www.great08challenge.info 1/19 pascal challenge pascal workshop, bled 28 jan 2008 sarah bridle (ucl)...
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www.great08challenge.info www.cosmocoffee.info 1/19
PASCAL Challenge
PASCAL Workshop, Bled 28 Jan 2008Sarah Bridle (UCL) on behalf of the GREAT08 Team
www.great08challenge.info www.cosmocoffee.info 2/19
…tbc
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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
~10 000 imagesdivided into ~10 sets
~100 000 000 images
Divided into ~1000 sets
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GREAT08 Results
You submit g1, g2 for each set of images
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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• ~8 Feb 2008 GREAT08 Handbook public• Feb 2008 Produce simulations• Mar 2008 Internal analysis of simulations• ~ May 2008 Release simulations
– Leaderboard starts containing best internal results
• ~ Nov 2008 Competition deadline• ~ Dec 2008 Workshop; Release final report
– Input shears public
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GREAT08 Summary
• 100 million images• 1 galaxy per image• De-noise, de-convolve, average → shear
• gi ~ 0.03 to accuracy 0.0003 → Q~1000 → Win!
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cosmocoffee.info
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GREAT08
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Understanding Cosmology
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GREAT08 Summary
• 100 million images• 1 galaxy per image• De-noise, de-convolve, average → shear
• gi ~0.03 to accuracy 0.0003 → Q~1000 → Win!
18/18
www.great08challenge.info www.cosmocoffee.info 23/19
Questions for you• Is there too much astronomy to learn?
– Yes– No
• Is timeline (~6 months) right?– Too short – Fine– Too long
• Is this potentially on your research agenda?– No– Maybe– Yes
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