Correlation of structure and stellar properties of galaxies

Establishing the correlation, or lack thereof, between the structure and stellar activity of galaxies is crucial to unravel their evolutionary histories. To that end, we have performed mass-based structural (bulge + disc) decomposition of all disc galaxies (1263) in the Herschel imaging area of the Stripe82 region using Ks-band images from the latest VICS82 survey. The resultant parameters are highly consistent with those obtained by Bottrell et al. (2019) in optical (ugriz) bands using deep co-added Sloan images. The match demonstrates that allowing bulge morphology to be fitted freely is essential for accurate decomposition. The scaling relations thus derived are used along with kinematics to select an indubitable class of classical (CB) and pseudo bulges (PB). The rest of the bulges (<20%) - which could not be stringently classified – are marked as “interim” bulges (IB). We find that del<mu_e> - bulge type indicator based on the Kormendy relation – exhibits a tight correlation with total stellar mass of the galaxy. The placement of the 3 bulge types indicates that mass increase in disc galaxies is accompanied by the transformation of their bulge morphologies from PB to IB to CB. Moreover, del<mu_e> exhibits a tight correlation with the global colour (Ks-r) where disc galaxies with PB occupy the blue end, CB occupy the red end and IB are intermittent to the two populations, suggesting that structural valley is the same as the green valley. Interestingly, although discs with IB are redder than those with PB, their SFR and sSFR is found to be similar, suggesting that either they are shrouded with dust or have composite populations. The overall trends suggest that morphological transformation is inherently involved in the quenching of galaxies with time.

Discussion Leader: 
Sonali Sachdeva
Tuesday, December 31, 2019 - 12:00pm to 1:00pm