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

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 – 10,270 ˚A at a spatial resolution of 0 ′′.05 – 0 ′′.1 and a spectral resolving power of λ/∆λ ≈ 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 202o. In addition to the broad emission lines detected by spectropolarimetry, the hot spot shows the “little blue bump ” in the 2000 – 4000 ˚A 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 towards 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, dominated by an old ( ≥ 2 x 109 years) stellar population, and includes a nuclear stellar cluster which is ∼200 pc in extent.