The centers of early-type galaxies with HST. III. Non-parametric recovery of stellar luminosity distributions

Karl Gebhardt, Douglas Richstone, Edward A. Ajhar, Tod R. Lauer, Yong Ik Byun, John Kormendy, Alan Dressler, S. M. Faber, Carl Grillmair, Scott Tremaine

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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 vld 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→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.

Original languageEnglish
Pages (from-to)105-113
Number of pages9
JournalAstronomical Journal
Volume112
Issue number1
DOIs
Publication statusPublished - 1996 Jul 1

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Gebhardt, K., Richstone, D., Ajhar, E. A., Lauer, T. R., Byun, Y. I., Kormendy, J., Dressler, A., Faber, S. M., Grillmair, C., & Tremaine, S. (1996). The centers of early-type galaxies with HST. III. Non-parametric recovery of stellar luminosity distributions. Astronomical Journal, 112(1), 105-113. https://doi.org/10.1086/117992