Optimizing automatic morphological classification of galaxies with machine learning and deep learning using Dark Energy Survey imaging

Ting-Yun Cheng*, Christopher J. Conselice, Alfonso Aragón-Salamanca, Nan Li, Asa F. L. Bluck, Will G. Hartley, James Annis, David Brooks, Peter Doel, Juan García-Bellido, David J. James, Kyler Kuehn, Nikolay Kuropatkin, Mathew Smith, Flavia Sobreira, Gregory Tarle

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)


There are several supervised machine learning methods used for the application of automated morphological classification of galaxies; however, there has not yet been a clear comparison of these different methods using imaging data, or an investigation for maximizing their effectiveness.We carry out a comparison between several common machine learning methods for galaxy classification [Convolutional Neural Network (CNN), K-nearest neighbour, logistic regression, Support Vector Machine, Random Forest, and Neural Networks] by using Dark Energy Survey (DES) data combined with visual classifications from the Galaxy Zoo 1 project (GZ1). Our goal is to determine the optimal machine learning methods when using imaging data for galaxy classification. We show that CNN is the most successful method of these ten methods in our study. Using a sample of ~2800 galaxies with visual classification from GZ1, we reach an accuracy of ~0.99 for the morphological classification of ellipticals and spirals. The further investigation of the galaxies that have a different ML and visual classification but with high predicted probabilities in our CNN usually reveals the incorrect classification provided by GZ1. We further find the galaxies having a low probability of being either spirals or ellipticals are visually lenticulars (S0), demonstrating that supervised learning is able to rediscover that this class of galaxy is distinct from both ellipticals and spirals.We confirm that ~2.5 per cent galaxies are misclassified by GZ1 in our study. After correcting these galaxies' labels, we improve our CNN performance to an average accuracy of over 0.99 (accuracy of 0.994 is our best result).

Original languageEnglish
Pages (from-to)4209-4228
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 1 Apr 2020


  • Galaxies: structure
  • Methods: data analysis
  • Methods: statistical


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