Cosmography working group

There are new workshop participants in the group. Could everyone please update the wiki-page on his/her research interests related to cosmography: Cosmography Group's Interests

Masamune Oguri's H0 paper is now here

New compilation of gravitational lens systems here.

Next meeting:

Meeting History:
1. Sept 22 (Friday) -- Phil Marshall leads discussion of Leiden meeting Hubble Constant working group report
2. Sept 25 (Monday) -- Rehash and extension of Hubble Constant discussion. Golden lenses? What would be most useful for getting a robust H_0 from lensing?
3. Oct. 2 (Monday) -- Discuss time delay measurements (mainly) and w (briefly). According to Neal Jackson, limited facility (VLA and MERLIN) that are over-subscribed and TAC's exponentially decreasing enthusiasm have stopped people from measuring time delays in radio. Discuss potential time delays from SLACS sample: Lexi Moustakas suspected 5-10% of the strong lenses have compact cores that may have intrinsic variability. Priya Natarajan has looked at measuring w from using sources at different redshifts in clusters.
4. Oct. 10 (Tuesday) -- Discuss sigma_8 from cluster arc statistics and cosmic shear. Discuss Omega_lambda from lenses and mention paper by Chuck Keeton (Rethinking Lensing and Lambda). Mention paper by Neal Dalal et al (Noise in Strong Lensing Cosmography).
5. Oct.19 (Thursday) -- Discuss lens environments (groups) and their effect on Ho, in particular the paper by Keeton and Zabludoff (Here). The SLACS lenses which are at z~0.1 did not require external shear - perhaps due to selection effects? Are there any large isolated galaxies not in groups? To address how many lenses are affected by groups, here is the list of tasks:
Action Item - Lens Environments
a) search through sloan photometric catalogues for isolated ellipticals (Eran)
b) search through SLACS to look at environment of these lenses (Phil)
c) find out which of the time delay lenses are affected by environments (Sherry)
6. Oct. 24 (Tuesday) -- continue discussion on lens galaxy environments. No strong correlation with redshifts, but low redshift systems appear to have smaller fraction of group/clutser association. The correlation of angles of external shear and convergence gradient as a possible indicator of the environment. About selection funtion of SLACS lenses - it should have very strong magnification bias (that's why we see many rings) - it is against strong environment or not? A short discussion on supernova lensing, LSST, ...

Tasks - Hubble Constant (feel free to add yourself to this list):
1. Compile list of current Hubble Constant measurements -- start with Leiden group table and expand if necessary (Ardis)
Overview over time delay meaurements
2. Compile list of groups working to measure time delays (Chris)
3. Find paper by Maoz relating to lensing statistics and the cosmological constant (Leon)
What went wrong?

4. Check out what current measurements say about radial profiles of elliptical galaxies. Is the assumption of a constant M/L ratio (i.e., the profile of the mass follows the profile of the stars) the steepest "reasonable" profile to use in the modeling? (Ann??)


Specific questions/issues [Tommaso]:
  1. Precision cosmography? Truth or delusion.
>
## What is uncertainty on the Hubble constant, really?
    1. Is there dark energy or is it a cosmological constant?
  1. Can lensing deliver precision measurements of cosmological parameters?
>

New issues from the coffee discussion on Friday (22 Sept):
1. Can lensing say something about sigma_8?
2. What can we learn from multiple arcs at multiple redshifts in clusters?
3. Are lensing statistics useless for cosmography?
4. Can we learn anything from lensing by clusters?
[more?? These are my vague memories of the discussion - Chris F.]


Reference -- It's worth noting the wikipage of the recent Lorentz Center workshop subgroup on H0, here

Draft Proceeding Lensing-Cosmography