Three-dimensional Optical Spectroscopy of the Superwind Galaxy NGC 2782

Abstract

We report on both the kinematical and excitation properties of the ionized gas in the nuclear starburst region of NGC 2782, based on our new optical three-dimensional observations of the central 2' × 18'' region of this galaxy. The emission-line regions consist of the central elongated emission-line region and an extension to the south manifested by the bright [O I] emission. The emission-line profiles cannot be described as a single Gaussian component in most parts of the observed area. We then find that they can be well decomposed into two kinematical distinct components: a broad (FWHM ~ 500 km s-1) component and a narrow (FWHM 150 km s-1) component. The broad component is associated spatially with the nucleus and the southern extension, whereas the narrow component is associated mostly with the northern arclike region. The kinematical properties obtained in this study show that the arclike region is a part of the circumnuclear rotating ring with a number of star-forming regions. The emission-line intensity ratios of the narrow component are consistent with those of H II regions. On the other hand, shock heating is the most viable excitation mechanism for the broad component emission. In particular, the outer part of the broad component emitting region has a higher electron density than the inner parts and the highest velocity dispersion. Because these properties can be interpreted in terms of shock compression, the superwind in NGC 2782 is still interacting with the interstellar medium within this galaxy. The overall morphology of the broad component region is quite similar to those of the published 5 GHz radio continuum maps. All these findings strongly suggest that the broad component region is the part of a pair of bubbles driven by the superwind, although we are seeing only the southern bubble and the northern rotating ring because of the heavy extinction.