Are galaxy discs optically thick?

Disney, Michael John, Davies, Jonathan Ivor and Phillipps, S. 1989. Are galaxy discs optically thick? Monthly Notices of the Royal Astronomical Society 239 (3) , pp. 939-976. 10.1093/mnras/239.3.939

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Abstract

We re-examine the classical optical evidence for the low optical depths traditionally assigned to spiral discs and argue that it is highly model-dependent and unconvincing. In particular, layered models with a physically thin but optically thick dust layer behave like optically thin discs. The opposite hypothesis, that such discs are optically thick is then examined in the light of modern evidence. We find it to be consistent with the near-infrared and IRAS observations, with the surface brightnesses, with the H I and CO column densities and with the Hα measurements. Ordinary disc galaxies may be shielded by up to two magnitudes of total extinction in the blue and so, in extreme cases, have bolometric luminosities as high as 1012L⊙. Stirring upward of the dust in such luminous galaxies to screen more of the stars could account for the most extreme IRAS galaxies without assuming massive bursts of star formation which, we argue, could in any case never be concealed from optical view without significant extinction outside the giant molecular clouds. We point briefly to the implications of dusty discs for general issues like the obscuration of background QSOs and implied mass-to-light ratios.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Uncontrolled Keywords:	optical thickness, spiral galaxies, astronomical models, brightness distribution, gas density, infrared astronomy satellite, mass to light ratios, surface properties
Publisher:	Wiley
ISSN:	0035-8711
Last Modified:	07 Aug 2024 11:08
URI:	https://orca.cardiff.ac.uk/id/eprint/39199

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