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Resolving the AGN and Host Emission in the Mid-infrared Using a Model-independent Spectral Decomposition

Hernán-Caballero, Antonio and Alonso-Herrero, Almudena and Hatziminaoglou, Evanthia and Spoon, Henrik W. W. and Ramos Almeida, Cristina and Díaz Santos, Tanio and Hönig, Sebastian F. and González-Martín, Omaira and Esquej, Pilar (2015) Resolving the AGN and Host Emission in the Mid-infrared Using a Model-independent Spectral Decomposition. Astrophysical Journal, 803 (2). Art. No. 109. ISSN 0004-637X.

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We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGNs) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method with no need to model extinction separately. We use full probability distribution functions to estimate expectation values and uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum with a 1σ dispersion of 0.12 dex in luminosity and typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGNs. This allows for unbiased studies of the AGN emission in intermediate- and high-redshift galaxies—currently inaccesible to ground-based observations—with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope. The decomposition code and templates are available at

Item Type:Article
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URLURL TypeDescription Paper
Alonso-Herrero, Almudena0000-0001-6794-2519
Spoon, Henrik W. W.0000-0002-8712-369X
Díaz Santos, Tanio0000-0003-0699-6083
Additional Information:© 2015 The American Astronomical Society. Received 2014 December 11; accepted 2015 February 12; published 2015 April 22. We thank the anonymous referee for useful comments that helped to improve this paper. A.H.-C. and A.A.-H. acknowledge funding by the Universidad de Cantabria Augusto González Linares programme and the Spanish Ministry of Economy and Competitiveness under grant AYA2012-31447, which is the party funded by the FEDER program. C.R.A. is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934). T.D.S was supported by ALPIA-CONICYI grant number 31130005. S.F.H. acknowledges support from the Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme (PIIF-GA-2013-623804). P.E. acknowledges support from the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA2012-31277. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, Caltech under NASA contract 1407. The Cornell Atlas of Spitzer/IRS Sources (CASSIS) is a product of the Infrared Science Center at Cornell University, supported by NASA and JPL.
Funding AgencyGrant Number
7th European Community Framework ProgrammePIIF-GA-2013-623804
Programa Nacional de Astronomía y AstrofísicaAYA2012-31277
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)31130005
Subject Keywords:galaxies: active; galaxies: Seyfert; galaxies: starburst; infrared: galaxies; methods: data analysis; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20150529-101846958
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Official Citation:Resolving the AGN and Host Emission in the Mid-infrared Using a Model-independent Spectral Decomposition Antonio Hernán-Caballero et al. 2015 ApJ 803 109
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57899
Deposited By: Jason Perez
Deposited On:01 Jun 2015 19:04
Last Modified:09 Mar 2020 13:19

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