Orc02

Daily tips:
I have received the draft of the paper. Should start to deal with the problems.
To complete the selection of Lyman break galaxies in z~ 1-3 as in xinwen's email.


Today, Genevieve Graves (Princeton University) gave us a talk about two works.  The first one is quite interesting. "They have recently developed a new method for weak lensing using background source magnification instead of using gravitational shear. " In the traditional method, people measured the shear signal by comparing the lensed morphology of a group galaxies with the random sample.
However, "Traditional magnification methods have struggled to match the signal-to-noise (S/N) per background source achieved by shear because the intrinsic dispersion of galaxy luminosities and radii are much larger than the intrinsic dispersion of ellipticities." 

We have solved this problem using knowledge about the galaxy population to predict the intrinsic radii to within ∼ 40%. Our new magnification method thus yields a signal that is nearly comparable to shear. Moreover, the dominant sources of systematic error are different from those in shear-based measurements. This means that combining shear and magnification can alleviate the worst biases in each method and produce a substantially more robust, higher S/N measurement of the dark matter distribution for a given survey than can be achieved with shear alone. As a proof-of-concept, we have used this technique to make a galaxy-galaxy lensing measurement using SDSS imaging and spectroscopic data. This talk will describe the new method, and present our first lensing measurements.