Ionization Structure in the 30 Doradus Nebula from WFPC-2 Imagery

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Session 82 -- HII Regions
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[82.01] Ionization Structure in the 30 Doradus Nebula from WFPC-2 Imagery

P.A. Scowen, J.J. Hester (ASU), J.S. Gallagher (U. Wisconsin), R. Lynds, E.J. O'Neil, Jr. (KPNO), G.E. Ballester, J.T. Clarke (U. Michigan), C.J. Burrows, J. Krist (STScI), S. Casertano, R.E. Griffiths (Johns Hopkins), D. Crisp, R.W. Evans, K.R. Stapelfeldt, J.T. Trauger (JPL), J.G. Hoessel (U. Wisconsin), J.A. Holtzman, A.M. Watson (Lowell), J.R. Mould (MSSSO), J.A. Westphal (Caltech)

Using the high resolution images taken of 30 Doradus by WFPC-2, we can resolve ionization structure down to scales around 8x10$^{16}$ cm, which is certainly larger than the [SII] PDR interface but should allow resolution of the boundary of the H ionized zone and where the [O~III] zone ends in relation to it (Hester 1991, PASP, 103, 853). At these scales we can compare the structure in 30 Doradus to the structure we observe in ordinary Galactic H~II regions where the incident ionization intensities are much lower. The ionizing flux in 30 Doradus is estimated to be about two orders of magnitude larger than that experienced by average H~II regions in our Galaxy, and it is this substantial difference that can cause a change in the traditional physics of the photodissociation region.

As part of the study we have identified a number of distinct objects positioned around the nebula of differing morphological type, exhibiting a range of ionization levels. Using this suite of data we perform a comparative analysis of the observable conditions at the photoionization boundary and attempt to evaluate the degree to which these interfaces are ionization bounded.

Since 30 Doradus is classified as a small superassociation, the physics we learn about in this object has implications for how other much larger objects ionize their environment. This will determine whether new considerations need to be made when studying superassociations, whether they should be viewed in terms of an ensemble of overlapping H~II regions or as a totally different class of ionized phenomena.

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