J/ApJ/803/109 Spitzer/IRS AGN spectral decomposition (Hernan-Caballero+, 2015)
Resolving the AGN and host emission in the mid-infrared using
a model-independent spectral decomposition.
Hernan-Caballero A., Alonso-Herrero A., Hatziminaoglou E., Spoon H.W.W.,
Ramos Almeida C., Diaz Santos T., Honig S.F., Gonzalez-Martin O., Esquej P.
<Astrophys. J., 803, 109 (2015)>
=2015ApJ...803..109H 2015ApJ...803..109H
ADC_Keywords: Active gal. nuclei ; Spectra, infrared ; Models
Keywords: galaxies: active; galaxies: Seyfert; galaxies: starburst;
infrared: galaxies; methods: data analysis; techniques: spectroscopic
Abstract:
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 0.12dex 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.
Description:
To demonstrate the power of our decomposition method, we select a
sample of local active galaxies for which there is available
Spitzer/IRS spectroscopy as well as ground-based MIR high
angular-resolution imaging. Our parent sample is drawn from the
sub-arcsecond-resolution MIR imaging atlas of local AGNs presented in
Asmus et al. (2014, J/MNRAS/439/1648). We performed a search by
coordinates in the CASSIS (Lebouteiller et al. 2011ApJS..196....8L 2011ApJS..196....8L)
version 6. We used a 10" search radius and found IRS spectra for 157
of the 253 sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 122 157 Parameters for best-fitting decomposition model
table2.dat 104 157 AGN properties derived from decomposition
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See also:
J/MNRAS/439/1648 : Subarcsecond mid-infrared atlas of local AGN (Asmus+, 2014)
J/MNRAS/414/500 : Spitzer/IRS ATLAS project source (Hernan-Caballero+, 2011)
J/ApJ/709/1257 : Spitzer-IRS spectra of Seyfert gal. II. (Tommasin+, 2010)
J/MNRAS/398/1165 : AGN in nearby galaxies (Goulding+, 2009)
J/ApJS/182/628 : Spitzer quasar and ULIRG evolution study (Veilleux+, 2009)
J/MNRAS/395/1695 : Spitzer MIR spectroscopy of LIRGs (Hernan-Caballero+, 2009)
J/MNRAS/386/1252 : SWIRE/SDSS quasars (Hatziminaoglou+, 2008)
J/ApJ/656/770 : Mid-IR spectrum of star-forming galaxies (Smith+, 2007)
J/A+A/418/465 : Mid-infrared and hard X-ray emission in AGN (Lutz+, 2004)
http://denebola.org/ahc/deblendIRS/ : Decomposition code and templates
available on DeblendIRS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name NED Name of AGN
25- 30 F6.4 --- zsp [0/0.3] Spectroscopic Redshift (G1)
32- 54 A23 --- PAH PAH template galaxy name
56- 60 F5.3 --- fPAH [0/1] PAH fraction in mid-IR integrated luminosity
62- 85 A24 --- AGN AGN template galaxy name
87- 91 F5.3 --- fAGN [0/1] AGN fraction in mid-IR integrated luminosity
93-103 A11 --- STR Stellar template galaxy name
105-109 F5.3 --- fSTR [0/1] STR fraction in mid-IR integrated luminosity
111-116 F6.2 --- chi2r [0/126] Reduced χ2 of decomposition fit
118-122 F5.3 --- CVrmse [0/0.52] Coefficient of variation of rmse (1)
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Note (1): the flux is assumed to be a linear combination of 3 templates for
PAH, AGN and STR. The coefficient of variation of the root-mean-square
error CVRMSE characterizes the accuracy of the fit (increases with
the noise). If Fi is the observed flux and fi the fitted flux:
each f = a fPAH + b fAGN + c fSTR
CVRMSE = sqrt(Σ(Fi-fi)2/N)/(ΣFi/N)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name NED Name
25- 30 F6.4 --- zsp [0.0002/0.3] Spectroscopic Redshift (G1)
32- 36 F5.2 [10-7W] logL6 [37.5/46] Monochromatic AGN luminosity at 6um
38- 42 F5.2 [10-7W] b_logL6 [37/46]? The 1σ lower value in logL6
44 A1 --- l_logL6 Limit Flag on logL6 (2)
45- 49 F5.2 [10-7W] B_logL6 [37.6/46] The 1σ upper value in logL6
51- 55 F5.2 [10-7W] logL12 [37.3/46] Monochromatic AGN luminosity at 12um
57- 61 F5.2 [10-7W] b_logL12 ? 1σ lower value in logL12
63 A1 --- l_logL12 Limit Flag on logL12 (2)
64- 68 F5.2 [10-7W] B_logL12 The 1σ upper value in logL12
70- 74 F5.2 --- alpha [-3/0.8] AGN Emission spectral 8.1-12.5um index
76- 80 F5.2 --- b_alpha The 1σ lower value in alpha
82- 86 F5.2 --- B_alpha The 1σ upper value in alpha
88- 92 F5.2 --- Ssil [-4/0.5] AGN Silicate 9.7µm strength
94- 98 F5.2 --- b_Ssil The 1σ lower value in Ssil
100-104 F5.2 -- B_Ssil The 1σ upper value in Ssil
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Note (2): Indicates that there 1σ value range is actually just
a 1σ upper limit; the lower value is then blank.
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Global notes:
Note (G1): Redshifts have been taken from NED and confirmed using the
Spitzer/IRS spectrum with the method presented in
Hernan-Caballero et al. (2012MNRAS.427..816H 2012MNRAS.427..816H).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 29-Jul-2015