AGNfitter: a Bayesian MCMC approach to fitting spectral energy distributions of AGNs

Journal Article · Sat Dec 10 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/833/1/98· OSTI ID:22868341

Calistro Rivera, Gabriela; Hennawi, Joseph F.; Hogg, David W. ^[1]; Lusso, Elisabeta ^[2]

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1. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
2. INAF Osservatorio Astrofisico di Arcetri, I-50125 Florence (Italy)

We present AGNfitter, a publicly available open-source algorithm implementing a fully Bayesian Markov Chain Monte Carlo method to fit the spectral energy distributions (SEDs) of active galactic nuclei (AGNs) from the sub-millimeter to the UV, allowing one to robustly disentangle the physical processes responsible for their emission. AGNfitter makes use of a large library of theoretical, empirical, and semi-empirical models to characterize both the nuclear and host galaxy emission simultaneously. The model consists of four physical emission components: an accretion disk, a torus of AGN heated dust, stellar populations, and cold dust in star-forming regions. AGNfitter determines the posterior distributions of numerous parameters that govern the physics of AGNs with a fully Bayesian treatment of errors and parameter degeneracies, allowing one to infer integrated luminosities, dust attenuation parameters, stellar masses, and star-formation rates. We tested AGNfitter’s performance on real data by fitting the SEDs of a sample of 714 X-ray selected AGNs from the XMM-COSMOS survey, spectroscopically classified as Type1 (unobscured) and Type2 (obscured) AGNs by their optical–UV emission lines. We find that two independent model parameters, namely the reddening of the accretion disk and the column density of the dusty torus, are good proxies for AGN obscuration, allowing us to develop a strategy for classifying AGNs as Type1 or Type2, based solely on an SED-fitting analysis. Our classification scheme is in excellent agreement with the spectroscopic classification, giving a completeness fraction of ∼86% and ∼70%, and an efficiency of ∼80% and ∼77%, for Type1 and Type2 AGNs, respectively.

• OSTI ID: 22868341
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 833; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ALGORITHMS
CLASSIFICATION
COSMIC DUST
DENSITY
EFFICIENCY
EMISSION
ENERGY SPECTRA
GALAXIES
GALAXY NUCLEI
LUMINOSITY
MARKOV PROCESS
MASS
MONTE CARLO METHOD
QUASARS
STARS
STATISTICS
UNIVERSE
X RADIATION