The nature of elongated ellipticals

Details The nature of elongated ellipticals The nature of elongated ellipticals

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283....1n&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 1-11

Astronomy and Astrophysics

Astrophysics

18

Elliptical Galaxies, Galactic Evolution, Galactic Structure, Isophotes, Lenticular Bodies, Disk Galaxies, Morphology, Radio Emission, X Ray Spectra

Scientific paper

We have analyzed the isophotal shapes of a sample of 63 elongated elliptical galaxies, previously classified E4, 5, 6 or 7. We sorted them according to their isophotal class, defined by the type of deviations from perfectly elliptical isophotal contours. These deviations are expected to appear clearly, because of the very favorable orientation of these galaxies. We find the following results, after exclusion of 6 non-elliptical galaxies: A large percentage (56%) of elongated E's are disky objects with pointed isophotes, while only 35% have either boxy or irregular isophotes, in equal proportions, and the remaining 6 galaxies (10%) are diffucult to classify. Furthermore, 38% of disky Es's also show slightly boxy spheroids. In almost all the galaxies of the sample, there is an angular range where the deviations are of the disk-type. The four galaxies not showing this effect are among the roundest ones in the sample, which suggests that projection effects hide detailed structures of this kind in many ellipticals. The correlations already reported in the literature between isophotal class and radio, X-ray emission and kinematical behavior are confirmed. In particular, there is a clear-cut correlation between velocity anisotropy and isophotal shape. The most elongated Hubble types tend to be disky E's. Boxy/irregular E's rarely exceed ellipticities of 0.45 while the maximum ellipticity of half of the disky Es's exceeds this value. These results confirm the dichotomy of E's, which fall roughly into two classes, disky and boxy/irregular ellipticals. They also show a physical continuity between disky E's and SO's and suggest that the Hubble types are strongly correlated with disk-to-bulge ratios throughout the Hubble sequence, even at its early-type end (round E's), for which the disk is hidden by orientation effects Galaxies escaping the correlations are the boxy/irregular Es's, resulting probably from strong merging processes.

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