Radio-galaxies and jetted AGN: discovery, properties and impact

1. Radio-galaxies and jetted AGN:discovery, properties and impact Historical perspectives The family of radio-loud AGN The unified model of radio-loud AGN FRI and FRII radio galaxies Jets Formation and basic properties Superluminal motion Jets and the cooling flow problem

2. IV.10 : The discovery of AGN Early 1960s� Radio astronomers started to survey the sky Found many mysterious radio sources Quasi-stellar radio sources (quasars for short) Very difficult to identify� radio images were too fuzzy to allow quasars to be localized on sky Cyril Hazard� Used �Lunar occultation� to localize 3C273 I.e., measure the precise time when the radio signal from the quasar is blocked by the Moon� � then use knowledge of the Moon�s position to determine position of quasar. Hazard could localize 3C273 to about 1 arcsec.

4. M.Schmidt Took Hazard�s position and observed it with optical telescope� in particular, he took a spectrum Clearly observed emission lines of hydrogen, but spectrum showed �huge� redshift, z=0.158 Hubble�s law ? huge distance (747 Mpc using WMAP cosmology) Thus, object must be 1000x more powerful than regular galaxy

5. IV.11 : Radio-loud AGN 3C273 is an example of a radio-loud AGN� a significant fraction of its luminosity emerges in the radio band Nature of radio-loud AGN Detailed studies with radio interferometers showed that radio emission was often coming from an extended region Often showed a �double� structure Martin Rees suggested that the radio emission is powered by jets emerging from the immediate region around a black hole

9. The zoo of radio-loud AGN Radio-galaxies Strong extended radio emission but rather weak nucleus� display either narrow optical emission lines (NLRG) or broad optical emission lines (BLRG) Radio-loud quasars Strong extended radio emission and a strong/variable nucleus showing broad optical emission lines Blazars Strong and variable emission across the whole spectrum; no emission lines; highly polarized

11. Radio-galaxies are sub-divided into Faranoff-Riley (FR) classes

14. IV.12 : Properties of jets We want to know� How fast are jets traveling? How much energy do they carry? What are they made of? Normal matter (protons+electrons)? Pair plasma (electrons+positrons)? Poynting flux? How are they accelerated and collimated? Why do some AGN have jets and others do not?

15. IV.12 : Properties of jets We want to know� How fast are jets traveling? How much energy do they carry? What are they made of? Normal matter (protons+electrons)? Pair plasma (electrons+positrons)? Poynting flux? How are they accelerated and collimated? Why do some AGN have jets and others do not?

16. How fast are jets traveling? Best constraints come from direct observations of blobs moving in AGN jets In some jets, see �superluminal motion�� apparent motion exceeding the speed of light Strong evidence that the jet material is moving at relativistic velocities [see discussion on board]

17. How much energy is carried by jets? Generally hard to determine Can estimate power if we see interaction of jet with surroundings E.g., jets can blow bubbles in the hot (X-ray emitting) gas Can estimate power needed to blow bubbles

18. How are the jets powered? Don�t know how jets are powered! But we know that some jet sources are efficient� Use X-ray observations to estimate density & temperature of hot gas close to BH Then compute Bondi accretion rate� find efficient conversion of accreted mass-energy into jet power Probably has something to do with winding of B-fields by the accretion disk

20. IV.13 : The heating of the ISM/ICM by AGN jets Back to the effect that AGN jets have on massive galaxies and cluster cooling flows Computer simulations can be used to model the interaction of jets with the surrounding ISC/ICM