Galaxy concentrations are trimodal |
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| Authors: | Jeremy Bailin William E Harris |
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| Institution: | Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4M1 |
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| Abstract: | We have analysed the distribution of inclination-corrected galaxy concentrations in the Sloan Digital Sky Survey. We find that unlike most galaxy properties, which are distributed bimodally, the distribution of concentrations is trimodal: it exhibits three distinct peaks. The newly discovered intermediate peak, which consists of early-type spirals and lenticulars, may contain ～60 per cent of the number density and ～50 per cent of the luminosity density of 0.1 Mr < ?17 galaxies in the local universe. These galaxies are generally red and quiescent, although the distribution contains a tail of blue star-forming galaxies and also shows evidence of dust. The intermediate-type galaxies have higher apparent ellipticities than either disc or elliptical galaxies, most likely because some of the face-on intermediate types are misidentified as ellipticals. Their physical half-light radii are smaller than the radii of either the disc or elliptical galaxies, which may be evidence that they form from disc fading. The existence of a distinct peak in parameter space associated with early-type spiral galaxies and lenticulars implies that they have a distinct formation mechanism and are not simply the smooth transition between disc-dominated and spheroid-dominated galaxies. |
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| Keywords: | galaxies: elliptical and lenticular cD galaxies: fundamental parameters galaxies: spiral galaxies: structure |
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