ARE (pseudo)bulges in isolated galaxies actually primordial relics?

Abstract

We present structural parameters and (g-i) bulge/disk colors for a large sample (189) of isolated AMIGA galaxies. The structural parameters of bulges were derived from the two-dimensional bulge/disk/bar decomposition of Sloan Digital Sky Survey i-band images using GALFIT. Galaxies were separated between classical bulges (nb > 2.5) and pseudobulges (nb < 2.5), resulting in a dominant pseudobulge population (94%) with only 12 classical bulges. In the 〈μ e 〉-R e plane, pseudobulges are distributed below the elliptical relation (smaller R e and fainter μ e ), with the closest region to the Kormendy relation populated by those pseudobulges with larger values of B/T. We derived (g-i) bulge colors using aperture photometry and find that pseudobulges show median colors (g-i) b 1.06, while their associated disks are much bluer, (g-i) d 0.77. Moreover, 64% (113/177) of pseudobulges follow the red sequence of early-type galaxies. Bluer pseudobulges tend to be located in galaxies with the highest likelihood of tidal perturbation. The red bulge colors and low B/T values for AMIGA isolated galaxies are consistent with an early formation epoch and not much subsequent growth. Properties of bulges in isolated galaxies contrast with a picture where pseudobulges grow continuously via star formation. They also suggest that environment could be playing a role in rejuvenating the pseudobulges. © 2014. The American Astronomical Society. All rights reserved..