1. Large Scale Structure Clusters and Groups Stellar systems
Stellar Clusters
Galaxies
Galaxy Groups and Clusters
Galaxy Superclusters
The Universe
Galaxies are not randomly distributed
Concentrations categorized by number of bright galaxies (more than 10% of Milky Way galaxy luminosity)
Groups are smaller
Less than 50 bright galaxies
Typically about 1013 MSun
Clusters are larger
50 – 1000 bright galaxies
Typically 1014 – 1015 MSun

2. The Local Group – Our Group
It has about 60 total galaxies
Two bright spirals
Milky Way Galaxy
Andromeda Galaxy (M31)
Several small satellites of these galaxies
Mostly ellipticals and irregulars
Several miscellaneous galaxies
Triangulum (M 33) – a spiral
Total diameter about 6 Mly
Q. 101: Why Called a Group?

3. The Milky Way

4. The Great Galaxy in Andromeda (M31)
Large Spiral Galaxy - or probably barred spiral (SBb)
About 50% brighter than our galaxy
About 50% more massive than our galaxy
2.5 Mly away
Moving towards Milky Way at 110 km/s
Will merge with us in 4 Gy?

5. Larger Magellenic Cloud
Our Companions
Larger Magellenic Cloud
Sculptor Dwarf
Carina Dwarf
Sextans Dwarf
Ursa Minor Dwarf
Draco Dwarf

6. Our Companions Leo I Canis Major Dwarf Smaller Magellenic Cloud
Sagittarius Dwarf Elliptical
Leo II

7. Companions of Andromeda
Cassieopeia Dwarf
M110
M32
NGC 147

8. Companions of Andromeda
Pegasus Dwarf
NGC 185
Andromeda III
Andromeda IV
Andromeda V

9. Other Members of Local Group
Phoenix Dwarf
IC 1613
Wolf-Lundmark-Melotte
Triangulum galaxy (M33)
Tucana Dwarf
Pisces Dwarf
IC 10
Leo A

10. Some Nearby Groups of Galaxies
Sculptor Group
Maffei Group

11. The Virgo Cluster More than 1000 galaxies Dozens of bright galaxies
Two giant ellipticals
Many bright spirals
54 Mly away
Total mass about 1.2 × 1015 MSun

12. The Norma Cluster Difficult to study because our galaxy in the way
About 220 Mly away
Total mass > 1015 Msun
Near the center of our supercluster

13. Other Clusters In Our Supercluster
Abell 3574
Hydra
Centaurus
Fornax
Eridanus

14. The Coma Cluster 1000+ galaxies visible Many bright galaxies
Many giant ellipticals, especially in the center
Bright spirals towards the edges
About 300 Mly away
Total mass about 3 × 1015 Msun
Center of Coma Supercluster

15. Cluster and Group Evolution
Galaxy Clusters and Groups change over time:
Heaviest galaxies fall towards the center
Tidal Friction will enhance this effect
Galaxies will merge
For clusters, over time:
System will form a spherical distribution (more regular)
In the center, galaxies will coalesce
Giant ellipticals concentrated in the center
Spirals more towards the edge
Collisions will knock gas out of the galaxies themselves
Twice as much gas between the galaxies as in the galaxies
Q. 102: Why Giant Ellipticals Mostly in Clusters?

16. Ancient Galaxy Cluster
Old Clusters
Old Galaxy Cluster
Ancient Galaxy Cluster

17. Where is the Mass in a Galaxy Cluster?
Galaxies have much more mass than is in the stars and gas
How about clusters?
Need to find mass of cluster
Gravitational lensing
Distant Source
Cluster
Observer
Much more mass than is visible
5% is in stars
10% is in hot gas
85% is in dark matter
Gravity bends light
See multiple images
Can estimate mass of cluster

18. Clusters as Gravitational Lenses

19. Clusters as Gravitational Lenses

20. Clusters as Gravitational Lenses

21. Superclusters Stellar systems Stellar Clusters
Galaxies
Galaxy Groups and Clusters
Galaxy Superclusters
The Universe
Groups/clusters are themselves grouped into larger structures called Superclusters
Size: Up to around 500 Mly
Our supercluster is called the “Laniakea Supercluster”
Book has this wrong – out of date!
Superclusters are much more poorly defined than clusters
At this scale, the universe hasn’t had time to reshape them
They are always irregular

22. Laniakea Supercluster
Discovered 2014
Study of “flow” of nearby clusters
Centered on Great Attractor, near Norma
500 Mly across

23. Structure Near Us Laniakea Supercluster Coma Supercluster
Perseus-Pisces Supercluster

24. Q. 103: How Much of Space is Filled?
Nearby Superclusters
Between the superclusters are “voids” almost devoid of galaxies
Little evidence of structure bigger than superclusters
No “hyperclusters”
Largest scale structure like soap bubbles
Mostly empty space
Superclusters are walls between the bubbles
Q. 103: How Much of Space is Filled?

25. Structure on the Largest Scale
Sloan Digital Sky Survey

26. Everyone Should Know Where They Live
Stellar systems
Stellar Clusters
Galaxies
Galaxy Groups and Clusters
Galaxy Superclusters
The Universe
Classification: Our Address
Stellar system Solar System
Star Cluster (none)
Galaxy Milky Way
Galaxy Group/Cluster The Local Group
Supercluster Laniakea
Universe Universe