The Galactic Halo Ionising Field

Publications of the Astronomical Society of Australia

J. Bland-Hawthorn¹ 

[1] P. R. Maloney

关键词: interstellar medium;    intergalactic medium;    individual object: Magellanic Stream;    Galaxy: corona;    halo;    interferometry;   

DOI  :  10.1071/AS97059

学科分类：天文学(综合)

来源: CSIRO

【 摘 要 】

There has been much debate in recent decades as to what fraction of ionising photons from star-forming regions in the Galactic disk escape into the halo. The recent detection of the Magellanic Stream in optical line emission at the CTIO 4 m and the AAT 3·9 m telescopes may now provide the strongest evidence that at least some of the radiation escapes the disk completely. We present a simple model to demonstrate that, while the distance to the Magellanic Stream is uncertain, the observed emission measures (εm ≈ 0·5 – 1 cm−6 pc) are most plausibly explained by photoionisation due to hot, young stars. This model requires that the mean Lyman-limit opacity perpendicular to the disk is τLL ≈ 3, and the covering fraction of the resolved clouds is close to unity. Alternative sources (e.g. shock, halo, LMC or metagalactic radiation) contribute negligible ionising flux.

【 授权许可】

Unknown