Gas and dust in the Magellanic Clouds

Ananta C. Pradhan*
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India

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The far-ultraviolet (FUV) di use emission is predominantly due to scattering of starlight from interstellar dust grains which shows a large regional variation depending on the relative orientations of dust and stars. The observations of the FUV (1000 – 1150 Å) diffuse radiation in the Magellanic Clouds (MCs) using serendipitous observations made with the Far Ultraviolet Spectroscopic Explorer (FUSE) are presented. The estimated contribution of FUV diffuse radiation to the total integrated FUV emission in the MCs is found to be typically 5% – 20% in the Large Magellanic Cloud (LMC) and 34% – 44% in the Small Magellanic Cloud (SMC) at the FUSE bands (λ = 905 – 1187 Å) and it increases substantially towards the longer wavelength (e.g., 63% for the SMC at 1615 Å). The less scattering of light in the FUV at the shorter wavelength than at the longer wavelength indicates that much of the stellar radiation at the shorter wavelength is going into heating the interstellar dust.

Five times ionized oxygen atom (O VI) is a tracer of hot gas (T ~ 3×105 K) in the interstellar medium (ISM). A wide survey of O VI column density measurements for the LMC is presented using the high resolution FUSE spectra. The column density varies from a minimum of log N(O VI) = 13.72 atoms cm-2 to a maximum of log N(O VI) = 14.57 atoms cm-2. A high abundance of O VI is observed in both active (superbubbles) and inactive regions of the LMC.

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Keywords : ISM: abundances – (ISM:) dust, extinction – ultraviolet: ISM – (galaxies:) Magellanic Clouds