Gas and Dust in the Magellanic Clouds

TL;DR

This paper investigates the far-ultraviolet diffuse emission and hot gas in the Magellanic Clouds, revealing regional variations in dust scattering and O VI ion presence, with implications for interstellar medium heating and structure.

Contribution

It provides new measurements of FUV diffuse radiation and O VI column densities in the Magellanic Clouds, highlighting regional differences and the role of dust and hot gas in the ISM.

Findings

FUV diffuse emission accounts for 5-20% in LMC and 34-44% in SMC of total FUV emission.

FUV scattering increases with wavelength, indicating dust heating at shorter wavelengths.

O VI column density varies significantly, present in both active and inactive regions.

Abstract

The far-ultraviolet (FUV) diffuse 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 \AA) diffuse radiation in the Magellanic Clouds (MCs) using serendipitous observations made with the Far Ultraviolet {\em 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 {\em FUSE} bands ($\lambda$ = 905 -- 1187 \AA) and it increases substantially towards the longer wavelength (e.g., 63% for the SMC at 1615 \AA). 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 {\small VI}) is a tracer of hot gas (T $\sim 3\times 10^{5}$ K) in the interstellar medium (ISM). A wide survey of O {\small VI} column density measurements for the LMC is presented using the high resolution {\em FUSE} spectra. The column density varies from a minimum of log N(O {\small VI}) = 13.72 atoms cm$^{-2}$ to a maximum of log N(O {\small VI}) = 14.57 atoms cm$^{-2}$. A high abundance of O {\small VI} is observed in both active (superbubbles) and inactive regions of the LMC.