Red galaxies with pseudo-bulges in the SDSS: closer to disk galaxies or to classical bulges?

Abstract

Pseudo-bulges are expected to markedly differ from classical, quasi-monolithically forming bulges in their star formation history (SFH) and chemical abundance patterns. To test this simple expectation, we carry out a comparative structural and spectral synthesis analysis of 106 red, massive galaxies issued from the SDSS, subdivided into bulgeless, pseudo-bulge and classical bulge galaxies according to their photometric characteristics, and further obeying a specific selection to minimize uncertainties in the analysis and ensure an unbiased derivation and comparison of SFHs. Our 2D photometry analysis suggests that disks underlying pseudo-bulges typically have larger exponential scale lengths than bulgeless galaxies, despite similar integral disk luminosities. Spectral synthesis models of the stellar emission within the 3" SDSS fiber aperture reveal a clear segregation of bulgeless and pseudo-bulge galaxies from classical bulges on the luminosity-weighted planes of age-metallicity and mass-metallicity, though a large dispersion is observed within the two former classes. The secular growth of pseudo-bulges is also reflected upon their cumulative stellar mass as a function of time, which is shallower than that for classical bulges. Such results suggest that the centers of bulgeless and pseudo-bulge galaxies substantially differ from those of bulgy galaxies with respect to their SFH and chemical enrichment history, which likely points to different formation/assembly mechanisms.

18 pages, 12 figure, accepted for MNRAS

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• Structural analysis of massive galaxies using HST deep imaging at z < 0.5
• Pseudo bulges in galaxy groups: the role of environment in secular evolution
• A new fitting concept for the robust determination of Sérsic model parameters
• Revisiting stellar properties of star-forming galaxies with stellar and nebular spectral modelling
• Semi-empirical AGN detection threshold in spectral synthesis studies of Lyman-continuum-leaking early-type galaxies