AN INFRARED JET IN CENTAURUS-A - A LINK TO THE EXTRANUCLEAR ACTIVITY IN DISTANT RADIO GALAXIES

High-resolution near-infrared images of the visually obscured central region of Centaurus A (NGC 5128) have been obtained in order to investigate the effects of the active nucleus on the surrounding galaxy. We present J(1.25 μm), H(1.65 μm), and K.(2.2 μm) images of the central 40″ of the galaxy, taken with the University of Texas InSb array camera on the Anglo Australian 3.9 m telescope. These images reveal an emission feature extending ∼ 10″ to the northeast of the nucleus at the same position angle as the X-ray and radio jets. This "infrared jet" is most prominent at the shortest wavelength (1.25 μm), where its brightness is comparable to that of the nucleus. No emission lines are found in its near-infrared spectrum, indicating that continuous emission processes predominate. In contrast to previously studied optical and infrared jets in nearby active galaxies, the short-wavelength prominence of the Cen A jet indicates that it cannot be attributed to synchrotron emission from a beam of relativistic electrons; we consider other mechanisms involving an interaction between the interstellar medium and the active nucleus, including induced star formation, free-free radiation from shock-heated gas, scattering of nonthermal radiation from the active nucleus, and destruction of grains in the edge-on dust lane that obscures the central part of the galaxy. The observed properties of the infrared jet are similar to those seen in distant radio sources, and studies of Cen A may bear on the nature of high redshift galaxies at earlier epochs.