Impact of cosmic web on galaxy properties and their correlations: Insights from Principal Component Analysis

Anindita Nandi, Biswajit Pandey

Published 2024-08-29Version 1

We use Principal Component Analysis (PCA) to analyze a volume-limited sample from the SDSS and explore how cosmic web environments affect the interrelations between various galaxy properties, such as $(u-r)$ colour, stellar mass, specific star formation rate, metallicity, concentration index, and $D4000$. Our analysis reveals that the first two principal components (PC1 and PC2) account for approximately $\sim 72\%$ of the data variance. We then classify galaxies into different cosmic web environments based on the eigenvalues of the deformation tensor and compare PC1 and PC2 across these environments, ensuring a mass-matched sample of equal size for each environment. We observe that PC1 displays clear bimodality across all cosmic web environments, with sheets and clusters showing distinct preferences for negative and positive PC1 values, respectively. PC2, on the other hand, shows a positively skewed unimodal distribution in all environments. A Kolmogorov-Smirnov (KS) test confirms that the distributions of PC1 and PC2 differ significantly across environments, with a confidence level exceeding $99.99\%$. Furthermore, we calculate the normalized mutual information (NMI) between the principal components and individual galaxy properties within different cosmic web environments. A two-tailed t-test reveals that for each relationship and each pair of environments, the null hypothesis is rejected with a confidence level $>99.99\%$. Our analysis confirms that cosmic web environments play a significant role in shaping the correlations between galaxy properties.