Galaxy Mass

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Galaxy Mass

• Star Number/Density
• Counting stars in a given volume
• Use volume of galaxy to estimate mass
• Good idea?

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• Rotation Curve
• Best for spirals (s for ellipticals)
• Based on Keplers Third Law
• Mass(R) R v2/G
• Mass(R) mass within radius R
• For Sun
• V220 km/s
• R7.5 kpc
• M 1011 M?
• Velocity Mass
• M/L values
• Sa/Sb gt Sc/Sd

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• Binary Galaxies
• Greater uncertainty
• M/L 20-80
• Galaxy Clusters
• Even greater uncertainty
• M/L up to 1000!

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Dark Matter

• Evidence
• Spiral Rotation Curves
• Large mass halo
• 2-10 x disk mass
• Gravitational Lensing
• Amount of mass found by degree of lensing
• Mass of clusters gt Luminosity of clusters
• 90 total mass of Universe!

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WIMPs vs MACHOs

• WIMPs
• Weakly Interacting Massive Particles
• Massive neutrinos
• Fast moving
• Hot Dark Matter (HDM)
• Detection Very difficult

• MACHOs
• Massive Compact Halo Objects
• Stars, planets, black holes
• Slow moving
• Cold Dark Matter (CDM)
• Detection Microlensing

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Microlensing

• Massive object distorts light
• Observe many stars, look for brightening
• MACHO surveys
• MACHO
• EROS
• OGLE
• And many more.
• Results?

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Many MACHOs detected but not enough Other
benefits from surveys
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Evolution of Galaxies

• Depends upon the evolution of its stars
• Low Mass stars
• More common
• Slower
• More complex than Pop I, Pop II
• Fe/H variations between galaxies
• Fe/H variations within galaxies (gradient)
• Why?

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Fe/H

• Comes from supernovae
• Which come from massive stars
• Which come from large areas of star formation
• Which come from large gas/dust clouds
• Which are found mainly in disks (mid-plane)
• So.
• Fe/H gradient (in R, z) linked to all of the
  above

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• Halo Objects Very low Fe/H
• Formation independent of disk
• Globulars formed before disk

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• What triggered the formation of galaxies?
• Early Universe not smooth
• Fluctuations 30 million pc
• Density Enhancements needed

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• Gravity versus Gas Pressure
• Jeans Length
• mhydrogen
• Jeans Mass
• Minimum mass that forms 100,000 M?

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• Further evolution information
• Star formation/evolution colors of galaxies
• Consistency of surface brightness laws
• Contraction leads to galaxy type?
• Angular momentum
• Magnetic fields
• Turbulence
• Chemical composition
• Current observations of galaxy formation
• Deep surveys (HUDF)

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Fully formed large galaxies seen at great
distance implications?
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• Or are they still forming at this distance?
• Ellipticals first, spirals later?
• Or galaxy building blocks first?
• Depends upon form of dark matter

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1996
2002
Galaxy formation star formation, when did it
start?
Are we sure?
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• Other galaxy evolution problems
• Bars
• Few seen at great distance
• Later evolutionary effect? Tidal effect?
• Influences later evolution
• Gas motion inward/outward
• Alters Fe/H gradient (big bar shallow
  gradient)
• Enhances star formation
• Bulge structure
• Alters galaxy type?

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