The structure and kinematics of the ionized gas within NGC 5128 (Cen A) – I. TAURUS observations

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Abstract
The TAURUS imaging Fabry–Perot system has been used at the Anglo–Australian Telescope to observe the ionized gas within Centaurus A. NGC 5128, the optical body of Cen A, is well known for the dust lane system which rotates rapidly about its projected major axis. A growing body of opinion affirms that the fact that this galaxy appears ‘peculiar’ is a testimony to its proximity and that it would look much like any other radio elliptical at comparable distances. In this case, the presence of gas within this galaxy provides an invaluable laboratory for the study of a number of physical phenomena, in particular: (i) the three-dimensional form of elliptical galaxies, (ii) the nature of orbits in early-type systems, and (iii) the origin of nuclear activity within radio galaxies. To conduct these experiments, TAURUS has been used to observe the ionized gas within NGC 5128 in the light of [N II] λ6548 and Hα. Seven independent TAURUS data sets were obtained along the dust lane at a spectral resolution of 36 km s−1 FWHM and at a spatial resolution limited by the seeing (∼1.5″). From these data, maps of the kinematics and intensities of the ionized gas have been derived over a region spanning 420″ in right ascension and 300″ in declination. The maps are the most complete to date for this object comprising 17 500 fitted spectra in Hα and 5300 fitted spectra in [N II] λ6548. The results are compared and contrasted with previous observations of the ionized gas. A preliminary interpretation of the observations suggests that the dust lane is the projection of a severely warped, thin disc of gas and dust. A more detailed kinematic analysis, presented in Paper II, confirms this model.

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