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Astron. Astrophys. 320, L21-L24 (1997)

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Letter to the Editor

The shape of galaxy disks: how the scale height increases with galactocentric distance *

R. de Grijs and R.F. Peletier

Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 5 November 1996 / Accepted 21 January 1997


We present the results of a detailed study of vertical surface brightness profiles of edge-on disk galaxies. Although the exponential disk scale height is constant to first order approximation, we show that for the large majority of galaxies in our sample, the scale height increases with distance along the major axis. The effect is strongest for early-type galaxies, where the increase of the scale height can be as much as a factor of 1.5 per scalelength, but is almost 0 for the latest-type galaxies. The effect can be understood if early-type disk galaxies have thick disks with both scale lengths and scale heights larger than those of the dominant disk component. Its origin appears to be linked to the processes that have formed the thick disk.

Key words: galaxies: fundamental parameters – - galaxies: photometry – - galaxies: spiral – - galaxies: statistics – - galaxies: structure

* Based on observations obtained at the European Southern Observatory, La Silla, Chile

Send offprint requests to: R. de Grijs

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998