Gas near active galactic nuclei: A search for the 4.7micron CO band

Abstract

In order to constrain the properties of dense and warm gas around active galactic nuclei, we have searched Infrared Space Observatory spectra of local active galactic nuclei for the signature of the 4.7micron fundamental ro-vibrational band of carbon monoxide. Low resolution spectra of 31 AGN put upper limits on the presence of wide absorption bands corresponding to absorption by large columns of warm and dense gas against the nuclear dust continuum. High resolution (R~2500) spectra of NGC 1068 detect no significant absorption or emission in individual lines, to a 3sigma limit of 7% of the continuum. The limits set on CO absorption in local AGN are much lower than the recent Spitzer Space Telescope detection of strong CO absorption by dense and warm gas in the obscured ultraluminous infrared galaxy IRAS F00183-7111, despite evidence for dense material on parsec scales near an AGN in both types of objects. This suggests that such deep absorptions are not intimately related to the obscuring `torus' material invoked in local AGN, but rather are a signature of the peculiar conditions in the circumnuclear region of highly obscured infrared galaxies like IRAS F00183-7111. They may reflect fully covered rather than torus geometries.

arXiv comment4 pages, 2 figures. Accepted for publication as an A&A Letter. Corrected nomenclature 'bandhead' to 'band'

References in corpus (9)

• The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects
• ISOCAM-CVF 5-12 mum Spectroscopy of Ultraluminous Infrared Galaxies
• A direct image of the obscuring disk surrounding an active galactic nucleus
• Ice features in the mid-IR spectra of galactic nuclei
• ISO-SWS spectroscopy of NGC 1068
• Detection of strongly processed ice in the central starburst of NGC4945
• Cold H2O and CO ice and gas toward the Galactic Center
• Infrared spectroscopy around 4micron of Seyfert 2 galaxies: Obscured broad line regions and coronal lines
• Bright CO ro-vibrational emission lines in the class I source GSS 30 IRS1: Probing the inner disk of a young embedded star

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• Obscured Activity: AGN, Quasars, Starbursts and ULIGs observed by the Infrared Space Observatory
• Compton-thick active galactic nuclei inside local ultraluminous infrared galaxies
• Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
• The 3-5 micron Spectrum of NGC 1068 at High Angular Resolution: Distribution of Emission and Absorption Features across the Nuclear Continuum Source
• The Near-Infrared CO Absorption Band as a Probe to the Innermost Part of an AGN Obscuring Material
• Extremely Buried Nucleus of IRAS 17208$-$0014 Observed at Sub-Millimeter and Near-Infrared Wavelengths
• Probing dynamics and thermal properties inside molecular tori with CO rovibrational absorption lines
• Origin of Warm High-Velocity Dense Gas in ULIRGs
• Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068