CosmoCoffee

With a lot of attention recently being focused on cosmic shear I think this is very interesting paper by the STEP group (the Shear TEst Programme). 16 different shape measurements codes have been run (blindly) on set of image simulations. It looks like many of the methods do well (and have improved since STEP1) and are able to achieve 2% precision, but this is still some way off what will be needed in the future (roughly 0.1% accuracy), I’m very curios to know if STEP3 will be able to push the methods towards this level of accuracy. And are we able to reach 2% on real data today?

The paper is very technical but there is a very nice discussion in section 5.8 that discusses ‘consequences for previously published measurements’, although figure 10 is a little worrying especially regarding the most recent cosmic shear measurements. Can someone comment on this? For a few years now it looks like the value of sigma8 measured through cosmic shear has been a little unstable (and a little inconsistent with WMAP3), so I’m very reassured that different methods being blindly tested/compared and the results published in a clear and transparent way.

It sounds like there will be a dataSTEP out soon that should help a great deal. Does anyone one when this will be done?

Adam Amara

Since nobody else has replied:
STEP3 is very similar to STEP2 except the simulations are for space-based observations (so PSFs which are intrinsically smaller but much more power in the wings). They were done on the same timescale as STEP2, so I doubt you'll see a dramatic improvement, it's more a test of how well the PSF correction can be applied for current HST images and the future JDEM mission (and other space based imaging telescopes).

STEP4 is in the planning stages, and will probably be a larger sequence of simluations trying isolate which particular stages in the correction process are producing the errors.