People's Interests

Sherry Suyu: I am interested in using lenses to obtain the Hubble constant. My current work on B1608 uses the entire extended source intensity distribution to reconstruct the lens potential and the source intensity on grids of pixels. This method is still limited by the mass-sheet degeneracy, and I am interested in finding a way to break (perhaps only partially) the degeneracy by including additional information such as the lens environment.

Another topic of interest is to use sources at different redshifts in clusters to measure distance ratios as functions of redshift for determining cosmological parameters. Current models of clusters predict arc locations whose rms offset is ~1”. How would we improve our models so as to be able to predict the arc locations accurately?

Masamune Oguri:
1. The standard lensing statistics to probe Lambda. We are now trying to construct a new statistical sample from the SDSS (here). In statistical analysis how should we treat evolution of red galaxies? The environmental convergence could have a large impact particularly at the tail of the image separation distribution (here): How should we get around the effect?

2. Statistics of cluster-scale strong lenses (large-separation lensed quasars, giant arcs) to study sigma_8 (e.g., here). It is important to address how baryons (gas, central galaxy) affect the lensing probabilities. In particular it is intriguing to check whether the low sigma_8 of WMAP3 is really compatible with these statistics.

3. Using stacked sample of strong lenses to constrain cosmological parameters. An example for the Hubble constant is here. Again it will be important to construct a good statistical sample to reduce any systematics. Can we really probe w from ensemble of image separations and/or time delays?

4. Strong lensing of supernovae. The magnification factor can in principle break the mass-sheet degeneracy (here). Is it really feasible? - Magnifications are quite sensitive to small-scale structure.

Eran Ofek:

(1) SDSS1004 is a z=1.73 quasar, which is lensed by a cluster of galaxies at redshift 0.68. In addition to the lensed quasar, the system contains several multiply-imaged lensed galaxies. The position of the lensed images, and the time-delays between the quasar images, will enable us to model the gravitational potential of the lens, and to constrain cosmological models by measuring the dependence of the deflection angle on the source redshift. The high redshift of the cluster, along with the wealth of observational constraints, make this system one of the best strong lenses for measuring the cosmological constant energy density. I am currently leading an intensive observational campaign of this system, which may substantially
improve our ability to use SDSS1004 for cosmographical application.

(2) Galaxy mass evolution - I am interested in measuring the galaxy mass evolution using lensing statistics. For that end, I am measuring the redshifts of a sample of quasar-lensing galaxies, in order to build a large sample of lensed quasars for which both the lens and source redshifts are known. I would like to use this sample to determine the mass evolution of galaxies between redshift zero and one.

Neal Jackson

I am interested in surveys to discover more lenses suitable for measuring the Hubble constant. In particular I have been involved in the CLASS survey, and am exploring ways to conduct future radio surveys in reasonable amounts of telescope time (e.g. astro-ph/0609818) both with existing instruments and with others currently being designed and built (EVLA, e-Merlin, Lofar and eventually SKA) to provide samples of lenses complementary to future large optical surveys. I am also interested in detailed observations of lens systems to try to allow improved mass models to be made.