A MULTIPARAMETRIC ANALYSIS OF THE EINSTEIN SAMPLE OF EARLY-TYPE GALAXIES. Ⅱ. GALAXY FORMATION HISTORY AND PROPERTIES OF THE INTERSTELLAR MEDIUM

摘要

We have conducted bivariate and multivariate statistical analysis of data measuring the integrated luminosity, shape, and potential depth of the Einstein sample of early-type galaxies (presented by Fabbiano et al. 1992). We find significant correlations between the X-ray properties and the axial ratios (a/b) of our sample, such that the roundest systems tend to have the highest L_X and L_X/L_B. The most radio-loud objects are also the roundest. We confirm the assertion of Bender et al. (1989) that galaxies with high L_X are boxy (have negative a_4). Both a/b and a_4 are correlated with L_B, but not with IRAS 12 μm and 100 μm luminosities. There are strong correlations between L_X, Mg_2, and σ_v in the sense that those systems with the deepest potential wells have the highest L_X and Mg_2. Thus the depth of the potential well appears to govern both the ability to retain an ISM at the present epoch and to retain the enriched ejecta of early star formation bursts. Both L_X/L_B and L_6 (the 6 cm radio luminosity) show threshold effects with σ_v, exhibiting sharp increases at log (σ_v) ≈ 2.2. Finally, there is clearly an interrelationship between the various stellar and structural parameters: The scatter in the bivariate relationships between the shape parameters (a/b and a_4) and the depth parameter (σ_v) is a function of abundance in the sense that, for a given a_4 or a/b, the systems with the highest σ_v also have the highest Mg_2. Furthermore, for a constant σ_v, disky galaxies tend to have higher Mg_2 than boxy ones. Alternatively, for a given abundance, boxy ellipticals tend to be more massive than disky ellipticals. One possibility is that early-type galaxies of a given mass, originating from mergers (boxy ellipticals), have lower abundances than " primordial" (disky) early-type galaxies. Another is that disky inner isophotes are due not to primordial dissipational collapse, but to either the self-gravitating inner disks of captured spirals or the dissipational collapse of new disk structures from the premerger ISM. The high measured nuclear Mg_2 values would thus be due to enrichment from secondary bursts of star formation triggered by the merging event.