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

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 $\to$ 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 $\to$ 0.3 and bluer colours, $(g-r)<0.25$ compared to low-mass galaxies on the MS.

5 pages, 3 figures