A quantitative determination of the AGN content in local ULIRGs through L-band spectroscopy |
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| Authors: | G Risaliti M Imanishi E Sani |
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| Institution: | INAF - Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy;Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA;National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;Dipartimento di Astronomia, Universitàdi Firenze, L.go E. Fermi 2, 50125 Firenze, Italy |
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| Abstract: | We present a quantitative estimate of the relative active galactic nucleus (AGN)/starburst content in a sample of 59 nearby ( z < 0.15) infrared bright ultraluminous infrared galaxies (ULIRGs) taken from the 1-Jy sample, based on infrared L -band (3–4 μm) spectra. By using diagnostic diagrams and a simple deconvolution model, we show that at least 60 per cent of local ULIRGs contain an active nucleus, but the AGN contribution to the bolometric luminosity is relevant only in ～15–20 per cent of the sources. Overall, ULIRGs appear to be powered by the starburst process, responsible for >85 per cent of the observed infrared luminosity. The subsample of sources optically classified as low-ionization nuclear emission-line regions (LINERs; 31 objects) shows a similar AGN/starburst distribution as the whole sample, indicating a composite nature for this class of objects. We also show that a few ULIRGs, optically classified as starbursts, have L -band spectral features suggesting the presence of a buried AGN. |
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| Keywords: | galaxies: active galaxies: starburst infrared: galaxies |
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