Smooth and clumpy dust distributions in AGN: a direct comparison of two commonly explored infrared emission models

By A. Feltre, E. Hatziminaoglou, J. Fritz, A. Franceschini. 2012

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The geometry of dust distribution within the inner regions of active galactic nuclei (AGN) is still a debated issue and relates directly to the AGN unified scheme. Traditionally, models discussed in the literature assume one of the two distinct dust distributions in what is believed to be a toroidal region around the supermassive black holes: a continuous distribution, customarily referred to as smooth, and a concentration of dust in clumps or clouds, referred to as clumpy. In this paper we perform a thorough comparison between two of the most popular models in the literature, namely the smooth models by Fritz et al. and the clumpy models by Nenkova et al., in their common parameter space. Particular attention is paid to the silicate features at similar to 9.7 and similar to 18?mu m, the width of the infrared bump, the near-infrared index and the luminosity at 12.3?mu m, all previously reported as possible diagnostic tools to distinguish between the two dust distributions. We find that, due to different dust chemical compositions used in the two models, the behaviour of the silicate features at 9.7 and 18?mu m is quite distinct between the two models. The width of the infrared bump and the peak of the infrared emission can take comparable values; their distributions do, however, vary. The near-infrared index is also quite different, due partly to the primary sources adopted by the two models. Models with matched parameters do not produce similar spectral energy distributions (SEDs) and virtually no random parameter combinations can result in seemingly identical SEDs.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/bc56da5f48013d5062b28c1331a98242e2d7112d

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Citations in the corpus

• Revisiting the Unified Model of Active Galactic Nuclei (2015, background): “The Feltre et al. (2012) work is an illuminating comparison of the first two types and the work of Lira et al. (2013) provides a comparison of two clumpy torus models based on fitting the spectra of type-II AGNs.”
• The WISE AGN Catalog (2017, background): “…toroidally distributed around the central engine (e.g., Krolik & Begelman 1988; Nenkova et al. 2002, 2008; Elitzur & Shlosman 2006; Tristram et al. 2007), although a number of uncertainties remain about the exact properties and distribution of the dust (e.g., Feltre et al. 2012; Netzer 2015).”
• The dusty torus in the Circinus galaxy: a dense disk and the torus funnel (2013, background): “Most torus models were designed to correctly reproduce the infrared spectral energy distributions (SEDs) of AGN and the silicate feature at 10 μm.”
• MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. II. PROPERTIES OF WISE-SELECTED ACTIVE GALACTIC NUCLEI IN THE NDWFS BOÖTES FIELD (2012, background): “…of the Si 9.7µm absorption feature typical of ULIRGs may be present in a few cases (W1427+3408, W1431+3525, W1432+3523 and W1432+3526), causing discrepancies between the models and the data, although this feature may also be observed in AGN under certain conditions (see, e.g., Feltre et al. 2012).”
• Tracing the cosmic growth of supermassive black holes to z ∼ 3 with Herschel (2014, methodology): “The AGN library of templates (Feltre et al. 2012; see also Fritz et al. 2006) includes around 2400 models, each one analysed for ten different lines of sight θ, uniformly distributed in θ from edge-on to face-on.”
• x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared (2020, unknown): “Following Duras et al. (2017), we update SKIRTOR with a new disk SED (Feltre et al. 2012) that is supported by observations, i.e. λLλ ∝ λ2 8 ≤ λ < 50 [nm] λ0.”
• Constraining the properties of AGN host galaxies with spectral energy distribution modelling (2015, methodology): “The second one is that it has been shown in Feltre et al. (2012) that the smooth torus library of Fritz et al. (2006) is highly degenerated with the clumpy torus library of Nenkova et al. (2008).”
• Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths (2015, background): “The power-law indices at longer wavelengths in expression (5) are taken from Feltre et al. (2012).”
• Active galactic nuclei: what’s in a name? (2017, background): “…feature at 9.7 µm in AGN, for example, seem to favour models where the dust is most prominently clumpy (Nenkova et al. 2008; Nikutta et al. 2009; Hatziminaoglou et al. 2015), but Feltre et al. (2012) has argued that observations are not yet able to discriminate between the different models.”
• Panchromatic spectral energy distributions of Herschel sources (2013, methodology): “The da Cunha et al. (2008) original code is now combined with the Fritz et al. (2006) AGN torus library (see also Feltre et al. 2012).”
• Universal bolometric corrections for active galactic nuclei over seven luminosity decades (2020, methodology): “In D17 the fit was performed with three emission components: 1. the accretion disk plus torus emission (using a combination of models by Feltre et al. (2012) and Stalevski et al. 2016), 2. the cold dust emission connected to the galactic star formation activity (modeled as a modified blackbody), 3.…”
• Modelling and interpreting spectral energy distributions of galaxies with BEAGLE (2016, methodology): “Finally, to extend the capabilities of the BEAGLE tool at mid- and far-infrared wavelengths, we also plan to include models to describe the emission from dust heated by stars (da Cunha et al. 2008) and an AGN (Fritz, Franceschini & Hatziminaoglou 2006; Feltre et al. 2012).”
• The Herschel* PEP/HerMES luminosity function - I. Probing the evolution of PACS selected Galaxies to z ≃ 4 (2013, methodology): “…presence of a possible AGN component, Berta et al. (2013) have developed a modified version of the MAGPHYS code by adding a torus component to the modelled SED emission, combining the Da Cunha et al. (2008) original code with the Fritz et al. (2006) AGN torus library (see also Feltre et al. 2012).”