Dusty Cradles in a Turbulent Nursery: The Sgr A East HII Region Complex at the Galactic Center

TL;DR

This study uses multi-wavelength infrared imaging to analyze dust and star formation in the Sgr A East HII region complex near the Galactic Center, revealing detailed dust properties and identifying heating sources.

Contribution

It provides the first detailed infrared imaging and dust modeling of the complex, identifying heating sources and dust characteristics with new spatial and spectral analysis.

Findings

Regions A-D show distinct dust temperatures and compositions.

Presence of very small grains and PAHs in multiple regions.

Heating sources are identified, with some stars not being the actual ionizing sources.

Abstract

We present imaging at 19, 25, 31, and 37 {\mu}m of the compact HII region complex G-0.02-0.07 located 6 pc in projection from the center of the Galaxy obtained with SOFIA using FORCAST. G-0.02-0.07 contains three compact HII regions (A, B, and C) and one ultra-compact HII region (D). Our observations reveal the presence of two faint, infrared sources located 23'' and 35'' to the east of region C (FIRS 1 and 2) and detect dust emission in two of the three "ridges" of ionized gas west of region A. The 19/37 color temperature and 37 {\mu}m optical depth maps of regions A - C are used to characterize the dust energetics and morphology. Regions A and B exhibit average 19/37 color temperatures of ~105 K, and regions C and D exhibit color temperatures of ~115 K and ~130 K, respectively. Using the DustEM code we model the SEDs of regions A - D and FIRS 1, all of which require populations of very small, transiently heated grains and large, equilibrium-heated grains. We also require the presence of polycyclic aromatic hydrocarbons (PAHs) in regions A - C in order to fit the 3.6, 4.5, 5.8, and 8.0 {\mu}m fluxes observed by Spitzer/IRAC. The location of the heating source for region A is determined by triangulation from distances and temperatures derived from DustEM models fit to SEDs of three different points around the region, and is found to be displaced to the northeast of the center of curvature near the color temperature peak. Based on total luminosity, expected 1.90 {\mu}m fluxes, and proximity to the mid-IR color temperature peaks we identify heating source candidates for regions A, B, and C. However, for region D, the observed fluxes at 1.87 and 1.90 {\mu}m of the previously proposed ionizing star are a factor of ~40 times too bright to be the heating source and hence is likely just a star lying along the line of sight towards region D.