1. The Milky Way Galaxy and the Formation of Spiral Galaxies
Prof. Ata Sarajedini
University of Florida
Department of Astronomy

3. The Milky Way Galaxy - Our Home
Pole-On View
Edge-On View

5. The Andromeda Galaxy - Our Nearest Large Neighbor
NGC 205
M32

6. • What is the significance of these satellite galaxies?
They are remnants from the formation of the Milky Way’s halo!
• Since the late 1970s, theories of galaxy formation have suggested that disrupted satellite galaxies formed the Milky Way’s halo.

7. Satellite Galaxies of the Milky Way and Andromeda

8. How do dwarf galaxies get disrupted?
Tidal Effects
DFg

9. The problem was that there was no concrete evidence for the buildup of spiral galaxies via the disruption and accretion of dwarf galaxies until 1994!

10. Velocity along the line-of-sight for stars toward the Galaxy’s Bulge
The “Smoking Gun” - the Sagittarius Dwarf Galaxy
(Discovered in 1994)
Sagittarius dwarf galaxy
Velocity along the line-of-sight for stars toward the Galaxy’s Bulge
Bulge stars with an average velocity of 0 km/s
Blue
Red

12. M55 turns out to be a foreground cluster!

13. Observations of stars known to be a part of the Sagittarius dwarf galaxy and its tidal tails.
Theoretical model of how the Sagittarius dwarf galaxy should be disrupted by the Milky Way.

14. • In 2003, another disrupted and digested dwarf galaxy was found…
Canis Major Dwarf Galaxy

15. • Globular clusters are also disrupted and accreted to form the Galaxy’s halo.

16. • We have even detected tidal streams and tidal tails composed of stars in the halo of the Andromeda galaxy.

17. • The halos of the Milky Way and Andromeda do indeed show evidence of having been formed via the disruption and accretion of dwarf satellite galaxies.

19. Conclusion
The halo of a spiral galaxy is like a bowl of spaghetti!

20. Today, NASA and the Space Telescope Science Institute released images of the Hubble Ultra Deep Field - the result of 11.3 days of total exposure time with the Advanced Camera for Surveys instrument.

23. Satellite Galaxies of the Milky Way and Andromeda

24. • Similar searches for tidally disrupted dwarf galaxies around the spiral galaxy M33 have turned up nothing significant.