Spatial Distributions of Dust and Polycyclic Aromatic Hydrocarbons in the Nearby Elliptical Galaxy NGC 4589 Observed with AKARI

Abstract

We report on near- to far-infrared (IR) observations of the nearby elliptical galaxy NGC 4589 by AKARI. NGC 4589 has acomplex stellar rotation field with aposition angle difference of 45° between the kinematic and morphological axes, although its morphology shows asmooth optical profile that closely follows the de Vaucouleurs law. The galaxy has aminor-axis dust lane, which is twisted toward the main stellar rotation. These properties strongly support that the galaxy is arelatively old merger remnant. We have obtained the spatial distributions of dust from far-IR emission and near-IR absorption, separately. We have also estimated the distribution of polycyclic aromatic hydrocarbons (PAHs) from the difference between images in the mid-IR bands. The spatial distributions of the dust and PAHs resemble each other, both showing significant deviations from the smooth stellar distribution. They extend to the main stellar rotation and the direction of the twisted inner dust lane, thus following the relics of the merger. Therefore, alarge fraction of the dust and PAHs in NGC 4589 are likely to originate from apast merger event.