Abstract:

Dark energy, a force that counteracts gravity and accelerates the expansion of the universe on the grandest of scales, continues to confound the astrophysicists. In order to constrain its behavior in the universe, cosmologists are undertaking large surveys to understand its effects. The Dark Energy Survey (DES) is surveying an eighth of the sky for galaxies with redshift 0.2 to 1.5 to observe weak lensing effects and analyze cosmic shear. DES measures galaxy photometry in the four distinct g r i z bands, and hope to constrain their redshift from these photometric measurements. The error associated with these photo-z's contribute significantly to the DES cosmological parameters' error from weak lensing. Invoking Self Organized Maps (SOM), we establish a novel method of estimating the N(z) associated with the tomographic bins created to organize the SOM cells which capture galaxies with discreet color properties, based on the photometric measurements. By using a better constrained photometric survey for a smaller subset of the sky, we can leverage the few known redshifts to inform our color measurements across the SOM, and estimate N(z) for the full survey sample. This method has proven to constrain the mean difference between estimated and true N(z) for a simulated survey within 4%.