Detection and characterisation of dark-matter halos by gravitational shear and flexion; constraints on the non-linear cosmic structure growth

• Applicant: Professor Dr. Matthias Bartelmann
• Subject Area: Astrophysics and Astronomy
• Term: from 2007 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 42389529

• Final Report Year: 2012

Final Report Abstract

Gravitational lensing is among the most powerful tools to study dark structures in the Universe and their growth over cosmological epochs. Over the past years, methods to precisely measure cosmic shear have developed impressively quickly, catalysed by dedicated simulation programmes STEP1, STEP2, and GREAT08, which provided common testbeds for all methods. We had already developed and implemented our own shear pipeline, based on the highly regarded, then novel shapelet method. During the funding period we clarified a conceptual flaw regarding the treatment of convolution with the point-spread function, one of the most critical effects in weak-lensing measurements, leading to a significant improvement of the recovery of the unconvolved galaxy shape. To further assess the shear accuracy of our pipeline, we made use of the publicly available data of simulation programmes mentioned above. To our dismay, we discovered a prominent bias despite our improvements in the deconvolution algorithm. A detailed investigation of this issue revealed a fundamental problem inherent in shapelet method which severely limits its applicability to weak-lensing measurements. By identifying this underlying flaw, we were able to construct a new method, dubbed DEIMOS, which avoids this flaw but maintains the accurate treatment of the deconvolution from the shapelet method. With a reanalysis of data from the GREAT08 programme, we could verify that our new method ranges among the most accurate methods to this date.

Publications

• (2006). The Shear Testing Programme–I. Weak lensing analysis of simulated ground-based observations. Monthly Notices of the Royal Astronomical Society, 368(3), 1323-1339
  Heymans, C., van Waerbeke, L., Bacon, D., Bergé, J. et al.
  
• (2007). Reliable shapelet image analysis. Astronomy & Astrophysics, 463(3), 1215-1225
  Melchior, P., Meneghetti, M. & Bartelmann, M.
  
• (2007). The Shear Testing Programme 2: Factors affecting high-precision weak-lensing analyses. Monthly Notices of the Royal Astronomical Society, 376(1), 13-38
  Massey, R., Heymans, C., Bergé, J., Bernstein, G. et al.
  
• (2008): Flowing with time: a new approach to non-linear cosmological perturbations. In: J. Cosmol. Astropart. Phys. 2008 (10), S. 36
  Pietroni, M.
  
• (2009). Deconvolution with shapelets. Astronomy & Astrophysics, 493(2), 727-734
  Melchior, P., Andrae, R., Maturi, M. & Bartelmann, M.
  
• (2010). Limitations of model-fitting methods for lensing shear estimation. Monthly Notices of the Royal Astronomical Society, 404(1), 458-467
  Voigt, L. M. & Bridle, S.
  
• (2010). Limitations on shapelet-based weak-lensing measurements. Astronomy & Astrophysics, 510, A75
  Melchior, P., Böhnert, A., Lombardi, M. & Bartelmann, M.
  
• 2010, Results of the GREAT08 Challenge*: an image analysis competition for cosmological lensing. MNRAS 405, 2044
  Bridle, S., Balan, S., Bethge, M., Gentile, M. et al.
  
• (2011). Biases in, and corrections to, KSB shear measurements. Monthly Notices of the Royal Astronomical Society, 410(4), 2156-2166
  Viola, M., Melchior, P., Bartelmann, M.
  
• (2011). Weak gravitational lensing with DEIMOS. Monthly Notices of the Royal Astronomical Society, 412(3), 1552-1558
  Melchior, P., Viola, M., Schäfer, B. M. & Bartelmann, M.