Constraints on bulge formation scenarios

A robust analysis of galaxy structural parameters, based on the modeling of bulge and disk shapes and brightnesses, was performed on a multi-band (BVRH) data set of 121 nearby late-type spirals. Each luminosity profile is decomposed into a generalized Sérsic bulge plus an exponential disk. The final set of galaxy parameters is studied for variations and correlations in the context of profile type differences and wavelength dependences. The Sérsic bulge shape parameter for nearby Type-I late-type spirals shows a range between n = 0.1-2 though, on average, the underlying surface density profile for the bulge is consistent with an exponential distribution. The size ratios of bulges and disks are coupled with an exponential distribution The size ratios of bulges and disks are coupled with (r_e/h) = 0:22±0:09, independent of wavelength and Hubble type. We interpret this result as evidence for regulated bulge formation by redistribution of disk material to the galaxy center, in agreement with models of bar forming instabilities of the disk.