Widely Extended [O III] 88µm Line Emission around the 30 Doradus Region Revealed with AKARI FIS-FTS

Abstract

We present a distribution map of the far-infrared [O II] 88 μm line emission around the 30 Doradus (30 Dor) region in the Large Magellanic Cloud obtained with the Fourier Transform Spectrometer of the Far-Infrared Surveyor on board AKARI. The map reveals that the [O III] emission is widely distributed by more than 10' around the super star cluster R 136, implying that the 30 Dor region is affluent with interstellar radiation field that is hard enough to ionize O²⁺. The observed [O III] line intensities are as high as (1-2) × 10^-6 W m^-2 sr^-1 on the peripheral regions 4'-5' away from the center of 30 Dor, which requires gas densities of 60-100 cm^-3. However, the observed size of the distribution of the [O III] emission is too large to be explained by massive stars in the 30 Dor region enshrouded by clouds with a constant gas density of 10² cm^-3. Therefore, the surrounding structure is likely to be highly clumpy. We also find a global correlation between the [O III] and the far-infrared continuum emission, suggesting that the gas and dust are well mixed in the highly ionized region where the dust survives in clumpy dense clouds shielded from energetic photons.