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Session 118 - Radiogalaxies.
Oral session, Thursday, January 16
Harbour A,
We present optical images of the nucleus of the nearby radio galaxy NGC 4374 (M84 = 3C272.1) obtained with the Wide Field/Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope (HST). Each of our three images covers a separate wavelength range, including the H\alpha + [N II] emission lines as well as the V and I continuum. Analysis of these images reveals that the H\alpha + [N II] emission in the central 5'' (410 pc), which is elongated along position angle (P.A.) \approx 72\deg, has three components, namely a nuclear gas disk and an ionization cone surrounded by outer filaments of emission. The nuclear disk of ionized gas has diameter \approx 2'' = 164 pc, major axis P.A. \approx 60\deg, and inclination i \approx 45\deg. The minor axis of this inner gas disk is tilted with respect to that of the H\alpha + [N II] emission at distances > 2'' from the nucleus, which is roughly aligned with the axis of the radio jets (P.A. \approx 170\deg). The ionization cone (whose apex coincides with the nucleus) extends 2'' along the axis of the radio jets. This feature is similar to the ionization cones seen in Seyfert nuclei, which are also aligned with the radio axes in these galaxies. In addition to two nuclear dust lanes, the V and I images also show an unresolved source of continuum emission at the nucleus, which we attribute to nonstellar light from the active galactic nucleus.
