Testing the Shear Ratio Test: (More) Cosmology from Lensing in the COSMOS FieldJames TaylorUniversity of Waterloo(Waterloo, Ontario, Canada)

DUEL Edinburgh, Summer Conference July 18-23 2010

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The COSMOS Survey P.I. Nick Scoville

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The COSMOS Survey

2 square degree ACS mosaic

lensing results from

1.64 square degrees

(~600 pointings)

2-3 million galaxies down to

F814WAB = 26.6 (0.6M to 26)

30-band photometry,

photo-zs with dz ~

0.012(1+z)

to z = 1.25 and IF814W = 24

follow-up in X-ray, radio, IR,

UV,

Sub-mm, …

WL Convergence Maps(cf. Rhodes et al. 2007; Massey et al. 2007; Leauthaud et al 2007)

cut catalogue down to 40 galaxies/arcmin2 to remove bad zs

correct for PSF variations, CTE

Get lensing maps, low-resolution 3D maps, various measures of power in 2D and restricted 3D

results compare well with baryonic distributions (e.g. galaxy distribution)

The Final Result:

E-modes (left) versus B-modes (right)

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recent updates:- improved photo-zs- improved CTE correction in images- new shear calibration underway+ updated group catalog(s)

so expect stronger signal around peaks in lensing map, and cleaner dependence on source and lens redshift

time for some 2nd generation tests of the lensing signal

The Final Result:

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3-D constraints on the amplitude of fluctuations:

Massey et al 2007

Measuring Geometry: Shear Ratio Test (Jain & Taylor 2003, Bernstein & Jain 2004, Taylor et al. 2007)

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Bartelmann & Schneider 1999

Relative Lensing Strength Z(z)

Your cluster goes here

Take ratio of shear of objects behind a particular cluster, as a function of redshift

Details of mass distribution & overall calibration cancel clean geometric test

Can extend this to continuous result by fitting to all redshifts Z(z) DLS/DS

But how big is the signal?

Use strength of signal behind cluster as a function of redshift to measure DA(z):

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

Use strength of signal behind cluster as a function of redshift to measure DA(z):

weak but distinctive signal; relative change (change in distance ratio) is only 0.5%

Lens at z = 0.2

0.5% relative change

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

How big is the signal?

Use strength of signal behind cluster as a function of redshift to measure DA(z):

weak but distinctive signal; relative change (change in distance ratio) is only 0.5%

Lens at z = 0.3

0.5% relative change

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

How big is the signal?

Use strength of signal behind cluster as a function of redshift to measure DA(z):

weak but distinctive signal; relative change (change in distance ratio) is only 0.5%

Lens at z = 0.5

0.5% relative change

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

How big is the signal?

Use strength of signal behind cluster as a function of redshift to measure DA(z):

weak but distinctive signal; relative change (change in distance ratio) is only 0.5%

Lens at z = 0.7

0.5% relative change

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

How big is the signal?

Use strength of signal behind cluster as a function of redshift to measure DA(z):

weak but distinctive signal; relative change (change in distance ratio) is only 0.5%

Lens at z = 1.0

0.5% relative change

Base: h = 0.73, m = 0.27( or X = 1 - m)

Variants (different curves):m = 0.25,0.30,0.32

w0 = -1,-0.95,-0.9,-0.85,-0.8

w(z) = w0 + wa(1-a)with w0 = -1, wa = 0.05, 0.1

h = 0.7, 0.75

Signal weak but distinctive

How big is the signal?

Previous detections with massive clusters

Signal has been seen previously behind a few clusters:

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e.g. Wittman et al. 2001~3e14 Mo cluster in DLS; detection, mass and redshift all from weak lensing(source photo-zs from 4 bands)

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Previous detections with massive clusters

Signal has been seen previously behind a few clusters:

e.g. Gavazzi & Soucail (2008): cluster Cl-02 in CFHTLS-Deep

(cf. also Medezinski et al. submitted: 1.25 M galaxies behind 25 massive clusters, in a few bands)

So why try this in COSMOS ?

Less signal (groups only, no truly massive clusters), but

far better photo-zs

can push techniques down to group or galaxy scales

nice test of systematics in catalogue selection, effect of

photo-z errors

test/confirm error forecasts for future surveys

Percival et al .2007: interesting indication of possible

mismatch in distance scales in BAO?

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Log(volume)

The sample of COSMOS Groups and Clusters

(plot from Leauthaud et al. 2009)

(X-ray derived Mass)

Log(volume)

The sample of COSMOS Groups and Clusters

(plot from Leauthaud et al. 2009)

(X-ray derived Mass)

~67 in top 14 objects?

Log(volume)

The sample of COSMOS Groups and Clusters

(plot from Leauthaud et al. 2009)

(X-ray derived Mass)

could get another~60 from less massive groups?

Shear vs. photo-z around peaks, along promising lines of sight

Shear vs. photo-z around peaks, along promising lines of sight

How to stack clusters?

Tangential shear goes as:

so redshift dependence enters via critical surface density:

Thus if we define (assumes flat models)

and

then

independent of cosmology

We see the signal!

Stack of regions within 6’ of~200+ x-ray groups

good fit in front of/behind cluster

significance still unclear; seems less than expected

effect of other structures along the line of sight decreases chi2, but hard to quantify

A Caveat

In a field this small, a few redshifts dominate the distribution of structure systematics in shear ratio

Prospects¶ Signal detected, well behaved, significance slightly lower than expected?

¶ Still studying noise versus radial weighting, catalogue cuts, path weighting

¶ Results roughly consistent with w0 ~ -1.0 +/- 1.0

¶ Future predictions for large surveys + CMB + BAO (Taylor et al. 2007):

w0 = 0.047, wa = 0.111 and 2% measurement of dark energy at z ~ 0.6

Or use CMB as an extra slice?(cf. Hu, Holz & Vale 2007; Das & Spergel 2009)

error forecasts from 20,000 deg2 survey (Taylor et al. 2007)