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The Bullet Cluster A Challenge to L CDM Cosmology

The Bullet Cluster A Challenge to L CDM Cosmology. Jounghun Lee (Seoul Nat’l). This Lecture is based on. J.L. & Eiichiro Komatsu (UT Austin) (arXiv:1003.0939). The Bullet Cluster: IE0657-56. Discovered as a failed cluster (Tucker et al.1995): a large cloud of hot-gas

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The Bullet Cluster A Challenge to L CDM Cosmology

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  1. The Bullet ClusterA Challenge to LCDM Cosmology Jounghun Lee (Seoul Nat’l)

  2. This Lecture is based on • J.L. & Eiichiro Komatsu (UT Austin) (arXiv:1003.0939)

  3. The Bullet Cluster: IE0657-56 • Discovered as a failed cluster (Tucker et al.1995): • a large cloud of hot-gas • First observed by Chandra (Markevitch et al.2002): • a bullet-like subcluster exiting its main cluster with a bow shock • a system of two colliding clusters at z=0.296 X-ray: Markevitch et al. (2004)Lensing Map: Clowe et al. (2006) Optical: Clowe et al. (2006)

  4. Main sub Uniqueness of IE0657-56 z=0.296 transverse trajectory first core passage

  5. ? SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  6. A Bizarre Universe • We understand nothing about dark matter (DM). • We understand less than nothing about dark energy (DE). • Our universe seems quite unnatural… -Kolb (2003)

  7. The Modified Gravity • Motivation • The general relativity has not been tested on large-scales • Unverified existence of the dark matter • Basic tenet: • All gravity forces are associated with baryonic components.

  8. Surprise 1 – Offset of CM Clowe et al. (2006, ApJ, 648, L109) Clowe et al. (2006, ApJ, 648, L109) direct proof of the existence of nonbaryonic dark matter

  9. SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  10. Likelihood of Bullet Cluster I • The number fraction of bullet-like subclusters in a LCDM universe. • large uncertainty due to the small sample size • based on inaccurate old data Hayashi & White (2006) based on the Millennium simulation (Springel et al. 2005)

  11. Likelihood of Bullet Cluster II • Farra & Rosen (2007) reestimated the likelihood of bullets, using the updated data on the Bullet Cluster: • The bullet cluster seems to be quite unusual in LCDM…

  12. SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  13. Likelihood of Bullet Cluster III • Based on hydrodynamic simulations (Springel & Farra 2007) The bullet cluster are not so rare in LCDM.

  14. SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  15. Springel & Farrar (2007) Surprise 2 – Escape of Gas IE0657-56 Gas of the main cluster escape the gravitational potential. Gas of the main cluster could not escape the gravitational potential. The velocity of the bullet cluster is not fast enough!

  16. Conditions for Bullet infall velocity cluster concentration mass ratio cNFW=6 NFW 1:10 1:6 bullet veloctiy In Springel-Farrar07 In Mastropietro-Burkert08

  17. SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  18. A Key to the Puzzle Main sub R200

  19. The Strategy

  20. MICE Simulation • Crocce et al. (2010) • A flat LCDM with • Wm=0.25, h=0.7 • ns=0.95, s8=0.8 • Lbox = 3h-1Gpc (largest ever!) • # of particles = 20483 • Mpar=2x1011 h-1Msun http://segre.ieec.uab.es/fosalba/MICE/

  21. MICE Catalog of Cluster Halos • Identified by the friends-of-friends algorithm with l=0.2 (FoF02).

  22. Clusters of Clusters main main The MICE cluster halo catalog Applying the FoF to the MICE catalog

  23. 3R200 2R200 Bullet-Like Systems (BLS) 2<R/R200<3 1:10 mass ratio head-on merging main

  24. Infall Velocity Distribution at z=0 1800 km/s

  25. Infall Velocity Distribution at z=0.5 • slows down the • structure formation 2500 km/s

  26. Surprise 3 – Infall Velocity • IE0657-56 requires Vc~3000 km/s at 2R200 (Masptropietro & Burkert 2008). • While LCDM predicts • IE0657-56 is incompatible with LCDM.

  27. SUPPORT LCDM CHALLENGE LCDM BULLET CLUSTER

  28. Discussion on Uncertainty I • How accurate is our estimate of R200 ? • It depends on the halo concentration and the number of particles. • Rfof/R200 ~ 1.1. • Good enough!

  29. Discussion on Uncertainty II • How does the final result depend on the linking length, b, used to identify clusters of clusters? • Almost no change as the value of b changes. • Statistically robust.

  30. Modified Gravity R E T U R N S

  31. Return of the Modified Gravity from Komatsu 2010, talk at the perimeter institute.

  32. The Other Candidates RXJI1347-1145 MACS J0025.4-1222 (Komatsu et al.2001) Vshock~ 4600 km/s (Bradac et al.2008)

  33. Conclusion • The observed property of IE0657-56 calls for a high infall velocity: 3000 km/s at 2R200. • This is impossible in a LCDM universe… • There are two possibilities: • We haven’t exhausted all the parameter space in the hydro simulations. • The LCDM is ruled out by the existence of the bullet cluster.

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