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PASCAL Challenge www.great08challenge.info www.cosmocoffee.info 1/21 www.great08challenge.info www.cosmocoffee.info 2/21 • The Problem •The Challenge •The Simulations •The Story So Far •The Future ... www.great08challenge.info www.cosmocoffee.info 3/21 Contents of our Universe 70% Dark Energy 5% Baryonic Matter 25% Dark Matter www.great08challenge.info www.cosmocoffee.info 4/19 Gravitational Lensing Light from a distant galaxy is bent around a mass www.great08challenge.info www.cosmocoffee.info 5/19 Gravitational Lensing Galaxies seen through dark matter distribution analogous to Streetlamps seen through your bathroom window www.great08challenge.info www.cosmocoffee.info 6/21 www.great08challenge.info www.cosmocoffee.info 7/19 Cosmic Lensing gi~0.2 Real data: gi~0.03 www.great08challenge.info www.cosmocoffee.info 8/21 Atmosphere and Telescope Convolution with kernel Real data: Kernel size ~ Galaxy size www.great08challenge.info www.cosmocoffee.info 9/21 Pixelisation Sum light in each square Real data: Pixel size ~ Kernel size /2 www.great08challenge.info www.cosmocoffee.info 10/21 Noise Mostly Poisson. Some Gaussian and bad pixels. Uncertainty on total light ~ 5 per cent www.great08challenge.info www.cosmocoffee.info 11/21 www.great08challenge.info www.cosmocoffee.info 12/19 Typical galaxy used for cosmic shear analysis Typical star Used for finding Convolution kernel www.great08challenge.info www.cosmocoffee.info 13/19 www.great08challenge.info www.cosmocoffee.info 14/19 GREAT08 Data 150 000 galaxies 3 000 000 galaxies One galaxy per image Kernel is given One shear per set Noise is Poisson 150 000 galaxies 27 000 000 galaxies All divided into sets containing 10 000 galaxies each www.great08challenge.info www.cosmocoffee.info 15/21 GREAT08 Data www.great08challenge.info www.cosmocoffee.info 16/21 GREAT08 Results You submit g1, g2 for each set of images Goal: Q = 1000 www.great08challenge.info www.cosmocoffee.info 17/21 GREAT08 Results Low Noise www.great08challenge.info www.cosmocoffee.info 18/21 GREAT09 and Beyond • • • • • • • • • • • Kernel is not given (just kernel images) Galaxies with more complicated shapes Kernel is more realistic Many objects in each image Correlated noise Poisson + Gaussian noise + bad pixels Shear is different for each galaxy Kernel is not the same for every galaxy Cosmic rays, satellite tracks, saturated stars Multiple exposures Pixels not exactly square or on a grid www.great08challenge.info www.cosmocoffee.info 19/21 GREAT08 Timeline • • • • Feb 2008 GREAT08 Handbook public Jun 2008 Internal release of simulations Aug 2008 First simulations public 27 Oct 2008 Launch of public challenge – Leaderboard starts containing internal results • 5 Jan 2009 – mid-term workshop at UCL • 30 Apr 2009 Competition deadline • ~June 2008 Workshop; Release final report – Input shears public www.great08challenge.info www.great08challenge.info www.cosmocoffee.info 20/21 GREAT08 Summary • • • • 30 million images 1 galaxy per image De-noise, de-convolve, average → shear gi ~ 0.03 to accuracy 0.0003 → Q~1000 → Win! www.great08challenge.info www.cosmocoffee.info 21/21