The Elliptical–Spheroidal and Elliptical–Elliptical Galaxy Dichotomies

This paper summarizes Kormendy et al. (2009, ApJS, in press, arXiv:0810.1681). We confirm that spheroidal galaxies have fundamental plane correlations that are almost perpendicular to those for bulges and ellipticals. Spheroidals are not dwarf ellipticals. They are structurally similar to late-type galaxies. We suggest that they are defunct (“red and dead”) late-type galaxies transformed by a variety of gas removal processes. Minus spheroidals, ellipticals come in two varieties: giant, non-rotating, boxy galaxies with cuspy cores and smaller, rotating, disky galaxies that lack cores. We find a new feature of this “E–E dichotomy”: Coreless ellipticals have extra light at the center with respect to an inward extrapolation of the outer Sérsic profile. We suggest that extra light is made in starbursts that swamp core scouring in wet mergers. In general, only giant, core ellipticals contain X-ray gas halos. We suggest that they formed in mergers that were kept dry by X-ray gas heated by active galactic nuclei. 1. High-Dynamic-Range Surface Photometry of E and Sph Galaxies Figure 1 shows examples of photometry of all known ellipticals in the Virgo cluster from Kormendy et al. (2009; hereafter KFCB). The key to this paper is the accuracy and large dynamic range attained when data from many telescopes with different resolutions and field sizes are combined into composite profiles. Figure 1. Major-axis brightness profiles of Virgo ellipticals from KFCB. Surface brightness μ is in V mag arcsec. The curve is a Sérsic (1968) fit between the vertical dashes; the index n and total galaxy absolute magnitude MV T are in the key. This figure illustrates the E–E dichotomy: NGC 4486 is a core galaxy with n > 4; NGC 4458 is an extra light galaxy with n ∼< 4 (§ 3).