Graduate Student Yingjie Cheng: Quantifying starburst feedback via X-ray spectroscopy of 30 Doradus

X-ray observations provide a potentially powerful tool to study the starburst feedback and its impact on the surrounding medium. So far, the analysis and interpretation of such observations remain challenging, due to various complications including the non-isothermality of the X-ray-emitting hot plasma, and the inhomogeneity of the foreground absorption. To illustrate such complications and mitigate their effects, we present a spatially resolved X-ray spectroscopic study of 30 Doradus in the Large Magellanic Cloud (LMC), based on a 100 ks Suzaku
observation. The high sensitivity and spectral resolution of this observation, together with the proximity of this starburst region, enable us to measure the thermal and chemical properties of the diffuse hot plasma, and to quantitatively confront them with the feedback expected from embedded massive stars. Spectral analysis shows that the plasma temperature varies spatially in the range of 2.5x10^6 K, indicating that it is significantly non-isothermal. We thus characterize the temperature distribution of the plasma emission measure with a log-normal model, which improves the fits to the data. The metal abundances of the plasma are typically 1-2 times higher than the average values of the host galaxy, and the total mass of the plasma is derived as 1-2x10^4 Msun From these estimates, the total metal enrichment is consistent with the expected ejection from the central stellar cluster with two age components of 2 Myr and 4 Myr and that ~62% of the plasma is mass-loaded from the ambient medium. We further conclude that our spatially resolved measurements can be reasonably well reproduced by a global modeling of 30 Doradus with a log-normal temperature distribution and log-normal differential foreground absorption. This log-normal distribution model may be suitable for the X-ray spectral modeling of other giant HII regions, especially for which spatially resolved spectroscopy is not practical. Finally, our spectral analysis shows tentative evidence for a diffuse
non-thermal X-ray component, which most likely arises from inverse Compton scattering of strong radiation in the nebula.