Planetary Camera observations of the M87 stellar cusp

Tod R. Lauer, S. M. Faber, C. Roger Lynds, William A. Baum, S. P. Ewald, Edward J. Groth, J. Jeff Hester, Jon A. Holtzman, Jerome Kristian, Robert M. Light, Earl J. O'Neil, Donald P. Schneider, Edward J. Shaya, James A. Westphal

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Analysis of V and I band HST Planetary Camera images of the giant elliptical galaxy M87 show that its central starlight distribution is consistent with the black hole M = 2.6 × 109 M cusp model proposed for M87 by Young et al. [ApJ, 221, 721 (1978)]. A combined approach of image deconvolution and modeling is used to investigate the starlight distribution into limiting radii of ≈0″.04 (3 pc at 16 Mpc). The central structure of M87 can be described by three components: a power-law starlight profile of the form μ(r) ∝ r -1/4 for r < 3″, a central nonthermal point source, and optical counterparts of the jet knots N1 and M identified by VLBI observations. M87 lacks a constant surface brightness core, and its central starlight luminosity density exceeds 103L pc-3 (I band) for r < 10 pc. The profile strongly resembles a stellar cusp associated with a massive black hole. A review of existing velocity dispersion observations suggests that the Young et al. black hole mass can be accommodated to the observations with minor adjustments of dynamical models. The central luminosity spike itself remains unresolved at HST resolution, with rc < 1 pc. The spike has optical spectral index α = -0.46 ± 0.20 and is at least as blue if not bluer than the rest of the M87 jet. The total nonthermal flux in the inner 1″ of M87 agrees well with the central radio flux and the radio-optical spectral index of the rest of the jet. It is also consistent with the spectral-line dilution seen by Dressler & Richstone [ApJ, 348, 120 (1990)]; we thus argue that the spike is completely nonthermal.

Original languageEnglish (US)
Pages (from-to)703-710
Number of pages8
JournalAstronomical Journal
Issue number3
StatePublished - Mar 1992

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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