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For refcode 1996AJ....112..105G:
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1996AJ....112..105G THE CENTERS OF EARLY-TYPE GALAXIES WITH HST. III. NON-PARAMETRIC RECOVERY OF STELLAR LUMINOSITY DISTRIBUTIONS KARL GEBHARDT AND DOUGLAS RICHSTONE Department of Astronomy, Dennison Building, University of Michigan, Ann Arbor, Michigan 48109 Electronic mail: gebhardt@astro.lsa.umich.edu, dor@astro.lsa.umich.edu EDWARD A. AJHAR AND TOD R. LAUER Kitt Peak National Observatory, National Optical Astronomy Observatories, P. O. Box 26732, Tucson, Arizona 85726 YONG-IK BYUN AND JOHN KORMENDY Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822 ALAN DRESSLER The Observatories of the Carnegie institution of Washington, 813 Santa Barbara Street, Pasadena, California 91101 S. M. FABER AND CARL GRILLMAIR UCO/Lick Observatories, Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz, California 95064 SCOTT TREMAINE Canadian institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, M5S 3H8, Canada Received 1995 November 3; revised 1996 March 8 ABSTRACT We have non-parametrically determined the luminosity density profiles and their logarithmic slopes for 42 early-type galaxies observed with HST. Assuming that the isodensity contours are spheroidal, then the luminosity density is uniquely determined from the surface brightness data through the Abel equation. For nearly all the galaxies in our sample, the logarithmic slope of the luminosity density (S = d log v/d log r) measured at 0.1" (the innermost reliable measurement with the uncorrected HST) is significantly different from zero; i.e., most elliptical galaxies have cusps. There are only two galaxies for which an analytic core (S approaches 0) cannot be excluded. The distribution of logarithmic slopes at 0.1" appears to be bimodal, confirming the conclusion of Lauer et al. [AJ, 110,2622(1995)] that early-type galaxies can be divided into two types based on their surface brightness profiles; i.e., those with cuspy cores and those whose steep power-law profiles continue essentially unchanged in to the resolution limit. The peaks in the slope distribution occur at S = -0.8 and - 1.9. More than half of the galaxies have slopes steeper than - 1.0. Taken together with the recent theoretical work of Merritt and Fridman, these results suggest that many (and maybe most) elliptical galaxies are either nearly axisymmetric or spherical near the center, or slowly evolve due to the influence of stochastic orbits.
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