Active Galactic Nuclei Flashcards
Describe Quasars.
compact centre outshining rest. nearly featureless. radio to x-ray. broad emission lines in optical.
Describe Blasars.
extremely luminous. weak emission lines, swamped by synch.
Describe Seyfert galaxies.
spiral, bright unresolved cores. strong optical emission from excitation. ionisation states too high to come from stars. weak or no radio.
Describe Radio galaxies.
elliptical in optical - 10^10 times brighter in radio. emission from nucleus +/ pair of symmetric lobes each side of nucleus.
Describe Fanaroff-Riley I.
collimated jets - ending bright hotpspots, brightest in lobes.
Describe Fanaroff-Riley II.
brightest in centre, less luminous. jets less collimated.
Distinguish between radio loud and quiet galaxies.
loud: >10 brighter in radio (5GHz) than in optical (440nm)
Recall the components of AGN.
central BH, accretion disk, hot corona, jets & lobes, broad/narrow line region, molecular torus.
What evidence do we have for BH in centre of galaxies?
gravitational red-shifts in X-ray Fe lines (double horn instead of Gaussian).
Describe the hot corona.
source of X-rays from AGN. IC scatters disk photons.
Describe the appearance of jets.
Depending on line of site, since jets relativistic, asymmetry due to Doppler boosting.
Describe the lobes.
relativistic e- terminate in hotspots, accelerated in shocks, fill lobes, young further out.
Theory of jet production.
B fields twist around rotation axis - confine jet (collimation) extract rotational energy from disk to accelerate e-
Describe the broad line region.
optical spectra of quasars and Seyferts. gas clouds ionised by photons from disk. too wide for thermal broadening (T => full ionisation). clouds must be 1pc from SMBH.
Describe narrow line region.
emission from clouds further out. move more slowly, still ionised by disk emission.
Describe the molecular torus.
BB emission from dust. torus absorbs emission from nucleus, re-emits IR. beyond accretion disk but in same place.
Radio-loud: 0
doppler boosted jet synch. drowns out emission lines. Blasar.
Radio-loud: intermediate
inner regions visible. radio galaxy with broad and narrow emission. beaming of jet emission (synch). Quasar.
Radio-loud: 90
disk, broad line emission, obscured by torus. narrow lines, jets, lobes visible.
Radio-quiet: intermediate
Seyfert with broad and narrow. S1 if high L. Quasar if low L.
Radio-quiet: 90
Seyfert 2 with no broad emission lines.
What is the aim in the derivation of the Minimum Energy Condition?
Find minimum B-field to produce given synch. emission. (source has energy in particles and B-field)
