6 Conclusions and discussion

In this work we have presented photometric data of 28 early-type galaxies with classification T< -3 in either the RC3 or ESO-Lauberts & Valentijn catalogues and their decompositions into bulge and disk. The decomposition method applied here is based on that developed by Scorza & Bender (1995) but the improved method allows for arbitrary surface brightness profiles of the disk models. We find three types of objects in this sample: bulge-dominated, with fully embedded close to edge-on disks; close to edge-on disk-dominated objects and objects with barred disks being modestly inclined down to face-on. Naturally we expect among the edge-on objects also barred ones but these cannot be detected easily because of the lack of unambiguous features. Bars are also difficult to identify in cases where the bar major axis is aligned with the projected major axis of the disk component. Due to the high flattening of the bar component, the galaxy may be interpreted as being more inclined than it actually is. The described ambiguities can be critical when interpreting the distribution of inclination angles for a sample of objects. The tendency is that one will always find an apparent overabundance of more edge-on objects relative to more face-on ones. The fact that face-on barless disks can hardly be identified at all if the disk-to-bulge ratio is lower than 30%, worsens this problem further.

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 early-type galaxies selected here. We find that the disks 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. We notice that after disk subtraction the bulge profiles follow more closely an r^1/4 law and many of them show still increasing ellipticity profiles. Five of the galaxies show signatures for embedded bar components. These become visible once the bulge has been subtracted. In three of these objects the surface brightness profile of the bar flattens in the inner parts. It is noticeable that this kind of profiles have been observed in many early-type SB0 galaxies (Elmegreen & Elmegreen 1985) and that their isophotal shape is rectangular, also typical of barred early-type galaxies (Athanassoula et al. 1990).

We find that the properties of the galaxies, most notably the disk-to-bulge ratio, correlate only modestly with the original classification of the galaxies. An extreme case is NGC 4564, classified as T = -5 (E0) in the RC3 catalogue and which has one of the largest D/B ratio of the examined sample (D/B = 0.40). Other examples for large diskiness are NGC 1700, NGC 3818, NGC 4473 and NGC 5018.

In a forthcoming paper (Scorza & Bender 1998) we present a statistical analysis of the sample of galaxies examined here and address questions concerning the continuity of the Hubble sequence towards smaller D/B ratios and the family likeness between disky ellipticals and S0s.