Active Galactic Nuclei

1. Active Galactic Nuclei Luke Corwin Crystal Austin May 1st, 2003

2. Outline • Act I: History / Overview • Act II: The Disk • Act III: The Black Hole • Act IV: Jet & Outflow • Act V: Different Types of AGN…Different Types of Physics • Act VI: Consequences for Cosmological Parameters

3. Act I: History and Overview • Why should we study AGN? • Observe galaxy evolution • Understand black hole physics • Possible use as standard rulers • Implications on Cosmological models and parameters • Particle Fountains are cool!

4. The first AGN discovered: 3G 273 • Originally classified as a radio star (1963) • Angular Diameter was small • Found that red shift was large, must have been a large, luminous extragalactic object • Had a variable spectra with emission lines • Theorized that were compact massive objects

5. Later… • More distant, compact objects were found • Emitting power ~ 1020 erg/g • Luminosity ~hundreds of galaxies • Appeared like point objects • Curiosity, Research, Theorizing… • First Black Hole discovered: Cygnus X-1 • Small, massive, radio object (1971) • Now believed that ‘Quasars’ were powered by black holes as well

6. Basic Review • The universe is full of galaxies, most of which have luminous bulges • A few of these galaxies have very luminous bulges, they are known as Active Galactic Nuclei • Most host galaxies of AGN are elliptical • Very distant AGN are known as quasars because they look quasi-stellar

7. Today • We have a basic physical understanding of black holes in the centers of galaxies • Modeling of AGN are still lacking many of the parameters • More research and modeling are needed • Do not know exactly how jets are formed or which galaxies are prone to AGN activity

8. Act II: The DiskThree Adiabatic Models • Advection (quasi-spherical inflow) • Torus Model • Super-Eddington Model • All models lead to rapid mass loss • Formation of funnel expected

9. Detection

10. Formation & Evolution • Accretion may start with formation of galactic bulge • Such a high accretion phase may be part of the normal evolution of all galaxies. • Correlation between black hole mass and properties of bulge • Must occur for ~ 5-10% of a galaxy’s life, otherwise holes would become too massive • AGN hosts and “normal” galaxies are indistinguishable

11. AGN host (0313-192) & NGC 4013

12. Radiation from Disk • Black Body emission from optical through X-ray • Compton scattered coronal X-rays • Thompson scattered coronal X-rays

13. The Magnetic Field • Magnetic field’s role is probably significant but not well understood. • May extract angular momentum from the spinning hole and transfer it to disk.

14. Act III: The Black Hole • Black holes in galactic nuclei can vary from 106 to 1010 M< (low mass black holes are usually radio quiet) • BHs are described by 3 parameters • Mass • Spin • Charge • BHs are thought to be in most normal galaxies (via kinematic studies)

15. How to detect AGN BHs • Observe inner disk kinematics • If the velocities are too great to be explained by the luminous mass, may indicate BH • Micro-lensing events • X-ray surveys for objects radiating above the Eddington limit for stellar mass holes • Binary systems where the orbital kinematics can predict the system’s mass and BH presence

16. Determining BH mass • Virial Method • Apply to broad emission line clouds • Direct Dynamical Methods • Gas Orbital Speeds very near the BH • Host Galaxy Properties • Stellar velocity dispersion • MH~1.3E8(s/200kms-1)3.65 • Bulge luminosity • Radio loudness

17. BH mass vs. Luminosity, Eddington Ratio There is no useable correlation between the bulge luminosity and the mass of the black hole. The plot of radio loudness vs. black hole mass showed a similar spread. Thus there is also no useable correlation with radio loudness.

18. BH Mass vs. Radio Loudness • There seems to be no correlation between the host galaxy’s radio loudness and the black hole mass • The best methods so far are stellar velocity dispersion or observing gas speeds outside of the space warping effects of the black hole

19. BH Rotation • Broad iron lines detected very close to the event horizon in AGN X-rays • Non-rotating BHs cannot have a stable disk structure within the 3 Schwarzschild radii • Structures out side of this radius, r=6m, would only produce thin lines • Rotating BHs allow for stable structures closer to the event horizon • Thus we may have a way to detect the spin if we can resolve how close we can detect the iron lines

20. Spin and Reduced Mass • For a non-spinning BH, the event horizon is given by r=2m • Rotating BHs show effects of spin, thus r becomes m+(m2-a2).5 • As the angular momentum per unit mass (a) increases, it reduces the effective mass of the black hole • This reduced mass energy becomes available to power high energy emission (jets) • Space-time is also dragged with the rotation thus spin cannot be measured directly

21. BH Charge and Magnetic Field • It is believed that charged black holes cannot exist in a stable state • Mainly exists for theorists (wormholes!) • Even though the BH is not charged, can still create a B ~ 104G • A heavy disk is necessary for this field • This field, disk interaction may help explain how stable jets on the Kpc scale are possible

22. Driving the AGN • Magnetic Field lines leaving the disk, approaching high latitude, and then plunge into the disk can extract energy and angular momentum driving the system. • Collimation effects of the Kerr field describes how particles in an accretion disc can be deflected to the rotational poles by a Kerr ring singularity. Galactic jets are evidence for gravitational collapse.

23. Act IV: Jet & OutflowClassification • By Orientation • Blazar (Almost on line of sight) • Quasar (≤45o from line of sight) • Radio Galaxy (≥45o from line of sight) • By Strength (Fanaroff-Riley) • Type I: Weak jets with diffuse appearance • Type II: Powerful jets with double radio lobes

24. FR1FR2

25. Jet Formation & Dissipation • Generated very near the hole • Two Models: • Energy extracted from BH angular momentum • Magnetic winds on inside of accretion disks • Scale depends on jet strength • Dissipates when it reaches sub-sonic speeds in halo gas or inter-galactic medium

26. Radiation Sources • Low-energy photons (IR through X-rays) produced by synchrotron emission from electrons • High energy photons (-rays) produced by Inverse Compton (IC) Scattering • In weaker sources, “synchrotron self-Compton” scattering dominates • In strong sources, external photons enter jet and undergo IC scattering

27. The Magnetic Field • Again, interactions important but not well understood • Field lines wrap around symmetry axis, collimate beam, and shield it from interactions with surrounding matter • May power phenomena in disk similar to that seen in the solar corona.

28. Act V: Different Types of AGN…Different Types of Physics • Different views, different data • Blazars: can get a view of what is going on near the black hole • Tests of the Kerr Metric and General Relativity • Quasars: turbulence and extra-galactic media research, • Radio Galaxies: why some galaxies are radio loud vs. radio quiet

29. Blazars • Light is highly polarized due to synchrotron radiation • Spectra is highly variable in the radio and optical • Relativistic effects amplify the spectral continuum that is produced close to the BH • Dominate over thermal emission, thus can use to probe the inner jet

30. Optically, Blazars are not similar • Spectrally, Blazars have similar features • 2 peaks in SED vs. luminosity • More Luminous sources peak at low energies • Less Luminous sources peak at high energies This can be interpreted as an increased cooling rate from the low power sources

31. Blazar Diagram Extragalactic relativistic jet. The flow is accelerated and collimated close to the BH. At a distance ~.01 pc part of the power is dissipated and those jets closely aligned to the line of sight appears as Blazars. After this region the jet will propagate with small dissipation.

32. New Quasar Physics • Ultraviolet quasar emission lines may be able to provide robust estimates of black hole masses from the observed optical spectra of quasars out to z > 2 • Quasars at z>=6 with large HII regions around them allows their L-a emissions to be transmitted with out lots-o-absorption. Theoretically, we could use this to study the evolution of galactic spatial distribution, ionization state of the intergalactic medium and the age of the quasars.

33. Radio Galaxy Physics • Study the evolution of galaxy clustering • Evolution of galaxies vs. time (graph) • z>3 radio galaxies found with giant Lya nebulae, agrees with CDM halo theories • Black holes with mass 108.5M< dominated the accretion history of the universe. These are the masses currently found in elliptical radio galaxies

34. Act VI: Consequences for Cosmological Parameters (e.g. Ω0) (Buchalter, et al.) • Cosmological models can be tested if we have a population of standard rods. • If rods are randomly oriented, upper limits can still be set on the Ω parameters.

35. Problems with previous attempts • Found evidence for Euclidean Universe • Systematic errors • Used data from multiple quasars surveys • Made too many assumptions about jet structure • Optical/Radio selection effects • Use samples below effective angular resolution • Intrinsic size may vary with red shift

36. Selection Criteria • Use only double-lobed FR-II Quasars • Z > 0.3 (eliminates confusion with faint near objects) • Use data from only one survey (VLA FIRST)

37. Analysis Method & Results • Coarsely bin angular sizes • Assume average angular size and other parameters vary as a power law functions of red-shift. • Extensive statistical analysis • Showed evidence that Friedmann Model is accurate • Could not distinguish between values of Ω0 and Ω. • All results and assumptions internally consistent

38. Results

39. Recapitulation • AGN seem to be part of normal galaxy evolution • AGN are powered by accretion disks onto super-massive black holes • Can be used as approximate standard rulers • Universe is not Euclidean