Probing The Extreme Environment Of The Galactic Center With Sofia/Forcast

Lau, Ryan

Probing The Extreme Environment Of The Galactic Center With Sofia/Forcast

Abstract

Within the inner 100 pc of the Milky Way Galaxy lies the supermassive black hole, Sgr A*, regions of recent star formation, and 3 young, massive stellar clusters: the Central, Quintuplet, and Arches clusters. In this thesis I will present images of the Circumnuclear Ring, the twin Luminous Blue Variable nebulae in and near the Quintuplet Cluster, and the Sgr A East HII Region Complex taken by the Faint Objected Infrared Camera for the SOFIA Telescope (FORCAST). The Circumnuclear Ring (CNR) is the inner edge of the molecular torus orbiting Sgr A* with a radius of 1.4 pc. The CNR exhibits features of a classic H II region and appears consistent with the prevailing paradigm in which the dust is heated by the Central cluster of hot, young stars. We find that clumps within the ring are not dense enough to be stable against tidal shear from Sgr A* and will be sheared out before completing a full orbit (~ 105 yrs). Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet Cluster 40 pc in projection from Sgr A*: qF362, the Pistol star, G0.120-0.048 (LBV3). Our images reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding LBV3. However, no detection of hot dust associated with qF362 is made. We argue that the Pistol star and LBV3 are identical "twins" that exhibit contrasting nebulae due to the external influence of their different environments. G-0.02-0.07, a complex consisting of three compact HII regions (A, B, and C) and one ultracompact HII region (D), is located at the edge of a molecular cloud 6 pc in projection to the east of Sgr A* and contains the most recent episode of star formation in the inner 10 pc of the Galactic center ( 105 yrs). We probe the dust morphology, energetics, and composition of the regions to study the young stellar objects and the surrounding dense molecular cloud. The location of the heating source for region A is determined by triangulation from distances and temperatures derived from fits to spectral energy distributions 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 luminosities, expected 1.90 [MICRO SIGN]m fluxes, and proximity to the mid-IR color temperature peaks we identify heating source candidates for regions A, B, and C. We present imaging at 19, 25, 31, and 37 [MICRO SIGN]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 [MICRO SIGN]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 [MICRO SIGN]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 [MICRO SIGN]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 [MICRO SIGN]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. iii

Date Issued

2014-08-18

Keywords

Astronomy; Astrophysics; Galactic Center

Committee Chair

Herter, Terry Lee

Committee Member

Flanagan, Eanna E
Chernoff, David Fisher
Stacey, Gordon John

Degree Discipline

Astronomy

Degree Name

Ph. D., Astronomy

Degree Level

Doctor of Philosophy

Types

dissertation or thesis