Reddening, emission-line, and intrinsic absorption properties in the Narrow-Line Seyfert 1 Galaxy Arakelian 564
journal contributionposted on 04.11.2016, 15:57 by D. M. Crenshaw, S. B. Kraemer, T. J. Turner, S. Collier, B. M. Peterson, W. N. Brandt, J. Clavel, I. M. George, K. Horne, G. A. Kriss, S. Mathur, H. Netzer, R. W. Pogge, K. A. Pounds, P. Romano, O. Shemmer, W. Wamsteker
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 Å bump and turns up toward the UV at a longer wavelength (4000 Å) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 Å 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 Lyα, 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 (NH = 1.6 × 1021 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.