Galactic Magnetism: Extended is the new Compact

点击翻译按钮获取中文摘要

Magnetic fields are one of the four primary components of the interstellar medium (ISM), or, 'the stuff between the stars'. The other components are gas, dust, and cosmic rays (highly energetic charged particles). Magnetic fields are believed to be important in galactic pressure balance, star formation, and perhaps even in the formation of galaxies themselves. Understanding the structure of magnetic fields within our Galaxy (and others) provides us with important constraints on models addressing how the Galactic magnetic field originally formed and how it is evolving. ***However, unlike the other constituents of the ISM, magnetic fields do not give off any form of light. Consequently, unless they are located in a region of space close enough to be measured in situ with a magnetometer (e.g., by spacecraft like Voyager 1 and 2), magnetic fields cannot be directly detected with any type of telescope. This makes determining the properties of magnetic fields more challenging than for the other ISM components.******Instead, we take advantage of the fact that magnetic fields can change the properties of light that is generated within their presence and they can affect light that passes through them, primarily through a process known as Faraday rotation.This process rotates the property of 'polarisation angle' of the incoming signal, and is dependent on the wavelength of the signal, as well as the magnetic field and electron density along the line-of-sight to the source. If we know something about the electron density, we can "work backwards" to determine what the magnetic field distribution must be to produce the rotation we measure. ***Most of what we currently know about the Galactic magnetic field has been determined using light from pulsars (exploded stars) and external galaxies as 'plumb-line' sources; the more sources we can look at, the more information we can piece together. Much like reconstructing an image from individual pixels, the goal has been to observe the Faraday rotation of as many sources as possible, at the highest density. From these data, we are piecing together the story of the Galactic magnetic field. ***However, many questions still remain. I believe the next big step forward in understanding Galactic magnetism will originate from studies using data from the 'extended emission'. Rather than looking at (polarised) light as it passes through the magnetic field of our Galaxy, we can use the (polarised) extended emission light that is being emitted from regions within the magnetic field. These data have the potential to bring all of the pieces of the Galactic magnetic field puzzle together. We are uniquely positioned in Canada to do this work, with the facilities and experience needed to address these questions. By doing this work, we will push back the boundaries of our knowledge of Galactic magnetism, and secure Canada's position as a world leader in the study of Cosmic magnetism.*** *** **