Thesis Defense

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Events on Tuesday, December 12th, 2023

Synthetic Source Injection in The Dark Energy Survey: Measurements of the Survey Transfer Function and Applications to Precision Cosmology
Time: 2:00 pm - 6:00 pm
Place: B343 Sterling
Speaker: Megan Tabbutt, Physics PhD Graduate Student
Abstract: Presented here is the Dark Energy Survey’s (DES) Synthetic Source Injection (SSI) methodology and applications to precision cosmology for our Y6 analysis of large-scale structure. Our methodology is predicated on injecting models of real objects obtained from our very high signal-to-noise Deep Field observations into our single-epoch wide field images Both of which are critical to the measurements of the three 2-point correlation functions, cosmic shear, galaxy clustering and galaxy-galaxy lensing, from which we constrain cosmological parameters. This methodology was introduced for our Y3 analysis, and was the first example of using SSI to directly calibrate the cosmological measurements from a WF survey. The refinement and expansion of the methodology is presented here. Specifically, we improved our mirroring of the WF image processing pipeline to now fully recreate it. We refactored our code-base to be able to run our SSI at multiple super-computing centers, minimizing wall time and maximizing allocations. We also developed a new injection scheme that injects sources which are preferentially more useful to the cosmological analyses. These as well as other updates, our initial Y6 SSI results, and their applications to precision cosmology will be discussed at length in this thesis. which are then processed identically to the original wide images. Inherent to this methodology, is that the synthetic sources automatically inherit the same systematics of the real wide field data, a highly sought after achievement for many systematics modeling pipelines that is nearly impossible to achieve from forward modeling techniques alone. In the end, we obtain wide field photometry catalogs of the deep field objects including their inheritance of the systematics. These catalogs are a Monte Carlo sampling of the transfer function of the survey and can be used for calibration and diagnostics, as well as aid in the calculation and validation of our 3x2pt analysis and consequentially our measurement of cosmological parameter constraints. Specifically, through the photometric redshift calibration of the weak lensing sources and the magnification bias estimate for the lens galaxy samples.
Host: Keith Bechtol
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