIA/FORCAST Imaging of the Circumnuclear Ring at the Galactic Center

TL;DR

This study provides detailed infrared imaging of the Galactic Center's circumnuclear ring, revealing its structure, temperature gradient, and dense clumps, enhancing understanding of the region's dust and gas dynamics.

Contribution

First high-resolution infrared images of the CNR at multiple wavelengths, with detailed analysis of its structure, temperature distribution, and clump properties.

Findings

CNR exhibits a radial temperature gradient from 65-85 K.

Clumps are dense but likely transient due to tidal shear.

Infrared emission closely traces ionized and PDR regions.

Abstract

We present 19.7, 31.5, and 37.1 {\mu}m images of the inner 6 pc of the Galactic Center of the Milky Way with a spatial resolution of 3.2 - 4.6'' taken by the Faint Object Infrared Camera on the Stratospheric Observatory for Infrared Astronomy (SOFIA). The images reveal in detail the "clumpy" structure of the Circumnuclear Ring (CNR)--the torus of hot gas and dust orbiting the supermassive black hole at the Galactic Center with an inner radius of 1.4 pc. The CNR exhibits features of a classic HII region: the dust emission at 19.7 {\mu}m closely traces the ionized gas emission observed in the radio while the 31.5 and 37.1 {\mu}m emission traces the photo-dissociation region beyond the ionized gas. The 19.7/37.1 color temperature map reveals a radial temperature gradient across the CNR with temperatures ranging from 65-85 K, consistent with the prevailing paradigm in which the dust is centrally heated by the inner cluster of hot, young stars. We produce a 37.1 {\mu}m intensity model of the CNR with the derived geometric properties and find that it is consistent with the observed 37.1 {\mu}m map of the CNR. Dense ($5 to 9 \times 10^{4} \, \mathrm{cm}^{-3}$) clumps with a FWHM of ~0.15 pc exist along the inner edge of the CNR and shadow the material deeper into the ring. The clumps are unlikely to be long-lived structures since they are not dense enough to be stable against tidal shear from the supermassive black hole.