Title: A robust cosmic shear measurement method

Speaker: Jun Zhang (Jiaotong University)

Time & Place: Thursday, 3:00pm, November 14th, 3rd floor Lecture Hall

Abstract:

  For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. We present a shear estimator defined with the Fourier transform of the galaxy image. It is accurate in the presence of background noise and finite pixel size, without assumptions on the morphologies of the galaxy and the PSF. In our recent work, we find a simple and rigorous way of removing the shear bias from the source Poisson noise, which is important for faint galaxies. Our noise treatment can be generalized for images made of multiple exposures through the multidrizzle algorithm. This is demonstrated with the COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming largescale galaxy survey.

Biog: Jun obtained his PhD from Columbia University in 2006, before taking postdoc fellowships at UC Berkley & UT Austin. He returned to China in 2012 to take up a faculty position at Jiaotong University