Reddening, emission-line, and intrinsic absorption properties in the narrow-line Seyfert 1 galaxy Arakelian 564

We use Hubble Space Telescope UV and optical spectra of the narrow-line Seyfert 1 (NLS1) galaxy Ark 564 to investigate its internal reddening and properties of its emission-line and intrinsic UV absorption gas. We find that the extinction curve of Ark 564, derived from a comparison of its UV/optical continuum to that of an unreddened NLS1, lacks a 2200 Angstrom bump and turns up toward the UV at a longer wavelength (4000 Angstrom) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 Angstrom that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The emission lines and continuum experience the same amount of reddening, indicating the presence of a dust screen that is external to the narrow-line region. Echelle spectra from the Space Telescope Imaging Spectrograph show intrinsic UV absorption lines due to Lyalpha, N V, C IV, Si IV, and Si III, centered at a radial velocity of -190 km s(-1) (relative to the host galaxy). Photoionization models of the UV absorber indicate that it has a sufficient column (N-H = 1.6 x 10(21) cm(-2)) and is at a sufficient distance from the nucleus (D > 95 pc) to be the source of the dust screen. Thus, Ark 564 contains a dusty "lukewarm absorber" similar to that seen in NGC 3227.