Active Galactic Nuclei

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Active Galactic Nuclei

• Ay 16, April 8, 2008

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AGN

• DEFINITION
• PROPERTIES
• GRAVITATIONAL LENSES
• BLACK HOLES
• MODELS

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WHAT IS AN AGN?

• Objects that emit significant amounts of
  radiation from non-thermal sources
• (i.e. not stars or dust or thermal gas).
• In order of discovery
• Seyfert Galaxies
• Radio Galaxies
• Quasars
• BL Lac Objects
• LINERS (Low Ionization Emission Regions)

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Early History

• Carl Seyfert strange emission line galaxies
  (1943)
• Birth of Radio Astronomy discovery of strong
  sources radio galaxies (40-50s)
• Greenstein Schmidt QSOs (1963)
• Surveys of Extremely Blue Objects (60-70s)
• Surveys at other Wavelengths (70s gt )

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• SY1
• AGN
• Spectra
• SY2
• QSO

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Mean UV QSO Spectrum
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LBQSO Spectrum
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• NGC 4151
• Typical
• SY1

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• Seyfert 1 galaxy and quasar spectra are dominated
  by broad line regions, lines often showing
  doppler velocities of 0.1c
• Seyfert 2 galaxies spectra are dominated by
  narrower lines, 1-2000 km/s wide
• LINER spectra are dominated by stars plus
  emission lines from multiple ionization states
  indicative of non-thermal excitation
• BL Lac spectra show almost no features but strong
  continua

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M87 Core In X-rays

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Markarian 231
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Markarian 421

• BL Lac in an E Galaxy
• TeV ? Source

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BL LAC SEDs

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Radio Galaxies

M87 Virgo A
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• M87 in the Radio
• (VLA)

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• M87
• Central
• Jet

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• M87
• Jet
• In 3 bands

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• Centaurus
• A
• Radio on
• Optical
• Image

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• Cygnus A (VLA Conway Blanco)

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Synchrotron Power

• related to kinetic enegy of electron
• (1 - (v/c)2)-1/2 (1 - ?2)-1/2
• where ? v/c

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Synchrotron Spectra
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AGN
NORMAL
LINERS
Baldwin, Phillips Terlevich
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Ly Alpha Forest
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Eddington Luminosity

• Largest Luminosity that can pass through a gas in
  hydrostatic equilibrium
• Outward Force of Radiation Pressure
• gt Inward Force of Gravity
• Gravity dP/dr -?g -GM?/r2
• Luminosity dP/dr -(?T?/mpc) (L/4?r2)
• ?T Thomson Cross section
• LEdd 4?GMmpc/?T
• 3.3 x 104 L?(M/M?)

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Gravitational Lensing

• Deflection of Light passing at a distance b by an
  object of mass M
• ? 4GM/bc2
• Bending of light by the Sun
• r 6.96 x 1010 cm M 1.989 x 1033 g
• ? 8.47 x 10-6 radians 1.74

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• Gravitational lensing

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22370305 Einsteins Cross
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Gravitational Redshift

• Photons lose E as the move out of a gravity well.
• For a photon E hc/?, m E/c2 h/c?
• Gravitational Potential E -GMm/r
• ?E -GMh/c?r
• ??/? GM/rc2
• which generally is pretty small except for NS
  and BH

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Black Holes

• Curvature around a point mass has a critical
  radius Schwarzchild Radius
• Inside this is a singularity
• RS 2GM/c2
• In units we know
• RS 3.0 km (M/M?)
• Gravitational redshift from RS ?

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NGC 4261 X-ray vs Optical
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?V 1100 km/s
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M87s central mass

• Given the HST observations, whats the enclosed
  mass?
• ?v 1100 km/s ? 1 D 16.1 Mpc
• R 0.078 kpc (78 pc)
• GMm/R 1/2 mV2 for circular orbits
• M 0.5 V2R/G
• G 4.309 x 10-6 kpc (km/s)2 / M?
• Mcore 1010 M?

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Reverberation Mapping

NGC5548
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Lag 20 days Size 20 light days 0.02 pc
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Maggorian Relation (Nuker team)
Almost every large galaxy has a central BH, and
the BH mass is directly correlated with the
galaxys total bulge mass!
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A Unified Model of AGNs

• We have come to believe that all AGN are
  essentially driven by the same phenomena --- a
  central black hole surrounded by an accretion
  disk, hot clouds of gas and dust. The disk is
  hot, 105 K plus. The AGN is powered by accretion
  onto the BH.
• And what you actually see is driven by the
  viewing angle.

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Unified AGN ModelBH Disk Torus

• SY2 SY1 BL Lac
  
• edge on tilted
  down the pipe