IAU00614
Presentation type requested: ORAL
ON THE FORMATION OF BULGES AND DISKS
Uta Fritze - v. alvensleben
Universitaetssternwarte Goettingen
The good news: HST allows for Bulge/Disk (B/D) decomposition of galaxies to fairly high redshifts. The bad news: first results seem fairly discrepant. We developed simplified evolutionary synthesis models for bulges (short timescale for Star Formation (SF)) and disks (long timescale for SF) and combine their spectra in proportions to yield, by z=0, the observed B-band B/D-light ratios of various galaxy types. To cope with presently discussed bulge and disk formation scenarios we explore models that start bulge and disk SF at the same epoch and at different epochs. Models predict a significant passband dependence of B/D-ratios at z=0 with B/D-ratios systematically larger if the B/D-decompositions is done at longer wavelengths (observationally confirmed by Eskridge et al. 2002). Exploring the redshift evolution of B/D-ratios of various galaxy types we find it to be very strong in UBV and still significant in the I-band widely used for observational studies. Our results significantly enhance the scarcity of bulge-strong systems at z>0 reported for HDF galaxies. We predict that B/D-decomposition in two (or more) passbands should allow to discriminate between the various galactic structure formation scenarios.
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