WEAK LENSING ANALYSIS OF ABELL 2390 USING FORCED MEASUREMENT
Creators: name: Dutta, Anirban
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 510103
subject: Cosmology and extragalactic astronomy

description: In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N &lt; 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N &lt; 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N &lt; 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.