Quasars

1
Quasars AGN

• Some supplemental reading GREAT compilation of
  review articles at http//nedwww.ipac.caltech.edu/
  level5/active_galaxies.html

2
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?

3
The (slightly) active nucleus of our galaxy

• Probable Black hole
• High velocities
• Large energy generation
• At a275 AU P2.8 yr ? 2.7 million solar masses
• Radio image of Sgr Aabout 3 pc across, with
  model of surrounding disk

From Horizons, by Seeds
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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 Genzels group
http//www.mpe.mpg.de/www_ir/GC/
5
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 Genzels group
http//www.mpe.mpg.de/www_ir/GC/
6
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).

7
NGC4151 with a range of exposures
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Spectra of Stars, Spectra of AGNs
Average quasar, from Brotherton et al. (2001)
Stars from Horizons by Seeds
9
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 (gt 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?

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3C31
Red radio Blue visible
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Many Views of Radio Galaxy Centaurus A
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Many Views of Active Galaxy Centaurus A
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Quasar Images
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Theoretical Paradigm

• Supermassive black hole (millions to billions of
  solar masses)
• Powered by an accretion disk.
• Jet mechanisms proposed, but very uncertain.
  Most quasars dont have strong jets. Some
  quasars clearly have outflowing winds not well
  collimated.
• Also, an obscuring torus seems to be present.
  (Unified models apply here.)

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AGN Accretion

• Old (1978!) basic accretion review paper
• http//nedwww.ipac.caltech.edu/level5/Rees3/Rees_c
  ontents.html

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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
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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?bi
  bcode1999PASP..111....1Kdb_keyASThigh3d657105
  1d23256
• 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 arent too complicated. Check out
  SS73
• 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

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Malkan (1983) Fitting the Big Blue Bump with a
power-law plus an accretion disk model using
three temperature zones
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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/Wilke
  s/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.

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Quasar Spectral Energy Distributions (SEDs)

• Wilkes (1997)

3C 273
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Orientation and Unified Models
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.
From Horizons by Seeds

• 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/ww
  w_astro/agn/agn_unified.html

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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 ? narrow emission lines
• Seyfert 1 galaxies Slightly tilted view Hot
  high velocity gas close to black hole is
  visible High velocities ? 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

From our text Horizons, by Seeds
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Spectral differences in Seyferts
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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 ? narrow emission lines
• Seyfert 1 galaxies Slightly tilted view Hot
  high velocity gas close to black hole is
  visible High velocities ? 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).

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Radio Source Unification
Core dominant
Lobe dominant

• 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.

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What makes an AGN active?

• Need a supply of gas to feed to the black hole
• (Black holes from 1 million to gt1 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 gt Quasars (quasar epoch
  around z2 to z3)
• Most galaxies have massive black holes in them
• They are just less active now because gas supply
  is less

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The AGN Zoo

• Quasars (M lt -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 gt -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

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Surveys/Catalogs

• SEDs immediately show AGNs dont 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/catalogu
  es/veron2_9/veron2_9.html
• Hewett Foltz (1994) on Quasar Surveys
  http//nedwww.ipac.caltech.edu/level5/Hewett/frame
  s.html

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AGN Emission Lines

• Hagai Netzers section in Saas-Fee Advanced
  Courses 20, 1990, available online
• http//nedwww.ipac.caltech.edu/level5/March02/Netz
  er/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).
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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).
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Quasar Host Galaxies

• Hard to see. Why?
• How can you do it?
• HST (Bahcall, others)
• Near Infrared (eg., McLeod et al. 1996)
• AOsort 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.

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Quasar Images II
34
Ties to Host Galaxy Evolution

• Quasar, star-formation evolution (from Boyle and
  Terlevich 1998)

35
Ties to Host Galaxy Evolution

• Central black hole masses seem to correlate with
  host galaxy magnitude (from McLure and Dunlop
  2001)

36
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.cal
tech.edu/level5/Sept01/Peterson2/Peter_contents.ht
ml
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Taking a step back to fundamentalsArguments 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 lt 1 day imply very small source
• Radio Jet Stability implies large, stable mass
  with large angular momentum

38
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)

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Max Planck Institutes Galactic Core Group
This plot shows the quantitative limits.
40
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)

41
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.

42
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).

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Virial Mass Estimates

• M f (r ?V2 / G)
• r scale length of region
• ?V 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).

44
Potential Virial AGN Mass Estimators

• Source Radius
• X-ray Fe Ka 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

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Reverberation Mapping (RM)
Kaspi et al. (2000) studied bright PG quasars,
particularly Hß, finding that R32.9(?L?5100/1044
erg s-1)0.7 lt-days For the Hß emitting gas.

• 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.

46
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)
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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

Ferrarese et al. (2001)
48
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)/4pR2nHc L/nHR2
• So, for same U, nH, then expect that
• R L0.5
• How about in reality?

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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!

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Vestergaard (2002)

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

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Vestergaard (2002)

• Single epoch BH Mass vs. RM BH mass

52
Vestergaard (2002)

• Extend Calibration to UV Line CIV ?1549
• This is a calibrated C IV Black Hole Mass not
  wholly independent should be tested at high-z,
  high-L

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Brotherton Scoggins (2004)

• Hß and C IV Black Hole Mass Comparison
• All high-z sources very luminous, massive, high
  L/Ledd. Please excuse the color code.

54
Brotherton Scoggins (2004)

• Hß and C IV Black Hole Mass Comparison
• All high-z sources very luminous, massive, high
  L/Ledd. Please excuse the color code.

55
Using O III FWHM as a Proxy for s

• Shields et al. (2003).

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From Peterson (2002)
57
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.?

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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!