1. Galaxy Mass Star Number/Density Counting stars in a given volume
Use volume of galaxy to estimate mass
Good idea?

2. Rotation Curve Best for spirals (s for ellipticals)
Based on Kepler’s Third Law
Mass(R) = R v2/G
Mass(R) = mass within radius R
For Sun
V=220 km/s
R=7.5 kpc
M ≈ 1011 M
Velocity – Mass
M/L values
Sa/Sb > Sc/Sd

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

4. Dark Matter Evidence 90% total mass of Universe!
Spiral Rotation Curves
Large mass halo
2-10 x disk mass
Gravitational Lensing
Amount of mass found by degree of lensing
Mass of clusters > Luminosity of clusters
90% total mass of Universe!

5. WIMPs vs MACHOs WIMPs MACHOs 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

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

7. Many MACHOs detected – but not enough
Other benefits from surveys

8. 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?

9. [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

10. Halo Objects – Very low [Fe/H]
Formation independent of disk
Globulars formed before disk

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

12. Gravity versus Gas Pressure
Jean’s Length
m=hydrogen
Jean’s Mass
Minimum mass that forms ~ 100,000 M

13. 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)

14. Fully formed large galaxies seen at great distance – implications?

15. Or are they still forming at this distance?
Ellipticals first, spirals later?
Or galaxy building blocks first?
Depends upon form of dark matter

17. 1996
2002
Galaxy formation – star formation, when did it start?
Are we sure?

18. 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?