NEW TECHNIQUES FOR DERIVING BULGE AND DISK MODELS OF 2-COMPONENT GALAXIES

A new method is introduced to ''separate'' the bulge and disk componen ts of early-type galaxies, i.e. S0's and disky E's, viewed at such inc linations that their isophotes depart significantly from ellipses. In our approach, the two components are assumed to have concentric and co axial ellipitical isophotes of arbitrary surface brightness (SuBr) and ellipticity profiles. These four funct ions are to be determined by c omparing calculated and easily measured quantities, i.e. the harmonics of the SuBr along suitable reference ellipses. The principle of the m ethod is straightforward and its implementation very easy in favourabl e cases. There are difficulties however with truly edge-on galaxies, w here the assumption of elliptical isophotes is perhaps no more valid f or the disk, and with objects of such inclinations that the geometrica l signature of the two-components structure tends to vanish. Our techn iques have been tested with a number of calculated model objects, and With 9 real galaxies, observed at sub-arcsec resolution at the CFHT or at the Pic du Midi. The results are compared with those of other auth ors, sometimes involving more uncertain assumptions: the one of neglig ible disk contributions to the minor axis SuBr is unsatisfactory for S 0 galaxies.