Mid-infrared selection of AGN

Abstract

Since a large fraction of active galactic nuclei (AGN) is missed in common UV-excess surveys and is even hard to find in radio, near-IR and X-ray surveys, we have used a new AGN selection technique which is expected to be not affected by extinction. Within the scientific verification of the ISOCAM Parallel Survey at 6.7 micron we have discovered objects with exceptional mid-infrared (MIR) emission. They are essentially not detected on IRAS-ADDSCANs and only very few of them show up in the NVSS and FIRST radio surveys. Various colour criteria of the 6.7 micron data with 2MASS and optical wavebands show that the sources reach more extreme IR colours than the sources in the Hubble Deep Field-South and the ELAIS survey. The comparison with known object types suggests that we have found AGN with a pronounced MIR emission, probably due to circum-nuclear dust. First results from optical spectroscopy of ten candidates corroborate this interpretation showing four AGN, two reddened LINER and four extremely reddened emission-line galaxies with MIR/FIR flux ratios higher than for known pure starburst galaxies. The results will make a significant contribution to the debate on the entire AGN population.

4 pages, 2 figures, accepted for publication as Letter in Astronomy & Astrophysics

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• The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus models
• The distribution of silicate strength in Spitzer spectra of AGNs and ULIRGs
• The Link Between Star Formation and Accretion in LINERs: A Comparison with other AGN Subclasses
• Chandra and XMM Observations of Type II Quasars from the SDSS
• Silicate absorption in heavily obscured galaxy nuclei
• The Past and Future of Mid-Infrared Studies of AGN
• Active Galactic Nuclei as seen by the Spitzer Space Telescope
• Normal Nearby Galaxies
• The ISO-2MASS AGN survey: On the type-1 sources
• The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - II. Multi-wavelength properties
• Narrow-line AGN in the ISO-2MASS Survey
• A population of extreme mid-to-near-infrared sources: obscured AGN and dusty starbursts
• The Second Byurakan Survey Galaxies. I. The Optical Database
• The reddest ISO-2MASS quasar
• Polycyclic aromatic hydrocarbon selected galaxies
• Compton-thick AGN Characterisation in a Multi-wavelength Context: Insights from the 70-Month \textit{SWIFT}/BAT Catalogue