Resolved Spectroscopy of the Narrow-Line Region in NGC 1068. I. The Nature of the Continuum Emission

Abstract

We present the first long-slit spectra of the Seyfert 2 galaxy NGC 1068 obtained by the Space Telescope Imaging Spectrograph (STIS) the spectra cover the wavelength range 1150-10270 Å at a spatial resolution of 0.05"-0.1" and a spectral resolving power of λ/Δλ~1000. In this first paper, we concentrate on the far-UV to near-IR continuum emission from the continuum ``hot spot'' and surrounding regions extending out to +/-6.0" (+/-432 pc) at a position angle of 202 deg. In addition to the broad emission lines detected by spectropolarimetry, the hot spot shows the ``little blue bump'' in the 2000-4000 Å range, which is due to Fe II and Balmer continuum emission. The continuum shape of the hot spot is indistinguishable from that of NGC 4151 and other Seyfert 1 galaxies. Thus, the hot spot is reflected emission from the hidden nucleus, due to electron scattering (as opposed to wavelength-dependent dust scattering). The hot spot is ~0.3" in extent and accounts for 20% of the scattered light in the inner 500 pc. We are able to deconvolve the extended continuum emission in this region into two components: electron-scattered light from the hidden nucleus (which dominates in the UV) and stellar light (which dominates in the optical and near-IR). The scattered light is heavily concentrated toward the hot spot, is stronger in the northeast, and is enhanced in regions of strong narrow-line emission. The stellar component is more extended, concentrated southwest of the hot spot, is dominated by an old (>=2x10⁹ yr) stellar population, and includes a nuclear stellar cluster that is ~200 pc in extent. Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.