1 / 30

THE CASE FOR MODIFIED GRAVITY

THE CASE FOR MODIFIED GRAVITY. James Binney Oxford University. Outline. MOND as a replacement for DM (Sanders & McGaugh 02) Absence of DM interior to the Sun (Bissantz et al 03, 04) TeVeS Lorentz-covariant MOND (Bekenstein 2004). NGC 3198. Begeman (1987).

pules
Download Presentation

THE CASE FOR MODIFIED GRAVITY

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. THE CASE FOR MODIFIED GRAVITY James Binney Oxford University

  2. Outline • MOND as a replacement for DM (Sanders & McGaugh 02) • Absence of DM interior to the Sun (Bissantz et al 03, 04) • TeVeS Lorentz-covariant MOND (Bekenstein 2004)

  3. NGC 3198 Begeman (1987)

  4. Modifying gravity • Modify Newtonian theory at large distances? or at low accelerations?

  5. Adding a0

  6. Bekenstein—Milgrom Eq.

  7. Deep MOND regime – when µ(x)~x At large r always enter deep MOND Tully-Fisher Sanders & Verheijen

  8. Fits to vc(r) for both LSB & HSB Galaxies (Sanders & McGaugh 02) a0=1.2 10-8 cm s-2 a0~H0c/2π; Λ~3(a0/c)2

  9. U Maj Sanders & Verheijen

  10. Recover predicted M/L values Data: Sanders & Verheijen Models: Bell & de Jong 01

  11. dSph galaxies η = Fi/Ft

  12. Clusters of Galaxies

  13. DM in the MW? • Bissantz & Gerhard (02) Determine near-IR luminosity density from COBE K & L photometry • Advances previous work by including spiral structure in disk • Bissantz Englmaier & Gerhard (03) study gas flow in Φ obtained with spatially const M/L + quasi-isothermal DM halo • Fit M/L, ωbar, ωspiral • M/L for stars set by dynamics of non-axisymmetric structure • DM halo makes up balance for terminal-velocity curve

  14. Bissantz Englmaier & Gerhard CO observed simulated

  15. Bissantz Englmaier & Gerhard (03) • Find ωbar in good agreement solar nhd kinematics • With 4 arms get good pattern of ridge lines • Vc near sun only ~185km/s unless add DM halo with a=10.7 kpc

  16. Famaey & Binney 05 • Replace BEG halo with MOND? • Predict vc(R) for 2 choices • (x)=x/(1+x2)1/2 or • (x)=x/(1+x)

  17. Cannot get vc(R0)=220 km/s • But vc(R0) not well determined • Can fit terminal velocities for range of models • Bottom lines: (a) vc(R0)<210 km/s (b) v1=170§5 km/s

  18. Microlensing • Microlensing optical depth measures only stellar density

  19. Optical depths Bissantz & Gerhard (02)

  20. Bissantz Debattista & Gerhard (04) • Use novel N-body technique to find dynamical model that reproduces Bissantz & Gerhard photometry • Adopt M/L, ω normalization from BEG • No free parameters in Φ • Reproduce proper motions of bulge stars in Baade’s window etc • For plausible mass function of stars, reproduce MACHO microlensing event duration distribution

  21. Conclusion: stars-only MW gives good fits to both optical depth & duration distribution (ML<,ML>)=(.04,10) or (.075,10)

  22. Klypin et al (02) • ΛCDM models of MW • Adiabatic compression & optional L exchange No L exchange L exchange

  23. TeVeS • Bekenstein (04) presents Lorentz-covariant theory (TeVeS) that reduces to MOND in appropriate limit

  24. Standard cosmologies • Grav. Lensing as if DM present • No superluminal modes

  25. TeVeS important development Link to effective field theory? • Can now extend MOND to CMB and large-scale structure • If not worse than CDM in these fields, must be favoured theory • Then question: significance of Uµ and Φ fields in TeVeS

  26. Conclusions • MOND has amazing ability to model data taken after it was invented • Excellent fits to galaxy rotation curves require M/L(colour) as from SS theory • Compelling evidence that negligible DM interior to Sun • Now limiting form of Lorentz covariant theory • MOND really might be the next great step in physics

  27. m=2 x 1.5

  28. Giant E galaxies Data: Romanowsky et al 03 Models: Milgrom & Sanders 03 Solid: isotropic

More Related