Peculiar Kinematics in the Core of NGC 474

Extract

We present absorption line profile analysis of NGC 474, an elliptical with prominent, irregular shells. Profiles are parameterized with Gauss-Hermite polynomials (van der Marel & Franx ApJ 407 1993; Rix & White MNRAS 254 1992). The fastest rotation (∼ 50 km s^–1) and steepest central velocity gradient along the intermediate photometric axis rules out the possibility that NGC 474 is a face-on S0 (Schombert & Wallin AJ 94 1987) and suggests that it is triaxial. The asymmetry of the LOSVDs (h3 up to 0.08) indicates the presence of a subsystem with rapid, ordered rotation. The minor axis velocity curve shows a kinematic feature at 3–4″ east of the nucleus, with no associated h3 or h4 features. Non-parametric LOSVD analysis (unresolved Gaussian decomposition, Kuijken & Merrifield MNRAS 264 1993) reveals a double-peaked profile at that location. In all position angles line-profiles are distinctly pointy for radii up to 2″, and are consistent with zero further out. We have found similar central positive h4 terms in the shell galaxy NGC 2865 (Hau et al. MNRAS in prep). Cores with pointy LOSVDs are uncommon in ellipticals (Bender, Saglia & Gerhard MNRAS 269 1994). Positive h4 terms might contain important clues on the shell-formation mechanism in ellipticals.