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The Local Group

The Local Group. Approximately 41 members All within 5 million light years of the Milky Way Clustered in two groups around the two dominant spiral galaxies (The Milky Way and Andromeda) Average apparent Magnitude = 11 Average Absolute Magnitude = -13 Average Diameter = 5 kpc.

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The Local Group

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  1. The Local Group • Approximately 41 members • All within 5 million light years of the Milky Way • Clustered in two groups around the two dominant spiral galaxies (The Milky Way and Andromeda) • Average apparent Magnitude = 11 • Average Absolute Magnitude = -13 • Average Diameter = 5 kpc The following images represent only the most visible members of the local group.

  2. The Large Magellanic Cloud

  3. The Small Magellanic Cloud

  4. NGC 6822 NGC 6822

  5. Characteristic Properties of the Local Group of Galaxies Just as we used the nearby stars to characterize the distribution of stars in the Milky Way galaxy, we will use the character of the nearest galaxies (i.e. The Local Group) to characterize the distribution of galaxies in the larger Universe. As you “click” through the following figures please pay attention to the (hopefully) useful notes and highlights that appear.

  6. 76% of Local Group galaxies are dwarf galaxies.

  7. 90% 66% 90% are invisible to the naked eye 66% are 100 times dimmer than the limit of visibility.

  8. Local Group galaxies appear to be clustered around the two largest members of the group: The Milky Way and the Andromeda (M31) galaxies which are separated by about 670 kpc (2 Mlyrs). The entire Local Group has a diameter of about 5 Mlyrs. The Milky Way Group Andromeda Group

  9. Each of the small red dots represents a Local Group galaxy as see from above the plane of the Milky Way Andromeda Group The Milky Way Group

  10. Absolute Magnitude of the Milky Way is about -20 About 80% of Local Group galaxies are 5 magnitudes less luminous. About 33% of Local Group galaxies are 10 magnitudes less luminous.

  11. 80% are less than 5 kpc in diameter (smaller than the bulge of the Milky Way).

  12. Positive Radial Velocities represent Motion Away from the Milky Way The Andromeda Galaxy (M31) is “falling” toward the Milky Way at 59 km/s. Negative Radial Velocities represent Motion Toward the Milky Way

  13. Summary of the Local Group Galaxies • The Local Group consists of about 41 galaxies. • 76% of Local Group galaxies are dwarf galaxies. • 90% are invisible to the naked eye and 66% are 100 times dimmer than the limit of visibility. • Local Group galaxies appear to be clustered around the two largest members of the group: The Milky Way and the Andromeda (M31) galaxies which are separated by about 670 kpc (2 Mlyrs). The entire Local Group has a diameter of about 5 Mlyrs.

  14. Summary of the Local Group Galaxies • 80% of Local Group Galaxies are less than 0.01 LMW and 33% are less than 0.0001 LMW • 80% are less than 5 kpc in diameter (smaller than the bulge of the Milky Way). • The Andromeda Galaxy is approaching the Milky Way and will impact our galaxy in less than 11 Byrs.

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