Published online by Cambridge University Press: 21 April 2018
Abstract
Active galactic nuclei (AGNs), the luminous, compact core regions of galaxies where accretion occurs onto supermassive black holes, can dramatically influence their entire host galaxy evolution by a process referred to as AGN feedback. Energy feedback to the galaxy is the result of combined radiation fields and directed outflows, and especially radio-loud active galaxies show pronounced jets and lobes. Their synchrotron radio emission indicates that dynamically important magnetic fields are at play in AGN jet collimation, stability, energy transfer to the intergalactic medium and their overall morphological appearance. Current knowledge on the launching mechanisms for such highly energetic relativistic jets, as well as the near black-hole accretion processes themselves, all invoke magnetic fields as active agents in angular momentum, mass and energy redistributions. In this review, we cover aspects of AGN feedback and the role played by magnetic fields, almost necessarily studied at vastly different length and timescales. We emphasize how typical large-scale galaxy interaction studies rely on parametric prescriptions for feedback, while detailed dedicated studies for near black-hole dynamics and relativistic jet propagation exist which take full account of magnetic field influences. We discuss representative hydro to magnetohydrodynamic (MHD) numerical simulations that exploit analogies with less energetic X-ray binary sources or even protostellar accretion-ejection systems, emphasize relativistic MHD descriptions, and point out that magnetic fields in accretion disks yield many linear instability routes to turbulence that have scarcely been recognized in the astrophysical community. In combination, they serve to show that magnetic field influences in AGN accretion, jet launch, energy feedback, and overall evolution are still far from completely understood, although many aspects have been disclosed by advanced analytical and numerical relativistic MHD studies.
Motivation: Astrophysical Jets
Radio galaxies confront us with dramatic views on energy redistributions at all scales, as mediated by central massive black holes lurking in their nucleus. A clear example is provided by the elliptical galaxy NGC5532, a nearby (red shift z = 0.0237, type S0) galaxy where the stellar distribution is in sharp contrast with its double-jetted appearance in radio images.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.