Transcript Cosmology with Galaxy Clusters Joe Mohr Ludwig-Maximilians University Max Planck Institute for Extraterrestrial Physics 47th Rencontres de Moriond, 2012 e-ROSITA SPT.

Cosmology with Galaxy Clusters
Joe Mohr
Ludwig-Maximilians University
Max Planck Institute for Extraterrestrial Physics
47th Rencontres de Moriond, 2012
e-ROSITA
SPT
Cosmology with Galaxy Clusters
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Cluster survey overview
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Recent results
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Multiband optical surveys
ROSAT X-ray surveys
SZE surveys
Ongoing surveys and next steps
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Cosmology and astrophysics
Selection in optical, X-ray and SZE
Improved mass calibration
Next generation surveys
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What Are Galaxy Clusters?
Galaxy clusters are the most massive,
collapsed structures in the universe.
They contain galaxies, hot ionized gas
(107-8K) and dark matter.
SPT-CLJ0205
In typical structure formation scenarios,
low mass clusters emerge in
significant numbers at z~2-3
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• X-ray emission
• Sunyaev-Zel’dovich Effect
• Light from galaxies
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Data and folded model data and folded model
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Clusters are good probes, because they
are massive and “easy” to detect
through their:
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Cluster Studies of Cosmology
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Clusters are easily observed, rare, high
mass astrophysical objects.
They have figured prominently in
cosmological studies over the past two
decades
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Evolution of the cluster abundance
Baryon fractions
Cluster structure- concentration
Local mass function
Cluster power spectrum
Distances using SZE+Xray, baryon
fractions, and isophotal sizes
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Redshift distribution is sensitive to distance-redshift
Bahcall
al 1999 growth
relation and
rate ofetstructure
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Cluster Surveys Provide a Rich Source of Information
Cluster Redshift Distribution
Sensitive to volume-redshift relation
and cluster abundance evolution
dN(z)
dV
=
( z) n ( z)
dzdW dz dW
Cluster Abundance Evolution
Depends on the amplitude and
shape of the power spectrum of
density fluctuations
Can be studied directly in N-body
simulations; simple “cosmology
independent” fitting formulae
exist
Warren et al ‘05
Bottom line: surveys measure
Distances
Growth rate of density perturbations
But you must know the mass
selection of your survey!
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A Toy Model:
The Press-Schechter Mass Function
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Consider the cosmic density field filtered on a mass scale M
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Leads to Gaussian distribution described by some s(M)
Assume that density perturbations have collapsed by the time their
linearly evolved overdensity exceeds some critical value dc
Abundance (number density) of collapsed objects with mass M is then
proportional to an integral over the tail of a Gaussian
collapsed
collapsed
dc
Abundance is exponentially sensitive to the
underlying linear density fluctuations
dc
Gaussian Distributed Perturbations on Scale M
n(M,z) =
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M
¥
dd exp{ s d(
ò
2ps ( M,z)
1
dc
-
2
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2
M ,z)
}
Withing LCDM framework the mass
function evolution is well studied
e.g. Sheth & Tormen 1999, Jenkins et al 2001,
Warren et al 2005, Tinker et al 2008
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Surveys Measure Cosmic Expansion History H(z)
Expansion history reflects changing energy
density of universe
Through the distance- redshift relation
Redshift distribution depends on volume {dN/dz=dV/dz*n(z)}
Cluster power spectrum provides standard rods for distances
Direct mass measurements depend on distances
Through growth rate of cosmic structures
Linear growth of density perturbations is sensitive to H(z) and to the
dark matter density
Surveys enable a consistency test of distance and
growth rate constraints
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8pG
H ( z) =
r ( z)
3
dA ( z) µ ò
z
0
dz'
H(z')
d˙˙ + 2H ( t )d˙ = 4 pGrod
where d º
dr
ro
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Context for Cluster Survey Cosmology
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Other methods for studies of cosmic acceleration
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CMB
SNe cosmology
Galaxy Clustering
Weak Lensing
Dark Energy Task Force preferred these two
Primary cluster survey challenges/dependencies:
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Structure formation theory
Observational Issues
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Precisely Understanding Cluster Selection
Precisely Calibrating Cluster mass-observable relations
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Cluster Selection: Optical/IR
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Optical/IR Surveys
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Typical Optical/IR signature only
crudely related to cluster massclean mass selection not possible
Completeness f(M,z)
for SDSS-like Survey
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Bgc
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Song et al 2012
Song et al 2012
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Problem: Galaxies (even red ones)
exist everywhere, not just in
clusters- contamination an issue
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Bgc=[100,416]
Bgc=[416,733]
Completeness of red sequence
methods seems quite good
Bgc=[733,1050]
Bgc=[1050,1366]
Bgc=[1366,1683]
Bgc=[1683,2000]
N
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0.3
0.2
Song et al 2012
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0.0
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log10M200
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Cluster Selection: X-ray
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ROSAT experience:
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With 25” FWHM PSF, archival surveys
delivered high completeness (~95%),
low contamination (~1%)
Chandra Image of Zw3158
Reiprich & Böhringer 2002
X-ray surveys
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X-ray luminosity tracks cluster mass
with ~45% scatter
AGN can boost flux, leading to
contamination by low mass systems
Unresolved clusters can be missed
unless there is complete multiband
optical imaging available to followup
all sources
Low scatter mass estimate (Yx or Micm
at ~15% available for a subset)
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BCS
Cluster Selection: SZE
Unique
spectrum
Unique
angular
scale
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Unique signature in frequency and
angle
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Need multiple frequencies!
Clean mass selection
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Contamination just a function of S/N
Need 10m telescope at 150GHz!
SZE flux proportional to the total
thermal energy in the electron
population
No cosmological dimming (indep of z)
Radio galaxies can bias flux, but these
are very rare at high frequency
SPT selection very clean- redshift
independent mass selection with 20% to
30% scatter
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Simulations from M. White
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Recent Results
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Recent analyses of X-ray cluster samples using existing datasets have
generally been quite successful, but some challenges have emerged with
the optical samples
SDSS and RCS were able to obtain interesting constraints on Wm and s8.
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RCS- 956 clusters over 72 deg2
SDSS- 104 clusters over 7,400 deg2
Gladders
al 2007
Rozo et alet2009
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400 deg2 ROSAT X-ray Archival Sample
Vikhlinin et al 2009
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Analysis:
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49 “local” + 37 z>0.35 clusters
Mass functions
12 clusters at z>0.55 require
Lambda
Independent constraints in good
agreement with WMAP+
cosmology
w constrained to 0.2(clus)/0.05(all)
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ROSAT X-ray All Sky Survey Sample
Mantz et al 2009
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Analysis:
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Mass function of full sample
Constant fICM from 42 “relaxed” systems
Mass-obs relation normalization freedom
allowed and constrained using 6 low z
clusters
Independent constraints
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s8 = 0.82 (0.05)
w=-1.01 (0.20)
Combined constraints
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WMAP+SNe+BAO+Clusters+fICM:
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s8 = 0.79 (0.03)
w=-0.96 (0.06)
DETF FOM =15.5 (~2x improvement)
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wo=-0.93 (0.16), wa=-0.16 (+0.47,-0.73)
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BCS
SPT systems from 2008 fields
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SPT is 10m telescope operating at the
south pole (PI J. Carlstrom)
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Vanderlinde
et al 2010
Andersson
et al 2011
Initial highest S/N sample of 21
clusters from 180 deg2 survey at
90GHz, 150GHz and 220GHz
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Multi-l at 90, 150 and 220 GHz
1 arcmin resolution- matched to clusters
Mass calibration from X-ray
Cosmological constraints:
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Clusters+BBN+H0:
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Benson et al 2011
s8 = 0.77 (0.09)
w=-1.09 (0.36)
WMAP+SNe+BAO+Clusters:
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s8 = 0.79 (0.03)
w=-0.97 (0.06)
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Constraints on Non-Gaussianity
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Flurry of results on non-Gaussianity
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Early detection results used flawed
analysis
(see Hotchkiss 2011 for discussion/clarification)
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Current status fnl=-192+/-310, 20+/-450
(from full likelihood analysis including selection
function of SPT sample)
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Interesting thread- combination of
cluster counts and power spectrum
greatly enhances constraints on fnl
Benson et al 2012
(i.e. see Sartoris et al 2010 for discussion)
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Lessons Learned?
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Cluster cosmology is competitive with other methods
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But sensitivity is not just about the number of clusters in the survey
Ideal survey would have:
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Clean selection through observable related closely to mass
Low scatter individual cluster mass estimates
Direct calibration of mass estimators using weak lensing and (perhaps)
velocity dispersions
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Ongoing Surveys
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X-ray surveys with XMM:
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Pencil Beam/Archival surveys
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Continguous/uniform surveys
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Pierre et al (XMM-LSS), Suhada et al (X-BCS), Pierre et al (XMM-XXL) – 50 deg2
Optical surveys continuing to scale up:
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Faßbender et al (XDCP), Römer et al (XCS)
RCS, SDSS, RCS2, CFHTLS, Pan-STARRS1…
SZE Surveys now delivering…
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SPT (10m) produced first SZE selected clusters
ACT (6m) is also now in operation
Planck has surveyed whole sky and is targeting candidates
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Planck is All Sky Multi-l Mission
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~200 clusters released in 2011, preparation of full sample continues
Interesting systems found, including this “Supercluster”!
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BCS
SPT Multi-frequency Survey
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SPT has completed high angular resolution 2500 deg2 survey
2 complete (158 clusters),
Followup underway- 750 deg
Galaxy Clusters!
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Galaxy Clusters!
Full sample of 550 clusters available in one year
Currently delivering unique sample of high mass clusters at high redshift
11 degree
degree
150
GHz
90 GHz
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Next Step: Mass Calibration
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Key systematic is cluster masses
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Want mass systematic to be smaller than
Poisson noise of sample (<3% for 103 clusters)
Our Program at z>0.8:
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Need robust mass measurements
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Cannot assume hydrostatic equilibrium
Weak lensing is key method
(when coupled to tests with simulations)
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Velocity dispersions are showing promise
• HST+VLT weak lensing studies
• Directly constrains mass-obs relation
• VLT/FORS2 velocity dispersion studies
• Directly constrains mass-obs relation
(when coupled to tests with simulations)
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Also need scatter of mass-observable
relation
• XMM/Chandra studies
• Helps constrain scatter
• Allows us to calibrate X-ray mass-obs
relations to prepare for eROSITA
(see Lima and Hu 2005 for discussion)
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Good progress at low redshift z~0.3
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LoCuSS – Graham Smith
Program needed over full range of cluster
samples (i.e. z~1.5 for SPT)
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Next Step: Future Surveys
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Requirement: build on demonstrated success with Xray and SZE surveys
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Next generation SZE surveys beginning (i.e. SPTpol, ACTpol, ++)
Next generation X-ray survey eROSITA two years from launch
Goal: resolve complexities of optical/IR cluster finding
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We are entering a period which will see surveys of unprecedented
size and depth (i.e. DES, HSC, EUCLID, LSST, ++)
The scientific payoff would be enormous- could push
cosmological tests to higher redshift!
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Next Generation X-ray: e-ROSITA
PI Peter Predehl (MPE)
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Collecting area of 2 XMM‘s with 1 deg diameter FOV
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7 Mirror Modules, 54 shells each
350 cm2 each (totals 2 x XMM-Newton)
Good angular resolution – 16 arcsec HPD on axis
Four year nominal mission
Characteristic flux limit is ~2x10-14 erg/s/cm2
(~30X deeper than ROSAT All Sky Survey w/ CCD spectroscopy)
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Summary
Cluster survey cosmology has broad science grasp
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Constrains expansion history + growth rate of structure
Constrains any process that affects the power spectrum of density
fluctuations ( + non-Gaussianity )
Recent optical, X-ray and SZE cluster cosmology results
promising
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No apparent tension with WMAP+BAO+SNe (except for RCS)
Cosmology from ~550 SZE selected clusters coming in ~1 year
XMM samples of similar size available and being analyzed (i.e. XCS)
Next steps for cluster cosmology
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Improve mass calibration using weak lensing +
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Statistical weak lensing using new generation of deep OIR surveys (i.e. DES,
HSC, Euclid, LSST) will play a key role
Scale up cleanly selected catalogs of clusters
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New SZE surveys beginning (SPTpol, ACTpol, ++)
The “ultimate” X-ray cluster survey- eROSITA - coming soon!
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