Unveiling the Hidden Nucleus of IC 5063 with NICMOS

Abstract

We present high-resolution near-infrared images of the Seyfert 2 galaxy IC 5063 obtained using the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) in broadband filters at 1.1, 1.6, and 2.2 μm (FWHM ≈ 021 at 2.2 μm). The images show a very red, unresolved point source at the center of the galaxy, confirming the existence of the obscured active nucleus inferred from previous ground-based studies. The 2.2 μm flux, supplemented with ground-based L'-band observations, suggests thermal emission equivalent to a blackbody at a temperature of 720 K. We ascribe the emission not to direct light from the nucleus, but to hot dust in the inner part of the torus. The 1.6 μm emission is only minimally affected by the hot dust emission. The luminosity of the central source producing most of the 1.6 μm emission, not corrected for extinction, is 1.5×1041 ergs s−1, integrated over the F160W filter only. We also present lower spatial resolution images of IC 5063 obtained with NICMOS in the emission lines of [Fe II] λ1.644 μm, Paα λ1.8756 μm, and H2 λ2.1218 μm. These images reveal a linear emission morphology comprised of two bright knots, separated by 18 on either side of a central knot that is at the location of the continuum nucleus. A comparison with high-resolution radio continuum maps shows that there is a one-to-one spatial correspondence between the radio lobes and the emission-line knots, directly implying that the [Fe II] and H2 emission is created by fast shocks produced by the advancing radio jets. The asymmetry in the [Fe II]/H2 ratio may suggest a difference in either the shock velocities or the molecular mass on the two sides of the nucleus.