Using Galaxy Clusters for Cosmology and the XCS

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Using Galaxy Clusters forCosmology and the XCS

• Ben Hoyle, Bob Nichol, David Bacon, Ed
  Lloyd-Davies, Kathy Romer the XCS

Cape Town April 08
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Overview

• Clusters
• Clusters Cosmology
• Cluster collapse cosmology
• Cluster surveys
• X-ray cluster catalogues
• The XMM Cluster Survey XCS
• Detecting clusters
• Cluster classification
• Redshift estimates
• High redshift cluster
• Mass estimate 1 Scaling relations
• Mass estimate 2 Weak lensing
• The magnification bias
• The future

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Clusters

• Properties of clusters of galaxies
• Size few Mpc
• Mass
• Emit broad range of EM
• Galaxies -gt optical
• ICM -gt X-rays

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Clusters cosmology

• The number density and mass of clusters, the mass
  function, n(M,z), are related to
  by

Press Schechter, spherical collapse

• Sheth Tormen, ellipsoidal collapse

Parameter Descritption Function of
Barrier value
Varience of density field
Normalisation Of den. field
Growth of strtucture
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Cluster collapse cosmology
Ellipsodial collapse
Spherical collapse
Vary matter content
Vary wconst
Schaefer Koyama
Modify Gravity
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Cluster surveys

• Cluster cosmology checklist
• Lots of clusters
• Broad redshift range
• Mass estimates

• Optical cluster catalogues
• Large numbers
• Redshifts
• No masses

• X-ray cluster catalogues
• Mass estimates
• Cavaliere Fusco-Femiano 78, Dai et al 06
• Small numbers
• Redshifts difficult

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X-ray cluster catalogues

• X-ray identified cluster catalogues are mainly
  taken from the literature.

Catalogue Clusters Redshifts? P.I.
XCS 1800 lt10 Romer 01
BCS 206 Yes Ebling 98
eBCS 107 Yes Ebling 02
R400D 242 Yes Burenin 02
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Overview

• Clusters
• Clusters Cosmology
• Cluster collapse cosmology
• Cluster surveys
• X-ray cluster catalogues
• The XMM cluster survey XCS
• Detecting clusters
• Cluster classification
• Redshift estimates
• High redshift cluster
• Mass estimate 1 Scaling relations
• Mass estimate 2 Weak lensing
• The magnification bias
• The future

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XMM Cluster Survey XCS

• The XCS
• Archival pointings
• Serendipitous detections
• 170 sq. deg. Present
• 500 sq. deg. Total
• 0.1ltzlt2
• Currently 1847
• Expect 2000

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Detecting clusters
Simulated clusters
Extended sources

• Color key
• Extended sources, Green ellipses
• Point sources, red circles
• Unsure, Pink circles

• From simulations we can recover our selection
  function.

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Cluster classification

• Cluster zoo
• SDSS optical images
• Centered on X-ray ra,dec
• Optical X-ray overlays
• X-ray photon density contours
• 610 XCS extended sources
• 7 classification types
• 9 classifications

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Cluster classification

• Results
• Gold sample
• High Z
• False detections
• Cuts improve sample

Soft counts Gold Clusters All Clusters
gt0 18 55
gt200 41 77
gt500 54 81
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Redshift estimates

• Empirically, see LRGs inhabit the central regions
  of clusters.

Look along line of sight of the cluster,
encounter an clump of LRGs. Assign LRG redshift
to cluster

• Test on ROSAT 400 sq. deg
• Spectroscopic redshifts

• SDSS LRGs
• Spec and Photo redshifts
• Good Agreement

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Redshift estimates

• Apply the LRG redshift estimate technique to the
  XCS

193 free cluster redshifts
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Redshift estimates

• Dedicated XCS photometric follow up NOAO XCS -gt
  NXS

More than 300 redshifts
136 for
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High redshift cluster

• The most distant spectroscopically confirmed
  cluster of galaxies found to date. XMM-XCS
  J2215.9-1738 or J2215.

• 5 pointings of a z2.215 quasar
• Cluster redshift 1.45
• Temp gt 6KeV

Standford et al astro-ph/0606075 Hilton et al
astro-ph/0708.3258
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High redshift cluster

• The most distant spectroscopically confirmed
  cluster of galaxies found to date. XMM-XCS
  J2215.9-1738 or J2215.

• 5 pointings of a z2.215 quasar
• Cluster redshift 1.45
• Temp gt 6KeV

Standford et al astro-ph/0606075 Hilton et al
astro-ph/0708.3258
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Overview

• Clusters
• Clusters Cosmology
• Cluster collapse cosmology
• Cluster surveys
• X-ray cluster catalogues
• The XMM Cluster Survey XCS
• Detecting clusters
• Cluster classification
• Redshift estimates
• High redshift cluster
• Mass estimates 1 Scaling relations
• Mass estimate 2 Weak lensing
• The magnification bias
• The future

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Mass estimate 1 Scaling relations

• Combining optical large numbers, no masses and
  X-ray small numbers, masses cluster catalogues
  to obtain a mass proxy applicable to optically
  selected clusters.

Examine properties of X-ray clusters with a
counter part in SDSS

• X-ray clusters
• eBCs,BCS,R400d,XCS
• Reprocessed equally
• Dai et al 06

Empirical Relationship

• Optical Clusters
• Mass estimates
• Constrain cosmology

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Mass estimates 2 Weak lensing

• The Sloan has enabled the creation of two massive
  optical catalogues

• MaxBCG clusters Koester et al 07
• 13.103
• 0.1ltzlt0.3 volume limited
• Well determined redshifts
• Number of galaxies
• Lack mass estimates
• Member Galaxy luminosity

• DR4 Quasars Richards et al
• 3.105
• 0.5ltzlt2.25
• 5-band SDSS magnitudes

We can follow Scranton et al 05, and use a weak
lensing mass measurement, called magnification
bias.
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The magnification bias

• The QSO unlensed source density

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The magnification bias

• Lensing changes the measured source density, by
  stretching the solid angle

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The magnification bias

• Lensing magnifies the source flux

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The magnification bias
The cross correlation, is a function of bias, b,
the weak lensing departure from unity, ,and
the line of sight integrated density contrast,
Schnieder Bartelmann astro-ph/9912508

• The sign of the correlation
• The signal strength

Where alpha is the gradient of the QSO
distribution, multiplied by 2.5 There is a change
of sign of
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The magnification bias, results

• We find preliminary results

Expect a strong correlation
Expect a weak anti-correlation
Stack similar clusters, expect the signal
strength to increase with cluster mass.
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The future

• Weak Lensing
• SDSS DR6 QSO
• 1 million QSOs
• Redo with full MaxBCG
• Check systematics

• Mass estimates
• Compare X-ray weak lensing mass measurements
• Assign MaxBCG clusters masses

• Cosmology
• Assume LCDM constrain cosmological parameters
• Constrain modified gravity models Schaefer
  Koyama 07