S319.11.02 — Beyond Bulges and Disks: Tracking the Metamorphosis of Galaxies at z<2.5

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Aug 14th at 9:00 AM until 9:15 AM

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Author(s): Jennifer Lotz1

Institution(s): 1. STScI

A galaxy’s assembly history is encoded in its stellar mass, star-formation history, kinematics, and morphology. The structures of galaxies provide direct insight into their most recent assembly events, as well as longer timescale secular processes that drive star-formation and quenching. Thanks to SDSS and HST, we now have a broad-brush picture of how galaxy structures evolve over the past 10 billion years. Yet the processes for bulge formation, star-formation quenching, and early-type galaxy assembly remain unclear. Coarse bulge/disk/irregular structural classifications fail to capture the complex processes responsible for the morphological transformation of galaxies. I will present new quantitative non-parametric methods for measuring structure and classifying galaxy morphology, which make minimal assumptions about the intrinsic shapes and statistical distributions of galaxies. When applied to galaxies at z > 1, this approach naturally separates quenched compact galaxies from larger, smooth proto-elliptical systems, and star-forming disk-dominated clumpy galaxies from star-forming bulge-dominated asymmetric galaxies. At > 5 x 10^10 Msun and z > 1, smooth extended bulge-dominated systems are more likely to be star-forming than compact galaxies; this is broadly consistent with cosmological zoom-in simulations that predict the minor-merger triggered appearance of extended star-forming disks at z~1-1.5 around compact cores formed at z>2. We track the observed 0.5 < z < 2.5 evolution of fixed non-parametric morphological classes, and find that much of the size evolution of Sersic-classified bulges and disks may be explained by the preferential quenching of disks in the smallest bulge + disk systems at a given epoch. These observational results are consistent with the theoretical picture derived from correlations among galaxy structure, star formation, mass, and kinematics at z=0 in the Illustris simulation: quenching and the resulting morphological transformations are natural consequences of the stellar + AGN feedback required to produce consistent global star-formation and halo occupation functions.