The average optical depth of disc galaxies

Trewella, M., Davies, Jonathan Ivor, Disney, Michael John and Jones, H. G. W. 1997. The average optical depth of disc galaxies. Monthly Notices of the Royal Astronomical Society 288 (2) , pp. 397-403.

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Abstract

The average optical depth of disc galaxies is calculated assuming that their infrared output originates from the dust reprocessing of stellar light. Essentially, the luminosity functions at both optical (B-band) and FIR (IRAS) wavelengths are integrated to give a local luminosity density in the optical and FIR. This method was first proposed by Saunders et al., who found a B-band optical depth of tau_B=0.26. In this paper we reconsider the method and employ more realistic models. We conclude that on average a B-band photon originates from a region with an optical depth of tau_B~0.9, a value that indicates that galaxies have high rather than low optical depths. Adjusting the FIR luminosity for flux at wavelengths longer than those detected by IRAS could increase this value further (to tau_B>1). Interpreting this, a galaxy with the dust distributed in a similar manner to the stars would have a central face-on optical depth of tau_B>2.5, and this `typical' galaxy would become optically thin at ~1 scalelength from the centre.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Uncontrolled Keywords:	Dust, extinction, galaxies: ISM, infrared: galaxies
Publisher:	Wiley-Blackwell
ISSN:	0035-8711
Last Modified:	04 Jun 2017 04:24
URI:	https://orca.cardiff.ac.uk/id/eprint/38499

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