1	ASTR 5460, Mon. Oct. 18, 2004 Quasars and Active Galactic Nuclei Reading: Shields History article, Combes et al. Chapter 9. Some images from Keel’s site.
2	Dates, Information Probably no class Monday, Nov. 1. I will be observing at WIRO with the Goddard NIR camera (please ask if you’d like to come up – you’re welcome! Observing and talking during observing kicks ass). Observing project will be due Wed. Nov. 3, in class. Probably a take-home exam also due for Wed., Nov. 3. Handed out the previous Wed. Does this work for everyone? Homework #4 handed out Oct. 20, due Wed. Oct. 27? I anticipate a “mini-TAC” exercise for early Nov.
3	Quasars and Active Galactic Nuclei (AGNs)
4	The (slightly) active nucleus of our galaxy Probable Black hole High velocities Large energy generation At a=275 AU P=2.8 yr Þ 2.7 million solar masses Radio image of Sgr A* about 3 pc across, with model of surrounding disk
5	The (slightly) active nucleus of our galaxy The Genzel et al. movie based on NIR speckle interferometry of the Galactic core. Basic orbital mechanics confirm, to high precision, a mass of 2.6 million solar masses that the stars are orbiting. X-ray flaring also seen.
6	The (slightly) active nucleus of our galaxy FYI, here is one of the the Genzel groups individual K-band images taken at high spatial resolution using the technique of speckle interferometry..
7	Active Galactic Nuclei: AGNs A small fraction of galaxies have extremely bright “unresolved” star-like cores (active nuclei) Shown here is an HST image of NGC 7742, a so-called “Seyfert galaxy” after Carl Seyfert who did pioneering work in the 1940s (you might look up his original papers).
8	NGC4151 with a range of exposures
9	Spectra of Stars, Spectra of AGNs
10	Active Galactic Nuclei: AGNs Small fraction of galaxies have extremely bright “unresolved” star-like nuclei Very large energy generation Brightness often varies quickly Implies small size (changes not smeared out by light-travel time) High velocities often seen (> 10,000 km/s in lines) Emission all over the electro-magnetic spectrum Jets seen emerging from galaxies Already talked about jets last week. Next two slides are review. Think about the implications of jets. Timescales, angular momentum. What do they imply?
11	3C31
12	Many Views of Radio Galaxy Centaurus A
13	Quasar Images 1
14	Theoretical Paradigm Supermassive black hole (millions to billions of solar masses) Powered by an accretion disk. Jet mechanisms proposed, but very uncertain. Most quasars don’t have strong jets. Some quasars clearly have outflowing winds not well collimated. Also, an “obscuring torus” seems to be present.
15	AGN Accretion
16	Accretion Disks Black hole is “active” only if gas is present to spiral into it Isolated stars just orbit black hole same as they would any other mass Gas collides, tries to slow due to friction, and so spirals in (and heats up) Conservation of angular momentum causes gas to form a disk as it spirals in
17	AGN Accretion Disks
18	Malkan (1983): Fitting the “Big Blue Bump” with a power-law plus an accretion disk model using three temperature zones:
19	Quasar Spectral Energy Distributions (SEDs) Very nice and relatively brief review article from “Quasars and Cosmology” conference by Belinda Wilkes (CfA), a world expert on the subject: http://nedwww.ipac.caltech.edu/level5/Sept01/Wilkes/Wilkes_contents.html Must account for physical processes producing prodigious luminosity from radio wavelengths through the X-ray and even gamma ray regimes. Particular features of interest include radio-jets and the radio-quiet vs. radio-loud dichotomy, the “big blue bump” that produces the optical/UV energy peak and is thought to arise from an accretion disk, and the far infrared that represents re-radiation by hot dust.
20	Quasar Spectral Energy Distributions (SEDs) Wilkes (1997):
21	Orientation and Unified Models “Unified Models” explain some of the different classes of AGN, particularly type 1 and type 2 Seyferts, via orientation. For specifics, see the Annual Reviews article by Antonucci, 1993, a “bishop” in the “Church of Unification.” Another nice website: http://www.mssl.ucl.ac.uk/www_astro/agn/agn_unified.html
22	Unified Models: Different Views of the Accretion Disk The torus of gas and dust can block part of our view Seyfert 2 galaxies: Edge on view Only gas well above and below disk is visible See only “slow” gas Þ narrow emission lines Seyfert 1 galaxies: Slightly tilted view Hot high velocity gas close to black hole is visible High velocities Þ broad emission lines BL Lac objects: Pole on view Looking right down the jet at central region Extremely bright – vary on time scales of hours Quasars: Very active AGN at large distances Can barely make out the galaxy surrounding them Were apparently more common in distant past
23	Spectral differences in Seyferts
24	Different Views of the Accretion Disk The torus of gas and dust can block part of our view Seyfert 2 galaxies: Edge on view Only gas well above and below disk is visible See only “slow” gas Þ narrow emission lines Seyfert 1 galaxies: Slightly tilted view Hot high velocity gas close to black hole is visible High velocities Þ broad emission lines BL Lac objects: Pole on view Looking right down the jet at central region Extremely bright – vary on time scales of hours Quasars: Very active AGN at large distances Can barely make out the galaxy surrounding them Were more common in distant past
25	Radio Source Unification Core-dominant sources are seen jet-on, have flat radio spectra, and are variable, optically polarized and beamed. Lobe-dominant sources are not very variable, have steep radio spectra dominated by optically thin synchrotron emission, and are not beamed strongly. Can measure orientation by various methods, e.g., LogR* = core/lobe radio flux at 5 GHz rest-frame (Orr & Browne 1982), also Rv which normalizes core flux with an optical magnitude (Wills and Brotherton 1995).
26	Radio Source Unification From Wills and Brotherton (1995), plotting Log R (which is rest-frame 5 GHz) core to lobe flux ratio), vs. the jet angle to the line of sight where the jet angle is estimated from VLBI superluminal motion.
27	What makes an AGN active? Need a supply of gas to feed to the black hole (Black holes from 1 million to >1 billion solar masses! Scales as a few percent of galaxy bulge mass.) Collisions disturb regular orbits of stars and gas clouds Could feed more gas to the central region Galactic orbits were less organized as galaxies were forming, also recall the “hierarchical” galaxy formation Expect more gas to flow to central region when galaxies are young => Quasars (“quasar epoch” around z=2 to z=3) Most galaxies may have massive black holes in them They are just less active now because gas supply is less
28	The AGN “Zoo”
29	Surveys/Catalogs
30	AGN Emission Lines
31	AGN Emission Lines
32	Quasar Host Galaxies Hard to see. Why? How can you do it? HST (Bahcall, others) Near Infrared (eg., McLeod et al. 1996) AO…sort of. Issues here. What are their properties? Are they related in any way to the activity? Very little known before advent of HST, AO, and large near-IR detectors. Still a challenging type of observation. Initially thought (based on Seyfert galaxies and radio galaxies) that radio properties were related to host type. Seems to have been a selection effect.
33	Quasar Images II
34	Quasar Images III: “Starburst-Quasar”
35	Post-starburst Quasars One of my current areas of research interest. I’ll hand out recent telescope proposals that may be useful with regard to your own proposal projects. You can tell me how good or how sucky they are (seriously!). I should be able to convince a non-expert that these observations are of interest.
36	Ties to Host Galaxy Evolution
37	Ties to Host Galaxy Evolution
38	Ties to Host Galaxy Evolution
39	Taking a step back to fundamentals: Arguments for Black Holes in AGNs Energy Considerations Nuclear luminosities in excess of 10¹³ suns Gravitational release capable of converting on order 10% rest mass to energy Rapid Variability Timescales < 1 day imply very small source Radio Jet Stability implies large, stable mass with large angular momentum
40	Measuring Black Hole Masses in “Nearby” Galaxies SgrA* in the Milky Way Water Masers in NGC 4258, a few others Spatially Resolved Gas or Stellar Dynamics Using the Hubble Space Telescope (HST)
41	Max Planck Institute’s Galactic Core Group
42	Water Masers in NGC 4258 Based on Greenhill et al. (1995) Warped Disk Model Radial Velocities and Proper Motions Measure a Mass of 4x10⁷ solar masses (20 times more massive than SgrA*)
43	Spatially Resolved Spectroscopy from Space Shows BH Signatures HST STIS shows evidence for a super massive black hole in M84 based on spatially resolved gas dynamics (Bower et al 1997). Can also be done by examining spatially resolved stellar absorption line profiles, plus complex 3D orbital modeling.
44	The “M-sigma” Relation Black Hole Masses are about 0.1% of the central galactic bulge mass (a big surprise to theorists) and tightest correlation is with the stellar velocity dispersion (after Gebhardt et al. 2000).
45	Virial Mass Estimates M = f (r ΔV²/ G) r = scale length of region ΔV is the velocity dispersion f is a factor of order unity dependent upon geometry and kinematics Estimates therefore require size scales and velocities, and verification to avoid pitfalls (eg. radiative acceleration).
46	Potential Virial AGN Mass Estimators Source Radius X-ray Fe Kα 3-10 R_s Broad-Line Region 600 R_s Megamasers 4x10⁴ R_s Gas Dynamics 8x10⁵ R_s Stellar Dynamics 10⁶ R_s Where Schwarzschild radius R_s = 2GM/c² = 3x10¹³ M₈ cm
47	Reverberation Mapping (RM) Broad lines are photoionized by the central continuum, which varies. The line flux follows the continuum with a time lag t which is set by the size of the broad-line emitting region and the speed of light. Recombination timescales are very short, BLR stable, and continuum source small and central.
48	Does the BLR obey the Virial Theorem? Four well studied AGNs, RM of multiple emission lines shows the expected relationship (slope = -2) between time lags and velocities (note each of the three will have different central black hole masses). NGC7469: 8.4x10⁶ M_☼ NGC3783: 8.7x10⁶ M_☼ NGC5548: 5.9x10⁷ M_☼ 3C 390.3: 3.2x10⁸ M_☼
49	Does the BLR obey the Virial Theorem? RM-derived masses follow the same M-sigma relationship as seen for normal galaxies that have black hole masses measured from HST spatially resolved gas or stellar dynamics. Not more points since obtaining sigma for AGN is difficult (the AGN dilutes the stellar absorption line EWs). Good to 0.5 dex
50	Expect that BLR Scales With Luminosity Photoionization and “LOC” Models (Baldwin et al. 1996) suggests that strong selection effects make line emission come from same physical conditions (same U, n) U = Q(H)/4πR²n_Hc ~ L/n_HR² So, for same U, n_H, then expect that… R ~ L^0.5 How about in reality?
51	Empirically BLR Scales With Luminosity Mentioned previously the Kaspi et al. (2000) result how R ~ L^0.7 (above). This permits the possibility of using single-epoch measurements to estimate black hole masses – much easier!
52	Vestergaard (2002) Single epoch FWHM vs. rms FWHM for Hβ Single epoch L vs. mean L
53	Vestergaard (2002) Single epoch BH Mass vs. RM BH mass
54	Vestergaard (2002) Extend Calibration to UV Line CIV λ1549 This is a calibrated C IV Black Hole Mass – not wholly independent – should be tested at high-z, high-L
55	Concerns about the Extrapolation FWHM of C IV and Hβ not well correlated (M~V²). High-z quasars span higher range in black hole mass and L/Ledd than calibration sample.
56	Brotherton & Scoggins (2003) Testing the Self-Consistency of Vestergaard (2002) with high-z, high-L quasars using near-IR spectra (tougher to do than optical work).
57	Brotherton & Scoggins (2004) Hβ and C IV Black Hole Mass Comparison All high-z sources very luminous, massive, high L/Ledd. Please excuse the color code.
58	Brotherton & Scoggins (2004) Hβ and C IV Black Hole Mass Comparison All high-z sources very luminous, massive, high L/Ledd. Please excuse the color code.
59	Brotherton & Scoggins (2004) Hβ and C IV Black Hole Mass Comparison All high-z sources very luminous, massive, high L/Ledd. Please excuse the color code.
60	Brotherton & Scoggins (2003) Vestergaard (2002) Confirms the self-consistency of Vestergaard (2002), although there remain some issues. For instance, C IV may slightly, systematically underestimate black hole masses (2 sigma effect).
61	From Peterson (2002)
62	Future Work: Real Astrophysics Black Hole Demographics (growth with z) Is all growth as AGN? Does that produce the mass seen in relic black holes at low z? How does the M-sigma correlation arise? That is, how is black hole growth linked to the growth of galaxy bulges and star formation? How do AGN behave as a function of mass, L/Ledd, viewing angle, etc.?
63	Using [O III] FWHM as a Proxy for σ_* Shields et al. (2003).
64	Quasar Absorption Lines Intrinsic Broad (BALs) Narrow (NALs) Intervening Galactic Lyman alpha Metal line systems
65	BALQSOs – What are they? Are they normal quasars with equatorial winds, seen edge-on? Or are they an evolutionary phase?
66	Radio-Loud BALQSOs Originally exclusively radio-quiet, but the first radio-loud BALQSOs found by Becker et al. 1997 and Brotherton et al. 1998. From Becker et al. (2000), 90% of the radio-selected BALQSOs are compact in FIRST maps (vs. 60% in the non-BAL sample), and BOTH steep and flat radio spectra are present. Seems to rule out simple orientation schemes, right?
67	Radio-Loud BALQSOs BALQSO Spectra from Brotherton et al. 1998.
68	Gravitational Lensing by Clusters (See Longair) Mass bends space and hence light paths (Einstein 1915; General relativity).
69	Gravitational Lensing by Clusters (See Longair) Not just one dimensional! Here’s the famous Einstein Cross (from Keel’s site)
70	Gravitational Lensing by Clusters (See Longair) Mass bends space and hence light paths (Einstein 1915; General relativity). Angular deflection by point mass is: Where p is the “collision parameter.” What happens when p goes to zero?
71	Gravitational Lensing by Clusters
72	Gravitational Lensing Previous derivation assumes Euclidean geometry (which WMAP says is OK!). Still OK if the distances are angular diameter distances (chapter 5). Expressing the result in physical terms: So, what is the typical size for galaxies? For clusters?
73	Gravitational Lensing by Clusters
74	Gravitational Lensing by Clusters OK, but clusters are not point sources. See discussion on P. 96-97 of Longair. For an isothermal gas sphere can derive the result that:
75	Gravitational Lensing by Clusters
76	Gravitational Lenses Individual systems are cataloged on the Castles webpage: http://cfa-www.harvard.edu/castles/ Also there is lensing software there available for downloading. Also lists binaries too (where I have a discovery).
77	Another look at the AGN model Not to scale!