The apparent and true ellipticities of galaxies of different Hubble types in the Second Reference Catalogue

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Abstract
We analyse the apparent ellipticities of 1750 galaxies listed in the Second Reference Catalogue (RC2) as having diameters in excess of about 2 arcmin to determine the distribution of true ellipticities at nine stages along the Hubble sequence from E to Im. The modal true axial ratio of elliptical galaxies lies near 0.62 irrespective of whether these systems are oblate or prolate. If ellipticals are prolate, the relative frequency of truly spherical galaxies is 50 per cent higher than if they are oblate. The true axial ratios of Magellanic irregulars are approximately uniformly distributed between 0.2 and 0.8. We are unable to obtain statistically satisfactory fits to the data for lenticular galaxies that use only circularly-symmetric bodies with axial ratios smaller than 0.5; we believe this effect is not due to selection against edge-on galaxies but indicates that more than 10 per cent of galaxies classified as S0 are dominated by non-elliptical bulges. Lite-type spirals tend to be flatter than the earlier types. The ellipticity distributions favour the possibility that many discs are slightly elliptical.

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