Tracking the Metamorphosis of Galaxy Structures

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Galaxies are the birthplace of stars and planets, and act as cosmic signposts for the invisible dark matter. The shapes and colors of galaxies provide important insight into how and when galaxies formed their stars and merged to become larger galaxies. Dr. Lotz and team will devise innovative software tools to measure the structures of thousands of nearby galaxies, and compare the distribution of shapes of today's galaxies to distant ones observed as they were ~10 billion years ago. By tracking the metamorphosis of galaxy shapes over cosmic time, and by comparing with simulations of galaxy evolution, the project will illuminate the physical processes governing the evolution of galaxies like our own Milky Way. The tools developed by this project will help to fully exploit future astronomy surveys with the Large Synoptic Survey Telescope and James Webb Space Telescope. Besides its scientific significance, the project will support the training of a postdoctoral fellow, and the education of a graduate student and a Baltimore-city high school student. The broader public will be engaged through a related citizen science project to study galaxy images. The stellar and gaseous structures of galaxies provide direct insight into their most recent assembly events, as well as longer timescale internal secular processes, both of which drive galaxy star-formation and quenching. However, the existing coarse structural classifications fail to capture the complex assembly processes responsible for the morphological transformation of galaxies over the past 10 billion years. Building upon working currently being done for redshifts 0.5<z<3, this project will develop new non-parametric, quantitative measures of galaxy structure, identifying galaxy mergers and classifying galaxy morphology, and apply this approach to nearby galaxies in the Pan-STARRS Optical Galaxy Survey. This low-redshift baseline will be compared to high-redshift observations by the Hubble Space Telescope to track the emergence of spheroidal galaxies and the frequency of different types of galaxy mergers over time. In concert with this observational analysis, the investigators will statistically compare cosmological hydrodynamical simulations from Illustris to the distribution and evolution of morphologies of observed galaxies at redshifts 0<z<3; this will provide physical insights into the measured structural quantities and distributions, and place constraints on the viable modes for galaxy assembly and evolution.