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

B. Ribeiro, C. Lobo, S. Antón, J. M. Gomes, P. Papaderos

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 Sloan Digital Sky Survey (SDSS), sub-divided 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 discs underlying pseudo-bulges typically have larger exponential scalelengths than bulgeless galaxies, despite similar integral disc luminosities. Spectral synthesis models of the stellar emission within the 3-arcsec SDSS fibre 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 centres 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.

Keywords
galaxies: bulges – galaxies: evolution – galaxies: general – galaxies: stellar content

Monthly Notices of the Royal Astronomical Society
Volume 456, Page 3899
March 2016

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