The nature of growing bulges within z < 1.3 galaxy disks in the GOODS-N field

TL;DR

This study investigates the properties and evolution of bulges in disk galaxies up to redshift 1.3, revealing that bulge growth is linked to nuclear star formation and AGN activity, with blue bulges evolving into pseudobulges.

Contribution

It provides new insights into bulge growth mechanisms at intermediate redshifts, highlighting the role of nuclear star formation and AGN activity in bulge evolution.

Findings

Blue, star-forming nuclei are found in low mu_0 galaxies at z < 0.8.

A significant fraction of high-surface brightness nuclei are blue at 0.8 < z < 1.3.

Blue bulges likely evolve into local pseudobulges, not classical bulges.

Abstract

We analyze central surface brightness mu_0, nuclear and global colors of intermediate redshift disk galaxies. On an apparent-diameter limited sample of 398 galaxies from ACS/HST Great Observatories Origins Deep Survey North (GOODS-N), we find 131 galaxies with bulges and 214 without. Up to z ~ 0.8, blue, star-forming nuclei are found in galaxies with low mu_0 only; all high-mu_0 nuclei show red, passive colors, so that nuclear and global (U - B) colors strongly correlate with central surface brightness, as found in the local Universe. At 0.8 < z < 1.3, a fraction ~ 27% of the high-surface brightness nuclei show blue colors, and positive nuclear color gradients. The associated nuclear star formation must lead to bulge growth inside disks. Population modeling suggests that such blue bulges evolve into local pseudobulges rather than classical bulges. We do not find evidence for rejuvenation of classical bulges at the sampled z. High luminosity AGNs become common at 0.8 < z < 1.3, perhaps pointing to a role of AGN in the growth or star formation truncation of bulges.