Stellar disks and embedded bars in early-type galaxies

I. 2-D photometric decomposition of 28 southern early-type galaxies

¹ Landessternwarte, Königstuhl, D–69117 Heidelberg, Germany
² Centro de Investigaciones de Astronomia CIDA, Apartado 264, Merida 5101-A, Venezuela
³ Universitätssternwarte, Scheinerstr. 1, D–81679 München, Germany
⁴ Osservatorio Astronomico Capodimonti, salita Moiariello 16, I-80131 Napoli, Italy and Dipartimento di Scienze Fisiche, Universita' Federico II, I-80100 Napoli, Italy
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A.

Send offprint request to: C. Scorza

Received: 23 December 1997
Accepted: 2 March 1998

Abstract

We present photometric disk-bulge decompositions of 28 southern early-type galaxies with types in either the RC3 or ESO-Lauberts & Valentijn catalogues. The decomposition method applied here is based on that developed by Scorza & Bender (1995) but the improved version allows for arbitrary surface brightness profiles of the disk models. We find three types of objects in this sample: bulge-dominated systems, with fully embedded close to edge-on disks; disk-dominated close to edge-on objects and objects with barred disks being modestly inclined down to face-on. Like in Scorza & Bender (1995), the analysis made here indicates that the superposition of a thin disk and an elliptical bulge can give good account for the morphology of most of the galaxies. We find the disks to have a diversity of surface brightness profiles, the most frequent case being that of a disk with an exponential profile, which becomes steeper at small radii. After disk subtraction, the bulges follow more closely the law. Five of the galaxies show signatures of embedded bar components. These have flat surface brightness profiles at small radii and rectangular shape, which are typical features of barred early-type galaxies. We find that the properties of the galaxies, most notably the disk-to-total ratio, correlates only modestly with the original classification of the galaxies.