1. Active Galactic Nuclei Astronomy 315 Professor Lee Carkner Lecture 19

2. Strange Galaxies  Some galaxies have a compact, powerful source of energy at their core  Among the most energetic objects in the universe    Need multiwavelength observations to understand them 

3. M87

4. Jet From M87

5. Seyfert Galaxies  Seyfert galaxies are spirals with optically bright, concentrated nuclei    Can change in brightness very quickly   Small, but very bright

6. Other Seyfert Properties  Some Seyferts have broad emission lines    These same Seyferts also are bright in high energy X-ray and UV radiation  Called Type 1 Seyferts 

7. Seyfert Clues  Are there any common properties shared by Seyfert galaxies?    Are Seyferts caused by gravitational interactions?

8. Radio Galaxies  Some galaxies are flanked on either side by a pair of radio lobes   Some central galaxies are also bright radio sources and some are not 

9. Cygnus A Radio Galaxy

10. Mapping the Lobes  Radio lobes often show hot spots of enhanced emission   Lobes are material ejected from the star and impacting the intergalactic medium   Radio galaxies produce bipolar jets (like young stars)

14. Source of Radio Waves  Radio emission is due to synchrotron radiation   Lobes must have magnetic field and galaxy must be ejecting electrons  Total energy stored in lobes is huge 

15. Radio Galaxy Properties  Central galaxy is often giant elliptical and in a crowded cluster  Often deformed   Jets sometimes are twisted   Some radio galaxies have broad and narrow lines, some just narrow lines 

16. BL Lac Objects  BL Lac objects look like stars but show rapid variations   They don’t show the broad or narrow lines we see in Seyfert galaxies  Don’t have radio lobes  

17. Quasars  Some sources of radio galaxies look like stars   Quasars have very large red shifts and very large distances   Since quasars are billions of light years away, we are seeing what they looked like billions of years ago 

20. Quasar Properties  In most cases you can’t see the host galaxy   Core must be brighter than regular AGN   Quasars are younger than “normal” AGNs  Type 1 quasars have broad emission lines, Type 2 quasars do not 

21. AGN Power Source  We have two questions about AGNs    Different types of AGNs are due to viewing matter falling into a black hole from different angles

22. Massive Black Holes  AGN black holes are a million to a billion times the mass of the Sun  Why do we think they have black holes?   Computed densities indicate black hole  AGNs vary so rapidly that the emitting region must be very small (small+massive=BH) 

23. Structure of the Core  Black hole pulls matter into an accretion disk   Outer disk is thick can block view of center    The moving material twists up the magnetic field creating a magnetic flux tube that the jets follow out the poles

24. Unified Model  How does this model account for the basic properties of AGNs?     We thus see the jet and disk regions in different ways, producing the observed type of AGN

25. Case 1 -- Face on  Can see the radio jets, but no lobes  Can’t see broad or narrow lines   Type of AGN 

26. Case 2 -- Inclined  Can see radio emission and lobes   Can also see broad and narrow lines   Types of AGN:   

27. Case 3 -- Edge on  Can see radio emission and lobes   Only see narrow lines   Types of AGN   

28. Unified Model for AGNs

29. Quasars and AGNs  Quasars act very much like extra powerful versions of radio galaxies or BL Lac objects   Quasars may be young active AGN, low red shift active galaxies may be AGN that have been refueled

30. AGN and Non-AGN  Why are some galaxies active and others not?  We think all galaxies have black holes   What makes a galaxy active is matter falling into it   Collisions and tidal forces may disrupt the center of galaxies and move material into the black hole

31. Next Time  Read 24.3, 25.1-25.4