Forum Springer Astron. Astrophys.
Forum Whats New Search Orders

Astron. Astrophys. 357, L1-L4 (2000)

Previous Section Next Section Title Page Table of Contents

3. Analysis

3.1. Disk model and fitting

Our model, as described in detail in Paper I and II, for the three-dimensional luminosity distribution for galactic disks is based upon the fundamental work of van der Kruit and Searle (1981a):


[FORMULA] is the central luminosity density in units of [[FORMULA] pc-3], R and z are the radial resp. vertical axes in cylindrical coordinates, h is the radial scalelength, and [FORMULA] the scaleheight. [FORMULA] describes three different fitting functions for the vertical distribution: exponential, sech, and the physically motivated isothermal (sech2) case (van der Kruit 1988). [FORMULA] is the cut-off radius, where the stellar luminosity density is assumed to be zero outside, mathematically expressed by a Heaviside function H[FORMULA]. These radii are defined at the position where the radial profiles bend nearly vertical into the noise, whereby a mean value is taken for the two different sides.

Depending on the inclination angle i, we numerically integrate this 3D-model along the line of sight and compare the two-dimensional result with the observed CCD image, leading to six free fitting parameters: the inclination i, the central luminosity density [FORMULA], the scalelength h, and -height [FORMULA], the cut-off radius [FORMULA], and the function for the z-distribution [FORMULA]. After our discussion about two different fitting methods in Paper II, we finally used our implemented "downhill simplex-method" (Nelder & Mead, 1965) to minimize the difference between model and observed disk. The possible influence of these parameters on the neglected dust distribution is estimated in Paper II.

Previous Section Next Section Title Page Table of Contents

© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000