ARE (PSEUDO)BULGES IN ISOLATED GALAXIES ACTUALLY PRIMORDIAL RELICS?

Abstract

We present structural parameters and (g-i) bulge/disk colors for a large\nsample (189) of isolated AMIGA galaxies. The structural parameters of bulges\nwere derived from the 2D bulge/disk/bar decomposition of SDSS i-band images\nusing GALFIT. Galaxies were separated between classical bulges (n_b>2.5) and\npseudobulges (n_b<2.5), resulting in a dominant pseudobulge population (94%)\nwith only 12 classical bulges. In the <mu_e>-Re plane, pseudobulges are\ndistributed below the elliptical relation (smaller Re and fainter mu_e), with\nthe closest region to the Kormendy relation populated by those pseudobulges\nwith larger values of B/T. We derived (g-i) bulge colors using aperture\nphotometry and find that pseudobulges show median colors (g-i)b~1.06, while\ntheir associated disks are much bluer, (g-i)d~0.77. Moreover, 64% (113/177) of\npseudobulges follow the red sequence of early-type galaxies. Bluer pseudobulges\ntend to be located in galaxies with the highest likelihood of tidal\nperturbation. The red bulge colors and low B/T values for AMIGA isolated\ngalaxies are consistent with an early formation epoch and not much subsequent\ngrowth. Properties of bulges in isolated galaxies contrast with a picture where\npseudobulges grow continuosly via star formation. They also suggest that\nenvironment could be playing a role in rejuvenating the pseudobulges.\n