Most galaxies are normal and fit the Hubble classification scheme'

1

• Most galaxies are normal and fit the Hubble
  classification scheme.
• However, some galaxies have very high
  luminosities (they emit extremely large amounts
  of EM radiation) and they emit most of their
  radiation at longer wavelengths than normal
  galaxies.
• There are two types of active galaxies
• Seyfert galaxies
• Radio galaxies
• And there are Quasars.

2
As we look further back in time we discover a
class of galaxies which differ from the ones we
see close by. Instead of shining from the
combined light of billions of stars, these
galaxies emit most of their energy in the radio
part of the spectrum. These are collectively
called active galaxies. While there are a
number of names associated with different
characteristics, we believe the under lying
physics is the same.
3
We have to look deep into the core of theses
galaxies to see what is going on. In general, it
looks like an accretion disk exists in the center
with large amounts of radiation and matter
streaming out of the poles.
4
We can tell the region of activity is small
because the intensity variations occur on time
scales of months. This indicates that the region
must be on the order of a few light months across.
5
M87 seen at different scales at different
wavelengths a) visible, b) short exposure
visible, c) radio, d) IR
6
Seyfert Galaxies

• Most are very far away.
• In visible light they look like normal galaxies.
• Nearly all their EM radiation is at short radio
  and IR wavelengths.
• The nuclei of large Seyfert galaxies emit about
  10 times the output of the whole Milky Way.
• There is rapid motion within the nucleus, as
  evident by the broadening of their spectral
  lines.

7
Radio Galaxies

• Active galaxies with EM emission peaking at long
  radio wavelengths.
• Core halo type most emission from nucleus
• Lobe radio galaxies most emission from radio
  lobes

8
Centaurus A, giant elliptical with dust plane and
once again, material being ejected out the poles.
9
Cygnus A. Thin pencil beams of material end in
large lobes where it appears the material is
slamming into the extra-galactic medium. These
images were taken in the radio spectrum.
10
A head-tail galaxy (NGC 1265)
11
We think all these zoo of objects are caused by
the same thing, we just see them from different
perspectives.
12
The central engine
13
Best images so far of a accretion disk with beams
of matter streaming out.
14
We think that super massive black holes are the
central engines at the heart of active galaxies
15
We can measure the Doppler velocities and combine
this with distances to use Keplers laws to
determine the mass of the engine. Answer (3
billion suns).
16
The source of the radio emission is called
Synchrotron radiation which is produced by
accelerating electrons. This radiation has a
fundamentally different spectrum than black body
radiation.
17
Quasars are some of the most distant objects.
They have very large red shifts and were named
because they are quasi-stellar-radio-sources.
18
Some of our best examples of gravitational
lensing are distant quasars whose images pass
through another galaxy on the way to us. This
produces Einstein rings and crosses.
19
Multiple arcs caused by gravitational lensing
20

• The nuclei of the brightest Seyfert galaxies are
  _____ as bright as the entire Milky Way Galaxy.
• a. one tenth
• b. just
• c. ten times
• d. one hundred times
• e. one thousand times

21

• In a lobe radio galaxy, the ultimate energy
  source for the entire galaxy is thought to
  reside
• a. In the lobes.
• b. In the galaxy's center.
• c. In the jets.
• d. all of the above
• e. none of the above