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Colloquium Details
Date and time: Thursday, September 10, 2009 at 4:10 PM
Location: 807 Dennison
Speaker: Eric Pellegrini from University of Michigan
Title/topic: 30 Doradus: Deconstructing the Structure and Physical Processes of a GEHIIR
Abstract:
We have completed of a new optical imaging and spectrophotometric survey region of 30 Doradus centered on R136 that covers key diagnostic emission lines. Using photoionization models, we focus on the physical conditions, geometry and equation of state on a point by point basis to test some of the simplifying assumptions that are necessary to model and interpret distant sites of star formation. The observed survey is a compromise between spatial density of the grid and areal coverage. While stellar winds and supernovae undoubtedly produce shocks, we find no spectral signature to indicate shocks are currently important for driving the large scale structure. We conclude that the considerable region covered by our survey is well described by photoionization from the central cluster where the ionizing continuum is dominated by the most massive O stars. The completeness of our survey allows us to create a composite spectrum of 30 Doradus, simulating the observable spectrum of a spatially unresolved, distant HII region. Using this spatially integrated spectrum we confront various strong line abundance techniques, which are typically applied to an entire HII region or galaxy, against abundance estimates using spatially resolved observations of 30 Doradus. We find that despite averaging over more than an order of magnitude in ionization parameter and density, the abundances estimated using the diagnostic lines of the composite spectrum are in agreement with spatially resolved abundance studies.
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