1. Galaxies

2. Galaxy Classification
Spiral (S)
Elliptical (E)
Irregulars (Irr)

3. Normal Spirals Sa, Sb, Sc From a to c Bulge becomes smaller
Arms less tightly wound

4. Barred Spirals SBa, SBb, SBc A to b to c similar to normal spirals.
Arms at end of a bar passing though bulge.

5. Elliptical Galaxies E0, E1, E2, E3, E4, E5, E6, E7 From E0 to E7
Get more elliptical in shape
Get fuzzy

6. Elliptical Galaxies Two types of elliptical galaxies,‘
Dwarf elliptical galaxies orbiting M31
Giant elliptical galaxy at
core of a galaxy cluster.
Two types of elliptical galaxies,
dwarfs and giants.

7. Irregular Galaxies
Small size
No defined shape
fuzzy

8. Irregular Galaxies
LMC
SMC
SMC and LMC are irregular galaxies orbiting the Milky Way.

9. Hubble Tuning Fork Diagram
There is no observational evidence that
this diagram shows galaxy evolution.
NOTE: S0’s are spirals without arms.

10. S0 Class Look like E0’s Contain dust and gas like spiral galaxies.
Therefore, they were named as S0’s.

11. Galaxy Clusters Galaxies tend to congregate into groups called galaxy
These clusters can be small
containing tens of galaxies
or large containing
hundreds or thousands
of galaxies.

12. Galaxy Clusters The Local Group
Small cluster to which the Milky Way belongs.
~ 1,000,000 pc in diameter.
Contains ~45 members.
Andromeda Galaxy ~2.2 million LY away.

13. Galaxy Clusters The Virgo Cluster
18 Mpc
2500 galaxies
M87, the central galaxy (giant elliptical)
Local Group may be like an appendage to the Virgo Cluster.
Super Clusters

14. Active Galactic Nuclei (AGN’s)
~20-25% of bright galaxies are not normal (do not fit Hubble classifications.)
Among the most energetic object in the universe.
Have bright nucleus
NGC 7742 looks like a fried egg.

15. Types of AGN’s
Seyfert Galaxies
Radio Galaxies
Quasars

16. Seyfert Galaxies Very bright central nucleus Faint spiral arms
Variable in brightness

17. Seyfert Galaxies Nucleus changes brightness
Time scales of weeks, months, and years.
PEGA at GSU has observed
AGN microvariblility on
time scales of minutes.

18. Radio Galaxies Large radio emitting lobes
Lobes extend out 10X larger than Milky Way or ~ size of The Local Group.

19. Radio Galaxies

20. M87

21. Cygnus A Colliding Galaxies

22. M86
Also near center of Virgo Cluster
Core-dominated radio galaxy

23. Quasars
Tiny blue stellar looking objects with large radio emission similar to radio galaxies.
Highly red shifted spectra.
~ 50,000 km/s or more.

24. Quasars Quasar means quasi-stellar object.
Distances from 240 Mpc to 9000 Mpc
They are the brightest thing in universe but appear faint

25. Quasars
They share characteristics of Seyfert galaxies and radio galaxies.
Over 30,000 known

26. AGN Model Super massive black hole at center. Accretion disk
Intense magneitc field
Jets of high speed particles.

27. AGN Model

28. AGN Model Viewing angle determines type of energy seen.
Viewing angle determines the type of AGN seen, Seyfert, radio galaxy, etc.

29. Possible Galaxy Evolution

30. Resources
Chaisson & McMillan, (2002, 2004). Astronomy Today (5th Ed.)