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drphilmarshall edited this page Nov 9, 2012 · 36 revisions

Reconstructing Every Galaxy - Is It Worth It, for Lens Cosmography?

Active investigators: Tom, Phil supported by Stefan

Questions:

  • How much of the total external convergence in a time delay lens system comes from visible galaxies? How does this change as a function of magnitude cut?

  • Where are the most important galaxies? Do the massive galaxies dominate, or is it the the galaxies nearest the optical axis, or some combination of these?

  • How many galaxies account for 50%, and 95% of the convergence on a typical line of sight?

  • Can the Hilbert (ray-traced) convergence be recovered by halo model lightcone reconstruction? With what scatter and bias? Which recipes are the dominant sources of these uncertainties?

Progress:

Outline of the Paper

  • MS lightcone exploration is underway: we have initial curves of growth and kappa PDFs, using the Keeton approximation. We see a few galaxies dominate the convergence from within 1 arcminute from the line of sight, but also significant contributions from galaxies outside this aperture. The smooth mass component and correct distances are already a concern. TC, PJM 2012-04-10 Read more...

  • Light cone reconstructions from halo (not photometric) catalogs: based on the halo information in the catalogs, we have been "reconstructing" the external convergence at the lightcone centre, still within the Keeton approximation. The halo truncation radius is a key parameter. The mass budget is not yet balanced in these reconstructions - we have a strategy for dealing with the smooth component. TC, PJM 2012-04-24

  • We can correct for the smooth component. We've come up with a method to balance the overall mass budget, and inplemented it. The histograms of kappa keeton-hilbert are now centred on 0 (\pm ~0.002), with scatter at the 0.02 level: we've run up against a wall - matter not in the halo catalogue. Read more... . TC 2012-05-22

  • Scatter on the Halo Mass decreases the accuracy of kappa reconstruction. We've investigated the effects of introducing scatter to the halo mass. Stefan's catalogue has an interesting M*-Mhalo relation, so we use Behroozi et al. instead. Read more... . TC 2012-06-05

  • Satellites and abundance matching. We've investigated the kappa contribution coming from satellites - it can be significant, and it's very hard to reconstruct satellite halo masses with abundance matching. Read more.... TC 2012-06-18

  • Kappa pdfs for lightcones. We've tested what happens when halo mass errors are introduced. For most lightcones, there is only a weak dependence on the inferred halo mass, but that's not always the case. Read more... TC 2012-06-28

  • Bias and the need to use the correct kappa formalism. If you are reconstructing overdense lines of sight < kappa keeton > is not equal to < kappa add >. We have to use the right one. We've also looked at the bias in assuming =0 to correct for voids. Read more... TC 2012-07-13

  • Shear, Long tails and B1608 Read more... TC 2012-08-27

  • Paper: figures and conclusions are here TC 2012-10-01

  • Regarding Comments click here TC 2012-11-07

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