Quasars & AGN• Some supplemental reading: GREAT compilation of

review articles at http://nedwww.ipac.caltech.edu/level5/active_galaxies.html

Quasars and Active Galactic Nuclei (AGNs)

• What are they?– Observational Properties– “Standard” Model

• Continuum, Lines, etc.

• How are they found?– A variety of survey types, a zoo of AGNs– Orientation and Unified Models

• How do they evolve?– Strongly!

• Quasar Black Hole Masses• Relationship with their host galaxies

– Mutual Evolution?

The (slightly) active nucleus of our galaxy

• Probable Black hole– High velocities– Large energy generation

• At a=275 AU P=2.8 yr 2.7 million solar masses

• Radio image of Sgr A*about 3 pc across, with model of surrounding disk

From: Horizons, by Seeds

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.

Other items from Genzel’s group: http://www.mpe.mpg.de/www_ir/GC/

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..

Other items from Genzel’s group: http://www.mpe.mpg.de/www_ir/GC/

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).

NGC4151 with a range of exposures

Spectra of Stars, Spectra of AGNs

Stars from Horizons by Seeds

Average quasar, from Brotherton et al. (2001)

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– Think about the implications of jets. Timescales, angular

momentum. What do they imply?

3C31

Red = radio Blue = visible

Many Views of Radio Galaxy Centaurus A

Many Views of Active Galaxy Centaurus A

Quasar Images

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. (Unified models apply here.)

AGN Accretion• Old (1978!) basic accretion review paper:

– http://nedwww.ipac.caltech.edu/level5/Rees3/Rees_contents.html

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

From our text: Horizons, by Seeds

AGN Accretion Disks• Modern disk paper with AGN application, Koratkar

and Blaes (1999), review in PASP:– http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999PASP..111....1K&db_key=AST&high=3d6571051d23256

• Basic ideas follow from Shakura and Sunyaev (1973) standard alpha thin disks, plus relativity, vertical disk structure, non-LTE, Comptonization, etc. The models of Hubeny et al. (2000) are the most advanced and available on-line:– http://www.physics.ucsb.edu/~blaes/habk/

• alpha-disk solutions illustrate some basic physics and aren’t too complicated. Check out S&S73

• My post-doc Shang and I fit these models to real AGN SEDs. See these at the Wyoming AGN group webpage at http://physics.uwyo.edu/agn

Malkan (1983): Fitting the “Big Blue Bump” with a power-law plus an accretion disk model using three temperature zones:

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.

Quasar Spectral Energy Distributions (SEDs)

Wilkes (1997):3C 273:

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

From Horizons by Seeds

As we have discussed, inner AGN structure believed to feature a black hole fed by an accretion disk. Jets may emerge along the spin axis, and the disk illuminates BLR and NLR clouds. A dense molecular torus exists on larger scales and can obscure the central engine from certain lines of sight.

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 viewOnly gas well above and below disk is visibleSee only “slow” gas narrow emission lines

• Seyfert 1 galaxies: Slightly tilted viewHot high velocity gas close to black hole is visibleHigh velocities broad emission lines

• BL Lac objects: Pole on view Looking right down the jet at central regionExtremely bright – vary on time scales of hours

• Quasars: Very active AGN at large distancesCan barely make out the galaxy surrounding themWere apparently more common in distant past

From our text: Horizons, by Seeds

Spectral differences in Seyferts

Different Views of the Accretion Disk

The torus of gas and dust can block part of our view

• Seyfert 2 galaxies: Edge on viewOnly gas well above and below disk is visibleSee only “slow” gas narrow emission lines

• Seyfert 1 galaxies: Slightly tilted viewHot high velocity gas close to black hole is visibleHigh velocities broad emission lines

• BL Lac objects: Pole on view Looking right down the jet at central regionExtremely bright – vary on time scales of hours

• Quasars: Very active AGN at large distancesCan barely make out the galaxy surrounding themWere more common in distant past

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).

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.

Core dominant

Lobe dominant

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 have massive black holes in them• They are just less active now because gas supply is less

The AGN “Zoo”• Quasars (M < -23)

– Radio-Loud• FR II Radio Galaxies (type 2 quasars)

• Radio-loud Quasars or just Quasars (type 1 quasars)– Optically violent variables (OVVs)

– Radio-Quiet• QSOs – type 1 (broad lines) and type 2 (only narrow lines)

– Infrared-Loud – IRAS quasars, Far-IR Galaxies, ULIRGs

• Low Luminosity AGNs (M > -23)– Radio-Loud

• FR I Radio Galaxies

• Bl Lac objects, AKA Blazars

– Radio-Quiet• Seyfert Galaxies – type 1 through type 2 (see QSOs)

• LINERs (Low ionization nuclear emission-line regions)

• Shields “A Brief History of AGN” astro-ph/9903401

Surveys/Catalogs• SEDs immediately show AGNs don’t look like stars

– Selection by optical colors works (e.g., Sloan is best, http://www.sdss.org, also 2dF: http://www.2dfquasar.org )

– Mutliwavelength works (e.g., radio, X-ray, IR, plus optical)• E.g., FIRST Bright Quasar Survey

– Also possible to find via• Variability (e.g., MACHO)

• Proper Motion (lack thereof)

• Grism Surveys (e.g., Large Bright Quasar Survey)

• Older compilation catalogs like that of Veron-Cetty and Veron (2000) are being surpassed by SDSS and 2dF. http://www.obs-hp.fr/www/catalogues/veron2_9/veron2_9.html

• Hewett & Foltz (1994) on Quasar Surveys: http://nedwww.ipac.caltech.edu/level5/Hewett/frames.html

AGN Emission Lines• Hagai Netzer’s section in Saas-Fee Advanced

Courses 20, 1990, available online:– http://nedwww.ipac.caltech.edu/level5/March02/Netzer/Netzer_contents.html

• Classic textbook on photoionization is AGN2 by Don Osterbrock, popular public tool is CLOUDY by Gary Ferland (http://thunder.pa.uky.edu/cloudy/ ). Section 9.1.2 in Combes et al.

Basically, treat ionization state, heating/cooling balance, and relate emission line ratios to metallicity, density, ionizing continuum, etc. Note “LOC” models (Baldwin et al. 1996).

AGN Emission Lines

From Netzer et al. 1994 (I did the figures), on the SED and unusual emission line profiles of the OVV 3C 279. Note the steep power-law spectrum. Optically polarization is high. There is optical beamed synchrotron radiation in this source.

In many quasars, the emission line profiles are similar from line to line (consistent with optically thick BLR clouds). Not so for all objects, and especially important for figuring out BLR kinematics and dynamics (which is still not so clear).

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.

Quasar Images II

Ties to Host Galaxy Evolution• Quasar, star-formation evolution (from Boyle and

Terlevich 1998):

Ties to Host Galaxy Evolution• Central black hole masses seem to correlate with

host galaxy magnitude (from McLure and Dunlop 2001):

Ties to Host Galaxy Evolution• Central black hole masses best correlate with host

galaxy stellar velocity distribution (from Ferrarese 2000):

Reverberation mapping yields AGN black hole masses. A good recent review is by Peterson. More slides on this ahead! http://nedwww.ipac.caltech.edu/level5/Sept01/Peterson2/Peter_contents.html

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

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)

Max Planck Institute’s Galactic Core Group

This plot shows the quantitative limits.

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*)

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.

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).

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).

Potential Virial AGN Mass Estimators

Source Radius

X-ray Fe Kα 3-10 Rs

Broad-Line Region 600 Rs

Megamasers 4x104 Rs

Gas Dynamics 8x105 Rs

Stellar Dynamics 106 Rs

Where Schwarzschild radius Rs = 2GM/c2 = 3x1013 M8 cm

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.

Kaspi et al. (2000) studied bright PG quasars, particularly Hβ, finding that

R=32.9(λLλ5100/1044 erg s-1)0.7 lt-days

For the Hβ emitting gas.

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☼Onken & Peterson (2002)

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 dexFerrarese et al. (2001)

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)/4πR2nHc ~ L/nHR2

– So, for same U, nH, then expect that…

– R ~ L0.5

• How about in reality?

Empirically BLR Scales With Luminosity

• Mentioned previously the Kaspi et al. (2000) result how R ~ L0.7 (above). Misty Bentz et al. (2006) showed that proper correction for host galaxy leads to a slope of 0.5! This permits the possibility of using single-epoch measurements to estimate black hole masses – much easier!

Vestergaard (2002)

• Single epoch FWHM vs. rms FWHM for Hβ• Single epoch L vs. mean L

Vestergaard (2002)

• Single epoch BH Mass vs. RM BH mass

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

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.

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.

Using [O III] FWHM as a Proxy for σ*

• Shields et al. (2003).

From Peterson (2002)

Current/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.?

Our Program at Wyoming

• Black Hole Masses fundamental– Based on Reverberation Mapping (RM)– Only 50 objects RMed, resource intensive– Likely biased by orientation, other properties

• Get continuum, line light curves, ~12 AGN– Targets include RLQs with orientation info– B, V photometry at RBO, perhaps NB filters– Spectroscopy at WIRO– Measure time lags, etc., to measure masses– Learn science, skills, contribute to astronomy!