Discovery of a Dark Matter Ring in

CL0024+17

Discovery of a Dark Matter Ring in

CL0024+17

Myungkook James JeeJohns Hopkins University, Baltimore,

USA

July 3, 2007 IAP

Myungkook James JeeJohns Hopkins University, Baltimore,

USA

July 3, 2007 IAP

Presentation OutlinePresentation Outline

1. Introduction A brief history Why is CL0024 interesting?

2. Gravitational Lensing Problems with previous analyses A new technique

3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

1. Introduction A brief history Why is CL0024 interesting?

2. Gravitational Lensing Problems with previous analyses A new technique

3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

A Brief HistoryA Brief History Discovered by Humason & Sandage

(1957). One of the first targets showing the

Butcher-Omler effect (Dressler & Gunn 1982).

Gravitational arcs were discovered by Koo (1988).

Depletion effect were detected by Fort et al. (1997).

Comprehensive mass reconstruction with HST/WFPC2 (Tyson et al. 1998).

Spectroscopic redshift of the arcs was obtained by Broadhurst et al. (2000).

Wide-field mass reconstruction (Kneib et al. 2003).

Discovered by Humason & Sandage (1957).

One of the first targets showing the Butcher-Omler effect (Dressler & Gunn 1982).

Gravitational arcs were discovered by Koo (1988).

Depletion effect were detected by Fort et al. (1997).

Comprehensive mass reconstruction with HST/WFPC2 (Tyson et al. 1998).

Spectroscopic redshift of the arcs was obtained by Broadhurst et al. (2000).

Wide-field mass reconstruction (Kneib et al. 2003).

Why is CL0024 so interesting?Why is CL0024 so interesting?

The cluster has the five multiple images that possess clear substructures.

A factor of 2-4 difference between X-ray and lensing masses (Ota et al. 2004; Zhang et al. 2005).

Spectroscopic data suggest that there was a high-speed line-of sight collision between two sub-clusters (Czoske et al. 2002).

The cluster has the five multiple images that possess clear substructures.

A factor of 2-4 difference between X-ray and lensing masses (Ota et al. 2004; Zhang et al. 2005).

Spectroscopic data suggest that there was a high-speed line-of sight collision between two sub-clusters (Czoske et al. 2002).

Solution is not unique!Solution is not unique!

The location of the critical curvedoes not change under the abovetransformation.

Mass-Sheet DegeneracyMass-Sheet Degeneracy

A family of solutions predicting the five multiple images!This also applies to weak-lensing analysis.Assumptions are required to break the degeneracy.Cause of discrepancy between strong- and weak-lensing.

Multiple systems at different redshifts. However…

Multiple systems at different redshifts. However…

Multiple image systems arefound astride critical curves.

They are only sensitive tothe inner mass profile.

The entire mass profile is obtained by extrapolating theinner profile.

Shapes of Background GalaxiesShapes of Background Galaxies

They contain tremendousinformation on the mass distribution in the cluster outskirts.

Weak-lensing Mass Reconstructions

CL 0152 at z=0.84 MS 1054 at z=0.83 Abell 2218 at z=0.17

CL 1252 at z=1.2 Lynx clusters at z=1.3

Our Mass Reconstruction AlgorithmOur Mass Reconstruction Algorithm

<- The target function we minimize.

<- Strong-lensing constraints.

Our Mass Reconstruction AlgorithmOur Mass Reconstruction Algorithm

<- The target function we minimize.

<- Strong-lensing constraints.

<- Weak-lensing constraints (ellipticity).

Our Mass Reconstruction AlgorithmOur Mass Reconstruction Algorithm

<- The target function we minimize.

<- Strong-lensing constraints.

<- Weak-lensing constraints (ellipticity).

<- Entropy-regularization.

Presentation OutlinePresentation Outline

1. Introduction A brief history Why is CL0024 interesting?

2. Gravitational Lensing3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

1. Introduction A brief history Why is CL0024 interesting?

2. Gravitational Lensing3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

Mass Reconstruction of CL0024Mass Reconstruction of CL0024

Original Background subtracted

Discovery of a dark matter ring at 75”

Possible Causes of the Ring?Possible Causes of the Ring?

Image alignment errors Inaccurate geometric distortion correction Imperfect PSF correction Inconsistency between Strong- and Weak-lensing

signals Regularization artifacts Edge effect (finite field inversion) Data overfitting Sampling violation

Image alignment errors Inaccurate geometric distortion correction Imperfect PSF correction Inconsistency between Strong- and Weak-lensing

signals Regularization artifacts Edge effect (finite field inversion) Data overfitting Sampling violation

Radial Profile and Tangential ShearRadial Profile and Tangential Shear

•The ring though a low-contrast structure appears as a bump at 75”.•The tangential shear also reflects the peculiar radial mass profile.•The error bars are overestimation of the true statistical errors because anydeviation from the azimuthal symmetry contribute to the error bars.

We are not alone in the detection of the dip in the tangential shear!

We are not alone in the detection of the dip in the tangential shear!

Kneib et al. (2003)

Mass vs GalaxiesMass vs GalaxiesIn the cluster core, brightelliptical galaxies definemass peaks.

The ring is not well tracedby the cluster galaxies.

Origin of the RingOrigin of the Ring

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Czoske et al. (2002)

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A high-speed collision?

Numerical Simulation of Cluster Collision

Numerical Simulation of Cluster Collision

Initially, the two clusters contractbecause of the increased gravity.

About 0.5 Gyrs after the coreImpact, the dark matterparticles flow outward.

At 1 Gyrs since the impact, the Decelerated outflow creates shell-like structures, which appearas a ring when projected ontothe plane of the sky.

Presentation OutlinePresentation Outline

1. Introduction2. Gravitational Lensing

Problems with previous analyses A new technique

3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

1. Introduction2. Gravitational Lensing

Problems with previous analyses A new technique

3. Results and Interpretation4. Frequently Asked Questions5. Conclusions

FAQ 1. Why can’t we see the ring in galaxy distribution?

FAQ 1. Why can’t we see the ring in galaxy distribution?

1. Galaxies sample the underlying dark matter only sparsely.

2. The ring is a low-contrast structure.

1. Galaxies sample the underlying dark matter only sparsely.

2. The ring is a low-contrast structure.

FAQ 1. Why can’t we see the ring in galaxy distribution?- Continued.FAQ 1. Why can’t we see the ring in galaxy distribution?- Continued.

FAQ 2. Can’t the dip at 75” in the tangential shear profile be caused by an isolated mass clump instead of the ring?

FAQ 2. Can’t the dip at 75” in the tangential shear profile be caused by an isolated mass clump instead of the ring?

1. The algorithm has been tested for artificial clusters with/without a ring.

2. There seems to be no isolated mass clumps at 75” in CL0024+17.

1. The algorithm has been tested for artificial clusters with/without a ring.

2. There seems to be no isolated mass clumps at 75” in CL0024+17.

FAQ 2. Can’t the dip at 75” in the tangential shear profile be caused by an isolated mass clump instead of the ring?

FAQ 2. Can’t the dip at 75” in the tangential shear profile be caused by an isolated mass clump instead of the ring?

3. The secondary mass clump in Abell 2218 is detected as an isolated mass clump in the mass reconstruction.

3. The secondary mass clump in Abell 2218 is detected as an isolated mass clump in the mass reconstruction.

Jee et al., in prep.

FAQ 3. Galaxy Clusters are dynamically hot. Then why the ring?

FAQ 3. Galaxy Clusters are dynamically hot. Then why the ring?

It must be a high-speed collision (~3000 km/s) to create shells (rings).

However, orbits of dark matter particles are important.

It must be a high-speed collision (~3000 km/s) to create shells (rings).

However, orbits of dark matter particles are important.

Highly TangentialHighly Tangential

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Moderately TangentialModerately Tangential

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IsotropicIsotropic

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FAQ 4. Why doesn’t the ICM of the cluster follow the ring?

FAQ 4. Why doesn’t the ICM of the cluster follow the ring?

When the system is fully relaxed, the gas of the cluster should follow the potential well dominated by the cluster dark matter.

When the system is fully relaxed, the gas of the cluster should follow the potential well dominated by the cluster dark matter.

FAQ 4. Why doesn’t the ICM of the cluster follow the ring?

FAQ 4. Why doesn’t the ICM of the cluster follow the ring?

Markevitch 2007, private communication

“I have to admit that the dark matter ring, as presented in the paper, looks like some kind of an artifact. However, there is an additional piece of data that, to me, adds confidence in the reality of this result (or at least shows that something strange is certainly going on in this cluster). If you play with colors in the Chandra image of this cluster, you will notice at least 2 rings, or edges, of X-ray emission around the center, one around r=40", and another right around r=75". You've probably missed them because you smoothed the image too heavily.”

ConclusionsConclusions

We discovered a ringlike dark matter structure in CL0024+17.

We claim that the ring is the result of the high-speed collision occurred along the line-of-sight direction.

The Chandra data suggest that the dark matter ring may be also traced by the cluster gas.

Useful laboratory where many fundamental questions in physics can be studied.

We discovered a ringlike dark matter structure in CL0024+17.

We claim that the ring is the result of the high-speed collision occurred along the line-of-sight direction.

The Chandra data suggest that the dark matter ring may be also traced by the cluster gas.

Useful laboratory where many fundamental questions in physics can be studied.

Resolving the Mass Discrepancy

The X-ray surface brightness profile is peculiar (open circles).

One component model (dashed) cannot explain the observed profile.

Two component model (solid) can nicely explain the peculiarity.

Jee et al. (2007)