Infrared spectroscopy around 4 μm of Seyfert 2 galaxies: Obscured broad line regions and coronal lines

D. Lutz*, R. Maiolino, A. F.M. Moorwood, H. Netzer, S. J. Wagner, E. Sturm, R. Genzel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The state of the matter that is obscuring a small circumnuclear region in active galactic nuclei can be probed by observations of its broad emission lines. Infrared lines are particularly useful since they penetrate significant columns of obscuring matter, the properties of which can be constrained by comparing infrared and X-ray obscuration. We report on new 4 μm spectroscopy with ISAAC at the ESO VLT of a sample of 12 Seyfert 2 galaxies, probing for broad components to the Brackett α 4.05 μm hydrogen recombination line. Broad components are observed in 3 to 4 objects. All objects with a broad component exhibit relatively low X-ray obscuring columns, and our results are consistent with a Galactic ratio of 4 μm obscuration to the BLR and X-ray column. In combination with observations of a non-Galactic ratio of visual obscuration of BLRs and X-ray obscuring column in Seyferts, and interpreted in a unified AGN scheme, this result can be reconciled with two interpretations. Either the properties of dust near the AGN are modified towards larger grains, for example through coagulation, in a way that significantly flattens the optical/IR extinction curve, or the ratio of dust obscuration to X-ray column varies for different viewing angles with respect to the axis of symmetry of the putative toms. Our spectra also provide a survey of emission in the [Si IX] 3.94 μm coronal line, finding variation by an order of magnitude in its ratio to Brα. The first extragalactic detection of the [Ca VII] 4.09 μm and [Ca V] 4.16 μm coronal lines is reported in the spectrum of the Circinus galaxy.

Original languageEnglish
Pages (from-to)439-448
Number of pages10
JournalAstronomy and Astrophysics
Issue number2
StatePublished - Dec 2002


  • Galaxies: ISM
  • Galaxies: Seyfert
  • Galaxies: active


Dive into the research topics of 'Infrared spectroscopy around 4 μm of Seyfert 2 galaxies: Obscured broad line regions and coronal lines'. Together they form a unique fingerprint.

Cite this