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Reproducible $k$-means clustering in galaxy feature data from the GAMA survey

Turner, S, Kelvin, LS, Baldry, IK, Lisboa, PJ, Longmore, SN, Collins, CA, Holwerda, BW, Hopkins, AM and Liske, J (2018) Reproducible $k$-means clustering in galaxy feature data from the GAMA survey. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711

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Abstract

A fundamental bimodality of galaxies in the local Universe is apparent in many of the features used to describe them. Multiple sub-populations exist within this framework, each representing galaxies following distinct evolutionary pathways. Accurately identifying and characterising these sub-populations requires that a large number of galaxy features be analysed simultaneously. Future galaxy surveys such as LSST and Euclid will yield data volumes for which traditional approaches to galaxy classification will become unfeasible. To address this, we apply a robust $k$-means unsupervised clustering method to feature data derived from a sample of 7338 local-Universe galaxies selected from the Galaxy And Mass Assembly (GAMA) survey. This allows us to partition our sample into $k$ clusters without the need for training on pre-labelled data, facilitating a full census of our high dimensionality feature space and guarding against stochastic effects. We find that the local galaxy population natively splits into $2$, $3$, $5$ and a maximum of $6$ sub-populations, with each corresponding to a distinct ongoing evolutionary mechanism. Notably, the impact of the local environment appears strongly linked with the evolution of low-mass ($M_{*} < 10^{10}$ M$_{\odot}$) galaxies, with more massive systems appearing to evolve more passively from the blue cloud onto the red sequence. With a typical run time of $\sim3$ minutes per value of $k$ for our galaxy sample, we show how $k$-means unsupervised clustering is an ideal tool for future analysis of large extragalactic datasets, being scalable, adaptable, and providing crucial insight into the fundamental properties of the local galaxy population.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Sebastian Turner, Lee S Kelvin, Ivan K Baldry, Paulo J Lisboa, Steven N Longmore, Chris A Collins, Benne W Holwerda, Andrew M Hopkins, Jochen Liske; Reproducible k-means clustering in galaxy feature data from the GAMA survey, Monthly Notices of the Royal Astronomical Society is available online at: http://dx.doi.org/10.1093/mnras/sty2690
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 10 Oct 2018 10:52
Last Modified: 10 Oct 2018 12:21
DOI or Identification number: 10.1093/mnras/sty2690
URI: http://researchonline.ljmu.ac.uk/id/eprint/9460

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