English

Morpho-Photometric Redshifts

Instrumentation and Methods for Astrophysics 2019-09-25 v2 Cosmology and Nongalactic Astrophysics

Abstract

Machine learning (ML) is a standard approach for estimating the redshifts of galaxies when only photometric information is available. ML photo-z solutions have traditionally ignored the morphological information available in galaxy images or partly included it in the form of hand-crafted features, with mixed results. We train a morphology-aware photometric redshift machine using modern deep learning tools. It uses a custom architecture that jointly trains on galaxy fluxes, colors and images. Galaxy-integrated quantities are fed to a Multi-Layer Perceptron (MLP) branch while images are fed to a convolutional (convnet) branch that can learn relevant morphological features. This split MLP-convnet architecture, which aims to disentangle strong photometric features from comparatively weak morphological ones, proves important for strong performance: a regular convnet-only architecture, while exposed to all available photometric information in images, delivers comparatively poor performance. We present a cross-validated MLP-convnet model trained on 130,000 SDSS-DR12 galaxies that outperforms a hyperoptimized Gradient Boosting solution (hyperopt+XGBoost), as well as the equivalent MLP-only architecture, on the redshift bias metric. The 4-fold cross-validated MLP-convnet model achieves a bias δz/(1+z)=0.70±1×103\delta z / (1+z) =-0.70 \pm 1 \times 10^{-3} , approaching the performance of a reference ANNZ2 ensemble of 100 distinct models trained on a comparable dataset. The relative performance of the morphology-aware and morphology-blind models indicates that galaxy morphology does improve ML-based photometric redshift estimation.

Keywords

Cite

@article{arxiv.1811.06374,
  title  = {Morpho-Photometric Redshifts},
  author = {Kristen Menou},
  journal= {arXiv preprint arXiv:1811.06374},
  year   = {2019}
}

Comments

MNRAS accepted

R2 v1 2026-06-23T05:17:01.322Z