1. Chapter 25 Active Galaxies and Quasars

2. Active galaxies are galaxies which are much more luminous than normal galaxies and have spectra that are nonstellar in nature.
This indicates that the energy they emit is not simply the accumulated light of many stars.
Most of the energy from active galaxies is in the radio and infrared portions of the spectrum.

3. Planck curves for Active and Normal Galaxies

4. Seyfert Galaxies
Look like normal spiral galaxies except with extremely bright central galactic nucleus.
The luminosity of the nucleus can exceed that of the rest of the galaxy.
Spectral lines are very broad, indicating rapid rotation.
Luminosities can vary by large amounts in fractions of a year.

5. Irregular variation of Seyfert galaxy luminosity “3C 94”

6. Radio Galaxies
Active galaxies that emit most of their energy in the radio part of the spectrum.
Comparable to Seyferts in total energy output.
Usually associated with elliptical galaxies.

7. Two Types Of Radio Galaxy
Core- Halo Radio Galaxy: Energy is emitted from a small central nucleus, as with a Sayfert Galaxy.
Lobe Radio Galaxy: Energy is emitted from enormous radio lobes. These lobes usually lie far beyond the galactic nucleus and are usually much larger than the visible part of the galaxy.

8. Radio contour of typical core-halo Radio galaxy

9. M87 At Different Wavelengths

10. Typical Lobe Radio Galaxy - “Centaurus A”

11. Difference between halo and lobe radio galaxies may just be a matter of perspective

12. Central energy source producing high-speed jets of matter may appear to us as either a lobe or core halo radio galaxy, depending on our location with respect to the jets and lobes.

13. Core-Halo & Lobe Radio Galaxy

14. Active Galaxies show some or all of the following properties.
High Luminosities.
Energy emission is nonstellar.
Energy output can be highly variable.
Often exhibit “jets” and other signs of explosive activity.
Spectra show broad emission lines - indicate rapid internal motions.

15. Central Engine of Active Galaxy

16. NGC 1461 in Virgo Cluster

17. M87 - Virgo Cluster

18. Energy Emission
Although the rotating supermassive black hole model is now widely accepetd, the actual mechanism for the energy production is uncertain.
One popular model which explains some features is the synchrotron radiation model.

19. Synchrotron Radiation
A type of nonthermal radiation produced by high-speed charged particles, such as electrons, as they are accelerated in a strong magnetic field.

20. Synchrotron Radiation

21. Quasi-stellar Objects (QUASARS)
Circa 1960, astronomers observe what appear to be faint blue stars identified with radio sources.
These objects had odd spectral lines which appeared broadened and extremely redshifted.

22. Early quasars
3C 275
Field of quasars
QSO

23. Optical Spectra of 3C 273

24. Some Quasars also have jets (3C 273)

25. Quasar

26. Quasars are :
believed to be some of the oldest objects in the universe.
some of the most distant objects from us.
the most luminous objects known.

27. Quasar Mirages - AC114
Example of gravitational lensing

28. Gravitational lens

30. Active Galaxy Formation
Possible evolutionary track for galaxies may be as follows:
Quasars --->
Radio/Sayfert Galaxies --->
Normal spiral and elliptical galaxies.
Black holes are always present, but reduce over time as they run out of fuel.

31. End Section and Ch 25

32. Final Exam- Spring 2002 Final Exam Schedule Wednesday, May 15 9:00 MWF
8:00 AM - 10:00 AM
11:00 MWF
10:30 AM - 12:30 PM
1:00 MWF
1:00 PM - 3:00 PM
Conflicts
3:30 PM - 5:30 PM