Paschen Lines and the Reddening of the Radio Galaxy 3C 109

This paper presents spectrophotometric observations from 0.8 to 2.5 μm of the broad emission line radio galaxy 3C 109. Three Paschen lines plus Hα are measured and combined with a published value for Hβ to estimate the reddening for the continuum source and the region producing the broad emission lines. A key factor in this determination is the foreground reddening due to the Galaxy. The recent COBE/IRAS maps of Schlegel, Finkbeiner, & Davis indicate a Galactic extinction of E(B-V) = 0.57, more than twice the value inferred from the H I measurements. If the former value is adopted, the in situ reddening is E(B-V) = 0.77. This value implies, per the analysis of Goodrich & Cohen, that 3C 109 is an object of extremes, displaying a dereddened UV-optical continuum that is extraordinarily blue (fν ∼ ν1.5) and harboring dust grains that are more efficient polarizers than any found in the Milky Way. Both extremes hint at some additional factor or mechanism, and a few possibilities are discussed. Regardless, the significant amount of internal reddening indicated by infrared spectroscopy is consistent with results from previous optical polarimetry and spectropolarimetry, optical and X-ray spectroscopy, and infrared photometry, in demonstrating that 3C 109 is an obscured quasar—a luminous object whose nuclear radiations from the soft X-ray to the near-infrared are absorbed, scattered, polarized, and reradiated further into the infrared by a circumnuclear envelope of dust.

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