We report maps of the 158 microns [C II] fine-structure line, the 63 microns and 146 microns [O I] fine-structure lines, the 2.2 microns H I Brγ line, the 2.1 microns H2 1-0 S(1) ro-vibrational line, and the 2.6 mm CO (1-0) rotational line toward the 30 Doradus complex in the Large Magellanic Cloud. Comparing our Brγ map with Hα and Hβ measurements, we find that visual to near-infrared extinction and reddening follow the standard dust extinction law and that the Brγ extinction is small, which allows for a reliable determination of the Lyman-continuum intensity. The Lyman continuum as derived from the Brγ emission and the far-UV derived from the far-infrared continuum match the average spectrum of the exciting stars in the 30 Doradus cluster. The observed H₂line intensity may be produced in dense clumps exposed to the stellar radiation fields. The maps of all tracers emphasize a shell-like structure of the 30 Doradus region, which is seen approximately edge-on. The warm molecular gas traced by the H2 line and the ionized gas traced by the Brγ line are intermixed, while the cold molecular gas as traced by CO (1-0) and the photodissociated gas as traced by [C ii] are coextensive over tens of parsecs. This distribution can be explained only by a highly fragmented structure of the interstellar medium that allows UV radiation to penetrate deep into the molecular cloud. Clumpiness is also the key to understanding the extremely high [C II]/CO line intensity ratio. Depending on cloud geometry and physical conditions, the relative beam-filling factors of the partly atomic, partly molecular photodissociated gas as seen in the FIR tracers, and of the purely molecular gas traced by CO, can differ substantially in a clumpy, low-metallicity environment. This effect also leads to a greatly increased H2/CO conversion factor because a major part of the H2 molecular gas may be contained in the photodissociation region where CO has been destroyed.
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Poglitsch et al. (1995) studied this question.