Cosmology with photometric redshifts

Thesis

Upcoming large scale photometric surveys will require accurate photometric redshifts (photo-zs) to optimally extract astrophysical information. This thesis investigates methods of making and improving cosmological measurements using photo-zs.

Gaussian Processes for Photometric Redshift Estimation (GPz) has been proven to provide accurate estimates and reliable uncertainty estimates. In Chapter 2 I evaluate the effects of adding near-IR magnitudes and angular size as features for training and find improvements in accuracy of ~15-20 per cent. A method of shifting the photo-zs based on Quantile-Quantile plots is also investigated and improves the bias by ~ 40 per cent. In Chapter 3 I use GPz based photo-zs to measure the baryon acoustic oscillations with SDSS galaxies. Two galaxy samples are used: one with all galaxy types and another with luminous galaxies. Using multi-wavelength photometry and morphological data, the errors on the photo-z estimates for the luminous galaxies showed an improvement on previous studies. Angular correlation functions are measured and BAO peaks are detected for the luminous galaxies at positions consistent with expected results. The whole galaxy sample, with a magnitude cut of i<21 results in BAO peaks for the bins 0.5

Authors: Gomes, Z

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English