Structural evolution of dying galaxies

While star-forming galaxies are primarily disks with spiral arms, red-and-dead quiescent galaxies are dominated by a spheroidal bulge. However, how galaxies evolve, and what is the link between their star formation and structure remain two of the most disputed questions in astronomy. To answer them, we studied the structure of quenching galaxies. We analyzed the morphology of three transitioning galaxy populations: cluster members, post-starbursts, and barred galaxies. First, we looked at the structure of galaxies in z=1.5 clusters. We found that two out of four clusters host compact bulge-dominated galaxies, suggesting that dense environments helped to build up galactic bulges, either through mergers, tidal interactions, or group pre-processing, as early as 10 Gyr ago. Next, we analyzed the structure of 26 local post-starburst galaxies that retain molecular gas. We found that 88% of them have disturbed morphologies, but many disturbances are due to small-scale dust structures, and are undetected in lower-resolution imaging such as SDSS. However, high-resolution space-based imaging is scarce. Meanwhile, there are large volumes of archival lower-resolution imaging. Thus, we turned to machine learning to overcome the need for high-resolution imaging to detect disturbances. In our third project, we developed a neural network to measure galaxy morphology independently of image quality. Finally, we studied how bars affect galaxy evolution. We used maps produced in the Galaxy Zoo 3D project identifying bar and spiral regions in galaxies, and trained a neural network to detect these regions automatically. We then measured bar strengths in a sample of 4046 galaxies. Our results agree with modes in which bars first drive the gas inwards, triggering star formation and building up the bulge, and then lead to quenching. Our work showed the power of morphological analysis in constraining the galaxies’ evolutionary pathways. In the future, we aim to extend morphological measurements to multi-wavelength data to also trace gas and dust. We will also perform a review of quenching mechanisms and their effect on multi-wavelength galaxy structure. With these tools in hand, we hope to finally determine the elusive and complex link between the structure of galaxies and their evolution