Are spiral galaxies optically thin or thick?

Xilouris, EM; Byun, YI; Kylafis, ND; Paleologou, EV; Papamastorakis, J

dc.contributor.author	Xilouris, EM	en
dc.contributor.author	Byun, YI	en
dc.contributor.author	Kylafis, ND	en
dc.contributor.author	Paleologou, EV	en
dc.contributor.author	Papamastorakis, J	en
dc.date.accessioned	2014-03-01T01:48:50Z
dc.date.available	2014-03-01T01:48:50Z
dc.date.issued	1999	en
dc.identifier.issn	0004-6361	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/25611
dc.subject	ISM : dust, extinction	en
dc.subject	galaxies : ISM	en
dc.subject	galaxies : photometry	en
dc.subject	galaxies : spiral	en
dc.subject.classification	Astronomy & Astrophysics	en
dc.subject.other	EDGE-ON GALAXIES	en
dc.subject.other	SURFACE-PHOTOMETRY	en
dc.subject.other	COLD DUST	en
dc.subject.other	PRODIGIOUS WARP	en
dc.subject.other	PISCES-PERSEUS	en
dc.subject.other	EXTINCTION	en
dc.subject.other	DISKS	en
dc.subject.other	NGC-5907	en
dc.subject.other	LIGHT	en
dc.subject.other	GAS	en
dc.title	Are spiral galaxies optically thin or thick?	en
heal.type	journalArticle	en
heal.language	English	en
heal.publicationDate	1999	en
heal.abstract	The opacity of spiral galaxies is examined by modelling the dust and stellar content of individual galaxies. The three dimensional model that we use assumes exponential distributions for the dust and the stars in the disk, while the R-1/4 law is used to describe the bulge. In this model, both absorption and scattering by the dust are taken into account. The model is applied to five late-type spiral galaxies (NGC 4013, IC 2531, UGC 1082, NGC 5529 and NGC 5907) using their optical land near infrared for IC 2531) surface photometry. For these galaxies we have determined the scalelengths and scaleheights of the stars and the dust in the disk, the bulge characteristics, the inclination angle and the face-on optical depth. Computation of the dust masses, as well as the extinction as a function of the wavelength, are also reported. Having analyzed a total of seven galaxies thus far, the five galaxies mentioned above plus UGC 2048 and NGC 891 presented in (Xilouris et al. 1997, 1998), we are able to draw some general conclusions, the most significant of which are: 1) The face-on central optical depth is less than one in all optical bands, indicating that typical spiral galaxies like the ones that we have modelled would be completely transparent if they were to be seen face-on. 2) The dust scaleheight is about half that of the stars, which means that the dust is more concentrated near the plane of the disk. 3) The dust scalelength is about 1.4 times larger than that of the stars and the dust is more radially extended than the stars. 4) The dust mass is found to be about an order of a magnitude more than previously measured using the IRAS fluxes, indicating the existence of a cold dust component. The gas-to-dust mass ratio calculated is close to the value derived for our Galaxy. 5) The derived extinction law matches quite well the Galactic extinction law, indicating a universal dust behaviour.	en
heal.publisher	SPRINGER VERLAG	en
heal.journalName	ASTRONOMY AND ASTROPHYSICS	en
dc.identifier.isi	ISI:000080027600020	en
dc.identifier.volume	344	en
dc.identifier.issue	3	en
dc.identifier.spage	868	en
dc.identifier.epage	878	en