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Astron. Astrophys. 327, 966-982 (1997)

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The z -structure of disk galaxies towards the galaxy planes *

R. de Grijs , R.F. Peletier ** and P.C. van der Kruit

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

Received 27 May 1997 / Accepted 21 July 1997


We present a detailed study of a statistically complete sample of highly inclined disk galaxies in the near-infrared [FORMULA] band. Since the [FORMULA] -band light is relatively insensitive to contamination by galactic dust, we have been able to follow the vertical light distributions all the way down to the galaxy planes.

The mean levels for the sharpness of the [FORMULA] -band luminosity peaks indicate that the vertical luminosity distributions are more peaked than expected for the intermediate sech(z ) distribution, but rounder than exponential. After fitting a generalized family of fitting functions characterised by an exponent 2/n ([FORMULA] for exponential, [FORMULA] for sech and [FORMULA] for sech2; van der Kruit 1988) we find that the mean value for 2/n in the [FORMULA] band equals [FORMULA] 2/n [FORMULA]. Since projection of not completely edge-on galaxies onto the plane of the sky causes vertical luminosity profiles to become rounder, we have performed simulations that show that it is possible that all our galaxies can have intrinsically exponential vertical surface brightness distributions.

We find that the profile shape is independent of galaxy type, and varies little with position along the major axis. The fact that we observe this in all our sample galaxies indicates that the formation process of the galaxy disks perpendicular to the galaxy planes is a process intrinsic to the disks themselves.

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
** Current address: Durham University, Physics Dept., South Road, Durham, DH1 3LE, United Kingdom

Send offprint requests to: R. de Grijs; grijs@astro.rug.nl

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998