1. Radio Loud and Radio Quiet AGN
Matthew Lister, Department of Physics & Astronomy, Purdue University
& K. I. Kellermann, National Radio Astronomy Observatory
ABSTRACT: Active galactic nuclei are the most powerful known phenomena in the Universe, in terms of total energetics, and are ideal laboratories for studying extreme physics, including relativistic MHD, general relativity, and high-energy particle acceleration and radiation. They play a key role in influencing large-scale structure formation at early cosmic epochs via powerful jetted outflows and feedback mechanisms. We describe here many of the fundamental aspects of AGN jet physics that remain poorly understood, and how they may be addressed via radio-through-submm studies.
Duty Cycles and Feedback
How important are factors such as galaxy mergers, jet feedback, host galaxy type, black hole mass and spin in determining whether an AGN has an active jet?
How do AGN jets evolve?
What is their typical on/off duty cycle?
Why do most powerful young radio jets never reach the large, double-lobed radio galaxy stage?
Key studies: radio imaging and classification surveys, VLBI kinematic studies, luminosity functions.
Fig. 1: The giant radio galaxy B , showing evidence of re-starting jets. (ATCA image by L. Saripalli et al. )
Fig. 2: Jets of the low-BH mass, high accretion rate narrow-lined Sy I galaxy J , as imaged at ~8 GHz on kpc and pc (inset) scales with the JVLA and VLBA (Richards & Lister 2015, ApJ 800, 8)
2. Radio Power
What roles do supermassive black hole (SMBH) spin, SMBH mass, accretion rate, and external environment play in determining the kinetic power and radio luminosity of AGN and their jets?
What is the radio emission mechanism in radio-quiet AGN – is it related to SMBH activity, star formation, or both?
What fraction of the radio luminosity of radio-quiet AGN is due to radio jets?
Can radio-loud AGN account for an unexplained non-thermal excess seen in the extragalactic radio background by ARCADE-2 and the GBT (Farnsworth et al. 2015, ApJ 779, 189) ?
Do radio-quiet AGN have a fundamentally different luminosity function and/or cosmic evolution than radio-loud quasars?
Key studies: radio imaging surveys, multiband radio AGN surveys
Fig. 3: ARCADE-2 plot from Fixsen et al. (2011, ApJ 734, 5) showing a radio continuum excess over the CMB above 3 GHz.
Fig. 4: Hybrid Morphology (HYMOR) quasar PKS displaying FR I and FR II morphology jets, with Chandra X-ray emission in false-color and 5 GHz VLA radio contours (Stanley et al. 2015, ApJ 807,48)
3. Emission Mechanisms
Are coherent and/or other emission mechanisms needed to explain the extremely compact radio-emitting regions seen in AGN jets? (see poster by Zensus et al.)
Extreme Lorentz factors (>> 100) have been invoked to explain how TeV gamma-rays can escape from rapidly variable AGN jet emission regions. Why are these so much faster than the jet speeds seen in direct proper motion studies? Can we find any direct evidence for a ultrafast TeV-emitting spine/slow radio-emitting sheath structure?
What role do MHD processes play in energizing portions of AGN jet flows? Are there plasma instabilities driven by the accretion disk/SMBH?
The spectral energy distributions (SEDs) of kpc-scale knots in many AGN jets cannot be fit with simple synchrotron or inverse-Compton scattering models - are there more complex particle acceleration mechanisms such as magnetic reconnection at work?
What is the connection between high-energy gamma-ray and radio emission in AGN? Is there an unseen population of radio-quiet, gamma-ray loud blazars? What are the counterparts to the large population of unassociated Fermi gamma-ray sources?
Key studies: VLBI proper-motion and imaging studies, multiband (total intensity and polarimetric) radio imaging, large SED surveys of AGN, radio/sub-mm follow-up of gamma-ray sources.
Fig. 5: Minute-timescale TeV variability in the quasar PKS (Aharonian et al. 2007, ApJ 664, L71)
Fig. 6: Distribution of maximum AGN jet speeds from the MOJAVE VLBA survey, indicating Lorentz factors up to ~40 (Lister et al. 2015, in prep).