Investigating the Nature of the Circumgalactic Medium Using Realistic Synthetic Observations

Hummels Cameron, Tucson AZ

Investigators

Abstract

Cameron Hummels is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Caltech. One of the most important open questions in the field of astrophysics is how galaxies acquire their gas and transform it into stars, a process that uniquely determines the evolutionary path of each galaxy over cosmic time. Observations of the circumgalactic medium, the gas reservoir surrounding a galaxy, are the key to understanding how galaxies accrete and process gas; however these observations are difficult to interpret because they require infrequent bright background objects to illuminate the foreground circumgalactic medium. Hummels will construct a "synthetic telescope," a piece of software for mimicking the observations made by real telescopes of this gas reservoir, and apply it to advanced supercomputer simulations of large volumes of the Universe containing thousands of galaxies. These simulated galaxies will provide context for better understanding observations made by real telescopes. In addition, Hummels will organize a public education program as a collaborative effort between Caltech and Pasadena City College. This outreach program will have frequent traditional and non-traditional events focused on increasing scientific interest and awareness in the general population of the greater Los Angeles area. Hummels will integrate several existing open-source codes into a "synthetic telescope" software pipeline for post-processing hydrodynamical simulations of galaxy evolution to generate simulated observations. This pipeline will account for (1) dust; (2) self-shielding effects of dense gas pockets; (3) atomic line transfer; (4) local photoionizing sources including stars and active galactic nuclei; (5) metagalactic ionizing background radiation; (6) collisional ionization; and (7) equilibrium and non-equilibrium ionization. It will be compatible with standard hydrodynamical codes and will produce photometric images, IFU data, and spectra spanning the wavelength range from the ultraviolet to the submillimeter. Hummels will apply this pipeline to the FIRE, CGM@HR, and AGORA simulations. He will compare these synthetic observations to the COS-Halos and KBSS surveys of the circumgalactic medium to investigate the origin and structure of the circumgalactic medium as it varies with galaxy mass, environment, and redshift, to better understand galactic gas accretion and ejection. Hummels will then release the software pipeline to the astrophysical community. Concurrent to this research effort, Hummels will organize a public education program to host frequent activities for scientific enrichment of the general public. This effort will use traditional and non-traditional events to focus on reaching out to people and communities who are otherwise ambivalent to science.