Box- and peanut-shaped bulges: II. NIR observations

Abstract

We have observed 60 edge-on galaxies in the NIR in order to study the stellar distribution in galaxies with box/peanut-shaped bulges. The much smaller amount of dust extinction at these wavelengths allows us to identify in almost all target galaxies with box/peanut-shaped bulges an additional thin, central component in cuts parallel to the major axis. This structure can be identified with a bar. The length of this structure scaled by the length of the bulge correlates with the morphologically classified shape of the bulge. This newly established correlation is therefore mainly interpreted as the projection of the bar at different aspect angles. Galaxies with peanut bulges have a bar seen nearly edge-on and the ratio of bar length to thickness, 14 +/- 4, can be directly measured for the first time. In addition, the correlation of the boxiness of bulges with the bar strength indicates that the bar characteristic could partly explain differences in the bulge shape. Furthermore, a new size relation between the box/peanut structure and the central bulge is found. Our observations are discussed in comparison to a N-body simulation for barred galaxies (Pfenniger & Friedli 1991). We conclude that the inner region of barred disk galaxies are build up by three distinct components: the spheroidal bulge, a thin bar, and a b/p structure most likely representing the thick part of the bar.