Correlation of structure and stellar properties of galaxies in Stripe 82

TL;DR

This study investigates the link between galaxy structure and stellar properties in Stripe 82, revealing clear bimodality between classical and pseudo bulge galaxies, with ambiguous bulges likely in the green valley.

Contribution

It provides a detailed 2D mass-based structural analysis of disc galaxies, distinguishing bulge types and their stellar activity, highlighting the effectiveness of the Kormendy relation as an indicator.

Findings

Pseudo bulge galaxies are all blue and star-forming.

Classical bulge galaxies are all red and quiescent.

Ambiguous bulge galaxies are mostly in the green valley.

Abstract

Establishing a correlation (or lack thereof) between the bimodal colour distribution of galaxies and their structural parameters is crucial to understand the origin of bimodality. To achieve that, we have performed 2D mass-based structural decomposition (bulge+disc) of all disc galaxies (total$=$1263) in the Herschel imaging area of the Stripe 82 region using $K_s$ band images from the VICS82 survey. The scaling relations thus derived are found to reflect the internal kinematics and are employed in combination to select an indubitable set of classical and pseudo bulge hosting disc galaxies. The rest of the galaxies ($<20\%$) are marked as discs with "ambiguous" bulges. Pseudo and classical bulge disc galaxies exhibit clear bimodality in terms of all stellar parameters ($M_*$, sSFR, $r-K_s$). All pseudo bulge disc galaxies are blue and star-forming and all classical bulge disc galaxies are red and quiescent with less than $5\%$ digressions. Ambiguous bulge disc galaxies are intermittent to pseudo and classical bulge disc galaxies in the distribution of all structural and stellar parameters. $\Delta$$\langle\mu_{eb}\rangle$ - based on the placement of bulges on the Kormendy relation - is found to be the most efficient single structural indicator of both bulge type and stellar activity. The placement of ambiguous bulge disc galaxies on scaling relations and fundamental plane, in addition to their peculiar stellar properties suggest that they are dominantly a part of the green valley.