Correlation between Global Parameters of Galaxies

TL;DR

This study confirms a strong correlation among key galactic parameters, suggesting galaxy structure is governed by a single dominant factor, but does not refute hierarchical formation models.

Contribution

It expands on previous work by analyzing a larger galaxy dataset with additional parameters and confirms the dominance of a single principal component in galactic properties.

Findings

The five basic galactic parameters are strongly correlated.

A single principal component explains 86% of the variation.

Color parameters are nearly independent of structural parameters.

Abstract

Recently Disney et al. (2008) found a striking correlation among the five basic parameters that govern the galactic dynamics: R50, R90, Lr, Md, and MHI . They suggested that this is in conflict with the LCDM model, which predicts the hierarchical formation of cosmic structures from bottom up. In light of the importance of the issue, we performed a similar analysis on global parameters of galaxies with a significantly larger database and two additional parameters, LJ and RJ, of the near-infrared J band. We used databases from the Arecibo Legacy Fast Arecibo L-band Feed Array Survey for the atomic gas properties, the Sloan Digital Sky Survey for the optical properties, and the Two Micron All Sky Survey for the near-infrared properties, of the galaxies. We conducted principal component analysis (PCA) to find relations among these observational variables and confirmed that the five parameters in the work of Disney et al. are indeed correlated. The first principal component dominates the correlations among the five parameters and can explain 86% of the variation in the data. When color (g - i) is included, the first component still dominates and the color forms a second principal component that is almost independent of other parameters. The overall trend in our near-infrared PCA is very similar, except that color (i - J) seems even more decoupled from all other parameters. The dominance of the first principal component suggests that the structure of galaxies is governed by a single physical parameter. This confirms the observational results in Disney et al. However, based on the importance of the baryon physics in galaxy formation, we are not convinced that the hierarchical structure formation scenario and the notion of cold dark matter are necessarily flawed.