Structure analysis of edge-on spiral galaxies

Abstract

The stellar distribution of a small sample of edge-on spiral galaxies is examined in B, V, R, and / by fitting model distributions to the light profiles, both perpendicular to the galaxy planes and along the major axes. We have developed a method to compare the fits for the models obtained for different galaxies by introducing a global goodness-of-fit parameter Pij. In general, the best fitting vertical model is more peaked than expected for an isothermal sheet distribution, i.e. it is either an exponential light distribution or a sech(z)-model. The most likely explanation for the deviations from an exponential or a sech(^) distribution at small z is dust extinction, whereas the excess light detected at large z for a few early-type spirals could be due to a thick disk component. The constancy of the exponential scale height of both the thin and the thick disks as a function of position along the major axis is confirmed, although it seems to lose strength in the radial outer parts. It is found that the vertical scale parameters for both the thin and the thick disks are confined within narrow ranges. We show that the scale lengths vary as a function of z-distance from the galaxy planes. The smallest scale lengths were measured in the galaxy planes. This can be explained by a combination of absorption effects and a young stellar population, that is supposed to be present in the galaxy planes. The mean ratio of the radial to the vertical scale parameter, HR/ZQ, is 5.9 ±0.4.