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

TL;DR

This study analyzes the structural and color properties of bulges in isolated galaxies, revealing most are pseudobulges with characteristics suggesting early formation and limited growth, contrasting with pseudobulge growth in denser environments.

Contribution

It provides a detailed analysis of bulge types and colors in isolated galaxies, highlighting their early formation and the influence of environment on pseudobulge evolution.

Findings

94% of bulges are pseudobulges with distinct structural properties.

Most pseudobulges have red colors, indicating early formation.

Environmental factors may influence pseudobulge rejuvenation.

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 2D bulge/disk/bar decomposition of SDSS i-band images using GALFIT. Galaxies were separated between classical bulges (n_b>2.5) and pseudobulges (n_b<2.5), resulting in a dominant pseudobulge population (94%) with only 12 classical bulges. In the <mu_e>-Re plane, pseudobulges are distributed below the elliptical relation (smaller Re and fainter mu_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 continuosly via star formation. They also suggest that environment could be playing a role in rejuvenating the pseudobulges.