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Image decomposition of galaxies is now routinely used to estimate thestructural parameters of galactic components. In this work, I address questionson the reliability of this technique. In particular, do bars and AGN need to betaken into account to obtain the structural parameters of bulges and discs? Andto what extent can we trust image decomposition when the physical spatialresolution is relatively poor? With this aim, I performed multi-component(bar/bulge/disc/AGN) image decomposition of a sample of very nearby galaxiesand their artificially redshifted images, and verified the effects of removingthe bar and AGN components from the models. Neglecting bars can result in aoverestimation of the bulge-to-total luminosity ratio of a factor of two, evenif the resolution is low. Similar effects result when bright AGN are notconsidered in the models, but only when the resolution is high. I also showthat the structural parameters of more distant galaxies can in general bereliably retrieved, at least up to the point where the physical spatialresolution is about 1.5 Kpc, but bulge parameters are prone to errors if itseffective radius is small compared to the seeing radius, and might suffer fromsystematic effects. I briefly discuss the consequences of these results to ourknowledge of the stellar mass budget in the local universe, and finish byshowing preliminary results from a large SDSS sample on the dichotomy betweenclassical and pseudo-bulges.

The Structural Parameters of Bulges, Bars and Discs in the Local Universe