Institute for Advanced Study Informal Astrophysics Seminar

The weak gravitational lensing of source galaxies divided into several redshift slices (tomography) is known to be a powerful cosmological probe that can be used to study the three dimensional distribution of dark matter, the nature of dark energy, potential modifications to General Relativity, and the formation of large scale structure. Key to the programme is the ability to accurately determine the mean redshift and distribution for the source galaxies in each redshift slice. For photometric galaxy surveys this can be accomplished by calibrating the photometry with a spectroscopic follow-up survey. However, for very large and deep surveys such as LSST, SNAP and others, obtaining spectra for a fair sub-sample of the data could be cumbersome and expensive. Fortunately, a promising alternative has been proposed; the redshift distribution of photometric galaxies can be determined from cross-correlating them with any overlapping spectroscopic survey whose members trace the same density field. In my talk I will discuss the applications of weak gravitational lensing tomography. I will outline the impact of properly calibrating photometric surveys and review the proposed cross-correlation method. I will explain briefly how the method works, highlighting its strengths and discussing potential drawbacks. I will present the results of using the halo model with N-Body CDM simulations to create mock galaxy catalogs that quantify the properties of this redshift distribution estimator.