Explaining deep learning of galaxy morphology with saliency mapping. Issue 4 (16th February 2022)

• Record Type: Journal Article
• Authors: Bhambra, Prabh; Joachimi, Benjamin; Lahav, Ofer
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 511:Issue 4(2022)
• Page Start: 5032
• Page End: 5041
• Publication Date: 2022-02-16
• Subjects: methods: data analysis -- techniques: image processing -- galaxies: bar -- galaxies: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac368
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We successfully demonstrate the use of explainable artificial intelligence (XAI) techniques on astronomical data sets in the context of measuring galactic bar lengths. The method consists of training convolutional neural networks on human classified data from Galaxy Zoo in order to predict general galaxy morphologies, and then using SmoothGrad (a saliency mapping technique) to extract the bar for measurement by a bespoke algorithm. We contrast this to another method of using a convolutional neural network to directly predict galaxy bar lengths. These methods achieved correlation coefficients of 0.76 and 0.59, and root mean squared errors of 1.69 and 2.10 respective to human measurements. We conclude that XAI methods outperform conventional deep learning in this case, which could be reasonably explained by the larger data sets available when training the models. We suggest that our XAI method can be used to extract other galactic features (such as the bulge-to-disc ratio) without needing to collect new data sets or train new models. We also suggest that these techniques can be used to refine deep learning models as well as identify and eliminate bias within training data sets.