1 / 19

Galaxy Mass

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 v 2 /G Mass(R) = mass within radius R For Sun V=220 km/s R=7.5 kpc

overton
Download Presentation

Galaxy Mass

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  4. 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 > Luminosity of clusters • 90% total mass of Universe!

  5. 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 WIMPs vs MACHOs

  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

  16. 1996 2002 Galaxy formation – star formation, when did it start? Are we sure?

  17. 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?

More Related