Cosmic rays in the multi-phase interstellar medium with dynamo-generated magnetic fields

Cosmic rays are relativistic particles (e.g. protons, heavier atomic nuclei and electrons) that propagate through space. Since cosmic rays carry an electric charge, these particles can interact with any magnetic fields that are present. It is believed that supernova explosions in the interstellar medium not only accelerate cosmic rays, but also lead to turbulent flows that drive dynamo action in galaxies. It is now well known that dynamo action of this type produces a complex magnetic field distribution, with very specific properties. The aim of this research is to explore the ways in which cosmic rays interact with the turbulent magnetic fields in the interstellar medium. Using detailed numerical simulations of dynamo action in a realistic local model of the interstellar medium we will explore the ways in which the cosmic ray distribution depends upon the properties of the interstellar gas (density, magnetic field, etc.). Existing propagation and diffusion models of cosmic ray particles rely on outdated models of magnetic fields, which take no account of the fact that these magnetic fields are the product of dynamo action due to supernova-driven turbulence. The gyration of cosmic rays around magnetic fields leads to synchrotron emission, which is one of the main observables in radio astronomy. We intend to use our numerical data to construct synthetic synchrotron maps of galaxies. Hence this project aims to bridge the gaps between radio astronomy, cosmic ray physics, dynamo theory and the physics of the interstellar medium.

Our results will be of interest to scientists working in various different subjects areas, including cosmic rays physics, dynamo theory, radio astronomy and the physics of the interstellar medium. In terms of academic impact, we will ensure that we attend conferences that will enable us to disseminate our results effectively to the international community of scientists working in these fields of research. Although our work is primarily theoretical, it is motivated by observations, and our intention is to produce results that can be used to interpret observational data. It will therefore be important for us to communicate effectively with observers. We shall be using some of the visitor money that we are requesting as part of this grant to further develop existing links with observers.

On an individual level, this research will also have a positive impact upon the PDRA's career. Clearly, they will gain important experience in this subject area. Furthermore, by developing and using a complex, state-of-the-art, general purpose numerical code in a parallel computing environment, they will gain significant expertise in numerical work. They will also develop their communication skills by presenting research at conferences. Even if the PDRA does not pursue an academic career, such skills are highly valued in many other employment sectors.

Cosmic ray research is particularly well suited to outreach work. For example, galactic cosmic rays may have important consequences for the health of astronauts in future manned space flights. Even at the Earth's surface, we are constantly exposed to cosmic rays, the flux of which depends crucially upon the magnetic fields that are associated with the solar wind. One of the CoI's already does outreach work with local schools, including giving "Masterclasses" on Applied Mathematics and lecturing at our "Partners" summer schools for pupils attending local schools, many in deprived areas, which do not send many students to University. Building upon our previous experience in this area, we intend to introduce simple ideas from our research into these outreach activities.