Dissecting the Main Sequence: AGN Activity and Bulge Growth in the Local Universe

TL;DR

This study uses Sloan Digital Sky Survey data to explore how active galactic nuclei (AGN) relate to star formation cessation and bulge growth in local galaxies, revealing ongoing bulge development across different galaxy masses.

Contribution

It provides new evidence linking AGN activity with star-formation quenching and bulge growth in both massive and low-mass galaxies, highlighting evolutionary pathways.

Findings

AGN-related galaxies account for ~60% of star formation in massive galaxies.

Bulge growth occurs in massive galaxies and continues as they quench and redden.

Low-mass starburst galaxies show increased bulge-to-total ratios and bluer colors above the main sequence.

Abstract

Local galaxies from the Sloan Digital Sky Survey are used to provide additional support for an evolutionary pathway in which AGN activity is associated with star-formation quenching. Composite, Seyfert 2 and LINER galaxies account for $\sim$60\% of all star-formation in massive galaxies ($M_\star > 10^{10.5} M_\odot$). Inclusion of these galaxies results in a "turnover" in the $SFR - M_\star$ relation for massive galaxies. Our analysis shows that bulge growth has already occurred in the most massive galaxies ($M_\star > 10^{10.5}$ $M_\odot$), and bulges continue to grow as galaxies quench and redden, $(g-r)$ = 0.5 $\rightarrow$ 0.75. Significant bulge growth is also occurring in low mass starburst galaxies ($M_\star < 10^{10.5} M_\odot$) at 0.5 dex above the "main sequence" (MS), where we find an increase in $B/T$ from 0.1 $\rightarrow$ 0.3 and bluer colours, $(g-r) < 0.25$ compared to low-mass galaxies on the MS.