The centers of early-type galaxies with HST. II. Empirical models and structural parameters

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

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116 Citations (Scopus)


We present a set of structural parameters for the central parts of 57 early-type galaxies observed with the Planetary Camera of the Hubble Space Telescope. These parameters are based on a new empirical law that successfully characterizes the centers of early-type galaxies. This empirical law assumes that the surface brightness profile is a combination of two power laws with different slopes γ and β for the inner and outer regions. Conventional structural parameters such as core radius and central surface brightness are replaced by break radius rb, where the transition between power-law slopes takes place, and surface brightness μb at that radius. An additional parameter α describes the sharpness of the break. The structural parameters are derived using a χ2 minimization process applied to the mean surface brightness profiles. The resulting model profiles generally give very good agreement to the observed profiles out to the radius of ~10″ imaged by the Planetary Camera. Exceptions include galaxies which depart from pure power laws at large radius, those with strong nuclear components, and galaxies partly obscured by dust. The uncertainties in the derived parameters are estimated using Monte Carlo simulations which test the stability of solutions in the face of photon noise and the effects of the deconvolution process. The covariance of the structural parameters is examined by computing contours of constant χ2 in multi-dimensional parameter space.

Original languageEnglish
Pages (from-to)1889-1900
Number of pages12
JournalAstronomical Journal
Issue number5
Publication statusPublished - 1996 May

Bibliographical note

Funding Information:
This work is supported by grants from the Projects of International Cooperation and Exchanges Ministry of Science and Technology of China (2013DFG32390) and the National Natural Science Foundation of China (31472059) to X.S. X.S is a recipient of the Young Thousand Talents program (KJ2070000026).

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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