Galaxy Mass Star Number/Density Counting stars in a given volume

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Presentation transcript:

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

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

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

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!

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

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

Many MACHOs detected – but not enough Other benefits from surveys

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?

[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

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

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

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

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)

Fully formed large galaxies seen at great distance – implications?

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

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

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?