  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.
