A Simulation-driven Deep Learning Approach for Separating Mergers and Star-forming Galaxies: The Formation Histories of Clumpy Galaxies in All of the CANDELS Fields

Ferreira, Leonardo; Conselice, Christopher J.; Kuchner, Ulrike; Tohill, Clár-Bríd

Abstract

Being able to distinguish between galaxies that have recently undergone major-merger events, or are experiencing intense star formation, is crucial for making progress in our understanding of the formation and evolution of galaxies. As such, we have developed a machine-learning framework based on a convolutional neural network to separate star-forming galaxies from post-mergers using a data set of 160,000 simulated images from IllustrisTNG100 that resemble observed deep imaging of galaxies with Hubble. We improve upon previous methods of machine learning with imaging by developing a new approach to deal with the complexities of contamination from neighboring sources in crowded fields and define a quality control limit based on overlapping sources and background flux. Our pipeline successfully separates post-mergers from star-forming galaxies in IllustrisTNG 80% of the time, which is an improvement by at least 25% in comparison to a classification using the asymmetry (A) of the galaxy. Compared with measured Sersic profiles, we show that star-forming galaxies in the CANDELS fields are predominantly disk-dominated systems while post-mergers show distributions of transitioning disks to bulge-dominated galaxies. With these new measurements, we trace the rate of post-mergers among asymmetric galaxies in the universe, finding an increase from 20% at z = 0.5 to 50% at z = 2. Additionally, we do not find strong evidence that the scattering above the star-forming main sequence can be attributed to major post-mergers. Finally, we use our new approach to update our previous measurements of galaxy merger rates 3/4=0.022±0.006×(1+z)2.71±0.31 .

Citation

Ferreira, L., Conselice, C. J., Kuchner, U., & Tohill, C.-B. (2022). A Simulation-driven Deep Learning Approach for Separating Mergers and Star-forming Galaxies: The Formation Histories of Clumpy Galaxies in All of the CANDELS Fields. Astrophysical Journal, 931(1), Article 34. https://doi.org/10.3847/1538-4357/ac66ea

• Journal Article Type: Article
• Acceptance Date: Apr 11, 2022
• Online Publication Date: May 23, 2022
• Publication Date: May 1, 2022
• Deposit Date: Dec 22, 2022
• Publicly Available Date: Dec 22, 2022
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 931
• Issue: 1
• Article Number: 34
• DOI: https://doi.org/10.3847/1538-4357/ac66ea
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/15168227
• Publisher URL: https://iopscience.iop.org/article/10.3847/1538-4357/ac66ea