Collaborative Research: Non-thermal Radio Halos of Spiral Galaxies as Clues to Galaxy Evolution

New Mexico State University, Las Cruces NM

Investigators

Abstract

To understand how stars like the Sun and planets like Earth came to be, we must understand how galaxies, such as our Milky Way, form and evolve. This project is an attempt to understand how interstellar gas and energetic particles are ejected from galaxy disks, where most of the gas and stars are found, and interact with the galaxy halo. This cyclical process is important for understanding how star formation proceeds in galaxies, and the rate at which galaxies grew when they were forming. The study makes use of radio images from the NSF-funded Karl G. Jansky Very Large Array (VLA) and the Green Bank Telescope (GBT), optical data from the Apache Point 3.5-meter telescope, as well as archival infrared data. The project will provide opportunities for two PhD student theses at Hispanic Serving Institutions, and the PIs will also contribute to a training program run by the National Radio Astronomy Observatory for faculty at small colleges. Galaxy growth and evolution depend on both the acquisition of gas from the galaxy environment and energetic outflows from disks. The detailed physics of these processes needs to be understood, and nearby edge-on galaxies are the best objects where it is possible to cleanly separate disk and halo components. The project leverages a major new survey of radio continuum emission from edge-on galaxies called CHANG-ES (Continuum Halos in Nearby Galaxies: an EVLA Survey). The first goal is to further our understanding of the dynamics of disk-halo flows by assessing the role of non-thermal gas pressure gradients in galaxy halos, using radio maps made from the VLA and GBT. The second goal focuses on identifying sites of cosmic ray (CR) injection and propagation into galaxy halos. For this, the spatial variation of the non-thermal spectral index will be mapped, after robustly separating thermal and non-thermal radio emission using CHANG-ES maps in conjunction with infrared data and H-alpha images. The third science goal is to examine the connection between CR outflows and disk-halo cycling of thermal gas, and whether this relation depends on factors such as star formation rate.