2000/09/30 by R. Maiolino, A. Marconi, M. Salvati +5 · 3 citations
Physics and Astronomy · #Absorption (acoustics) #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Cosmic dust #Extinction (optical mineralogy) #Galaxy #Grism #Infrared #Interstellar medium #Physics #QSOS #Quasar #Redshift #Spectral line #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1051/0004-6361:20000177
9 pages, 3 figures, accepted for publication in A&A
arxiv created 2000/09/30 · openalex publication_date 2001/01/01 · arxiv updated 2009/12/01 · openalex created_date 2022/09/17 · openalex updated_date 2026/08/01
We present observational evidences that dust in the circumnuclear region of AGNs has different properties than in the Galactic diffuse interstellar medium. By comparing the reddening of optical and infrared broad lines and the X-ray absorbing column density we find that the ratio is nearly always lower than Galactic by a factor ranging from ∼3 up to ∼100. Other observational results indicate that the ratio is significantly lower than Galactic in various classes of AGNs including intermediate type 1.8-1.9 Seyferts, hard X-ray selected and radio selected quasars, broad absorption line QSOs and grism selected QSOs. The lack of prominent absorption features at 9.7 μm (silicates) and at 2175 Å (carbon dip) in the spectra of Seyfert 2s and of reddened Seyfert 1s, respectively, add further evidence for dust in the circumnuclear region of AGNs being different from Galactic. These observational results indicate that the dust composition in the circumnuclear region of AGNs could be dominated by large grains, which make the extinction curve flatter, featureless and are responsible for the reduction of the and ratios. Regardless of the physical origin of these phenomena, the reduced dust absorption with respect to what expected from the gaseous column density should warn about a mismatch between the optical and the X-ray classification of the active galactic nuclei in terms of their obscuration.