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PASCAL Challenge



• The Problem

•The Challenge

•The Simulations

•The Story So Far

•The Future ...


Contents of our Universe

70% Dark Energy

25% Dark Matter

5% Baryonic Matter


Gravitational Lensing

Light from a distant galaxy is bent around a mass


Gravitational Lensing

Galaxies seen through dark matter distribution analogous to

Streetlamps seen through your bathroom window



Cosmic Lensing

Real data:gi~0.03

gi~0.2


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



Typical starUsed for finding Convolution kernel

Typical galaxyused for cosmicshear analysis



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


GREAT08 Data


GREAT08 Results

You submit g1, g2 for each set of images

Goal:

Q = 1000

www.great08challenge.info www.cosmocoffee.info

GREAT08 ResultsLow Noise

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


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


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 1/21 PASCAL Challenge.

Documents

great08 data slide

mass slide

grid slide

cent slide

galaxy size slide

baryonic matter slide

pascal challenge slide

galaxy kernel