Clusters and Lenses: Analyzing Ten Gravitational Lensing Systems - - PowerPoint PPT Presentation

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Clusters and Lenses: Analyzing Ten Gravitational Lensing Systems - - PowerPoint PPT Presentation

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Clusters and Lenses: Analyzing Ten Gravitational Lensing Systems Discovered in the Sloan Digital Sky Survey Matthew P. Wiesner Northern Illinois University Department of Physics Huan Lin (Fermilab), Michael Fortner (NIU), Elizabeth

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Clusters and Lenses: Analyzing Ten Gravitational Lensing Systems Discovered in the Sloan Digital Sky Survey

Matthew P. Wiesner Northern Illinois University Department of Physics Huan Lin (Fermilab), Michael Fortner (NIU), Elizabeth Buckley-Geer, James Annis, Sahar Allam, Jeffrey Kubo,

  • H. Thomas Diehl, Douglas Tucker, Donna Kubik

(Fermilab)

Fermilab New Perspectives Conference, 2011

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Outline

1) Introduction to the astrophysics 2) The data and how it was taken 3) Properties of the galaxy clusters 4) Properties of the gravitational lenses 5) Initial cosmological conclusions

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1) The Astrophysics

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What is a galaxy cluster?

  • Collection of

galaxies

  • Dark matter

presence

Abell 2255 (SDSS.org) (Penn State University)

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SLIDE 5

What is a gravitational lens?

  • System where light bends due to presence of mass
  • Effect of General Relativity (light follows curvature)

(NASA/CXC/M.Weiss)

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SLIDE 6

2) The Data

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SLIDE 7

The ten systems

  • Color images from g,r,i filters
  • Found in Sloan Digital Sky Survey
  • Follow-up data taken at WIYN telescope
  • Each includes a blue arc and a galaxy cluster
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SLIDE 8

SDSS J1209+2640 The Richest Cluster

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SDSS J1038+4849 The Happiest Cluster

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SLIDE 10

The telescopes

SDSS.org NOAO/AURA/NSF The Wisconsin-Yale-Indiana- NOAO (WIYN) Telescope The Sloan Digital Sky Survey (SDSS) Telescope

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SLIDE 11

3) Properties of the Galaxy Clusters

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How do we find galaxy clusters?

MaxBCG Method for Finding Galaxy Clusters

(Koester et al. 2007) Look for: (1)Groups of galaxies where density increases near center (2)Constant color (3)Central Brightest Cluster Galaxy (BCG)

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Defining a cluster galaxy

Counting Galaxies— Quantifying Richness

  • Ngals, number within

1 Mpc Used Fortran program to find

  • bjects that were:

A.Galaxies, not stars B.Within 1 Mpc of BCG C.Within 2σ of particular color D.At least as bright as 0.4L* (min brightness criterion)

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SLIDE 14
  • A. Galaxy-

Star Separation

Find stellar locus by plotting magnitude difference vs. variable aperture magnitude

  • C. Selecting

Cluster Members

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SLIDE 15

Results for Ngals

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Finding N200

Mpc h N r

gal 1 6 . 200

) ( 156 .

−

=

Radius of sphere within which ρ=200ρc (Hansen et al. 2005)

G z H z

c

π ρ

8 ) ( 3 ) (

2

=

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SLIDE 17

Finding M200

N

N M N M

α

      =

20 ) (

200 20 | 200 200 200

M200 (Johnston et. al. 2007). N200 from MaxBCG catalog, mass found from weak lensing.

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Finding Velocity Dispersion

      + =

25 ln ln

200

N B A

v

σ

Velocity dispersion (Becker et. al. 2008)

  • Found σv from

spectroscopy in N200 bins.

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SLIDE 19

4) Properties of the Gravitational Lenses

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Modeling the lens as a sphere

Einstein Radius

  • Describes size of

gravitational lens. For a perfect circle (Einstein ring) this is the radius of the ring.

SDSS J0900+2234

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Properties of the lens

        =

ds s d E

D D D G c M 4

2 2

θ

Narayan & Bartelmann (1997)

d s ds E

D D D c GM

2

4

= θ

Einstein radius Lens Mass

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SLIDE 22

Velocity Dispersion

ds s E v

D D c

π θ σ

4

2

=

Narayan & Bartelmann (1997)

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5) Initial Cosmological Conclusions

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ΛCDM

  • Standard model of cosmology

– Cosmological principle – Expansion of universe with Big Bang, cosmological redshift – Flat spatial geometry – Cosmological constant – Dark matter cold, non-baryonic, dissipationless (cannot cool by radiating), collisionless

NASA/WMAP Science Team

Gralla et. al. 2010

A Disagreement with ΛCDM?

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SLIDE 25

A Disagree- ment with ΛCDM?

  • Higher than expected concentrations: Cluster cores collapsing

faster than we thought? Why? (Broadhurst and Barkana 2008)

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Conclusion

  • We studied ten galaxy clusters and

gravitational lenses

  • Found richness and mass of clusters
  • Found size and mass of lenses
  • Found that current predictions for

Einstein radius as a function of cluster mass do not match data

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Acknowledgements

  • Fermilab Graduate Student Association
  • Dr. Huan Lin
  • Dr. Michael Fortner
  • The Fermilab Experimental Astrophysics

Group

  • Dr. Laurence Lurio and the NIU

Department of Physics

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SLIDE 28

Questions?

http://catalog.instructionalimages.com/einsteinquestion-pi-27.html