Www.great08challenge.info 1/19 PASCAL Challenge PASCAL Workshop, Bled 28 Jan 2008 Sarah Bridle (UCL)...

www.great08challenge.info www.cosmocoffee.info 1/19

PASCAL Challenge

PASCAL Workshop, Bled 28 Jan 2008Sarah Bridle (UCL) on behalf of the GREAT08 Team


…tbc


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

~10 000 imagesdivided into ~10 sets

~100 000 000 images

Divided into ~1000 sets


GREAT08 Results

You submit g1, g2 for each set of images


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• ~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

www.great08challenge.info


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!


cosmocoffee.info


GREAT08


Understanding Cosmology


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


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

Www.great08challenge.info 1/19 PASCAL Challenge PASCAL Workshop, Bled 28 Jan 2008 Sarah Bridle (UCL)...

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