A multivariate statistical analysis of spiral galaxy luminosities. I. Data and results

We have performed a multiparametric analysis of luminosity data for a sample of 234 normal spiral and irregular galaxies observed in X-rays with the Einstein Observatory. This sample is representative of S and Irr galaxies, with a good coverage of morphological types and absolute magnitudes. In addition to X-ray and optical data, we have compiled H-band magnitudes, IRAS near- and far-infrared, and 6 cm radio continuum observations for the sample from the literature. We have also performed a careful compilation of distance estimates. We have explored the effect of morphology by dividing the sample into early- (S0/a-Sab), intermediate- (Sb-Sbc), and late-type (Sc-Irr) subsamples. The data were analyzed with bivariate and multivariate survival analysis techniques that make full use of all the information available in both detections and limits. We find that most pairs of luminosities are correlated when considered individually, and this is not due to a distance bias. Different luminosity-luminosity correlations follow different power-law relations. Contrary to previous reports, the L-X-L-B correlation follows a power law with exponent larger than 1. Both the significances of some correlations and their power-law relations are morphology dependent. Our analysis confirms the representative nature of our sample, by returning well-known results derived from previous analyses of independent samples of galaxies (e.g., the L-B-L-H, L-12-L-FIR, and L-FIR-L-6 cm correlations). Our multivariate analysis suggests that there are two fundamentally strong correlations, regardless of galaxy morphology, when all the wave bands are analyzed together with conditional probability methods. These are the L-B-L-H and the L-12-L-FIR correlations. As it is well known, the former links stellar emission processes and points to a basic connection between the initial mass function of low-mass and intermediate- to high-mass stars. The latter may be related to the heating of small and larger size dust grains by the same UV photon field. Other highly significant fundamental correlations exist but are morphology dependent. In particular, in the late sample (Sc-Irr) we see an overall connection of mid-IR, far-IR, and radio continuum emission, which could be related to the presence of star-forming activity in these galaxies, while in early-type spirals (S0/a-Sab), we find no strong direct link of FIR and radio continuum. This paper gives a compilation of both input data and results of our systematic statistical analysis, as well as a discussion of potential biases. Results relevant to both X-ray and multiwavelength emission properties are analyzed further and discussed in Paper II.