Galaxy Evolution and Environment -- Disk-Halo Outflows, Feedback and Magnetic Fields

点击翻译按钮获取中文摘要

My program involves a study of outflows from spiral galaxies and their effect on galaxy formation and evolution. Current models require strong outflows (called 'feedback') in order to form the galaxies that we see today. But the details of feedback mechanisms are not well known and current computer simulations must include assumptions about feedback which are reasonable, but not verified through observation. Fortunately, we now know that nearby fully formed galaxies also experience outflows that are lower in power yet similar in nature to those that occurred at a time when galaxies first formed. Nearby galaxies, not only are fully formed versions of their infant counterparts, but also represent local laboratories within which outflows can be studied in great detail. With careful scrutiny, we can identify and quantify the important physics, dynamics, causes and effects of this important activity. In this Discovery Grant (DG) cycle, I will primarily focus on radio continuum emission from the interaction between cosmic rays and magnetic fields.****The consequences of outflows are substantial. Significant gas is expelled from the disk leading to modifications in the galaxy's evolution (e.g. adjusted star formation rates, re-distribution of chemical elements, altered magnetic field structures). There are important implications both locally (such as around our own Sun) and globally across a galaxy. For example, our Sun exists in a 'local hot bubble' which is believed to have been excavated by previous supernova activity. Could this have affected the formation and evolution of our Sun and, by implication, the Earth itself? Indeed the Galactic `habitable zone' will certainly be affected by outflows. ****My first goal is to complete the full data release of CHANG-ES (Continuum Halos in Nearby Galaxies -- an EVLA Survey), an international consortium of which I am principal investigator. We have used the EVLA (Expanded Very Large Array) radio telescope, whose correlator was built in Canada, to observe 35 edge-on galaxies in a variety of telescope configurations, at an opportunistic time prior to the future Square Kilometre Array. Our 405 hours of EVLA data constitute 175 data sets which include, for the first time, information on the magnetic field direction in edge-on galaxies. Green Bank Telescope time has also been awarded.****Canada, via CHANG-ES, has become a center of excellence in high quality training for processing interferometric data sets and dealing with `big data'. Our first legacy-value public data release occurred in August/2015 and there will be two more over the time period of this DG. Our own consortium is making new discoveries from these data (see text). With the public data release, other scientists will also benefit from the results, leveraging our own work. Our group's focus has shifted more and more towards the science, and we anticipate many more answers (and surprises) in the future.****