The evolutionary history of galactic bulges : photometric and spectroscopic studies of distant spheroids in the GOODS fields

We report on the first results of a new study aimed at understanding the diversity and evolutionary history of distant galactic bulges in the context of now well-established trends for pure spheroidal galaxies. To this end, bulges have been isolated for a sample of 137 spiral galaxies within the redshift range 0.1 0.2 show similar patterns of evolution to those seen for pure spheroidals such that the stellar populations of all spheroids with M > 10^(11) M⊙ are consistent with a single major burst of star formation at high redshift (z_f ≳ 2), while bulges with M < 10^(11) M⊙ must have had more recent stellar mass growth (~10% in mass since z ~ 1). Although further data spanning a wider range of redshift and mass are desirable, the similarity between the assembly histories of bulges and low-mass spheroidals seems difficult to reconcile with the picture whereby the majority of large bulges form primarily via secular processes within spiral galaxies