When are Disk Galaxies First Assembled?

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Today nearly all galaxies that are actively forming stars are disk galaxies. Our own galaxy, the Milky Way, is one example. Disk galaxies are composed of a thin and symmetric rotating disk of stars and gas. This project will determine when disk galaxies first formed in significant numbers. Researchers will measure the fraction of disk galaxies over the last 10 billion years. These fractions will be compared with two theoretical models for disk formation in order to understand how disks form. In addition, simulated observations will be made of theoretical models of galaxies. A large set of these simulated observations will be used to train a classification algorithm to automatically distinguish between disks and colliding galaxies, which are easily mistaken for disks. The resulting algorithm will then be applied to existing observations of hundreds of galaxies in order to identify the fraction of disks. This project will also establish an "Astro Scholars" annual week-long intensive mini-course targeted at students in local Historically Black Colleges and Universities (HBCUs). Scholars will receive financial support. Monthly follow- up after the summer program will extend the impact of the program for 6 months. Current measurements of the fraction of disk galaxies are inaccurate. They do not take into account that some colliding galaxies can appear to be disk galaxies. To measure the fraction of disks over time, researchers will create disk criteria. These criteria will determine if a given observation indicates a disk or colliding galaxies. The criteria will be created with models of galaxies using publicly available suites, VELA and FIRE, of computer simulations. Researchers will simulate observations with mock catalogues that will be compared directly to observations, taking into account the blurring effects of the Earth's atmosphere. Researchers will create disk criteria by comparing the intrinsic states of the simulations (disk or collision) with the simulated observations. These criteria will indicate the probability an observation is a disk or colliding galaxies. These criteria will be applied to KMOS3D integral field unit observations of nearly 600 galaxies. They will measure the fraction of star-forming galaxies which are disks over time. The disk criteria will serve as a powerful tool for recent (and ongoing) large surveys of galaxy kinematics. They will be key for next-generation surveys that will push observations of galaxy kinematics to the very early universe, when the first galaxies formed, and galaxy collisions were even more frequent. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.