Introduction

An important tool for galaxy research is the study of the surface brightness (SB) distribution. For spiral galaxies the determination of the scale length of the exponential disk has a long traditition (e.g. Courteau 1996). However, the errors in these results are still rather large (Knapen & van der Kruit 1991).

For a better understanding of spiral galaxies it is necessary to study the structure of both disk and bulge as well. In order to separate non-axisymmetric structures as bars or triaxial bulges from the axisymmetric disk, two-dimensional fits are advantageous (e.g. de Jong 1996). In the following I present a generalization of a nonlinear direct fit method to the two-dimensional SB distribution of near-infrared (NIR) images of spiral galaxies.

NIR Data

The aim of this project is the study of the distribution of the mass-carrying evolved stars in spiral galaxies of different Hubble types. For this purpose, NIR observations are advantageous since they have much less perturbations due to dust or especially bright young stars.

The observations were performed during several runs at the 2.2m telescope of the German-Spanish observatory on Calar Alto, Spain. The detector was the MAGIC-NIR-camera with a NICMOS chip of (0.67″) 256×256 pixels, for a total field of view of ≈ 3′ × 3′.