Distances

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Distances

• Edwin Hubble
• Distance scale ladder
• 1 AU calibrates pc
• Clusters calibrates Cepheids, RR Lyrae
• Nearby galaxies calibrates many objects
• Remote galaxies calibrates supernovae,
  Tully-Fisher, Faber-Jackson
• And so on and so on

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• Hubble correlated distances with redshift
• Relation The Hubble Law
• V Ho d
• Ho current value of the Hubble Constant
• Initial value around 520 km/s/Mpc
• Young age?
• Mistakes?

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Evolution of Ho

• Allan Sandage
• Corrections to Hubbles distances
• Ho closer to 75 km/s/Mpc

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Results
de Vaucouleurs
Sandage
Ho 72 8
Launch of HST
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Clusters Groups

• Cluster more galaxies, denser
• Groups less galaxies, scattered
• Group Characteristics
• Main galaxy Spirals, SO (disk galaxies)
• Lower velocities in group
• Many interactions starbursts
• Irregular distribution
• Radio sources, not usually x-ray

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• Cluster Characteristics
• More large ellipticals (cD)
• Ellipticals in center, spirals on edges
• Rich vs Poor
• gt1000 galaxies, most dwarfs
• Regular shape/distribution
• X-ray emitting gas
• gt 100 million K
• Most dominant light in cluster
• Most mass from this intercluster gas
• Cannibalism?

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X-ray
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Hydra cluster visible x-ray
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Visible, IR, x-ray of Coma
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Superclusters
1.6 million galaxies
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• Supercluster characteristics
• Size 30-300 Mpc
• 1016 M?
• Non-spherical, stringy
• All rich clusters in superclusters
• 95-99 of all clusters/groups
• Voids spherical, no bright galaxies
• Local Supercluster
• Virgo, Centaurus, Hydra
• Center 20 Mpc

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Great Attractor

• Peculiar Velocity
• Local Group vel270 km/s (towards Virgo)
• Local SC vel600 km/s (towards what?)
• Towards the Great Attractor!
• Mass 5 x 1016 M?
• 65 Mpc away
• What is it?

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Formation of structure

• How did the structure form?
• Depends on dark matter!
• Bottom-up (small first, big later), CDM
• Top-down (large first, small later), HDM
• CDM Currently favored
• Proto-galaxy pieces
• Galaxies
• Clusters
• Superclusters

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