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Dark matter and strong lensing

Dark matter and strong lensing. TOMMASO TREU (UCSB). Outline. Introduction Cosmography Three key questions: Are dark matter halo profiles universal? (warm/ interactive dark matter?) Universal halos or universal stellar initial mass function? (a.k.a. non-baryonic dark matter?)

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Dark matter and strong lensing

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  1. Dark matter and strong lensing TOMMASO TREU (UCSB)

  2. Outline • Introduction • Cosmography • Three key questions: • Are dark matter halo profiles universal? (warm/ interactive dark matter?) • Universal halos or universal stellar initial mass function? (a.k.a. non-baryonic dark matter?) • Is there dark matter substructure? (mass of the dark matter particle?)

  3. Strong gravitational Lensing Image separation is a direct measurement of mass, luminous or dark!

  4. Why is it called Lensing? Courtesy of P.J.Marshall

  5. Strong lensing is rare (1/1000 galaxy) but we know how to find lots of them

  6. Strong lensing in terms of Fermat’s principle Fermat distance Shapiro delay Excess time delay geometric time delay

  7. Cosmography

  8. H0 is needed for accurate measurements of • Dark matter density • Flatness • Neutrino masses • Dark energy equation of state • ….. See Verde’s and Reid’s talk

  9. Cosmography from time delays: how does it work?

  10. Cosmography with strong lenses:4 solved problems • Time delay – 2-3 % • Astrometry – 10-20 mas • Lens potential (2-3%) • Structure along the line of sight (2-3%) Suyu et al. 2010

  11. Constraints for w=-1 Suyu et al. 2010

  12. Constraints on Dark Energy For curved wCDM • With WMAP7: • B1608+656 is comparable to BAO [Percival et al. 2010] • B1608+656 and BAO both primarily constrain k • SN [Hicken et al. 2009] primarily constrainsw

  13. Future Prospects • Precision is 6-7% per system on H0 • Currently ~10 lenses have precise time-delays • Precision on H0 of <3% is attainable now • Future telescopes (e.g. LSST) will discover and measure 100s of time delays (Oguri & Marshall 2010; Treu 2010)

  14. Are dark matter profiles universal? (warm/self interacting dark matter?)

  15. The mass density profile of dark matter halos • Is the dark matter profile universal and “cuspy” as suggested by simulations? • If not, it may be a sign that dark matter is warm or self- interacting De Blok’s talk

  16. Observational challenges… • Precision over a large dynamic range in mass • Disentangle luminous and dark matter • Control systematics

  17. … can be overcome in clusters by combining methods • Stellar kinematics (<30 kpc) • Strong lensing (<100 kpc) • X-ray (0.05 – 0.5 Mpc) • Weak lensing (0.1-3 Mpc) Sand, Treu, Ellis 2002; Sand et al. 2004,2008; Newman et al. 2009,2011

  18. Newman et al 2011

  19. Results for Abell 611 Newman et al. 2009

  20. Results for Abell 383 Range of N-body results for pure DM halo Newman et al. 2011 More clusters on the way, see also Postman’s MCT

  21. The role of baryons • Baryonic cooling and star formation tends to drive material towards the center and thus make the inner slope steeper than for DM only • In simulations, the amount of steepening depends on the cluster merger history and the details of baryonic physics, because dynamical friction can counterbalance - at least in part - the effect

  22. Universal Halos or Universal Stellar Initial Mass function?(Baryonic or non baryonic?)

  23. Massive ellipticals have “too much” dark matter? Treu et al. 2010 Stellar mass from from colors Stellar mass from lensing and dynamics

  24. Universal halos or IMF? Salpeter IMF “mismatch” Kroupa Chabrier Mass dependency Auger, TT et al. 2010

  25. What about spirals? Dutton et al. 2011; Treu et al. 2011

  26. What about spirals? Treu et al. 2011 Dutton et al. 2011

  27. Is there dark matter substructure? (Mass of the dark matter particle)

  28. Milky Way (missing) satellites Kravtsov 2010 Strigari et al. 2007 Are they dark or do they not exist?

  29. “Missing satellites” and strong lensing • Strong lensing detects satellites based on mass • Satellites are detected as “anomalies” in the gravitational potential ψ • ψ’’ = magnification anomalies • ψ’ = astrometric anomalies • ψ = time delay anomalies Moustakas’ talk

  30. Gravitational mass imaging: idea Mass substructure distorts extended lensed sources

  31. Direct detection of a dark substructure Vegetti et al 2010

  32. Dark matter and strong lensing: Answers • Is there dark matter? What is it? • Yes. We can help find out with time-delays • Are dark matter halo profiles universal? • No. Either we do not understand baryons or we do not understand dark matter • Is the IMF universal? • No, If we understand dark matter halos. • Is there dark matter substructure? • Yes. Not clear if there is enough (or maybe too much)

  33. The end

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