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The Cosmic Distance Scale

The Cosmic Distance Scale. Convergent point method. Convergent point method. Main-sequence fitting. This shows the HR diagram for the solar neighbourhood from the Hipparcos satellite. Variable stars: Cepheids. Cepheids: P-L relations. Type Ia Supernovae. Type Ia Supernovae.

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The Cosmic Distance Scale

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  1. The Cosmic Distance Scale

  2. Convergent point method

  3. Convergent point method

  4. Main-sequence fitting This shows the HR diagram for the solar neighbourhood from the Hipparcos satellite

  5. Variable stars: Cepheids

  6. Cepheids: P-L relations

  7. Type Ia Supernovae

  8. Type Ia Supernovae Accurate standard candles, luminosity depends on the physics of core collapse in stars and therefore is mostly independent of the host galaxy properties.

  9. Evidence for dark matter

  10. Galaxy rotation curves

  11. Galaxy rotation curves

  12. Galaxy velocities in clusters

  13. Galaxy cluster velocity dispersion

  14. X-ray emission (baryons)

  15. Motion of galaxies within large-scale structure

  16. Cluster gravitational lenses imply large amounts of dark matter

  17. CBR dipole: large scale motion

  18. More on galaxy rotation curves

  19. Rotation curves: Explanations MOdified Newtonian Dynamics (MOND) (Milgrom 1983) F = m (a/a0) a Where (x) = 1 if x>>1 and (x) = x if x<<1 So for low acceleration F = ma2/a0 = GMm/r2 M(r) = v4 / (a0G) a0 ~ 10-10 ms-2 Using Newton F = ma = GMm/r2 a = v2/r M(r) = v2 r / G Implies dark matter

  20. Clowe et al. 2006 • Stellar masses • Integrate I-band light, apply M/LI = 2 (range 0.5 to 3 for typical galaxies in solar units) • Plasma masses • Integrate X-ray luminosity, apply M/LX from 3D model using hydrostatic equilibrium, T~6 keV (sub-cluster) and 14 keV (main) • Weak lensing masses

  21. Weak gravitational lensing Method is statistical; see intrinsic aspect ratios shown below; expect signal of 0.02-0.10 Figures by B. Jain

  22. Weak lensing by cluster Cluster z~0.3; mean background galaxies at z~1 for Clowe et al. 2006 Away from mass Around cluster Figures by B. Jain

  23. Figure 1a from Clowe et al. 2006

  24. Figure 1b

  25. Conclusion • Lensing mass map peaks around stars as expected for dark matter

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