The Counterrotating Core and the Black Hole Mass of IC 1459

Abstract

The E3 giant elliptical galaxy IC 1459 is the prototypical galaxy with a fast counterrotating stellar core. We obtained one HST/STIS long-slit spectrum along the major axis of this galaxy and CTIO spectra along five position angles. The signal-to-noise (S/N) of the ground-based data is such that also the higher order Gauss-Hermite moments (h3–h6) can be extracted reliably. We present selfconsistent three-integral axisymmetric models of the stellar kinematics, obtained with Schwarzschild’s numerical orbit superposition method. The available data allow us to study the dynamics of the kinematically decoupled core (KDC) in IC 1459 and we find it consists of stars that are well-separated from the rest of the galaxy in phase space. In particular, our study indicates that the stars in the KDC counterrotate in a disk on orbits that are close to circular. We estimate that the KDC mass is ≈ 0.5 % of the total galaxy mass or ≈ 3 × 10 9 M⊙. We estimate the central black hole mass M • of IC 1459 independently from both its stellar and its gaseous kinematics. Although both tracers rule out models without a central black hole, neither yields a particularly accurate determination of the black hole mass. The main problem for the stellar dynamical modeling is the fact that the modest S/N of the STIS spectrum and the presence of strong