cosmology with cluster surveys subha majumdar canadian institute of theoretical astrophysics toronto...
TRANSCRIPT
Cosmology with
Cluster Surveys
Subha Majumdar
Canadian Institute of Theoretical Astrophysics Toronto
along with Joe Mohr, Martin White & Jose Diego
International Conference on Gravitation and Cosmology, Kochi, 5th January 2004
Jan 2004Jan 2004 ICGC – 04, KochiICGC – 04, Kochi
Overview Introduction to Galaxy Clusters
Introduction to the Surveys
Studying Dark Energy with Galaxy Cluster Surveys,
the stress in on the eqn. of state “w” of dark energy
(This was the parameter that was not constrained by WMAP+SDSS!
But knowledge of “w” is fundamental to our understanding of dark
energy)
Something new: Self Calibration in cluster surveys
and precision cosmology
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Galaxy clusters are the most massive, collapsed structures in the universe. They contain galaxies, hot, ionized gas (107-8K) and dark matter.
In typical structure formation scenarios, low mass clusters emerge in significant numbers at z~2-3
Clusters are good probes, because they are massive and “easy” to detect through their:
What Are Galaxy Clusters?
• X-ray emission• Sunyaev-Zel’dovich Effect• Gravitational lensing
Chandra Image of Zw3158
SZEX-ray
HST
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The Basics of SZ Effect
sightofline
pressuregasamplitude
clusteramplitudedependencefreqdistortion
_
)(_
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Whats nice about SZE?
1) Ofcourse, the distinct spectral signature2) Measures the total thermal content of the cluster3) More or less redshift independent4) Less susceptible to messy cluster substructure, core physics (prop to density and not density squared as in XRays)
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Example: Local Abundance/Mass Function Reiprich & Boehringer 2001
Look at the large error bars!! We want to do much better.
Things will change drastically with future surveys.Especially as a probe of dark energy eqn `of state “w”
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Upcoming Cluster SurveysSZ-surveys:
Planck : 2008(?) 7,000/8,000 – 30,000/40,000
SPT : 2005(?) 20,000-30,000
ACT : late 2004 few thousands
APEX : middle 2004 few thousands
X-Ray surveys
DUET : Unsuccesful 20,000-30,000 DUO : very +ve report, late 2004 ~10,000XMM-LSS : 2004+ , ~1000(?)
Cluster surveys will be a thrust area for some time to come!
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From observations to detecting clusters: an example
Diego & SM 04
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The Cluster Redshift Distribution
Cluster redshift distribution probes:
dN(z)dzd
dV
dzdn z c
H z dA2 1 z 2
dM f M dn M , z dM0
1) volume-redshift relation
2) abundance evolution
Volume Element
Abundance
Mass Selection Function
dN(z)dzd
dV
dzdn z
Volume Abundance
3) cluster structure and evolution.
One can get dN/dz if we can get the redshifts of the detected clusters
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Sensitivity of Cluster Redshift Distribution to Dark Energy Equation of State
Increasing w keeping E fixed hasthe following effects
Volume effect Growth EffectFig courtesy Joe Mohr
It decreases volume surveyed
It decreases growthrate of perturbations
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Potential for different methods to constrain `w’
Levine, Shultz & White 2002
Complimentary&
Highly Competetive
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Dual Nature of Galaxy Clusters It’s critical- for almost any analysis- to keep in mind that clusters
are young objects and yet as a population they exhibit striking regularity
Statistical studies of (x-ray flux limited samples of) galaxy clusters reveal that more than half exhibit merger signatures.
There’s lot of substructures.
Statistical studies of (x-ray flux limited samples of) galaxy clusters reveal regularity
Existence of simple flux-mass relation
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Self-Calibration in SZ surveys Two surveys, the South Pole Telescope
Survey and the Planck all sky survey (yielding > 20000 clusters), contain enough information to constrain the interesting cosmological parameters and solve for the structure of galaxy clusters simultaneously!
Assumptions required:1. Hierarchichal structure formation is correct
2. A mass-X-ray luminosity relation exists (or a mass-SZE luminosity relation exists)
3. Crude redshift estimates are available for each cluster detected in the survey
Survey m tot w 8 h n b Norm Slope
Priors flat 0.07 0.050 0.004
Planck 0.017 - 0.075 0.013 0.053 0.041 0.004 24% 0.004
SPT 0.024 - 0.062 0.013 0.047 0.048 0.004 21% 0.005
fx z 4dL2 AM E 2 z
SM & J. Mohr 2003
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Self-Calibration : Continued
A Caveat: What if there is “evolution” ??
fx z 4dL2 AM E 2 z 1 z
Everything is lost ! Or is it?
Self Calibration can be regained (by adding complimentary info) ! 1. Need to do follow-up mass estimates of a few clusters 2. Cluster power spectrum, P(k)
Not impressive by themselves, when combined with dN/dz they do wonders
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An Example: Planck All Sky Cluster SurveyNclusters ~ 22000
SM & J. Mohr, 2004
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How well do we get `w’ ?
Survey On its own
+ P(k) +100 clusters
follow-up
+ Both
SPT 0.18 0.16 0.06 0.035
Planck 0.39 0.10 0.12 0.041
1 error around w=-1, normalized over 9 other parameters
Note: WMAPext gives ~ 0.11
To pin down dark energy we must have cluster surveys + (CMB+SNe)
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So what did I say, Upcoming large yield cluster surveys would unveil a new
era of doing cosmology with clusters.
It has the promise to become 4th pillar of precision cosmology
along with CMB, SNe and weak lensing.
As an example, we have shown that these surveys provide us an
opportunity to probe the enigma of dark energy with high precision (the other great way is to do weak lensing tomography)
Most importantly, we’ve seen that even with uncertainties in cluster
physics, `self-calibration’ in these surveys makes clusters an important
tool in precision cosmology ( “w” to few percents, certainly competetive or maybe
even better than what can be done with CMB or SNe alone. )