Detection and characterisation of dark-matter halos by gravitational shear and flexion; constraints on the non-linear cosmic structure growth
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.
(See online at https://doi.org/10.1111/j.1365-2966.2006.10198.x) - (2007). Reliable shapelet image analysis. Astronomy & Astrophysics, 463(3), 1215-1225
Melchior, P., Meneghetti, M. & Bartelmann, M.
(See online at https://doi.org/10.1051/0004-6361:20066259) - (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.
(See online at https://doi.org/10.1111/j.1365-2966.2006.11315.x) - (2008): Flowing with time: a new approach to non-linear cosmological perturbations. In: J. Cosmol. Astropart. Phys. 2008 (10), S. 36
Pietroni, M.
(See online at https://doi.org/10.1088/1475-7516/2008/10/036) - (2009). Deconvolution with shapelets. Astronomy & Astrophysics, 493(2), 727-734
Melchior, P., Andrae, R., Maturi, M. & Bartelmann, M.
(See online at https://doi.org/10.1051/0004-6361:200810472) - (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.
(See online at https://doi.org/10.1111/j.1365-2966.2010.16300.x) - (2010). Limitations on shapelet-based weak-lensing measurements. Astronomy & Astrophysics, 510, A75
Melchior, P., Böhnert, A., Lombardi, M. & Bartelmann, M.
(See online at https://doi.org/10.1051/0004-6361/200912785) - 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.
(See online at https://doi.org/10.1111/j.1365-2966.2010.16598.x) - (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.
(See online at https://doi.org/10.1111/j.1365-2966.2010.17589.x) - (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.
(See online at https://doi.org/10.1111/j.1365-2966.2010.17875.x)
