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

TL;DR

This study compares the structural and stellar population properties of pseudo-bulges, classical bulges, and bulgeless galaxies in SDSS, revealing distinct formation histories and chemical enrichment patterns, with pseudo-bulges resembling disk galaxies more than classical bulges.

Contribution

It provides a detailed comparative analysis of pseudo-bulges and classical bulges, highlighting their different star formation and chemical evolution histories based on SDSS data.

Findings

Pseudo-bulges have larger disk scale lengths than bulgeless galaxies.

Pseudo-bulges and bulgeless galaxies differ from classical bulges in age-metallicity relations.

Pseudo-bulges show a shallower stellar mass growth over time.

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.