Separating the blue cloud and the red sequence using Otsu's method for image segmentation

Separating the blue cloud and the red sequence using Otsu's method for image segmentation by Biswajit Pandey. on Tuesday 29 November The observed colour bimodality allows a classification of the galaxies into two distinct classes: the `blue cloud' and the `red sequence'. Such classification is often carried out using empirical cuts in colour and other galaxy properties that lack solid mathematical justifications. We propose a method for separating the galaxies in the `blue cloud' and the `red sequence' using Otsu's thresholding technique for image segmentation. We show that this technique provides a robust and parameter-free method for the classification of the red and blue galaxies based on the minimization of the inter-class variance and maximization of the intra-class variance. We also apply an iterative triclass thresholding technique based on Otsu's method to improve the classification. The same method can also be applied to classify the galaxies based on their physical properties, such as star formation rate, stellar mass function, bulge-to-disk mass ratio and age, all of which have bimodal distributions. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15642v1