Marusa Bradac (KIPAC)Doug Clowe (Ohio U.)

Anthony Gonzalez (U. Florida)

Maxim Markevitch (CfA)Christine Jones (CfA)

Phil Marshall (KIPAC)Scott Randall (CfA)Tim Schrabback (AlFA, Bonn)

William Forman (CfA)

Dennis Zaritsky (U. Arizona)

Bradac et al., 2006, ApJ, 652,937Clowe et al., 2006, ApJL, 648,108

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Zwicky (1933) : Coma Cluster (400x observed mass)Smith (1936) : Virgo Cluster

The Case for Dark Matter

H.D. Babcock (1938; PhD - unpublished) M 31, M/L ~ 50

Kahn & Woltjer (1959): Local Group Timing

argument

de Blok et al. 2001

MOND (Milgrom)

The PROBLEM : Coincidence of Baryons & Dark Matter

Sanders & McGaugh 2002

Dark Matter (mass)

Gas

Galaxies

Gonzalez, Zaritsky, Zabludoff 2006

We see all the baryons!

Dark Matter (mass)

Gas

Galaxies

Scenario 1: ‘New’ Gravity - mass follows gas

Dark Matter (mass)

Gas

Galaxies

Scenario II: Collisionless DM

Dark Matter (mass)

Gas

Galaxies

Scenario III: Self-Interacting DM

1E0657-56 (The Bullet Cluster)

• Supersonic merger• z=0.30 (3.35 Gyr ago, or 1.2 Gpc away)

Gravitational Lensing

We see all the matter!

Strong lensing

Weak lensing

Weak lensing by cluster at z ~ 0.5

Mass overlay

1E0657-56 (The Bullet Cluster)

8 sigma offsets from X-ray peaks

Bradac et al. Strong + weak lensing

Conclusions

Rare high-v, face-on merger provides unique opportunity

plasma dominates baryons (lensing signal seen)

galaxies/dark matter separated from plasma

other “lumpy” clusters have X-ray/mass co-centered

data at http://flamingos.astro.ufl.edu/1e0657/public_html