The Role of Cosmic Magnetic Fields in Galaxy Evolution

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The Role of Magnetic Fields in Galaxy Formation Earth's magnetic field protects our atmosphere from the onslaught of the solar wind: a stream of plasma flowing from the Sun through the Solar System. A disturbance in the Sun's magnetic field can trigger a massive ejection of matter into space that can cause power outages and disruption of GPS equipment and satellite communication when it interacts with the Earth's magnetic field. Recently, NASA's Voyager 1 space probe recorded a sudden change in magnetic field strength, but not direction, as it presumably entered interstellar space. Magnetic fields pervade the universe. In many astrophysical situations from small to very large, magnetic fields play a decisive part in the motion of matter in the cosmos. In return the structure of cosmic magnetic fields is intimately related to the motion of matter. Understanding magnetic fields is necessary to understand the formation of structure, and its subsequent evolution. In this proposal I outline a research program that investigates the physics of magnetic fields in relation to the formation and evolution of galaxies. This includes galaxy assembly by accretion of matter, but also the interaction between magnetic fields and matter inside galaxies, and activity in the centre of galaxies (Active Galactic Nucleus or AGN) that ejects vast amounts of energy in the form of beams of matter into intergalactic space. For the moment, we know very little with confidence about magnetic fields in galaxies. This is in part due to limitations in the predictive nature of dynamo theory that describes how large-scale magnetic fields can be amplified and sustained from motions in an astrophysical plasma. In part, our lack of understanding of cosmic magnetic fields is due to limitations in our ability to derive quantitative information from observations. The latter will make significant steps forward in the next decade because of recent developments in receiver technology, and the design of a new international facility for radio astronomy called the Square Kilometre Array (SKA). One of five key science goals for the SKA is to study the origin and evolution of cosmic magnetism, and another includes galaxy evolution and cosmology. For normal galaxies, I investigate the relation of the magnetic field to global properties such as the rate of star formation and dynamics of a galaxy. To this end, I lead surveys with the Effelsberg radio telescope and the Expanded Very Large Array (EVLA). On much smaller scales in our own Milky Way galaxy, I investigate the connection between the gas and the small-scale magnetic field. I lead the polarization side of a survey of part of the disk of the Milky Way (THOR), and an early science project of the GALFACTS survey with the Arecibo 300-m radio telescope. Through collaboration on deep surveys of small areas of the sky, we investigate the properties of distant galaxies and AGN-powered radio sources. The magnetic field properties of radio galaxies are also the subject of a statistical investigation using a technique called stacking, and another early science project with the GALFACTS survey. This work includes both observations with state of the art facilities and modeling of radio emission and magnetic fields. In support of development of future sky surveys with SKA and its path finders, I am also investigating new applications to extract information from broad-band observations of the polarization of radio waves, the principal source of information about cosmic magnetic fields. This will lead to a deeper understanding of the origin of magnetic fields in the cosmos, and their role in the formation of structure in the universe.