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: http://www.stsci.edu/~kgordon/papers/2011A&A...531A.137H.html
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Aims: We present an analysis of a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of which the infrared (IR) emission is entirely dominated by emission associated with the active galactic nucleus. Methods: We present the 5-37 ЮМm Spitzer/IRS spectrum and broad wavelength spectral energy distribution (SED) of SAGE1CJ053634.78-722658.5, an IR point-source detected by Spitzer/SAGE. The source was observed in the SAGE-Spec program and was included to determine the nature of sources with deviant IR colours. The spectrum shows a redshifted (z = 0.14 ТБ 0.005) silicate emission feature with an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic hydrocarbon (PAH) emission bands. We compare the source with models of emission from dusty tori around AGNs. We present a diagnostic diagram that will help to identify similar sources based on Spitzer/MIPS and Herschel/PACS photometry. Results: The SED of SAGE1CJ053634.78-722658.5 is peculiar because it lacks far-IR emissiondue to cold dust and a clear stellar counterpart. We find that the SED and the IR spectrum can be understood as emission originating from the inner ~10 pc around an accreting black hole. There is no need to invoke emission from the host galaxy, either from the stars or from the interstellar medium, although a possible early-type host galaxy cannot be excluded based on the SED analysis. The hot dust around the accretion disk gives rise to a continuum, which peaks at 4 ЮМm, whereas the strong silicate features may arise from optically thin emission of dusty clouds within ~10 pc around the black hole. The weak PAH emission does not appear to be linked to star formation, as star formation templates strongly over-predict the measured far-IR flux levels. Conclusions: The SED of SAGE1CJ053634.78-722658.5 is rare in the local universe but may be more common in the more distant universe. The conspicuous absence of host-galaxy IR emission places limits on the far-IR emission arising from the dusty torus alone. Based on observations obtained with Spitzer.
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Copyright © 2012 Karl D. Gordon All Rights Reserved