Quantifying Dark Energy using Cosmic Shear Thank introducer. Thank everyone for coming. Sarah Bridle University of Manchester

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey LSST

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey LSST

Concordance Model 75% Dark Energy 5% Baryonic Matter 20% Cold Dark Matter

Why is the Universe Accelerating? Einstein’s cosmological constant A new fluid called Dark Energy Equation of state w = p/ General Relativity is wrong Answers: 50% Lambda; ~3 people DE; ~ no people MG

The Future HSC AFTA JDEM

Comparison of different methods Galaxy clustering Supernovae Gravitational shear Quality of dark energy constraint Example for optical ground-based surveys Dark Energy Task Force report astro-ph/0609591

Seeing the Invisible: Is there something in between us and the wall and tree?

Simulated Dark Matter Map

Shear Map

Results from the HST COSMOS Survey

Credit: NASA, ESA and R. Massey (California Institute of Technology)

The Visible The Invisible Credit: NASA, ESA and R. Massey (California Institute of Technology) Credit: NASA, ESA and R. Massey (California Institute of Technology)

In 3 Dimensions Pictures + videos from http://www.spacetelescope.org/news/html/heic0701.html

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey LSST

Comparison of different methods Galaxy clustering Supernovae Gravitational shear Quality of dark energy constraint Example for optical ground-based surveys Dark Energy Task Force report astro-ph/0609591

Cosmic Shear: Potential systematics Shear measurement Photometric redshifts Intrinsic alignments Accuracy of predictions

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey

Cosmic Shear gi~0.2 Real data: gi~0.03

Atmosphere and Telescope Convolution with kernel Real data: Kernel size ~ Galaxy size

Pixelisation Sum light in each square Real data: Pixel size ~ Kernel size /2

Noise Mostly Poisson. Some Gaussian and bad pixels. Uncertainty on total light ~ 5 per cent

Bridle et al 2010

A typical galaxy image for cosmic shear Intrinsic galaxy shape b/a ~ 0.5 Uncertainty due to noise σb/a ~ 0.5 Modification due to lensing Δb/a ~ 0.05 Effect of changing w by 1% δb/a ~ 0.0005

GREAT08 Results in Detail Bridle et al 2010 See also GREAT10 Kitching et al, and GREAT3 Rowe, Mandelbaum et al

m3shape Shear Measurement Code Tomek Kacprzak Barney Rowe Michael Hirsch Sarah Bridle Lisa Voigt Joe Zuntz Forward model and fit Default: Galaxy is sum of two co-elliptical Sersics; PSF is Moffat Default: Maximum Likelihood. Takes about 1 second per galaxy Zuntz, …, SB et al 2013

What causes the bias? For model fitting methods Noise bias Refregier, SB et al; Kacprzak, SB et al 2012 Maximum likelihood methods are biased Calibration works well enough Model bias Voigt & Bridle 2009 e.g use wrong profile in fit e.g. use elliptical isophote model in fit

Noise Bias Many identical images with different noise Kacprzak, Zuntz, Rowe, Bridle et al 2012

Bias disappears at high S/N Above requirements at low S/N Refregier, Kacprzak, Amara, Bridle, Rowe 2012 Kacprzak, Zuntz, Rowe, Bridle et al 2012

What causes the bias? For model fitting methods Noise bias Refregier, SB et al; Kacprzak, SB et al 2012 Maximum likelihood methods are biased Calibration works well enough Model bias Voigt & Bridle 2009 e.g use wrong profile in fit e.g. use elliptical isophote model in fit

But galaxies aren’t simple…

The effect of realistic galaxy shapes

Impact on dark energy constraints Kacprzak, SB, et al 2013

The GREAT3 Challenge From the GREAT3 Challenge Handbook (Mandelbaum, Rowe, et al 2013)

The GREAT3 Challenge From the GREAT3 Challenge Handbook (Mandelbaum, Rowe, et al 2013)

Typical data – multiple exposures

How to deal with overlaps?

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey LSST

The Future HSC AFTA JDEM

The Dark Energy Survey Blanco 4-meter at CTIO Survey project using 4 complementary techniques: I. Cluster Counts II. Weak Lensing III. Large-scale Structure IV. Supernovae • Two multiband surveys: 5000 deg2 grizY to 24th mag 30 deg2 repeat (SNe) • Build new 3 deg2 FOV camera and Data management system Survey 2013-2018 (525 nights) Facility instrument for Blanco

DES Collaboration The DES is an international project to “nail down” the dark energy equation of state. Funding from DOE, NSF and collaborating institutions and countries Fermilab, UIUC/NCSA, University of Chicago, LBNL, NOAO, University of Michigan, University of Pennsylvania, Argonne National Laboratory, Ohio State University, Santa-Cruz/SLAC Consortium, Texas A&M UK Consortium: UCL, Cambridge, Edinburgh, Portsmouth, Sussex, Nottingham ET Zurich LMU Ludwig-Maximilians Universität Spain Consortium: CIEMAT, IEEC, IFAE Brazil Consortium: Observatorio Nacional, CBPF,Universidade Federal do Rio de Janeiro, Universidade Federal do Rio Grande do Sul 120+ scientists 12+ institutions CTIO

DES First Light 12 Sep 2012

First Confirmed SNe from DES Nov. 7 Dec. 15 SN Ia at z=0.2 confirmed at AAO

DECam image of deep SN field will be visited many times during survey, resulting in very deep co-add

grizY co-add image of SPT DECam 1x1deg grizY co-add image of SPT cluster z=0.32 ~50,000 galaxies in this image

High Redshift Cluster Discovered by DES from DES Science Verification data in November

DES Cluster Weak Lensing Stacked (statistical) Weak Lensing cluster shear profiles will calibrate cluster mass-observable relations Preliminary cluster mass map from DES Science Verification data Melchior et al in prep

Quantifying Dark Energy Using Cosmic Shear Introduction to Cosmic Shear Potential limitations Shear measurement Intrinsic alignments Dark Energy Survey LSST

Sign up to get involved https://docs. google. com/spreadsheet/ccc Current status: 2 page SoI went to Science Board on Friday! Hopefully invited to submit full proposal for ~April

Summary Cosmic shear the greatest potential of all for DE Intrinsic alignments can be marginalised away We plan to calibrate shear measurement biases Dark Energy Survey early data now in Survey started September for 5 years Get involved in the Large Synoptic Survey Telescope (LSST)