Active Galactic Nuclei

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Active Galactic Nuclei

• Thomas Schlenker
• University of Washington
• Department of Physics
• PHYS 496

• What is an AGN?
• What kinds of AGNs are out there?
• Unified theory for a single kind of AGN.

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What is an AGN?
An AGN is a nucleus (of a galaxy) that has a
higher luminosity than the rest of the galaxy.

• At the center of each galaxy is a region of
  densely packed matter called the nucleus.
• In Active Galaxies, these nuclei are actually
  more luminous than all other objects within that
  galaxy through out all (or at least most) of the
  spectrum, from radio to gamma rays.
• i.e. AGNs are among the most luminous objects in
  the universe.

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What kinds of AGNs are out there?

• Several classes of AGNs are strong radio
  emitters (Radio Loud) others are not (Radio
  Quiet) so it serves as a good way to break the
  classes into two groups.
• Radio Quiet AGNs
• Seyfert Galaxies
• Type 1
• Type 2
• Quasars
• Radio Quiet
• Radio Loud AGNs
• Quasars
• Radio Loud
• Blazars
• BL Lacertaes (BL Lacs)
• Optically Violently Variable Quasars (OVVs)
• Radio Galaxies
• Narrow Line
• Broad Line

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Seyfert Galaxies

• Characteristics of both Type 1 and Type 2 Seyfert
  Galaxies
• Seyferts are strong sources of low energy gamma
  rays, with luminosity peaking around 100 KeV then
  dropping off for higher energy photons.
• Their host galaxies are often spiral or
  irregularly shaped galaxies.
• Seyferts are actually fairly common. (There is
  thought to be a Seyfert AGN at the center of
  about 1 of spiral galaxies.)
• Seyfert Galaxies are broken into two sub classes,
  Type 1 and Type 2, based on the emission lines
  appearing in their spectra.

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Seyfert Galaxies Continued

• Type 1
• These have both narrow line AND broad line peaks
  in their spectrum.

Emission Lines (Type 1) Top graph shows full
peaks, bottom zooms in along y axis to better
show the difference between peak widths. X-axis
Wavelength (Angstroms) from the AGNs frame of
reference. Y-axis Intensity of flux (no units)
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Seyfert Galaxies Continued

• Type 2
• These have only narrow emission lines visible in
  their spectrum.

Emission Lines (Type 2) Only narrow peaks are
present.
Intensity of flux (no units)
4000
5000
6000
Wavelength in Angstroms
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Quasars

• Radio Quiet Quasars
• Strong emissions in both the optical and X-ray
  spectrums.
• Within the optical spectrum, both broad and
  narrow emission lines are present, similar to a
  Type 1 Seyfert Galaxy.
• Host is usually an elliptical galaxy. But less
  commonly, it might be a spiral.
• Radio Loud Quasars
• All the same characteristics of a Radio Quiet
  Quasar with the addition of having strong radio
  emissions.

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Blazars

• Characteristics of both classes of Blazars
• Blazars are strong sources of high energy
  emissions (energies greater than 100 MeV).
  However they are luminous over the entire range
  of the spectrum, from radio up through gamma
  emission.
• The host galaxies of Blazars are often Giant
  Elliptical galaxies.
• There are two subclasses of Blazars, BL Lac
  objects and Optically Violently Variable quasars
  (OVVs). Again, classified by their emission
  spectrum.

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Blazars Continued

• BL Lacs
• Emission spectrum of BL Lacs are relatively flat
  and featureless when compared to other AGNs
  (such as a quasar bellow).
• Highly polarized in the optical spectrum.
• Luminosity varies rapidly (on the order of a
  day).
• OVVs
• Spectrum has features unlike BL Lacs.
• Luminosity varies rapidly as with BL Lacs (on the
  order of one day) but by a very large amount
  (around 10 of its overall luminosity)

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Blazars Continued
Comparison of BL Lac and quasar Emission
Lines BL Lac emissions shown on top, emisson of
a quasar shown bellow. Note The BL Lac has no
emission lines.
Wavelength (Angstroms)
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Radio Galaxies

• Except for being highly luminous along the radio
  wavelengths, Radio Galaxies do not have many
  common characteristics. Their properties may be
  different from object to object. However, they
  can be classified into two smaller sub groups.
  (Again, based on the widths of their emission
  lines.)
• Broad Line Radio Galaxies
• Emission line widths similar to those in a
  Seyfert Type 1
• Narrow Line Radio Galaxies
• Emission line widths similar to those in a
  Seyfert Type 2

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Ties Between Classes of AGNs

• As more was learned about each class of AGN
  scientists began to link classes together,
  theorizing that two objects of different classes
  might be similar to one another, only appearing
  dissimilar due to the observers orientation.

Seyfert AGNs were theorized to be similar
objects. If the observer (Earth) had and
un-obscured view of the active nucleus it then it
appeared as a Type 1 (with both narrow and broad
lines still visible) however if the observers
view is obscured by an accretion disk the broad
line emissions and low energy X-rays would be
blocked and it would appear as a Type 2.
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Unification of AGNs

• Current model of an AGN
• Within its nucleus many galaxies are thought to
  have an SMBH. A Super Massive Black Hole of mass
  gtgt 100,000 Solar Masses.
• In AGNs this SMBH is surrounded by an accretion
  disk (a flat disk of matter orbiting the black
  hole) which is then surrounded by a Torus, a
  cloud of matter orbiting the black hole like an
  inner tube.
• As matter from the accretion disk orbits closer
  and closer to the SMBH some is accelerated to
  near c and propelled out away from the SMBH (just
  before entering the event horizon) perpendicular
  to the orbital plane of the accretion disk and
  Torus.

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Basic sketch of an AGN.
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Different classifications.The same object!

• Blazars
• BL Lacs
• OVV
• Quasars
• Radio Loud
• Radio Quiet
• Radio
• Narrow Line
• Broad Line
• Seyfert
• Type 1
• Type 2

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Sources

• http//imagine.gsfc.nasa.gov/docs/science/know_l1/
  active_galaxies.html
• http//imagine.gsfc.nasa.gov/docs/science/know_l2/
  active_galaxies.html
• http//en.wikipedia.org/wiki/Active_galaxy
• http//rocinante.colorado.edu/pja/astr3830/lectur
  e22.pdf
• http//en.wikipedia.org/wiki/Quasar
• http//www-xray.ast.cam.ac.uk/xray_introduction/AG
  N.gif