Figure 37 -- The dichotomy between elliptical and spheroidal galaxies: Ellipticals (blue and red points) and S0 bulges (turquoise points) together define a Fundamental Plane in parameter space that has small scatter when seen nearly edge-on (top panel) and that is clearly distinct from the almost-perpendicular sequence of spheroidal galaxies (green points). It is even more distinct when near-central parameters are used (see the paper). Here r_e is the "effective radius" that contains half of the light of the galaxy and mu_e is the surface brightness at r_e. These are the parameters of Sersic function fits to the major-axis profiles. The total absolute magnitude M_VT is measured by adding up all the light in the profile. The symbols are explained in the paper. The two distinct parameter sequences are consistent with our understanding of their different formation processes: galaxy mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. KFCB confirms results of Kormendy (1985) and (1987).
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