Photometric Redshifts for Cosmology: Improving Accuracy and Uncertainty Estimates Using Bayesian Neural Networks

TL;DR

This paper explores the use of Bayesian neural networks to improve the estimation of galaxy redshifts and their uncertainties from photometric data, which is crucial for cosmological studies involving large sky surveys.

Contribution

It introduces a new galaxy dataset and demonstrates how Bayesian neural networks can provide both accurate redshift predictions and meaningful uncertainty estimates.

Findings

BNNs offer valuable uncertainty estimates for redshift predictions.

Non-Bayesian neural networks outperform BNNs in point estimate accuracy.

Uncertainty quantification enhances cosmological parameter inference.

Abstract

We present results exploring the role that probabilistic deep learning models can play in cosmology from large scale astronomical surveys through estimating the distances to galaxies (redshifts) from photometry. Due to the massive scale of data coming from these new and upcoming sky surveys, machine learning techniques using galaxy photometry are increasingly adopted to predict galactic redshifts which are important for inferring cosmological parameters such as the nature of dark energy. Associated uncertainty estimates are also critical measurements, however, common machine learning methods typically provide only point estimates and lack uncertainty information as outputs. We turn to Bayesian neural networks (BNNs) as a promising way to provide accurate predictions of redshift values. We have compiled a new galaxy training dataset from the Hyper Suprime-Cam Survey, designed to mimic large surveys, but over a smaller portion of the sky. We evaluate the performance and accuracy of photometric redshift (photo-z) predictions from photometry using machine learning, astronomical and probabilistic metrics. We find that while the Bayesian neural network did not perform as well as non-Bayesian neural networks if evaluated solely by point estimate photo-z values, BNNs can provide uncertainty estimates that are necessary for cosmology