The Milky Way Galaxy and the Formation of Spiral Galaxies Prof. Ata Sarajedini University of Florida Department of Astronomy
The Milky Way Galaxy - Our Home Pole-On View Edge-On View
• 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.
DFg DFg DFg How do dwarf galaxies get disrupted? Tidal Effects
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!
Sagittarius dwarf galaxy Bulge stars with an average velocity of 0 km/s The “Smoking Gun” - the Sagittarius Dwarf Galaxy (Discovered in 1994) Velocity along the line-of-sight for stars toward the Galaxy’s Bulge Blue Red
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.
• In 2003, another disrupted and digested dwarf galaxy was found… Canis Major Dwarf Galaxy
• Globular clusters are also disrupted and accreted to form the Galaxy’s halo.
• We have even detected tidal streams and tidal tails composed of stars in the halo of the Andromeda galaxy.
• 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.
Conclusion The halo of a spiral galaxy is like a bowl of spaghetti!
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.
• Similar searches for tidally disrupted dwarf galaxies around the spiral galaxy M33 have turned up nothing significant.