Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..523e&link_type=abstract
Astrophysical Journal (ISSN 0004-637X), vol. 442, no. 2, Part 1, p. 523-537
Astronomy and Astrophysics
Astronomy
33
Bivariate Analysis, Galactic Evolution, Galactic Structure, Interstellar Matter, Luminosity, Potential Fields, Spaceborne Astronomy, Galactic Mass, Heao 2, Radio Sources (Astronomy), Star Formation, Statistical Correlation, X Ray Astronomy, X Ray Sources
Scientific paper
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 Lx and Lx/LB. The most radio-loud objects are also the roundest. We confirm the assertion of Bender et al. (1989) that galaxies with high Lx are boxy (have negative a4). Both a/b and a4 are correlated with LB, but not with IRAS 12 um and 100 um luminosities. There are strong correlations between Lx, Mg2, and sigmanu in the sense that those systems with the deepest potential wells have the highest Lx and Mg2. 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 Lx/LB and L6 (the 6 cm radio luminosity) show threshold effects with sigmanu exhibiting sharp increases at log sigmanu approximately = 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 a4) and the depth parameter sigmanu is a function of abundance in the sense that, for a given a4 or a/b, the systems with the highest sigmanu also have the highest Mg2. Furthermore, for a constant sigma(sun nu), disky galaxies tend to have higher Mg2 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 dissipation 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 Mg2 values would thus be due to enrichment from secondary bursts of star formation triggered by the merging event.
Eskridge Paul B.
Fabbiano Giuseppina
Kim Dong-Woo
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