A New Mid-Infrared Diagnostic between AGN and Starbursts |
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| Authors: | O Laurent IF Mirabel V Charmandaris P Gallais M Sauvage L Vigroux C Cesarsky |
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| Institution: | (1) CEA/DSM/DAPNIA, Service d'Astrophysique, France;(2) Instituto de Astronomía cc 67, suc 28, 1428 Buenos Aires, Argentina;(3) Observatoire de Paris, DEMIRM, France |
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| Abstract: | We present a new set of diagnostics which allow us to trace and classify in a statistical manner the mid-IR emission produced
by active galactic nuclei (AGN) and star-forming regions. We construct a diagram based on the strength of the unidentified
infrared band (UIB)at 6.2 μm, and the intensity of the continuum at short (6 μm) and long wavelengths (15 μm). We interpret
the integrated mid-IR emission in late-type galaxies as resulting from three individual contributions coming from HII regions,
diffuse/photodissociation regions (PDRs), and AGN. Based on this assumption, our diagnostic diagram provides a quantitative
estimate of the AGN and starburst contribution to an observed mid-IR spectrum. We show that UIB emission is very faint or
absent in regions harbouring intense and hard radiation fields as in the case of AGN or ‘pure’ HII starburst regions where
UIB carriers can be destroyed by photodissociation. However, contrary to starburst spectra, typical AGN spectra present a
strong hot continuum below 9 μm originating from hot dust heated by the AGN radiation field. An extrapolation of this diagnostic
towards other mid-IR observations should improve our knowledge of the AGN/starburst connection.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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