The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Richard Massey - One of the best experts on this subject based on the ideXlab platform.
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the Shear Testing programme 2 factors affecting high precision weak lensing analyses
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Richard Massey, Douglas Clowe, Thomas Erben, Catherine Heymans, Joel Berge, G M Bernstein, S L Bridle, H Dahle, Richard S Ellis, M HetterscheidtAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging Shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known Shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate Shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by Testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative Shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of Shear in different directions, leading to an overall underestimation of Shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of Shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.
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The Shear Testing programme - I. Weak lensing analysis of simulated ground-based observations
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: Catherine Heymans, David Bacon, Vera Margoniner, Gary Bernstein, Patrick Hudelot, Emmanuel Bertin, Michael L. Brown, Joel Berge, Richard Massey, Konrad Kuijken, Ludovic Van Waerbeke, Mike Jarvis, Henk Hoekstra, Marco Hetterscheidt, Meghan Gray, Thomas Erben, HÃ¥kon Dahle, Douglas Clowe, Sarah Bridle, Yannick MellierAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper, we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic Shear pipelines that have been used to constrain cosmology, we find weak lensing Shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with Shear measurements accurate to better than 7 per cent. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured Shear is over or underestimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the Shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of Shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent Shear of 0.001, an order of magnitude below cosmic Shear distortions on the scales probed by current surveys. Our results provide a snapshot view of the accuracy of current ground-based weak lensing methods and a benchmark upon which we can improve. To this end we provide descriptions of each method tested and include details of the eight different implementations of the commonly used Kaiser, Squires & Broadhurst method (KSB+) to aid the improvement of future KSB+ analyses.
M Hetterscheidt - One of the best experts on this subject based on the ideXlab platform.
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the Shear Testing programme 2 factors affecting high precision weak lensing analyses
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Richard Massey, Douglas Clowe, Thomas Erben, Catherine Heymans, Joel Berge, G M Bernstein, S L Bridle, H Dahle, Richard S Ellis, M HetterscheidtAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging Shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known Shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate Shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by Testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative Shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of Shear in different directions, leading to an overall underestimation of Shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of Shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.
Catherine Heymans - One of the best experts on this subject based on the ideXlab platform.
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the Shear Testing programme 2 factors affecting high precision weak lensing analyses
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Richard Massey, Douglas Clowe, Thomas Erben, Catherine Heymans, Joel Berge, G M Bernstein, S L Bridle, H Dahle, Richard S Ellis, M HetterscheidtAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging Shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known Shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate Shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by Testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative Shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of Shear in different directions, leading to an overall underestimation of Shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of Shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.
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The Shear Testing programme - I. Weak lensing analysis of simulated ground-based observations
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: Catherine Heymans, David Bacon, Vera Margoniner, Gary Bernstein, Patrick Hudelot, Emmanuel Bertin, Michael L. Brown, Joel Berge, Richard Massey, Konrad Kuijken, Ludovic Van Waerbeke, Mike Jarvis, Henk Hoekstra, Marco Hetterscheidt, Meghan Gray, Thomas Erben, HÃ¥kon Dahle, Douglas Clowe, Sarah Bridle, Yannick MellierAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper, we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic Shear pipelines that have been used to constrain cosmology, we find weak lensing Shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with Shear measurements accurate to better than 7 per cent. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured Shear is over or underestimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the Shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of Shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent Shear of 0.001, an order of magnitude below cosmic Shear distortions on the scales probed by current surveys. Our results provide a snapshot view of the accuracy of current ground-based weak lensing methods and a benchmark upon which we can improve. To this end we provide descriptions of each method tested and include details of the eight different implementations of the commonly used Kaiser, Squires & Broadhurst method (KSB+) to aid the improvement of future KSB+ analyses.
Joel Berge - One of the best experts on this subject based on the ideXlab platform.
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the Shear Testing programme 2 factors affecting high precision weak lensing analyses
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Richard Massey, Douglas Clowe, Thomas Erben, Catherine Heymans, Joel Berge, G M Bernstein, S L Bridle, H Dahle, Richard S Ellis, M HetterscheidtAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging Shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known Shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate Shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by Testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative Shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of Shear in different directions, leading to an overall underestimation of Shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of Shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.
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The Shear Testing programme - I. Weak lensing analysis of simulated ground-based observations
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: Catherine Heymans, David Bacon, Vera Margoniner, Gary Bernstein, Patrick Hudelot, Emmanuel Bertin, Michael L. Brown, Joel Berge, Richard Massey, Konrad Kuijken, Ludovic Van Waerbeke, Mike Jarvis, Henk Hoekstra, Marco Hetterscheidt, Meghan Gray, Thomas Erben, HÃ¥kon Dahle, Douglas Clowe, Sarah Bridle, Yannick MellierAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper, we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic Shear pipelines that have been used to constrain cosmology, we find weak lensing Shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with Shear measurements accurate to better than 7 per cent. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured Shear is over or underestimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the Shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of Shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent Shear of 0.001, an order of magnitude below cosmic Shear distortions on the scales probed by current surveys. Our results provide a snapshot view of the accuracy of current ground-based weak lensing methods and a benchmark upon which we can improve. To this end we provide descriptions of each method tested and include details of the eight different implementations of the commonly used Kaiser, Squires & Broadhurst method (KSB+) to aid the improvement of future KSB+ analyses.
Douglas Clowe - One of the best experts on this subject based on the ideXlab platform.
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the Shear Testing programme 2 factors affecting high precision weak lensing analyses
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Richard Massey, Douglas Clowe, Thomas Erben, Catherine Heymans, Joel Berge, G M Bernstein, S L Bridle, H Dahle, Richard S Ellis, M HetterscheidtAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging Shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known Shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate Shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by Testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative Shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of Shear in different directions, leading to an overall underestimation of Shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of Shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.
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The Shear Testing programme - I. Weak lensing analysis of simulated ground-based observations
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: Catherine Heymans, David Bacon, Vera Margoniner, Gary Bernstein, Patrick Hudelot, Emmanuel Bertin, Michael L. Brown, Joel Berge, Richard Massey, Konrad Kuijken, Ludovic Van Waerbeke, Mike Jarvis, Henk Hoekstra, Marco Hetterscheidt, Meghan Gray, Thomas Erben, HÃ¥kon Dahle, Douglas Clowe, Sarah Bridle, Yannick MellierAbstract:The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper, we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic Shear pipelines that have been used to constrain cosmology, we find weak lensing Shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with Shear measurements accurate to better than 7 per cent. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured Shear is over or underestimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the Shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of Shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent Shear of 0.001, an order of magnitude below cosmic Shear distortions on the scales probed by current surveys. Our results provide a snapshot view of the accuracy of current ground-based weak lensing methods and a benchmark upon which we can improve. To this end we provide descriptions of each method tested and include details of the eight different implementations of the commonly used Kaiser, Squires & Broadhurst method (KSB+) to aid the improvement of future KSB+ analyses.
