1 / 27

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

IV.10 : The discovery of AGN. Early 1960s Radio astronomers started to survey the skyFound many mysterious radio sourcesQuasi-stellar radio sources (quasars for short)Very difficult to identify radio images were too fuzzy to allow quasars to be localized on skyCyril Hazard Used Lunar occu

benson
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    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 Moons position to determine position of quasar. Hazard could localize 3C273 to about 1 arcsec.

    4. M.Schmidt Took Hazards 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 Hubbles 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? Dont 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

More Related