1. No category

X­ray results from the first SZ­selected galaxy cluster sample
MIT Cluster Workshop
Chandra
South Pole Telescope
XMM­Newton
Karl Andersson
MIT Kavli Institute for Astrophysics and Space Research
with Bautz, Benson, Carlstrom, Forman, Jones, Mohr, Murray, Vikhlinin and SPT collaboration etc.
2010­01­15
Outline
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The SZ­effect
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Cosmology with X­ray selected samples
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SPT cluster survey and X­ray follow­up
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X­ray results from the first SZ­selected sample
The SZ­effect
y=
T k B
me c
2
∫ n e T e dl
SZ shifts CMB BB spectrum
Y SZ ≡∫ y d  ∝ M gas T mg
More on SZ selection
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In principle z­independent
However, z­dependent confusion with CMB anisotropy – less low­z objects
Point sources can complicate selection – but multiple passbands help
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Unprecedented high­z massive­cluster finder
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SPT finds hundreds of new clusters
Existing X­ray selected surveys
Number of clusters, N(>M,z) – Mass function
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X­ray selected with only 40 high­z objects
Mass function evolution clearly detected
Tight constraints on ΩM
and σ8
Vikhlinin et al 2009
Dark energy constraints from X­ray mass function
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Already competitive constraints on dark energy parameters
Add SZ­data
Higher z sample
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Additional information about mass proxies from joint X­ray/SZ analysis
Vikhlinin et al 2009
SPT Cluster survey
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SPT will search for clusters in 1000s of sq degs. (yellow)
~800 sq deg observed
This talk covers 200 sq deg (magenta)
100s of new clusters now found
Follow up with X­ray instruments
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Optical verification is important but need X­ray observations to estimate mass accurately etc
From 200 sq deg, 2008 SPT fields, select 16 highest S/N candidates
XMM­Newton
Plan large Chandra+XMM­
Newton program
Full program will (hopefully) cover ~1000sq deg, ~75 clusters
Purpose of X­ray observations
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0517­5430 (z=0.29)
0547­5345 (z=0.90)
0509­5342 (z=0.46)
0528­5300 (z=0.77)
Statistical power of SPT sample – potentially high
Precise mass estimates can significantly improve constraints
X­ray data allows calculation of kT, Mgas, YX
Joint SZ­X­ray analysis can give additional constraints on gas properties
YX, mass proxy
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YX = MgasTX
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X­ray mass proxy YX has low scatter
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Simulations find < 8%
Confirmed by observations
X­ray equiv of YSZ
Kravtsov et al. 2006
Current X­ray observations
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Currently have observations of 15/16 cluster candidates (12 Chandra, 3 XMM)
“Only” 1 false detection, turned out to be an unusual primary CMB fluctuation
Total of 950ks of Chandra time plus 60ks XMM time (38ks usable)
Goal to get ~1500 detected photons per object for accurate kT estimates
First SZ­selected cluster sample in X­rays
Andersson et al. in prep
.....soon with complete X­ray follow­up
Self­similar scaling relations
Mass proxies
SZ – X­ray scaling relations
M ∝ E ( z) T
M ∝ Mg
−1
M ∝ E ( z)
−2 / 5
YSZ ∝ E ( z ) T
3/ 2
YX , SZ
−1
YSZ ∝ E ( z )
YSZ ∝ YX
3/ 5
X­ray only scaling relations
2
M gas ∝ E ( z ) T
−1
3/ 2
M gas
5/3
Tests cluster evolution, DA(z)
LOW scatter – from X­ray obs
LX ∝ E ( z )T
2/3
5/ 2
X­ray + SZ = DA(z) test
 T SZ ∝ ∫ ne T e dl
DA∝
2
e
S X ∝∫ n  ee dl
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Assume cluster is spherically T
2
e ,0
Birkinshaw et al 1991
Reese et al. 2002
Bonamente et al. 2004
Utilize different ne­dependence and ●
extent on sky to yield DA=dl/dθ
Similarly can use YX/YSZ
relation → D (z)
SX ,0
 ee
e.g.
symmetric
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T
2
SZ ,0
dl=DAdθ
First results from SZ/X­ray survey
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Want to verify YSZ as a mass estimator
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Compare YSZ against X­ray mass proxies
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Many objects still have <1500 source counts
–
I include all clusters here
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More X­ray observations underway
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Sample complete ~ 2nd half 2010
Cluster modeling
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Data depth allows for 1 kT measurement
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No hydrostatic masses
Model gas density using surface brightness in 0.5­2. keV band
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Low kT dependence −
n e n p =n
2
0
r /r c 
2
2 3 − / 2
1r / r c 
1
 e/ 
1r / r s 

Results from SZ/X­ray sample
Andersson et al in prep
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X­ray mass proxies Mgas­TX Combined M500­TX Same cluster
Preliminary
and M500­Mgas XMM
Objects with insufficient data
relations from Vikhlinin et al (2009)
Chandra
Slope: 2.01+­0.68, expect 1.5
However, good agreement fit if fgas is mass­dependent
Results from SZ/X­ray sample
Andersson et al in prep
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X­ray mass proxies LX,bol­TX
Preliminary
XMM
Chandra
Slope: 2.78+­0.93, expect ~3
Results from SZ/X­ray sample
Andersson et al in prep
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YSZ vs X­ray mass proxies. YX
Caution!
Preliminary
Comparing cylindrical YSZ with spherical YX !
XMM
Renormalize!
2
A
Y SZ D =
Chandra
Slope: 0.84+­0.15, expect 1
T
me c
2

1
m p e
CY X
∫C ne r  dV
C=
n
r

dV
∫
e
S
Isothermal
Results from SZ/X­ray sample
Andersson et al in prep
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YSZ vs X­ray mass proxies. Mgas, TX
Preliminary
Preliminary
XMM
XMM
Chandra
Slope: 1.15+­0.16, expect 1.66
Chandra
Slope: 2.79+­1.10, expect 2.5
Results from SZ/X­ray survey
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YX­derived M500 vs 150 GHz S/N
Many sources still with low X­ray exposure
Expect scatter to improve somewhat once all data are in.
Preliminary
XMM
Candidates scattered in from lower S/N?
Understanding scatter in S/N for fixed M Chandra
will be very important for calibration of S/N selection.
Slope: 0.71+­0.19, expect ~1
Summary
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SPT science looks promising
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Many NEW clusters found, new exciting sample
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X­ray data can enhance reliability of SPT mass function estimates, independent Mtot indicators
DA(z) test only possible with SZ + X­ray
Scaling relations show mostly good agreement with expectations
Look for paper on astro­ph in February­March