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PASCAL Challenge
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• The Problem
•The Challenge
•The Simulations
•The Story So Far
•The Future ...
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Contents of our Universe
70% Dark Energy
25% Dark Matter
5% Baryonic Matter
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Gravitational Lensing
Light from a distant galaxy is bent around a mass
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Gravitational Lensing
Galaxies seen through dark matter distribution analogous to
Streetlamps seen through your bathroom window
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Cosmic Lensing
Real data:gi~0.03
gi~0.2
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Atmosphere and Telescope
Convolution with kernel
Real data: Kernel size ~ Galaxy size
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Pixelisation
Sum light in each square
Real data: Pixel size ~ Kernel size /2
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Noise
Mostly Poisson. Some Gaussian and bad pixels.Uncertainty on total light ~ 5 per cent
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Typical starUsed for finding Convolution kernel
Typical galaxyused for cosmicshear analysis
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GREAT08 Data
One galaxy per imageKernel is givenOne shear per setNoise is Poisson
150 000 galaxies
27 000 000 galaxies
3 000 000 galaxies
150 000 galaxies
All divided into sets containing 10 000 galaxies each
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GREAT08 Data
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GREAT08 Results
You submit g1, g2 for each set of images
Goal:
Q = 1000
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GREAT08 ResultsLow Noise
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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
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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
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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!