Transcript Active Galactic Nuclei Thomas Schlenker University of Washington Department of Physics PHYS 496 -What is an AGN? -What kinds of AGN’s are out there? -Unified theory for.

Active Galactic Nuclei
Thomas Schlenker
University of Washington
Department of Physics
PHYS 496
-What is an AGN?
-What kinds of AGN’s are out there?
-Unified theory for a single kind of AGN.
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. AGN’s are among the most luminous objects
in the universe.
What kinds of AGN’s are out there?
• Several classes of AGN’s 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 AGN’s:
• Seyfert Galaxies
– Type 1
– Type 2
• Quasars
– Radio Quiet
– Radio Loud AGN’s:
• Quasars
– Radio Loud
• Blazars
– BL Lacertaes (BL Lacs)
– Optically Violently Variable Quasars (OVV’s)
• Radio Galaxies
– Narrow Line
– Broad Line
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.
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 AGN’s frame of reference.
Y-axis: Intensity of flux (no units)
Seyfert Galaxies – Continued
• Type 2:
Emission Lines (Type 2):
Only narrow peaks are
present.
Intensity of flux (no units)
– These have only narrow emission lines visible in their
spectrum.
4000
5000
Wavelength in Angstroms
6000
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.
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 (OVV’s).
Again, classified by their emission spectrum.
Blazars – Continued
• BL Lacs:
– Emission spectrum of BL Lacs are relatively flat and
featureless when compared to other AGN’s (such as a
quasar bellow).
– Highly polarized in the optical spectrum.
– Luminosity varies rapidly (on the order of a day).
• OVV’s:
– 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 it’s overall luminosity)
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)
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
Ties Between Classes of AGN’s
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 AGN’s 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.
Unification of AGN’s:
• Current model of an AGN:
– Within it’s nucleus many galaxies are thought to have
an SMBH. A Super Massive Black Hole of mass >>
100,000 Solar Masses.
– In AGN’s 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.
Basic sketch of an AGN.
Different classifications.
The same object!
• Blazars
– BL Lacs
– OVV
• Quasars
– Radio Loud
– Radio Quiet
• Radio
– Narrow Line
– Broad Line
• Seyfert
– Type 1
– Type 2
Sources:
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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/lecture22.pdf
http://en.wikipedia.org/wiki/Quasar
http://www-xray.ast.cam.ac.uk/xray_introduction/AGN.gif