The near-infrared spectrum of Mrk 1239: direct evidence of the dusty torus?

Abstract

Abstract We report 0.8–4.5 μm SpeX spectroscopy of the narrow-line Seyfert 1 galaxy Mrk 1239. The spectrum is outstanding because the nuclear continuum emission in the near-infrared (NIR) is dominated by a strong bump of emission peaking at 2.2 μm, with a strength not reported before in an active galactic nucleus. A comparison of the Mrk 1239 spectrum to that of Ark 564 allowed us to conclude that the continuum is strongly reddened by E(B−V) = 0.54. The excess of emission, confirmed by aperture photometry and additional NIR spectroscopy, follows a simple blackbody curve at T∼ 1200 K. This suggests that we may be observing direct evidence of dust heated to near to the sublimation temperature, likely produced by the putative torus of the unification model. Although other alternatives are also plausible, the lack of star formation, the strong polarization and low extinction derived for the emission lines support the scenario where the hot dust is located between the narrow line region and the broad line region.