Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...454..293p&link_type=abstract
Astrophysical Journal v.454, p.293
Astronomy and Astrophysics
Astronomy
76
Ism: Dust, Extinction, Ism: Clouds, Ism: Structure, Ism: Individual Name: 30 Doradus, Galaxies: Magellanic Clouds, Infrared: Ism: Lines And Bands
Scientific paper
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 H_{2 }line 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.
Geis Norbert
Johansson Lars E. B.
Krabbe Alfred
Madden Suzanne C.
Nikola Thomas
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