About

I am a Panofsky Fellow at SLAC/KIPAC. The primary research interest of my group is weak gravitational lensing as a tool to study large structures in the Universe, such as galaxies and clusters of galaxies [1,2,3,4]. The census and evolution of these structures is interesting in its own right, but it can also give us a better understanding of two of the greatest mysteries of modern physics, dark matter and dark energy. To reach that goal, we need to develop new methods in statistics and data analysis for the extraction of reliable and powerful information from optical surveys.

I am co-coordinator of the weak lensing working group of the Dark Energy Survey, the leading weak lensing experiment to date. DES has already released its first competitive cosmological constraints [5,6,7,8]. These were announced in the live-streamed talk shown below, which is also an introduction of how to use lensing for cosmology. In addition, we have published the next generation of methods for weak gravitational lensing measurements in three years of DES data [9,10,11].

I did my PhD [12] and a brief post-doc at University Observatory Munich and the Max Planck Institute for extraterrestrial Physics, before moving to Stanford as a post-doctoral researcher and NASA Einstein Fellow in the X-ray Astronomy and Observational Cosmology group of Prof. Steve Allen. At Stanford, I also collaborate a lot with the Galaxy Formation and Cosmology group of Prof. Risa Wechsler, and with Prof. Aaron Roodman's group at SLAC. In summer 2021, I will be moving to LMU Munich to start the chair of Astrophysics, Cosmology, and Artificial Intelligence.

I have devised a new density split statistic to measure the full probability distribution function of the matter density field [10]. With the Dark Energy Survey, I have used those measurements for unprecedented tests of gravity beyond the power spectrum and improved constraints on cosmology [13,14].

I use machine learning and other data science techniques to develop new statistical methods for accurate weak lensing measurements, especially for estimating and calibrating photometric redshifts [15,16]. The new methods I helped develop to that end [17] have motivated the final major observing program of the Dark Energy Survey, explained in this video.



I have worked on developing new ways of measuring shapes of faint background galaxies. In the course of this work, I also got interested in the correction of instrumental features [18] required for precision analyses. I have also done the actual data reduction and weak lensing analysis of a number of clusters of galaxies, among them the pictures you see on top of this page.

Together, these topics lead the way from pixels to cosmology, and prepare us for the next great observing program: the Rubin Observatory's Legacy Survey of Space and Time (LSST). You can find out more about LSST and the work happening at SLAC in this video

If you are a student and interested in getting involved in the next generation of gravitational lensing research: please contact me about research opportunities at LMU Munich.