Revisiting the infrared spectra of active galactic nuclei with a new torus emission model

By J. Fritz, A. Franceschini, E. H. D. D. Astronomia, Padova, Instituto de Astrof'isica de Canarias, Tenerife. 2005

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We describe improved modelling of the emission by dust in a toroidal-like structure heated by a central illuminating source within active galactic nuclei (AGNs). We have chosen a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type 1 AGNs. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type 1 and type 2) sources using archival optical and infrared data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-infrared luminosity is found to be higher in type 1 sources, with all the type 2 requiring a substantial contribution from a circumnuclear starburst. Our results appear in agreement with the AGN unified scheme, because the distributions of key parameters of the torus models turn out to be compatible for type 1 and type 2 AGNs. Further support to the unification concept comes from comparison with medium-resolution infrared spectra of type 1 AGNs by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 μm, which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGNs characterized by high equatorial optical depths (A v ≃ 100), moderate sizes (R max < 100 pc) and very high covering factors (f ≃ 80 per cent) on average.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

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Citations in the corpus

• Modelling the spectral energy distribution of galaxies - V. The dust and PAH emission SEDs of disk galaxies (2010, methodology): “…1992, Efstathiou & Rowan-Robinson 1990, Granato & Danese 1994, Efstathiou & RowanRobinson 1995, Nenkova et al. 2002, Dullemond & van Bemmel 2005, Fritz et al. 2006, Hönig et al. 2006, Schartmann et al. 2008,Nenkova et al. 2008. keeping with the decoding approach that we have adopted, we…”
• The dusty heart of nearby active galaxies. II. From clumpy torus models to physical properties of dust around active galactic nuclei (2009, background): “Initially, most authors used smooth dust distributions with different kind of radial and vertical density profiles (e.g. Pier & Krolik 1993; Granato & Danese 1994; Efstathiou & Rowan-Robinson 1995; Schartmann et al. 2005; Fritz et al. 2006).”
• Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources (2006, background): “…suggest that the dusty torus becomes optically thin at wavelengths in the FIR (see, e.g., Pier & Krolik 1992; Granato & Danese 1994; Granato et al. 1997; Nenkova et al. 2002; Schartmann et al. 2005; Fritz et al. 2006), suggesting a direct test of FR II galaxy/quasar orientation-based unification.”
• The Distribution of Silicate Strength in Spitzer Spectra of AGNs and ULIRGs (2006, methodology): “The distribution will constrain the models of AGNs (e.g., Efstathiou 2006; Fritz et al. 2006; Dullemond & van Bemmel 2005; Nenkova et al. 2002; Pier & Krolik 1993, 1992) and in turn provide insights into the geometry of the dusty structure, the optical depth of the clouds, and the filling factor…”
• Constraining the properties of AGN host galaxies with spectral energy distribution modelling (2015, methodology): “For these parameters the overall systematic trends in Figure 12 are similar to those observed in Figure 6 where the modeling of the mock galaxies is made with Fritz et al. (2006) models.”
• AGN Dusty Tori. II. Observational Implications of Clumpiness (2008, background): “In contrast, smoothdensity models require viewing angles 22 Y30 above the equatorial plane in order to bring into view the warm face of the torus backside (Granato et al. 1997; Gratadour et al. 2003; Fritz et al. 2006).”
• Active galactic nuclei: what’s in a name? (2017, background): “distributed in the torus (Pier and Krolik 1992; Dullemond and van Bemmel 2005; Fritz et al. 2006), whether it is clumpy in the form of optically and geometrically thick clouds (Krolik and Begelman 1988; Nenkova et al.”
• CIGALE: a python Code Investigating GALaxy Emission (2018, methodology): “…page 16 of 33 A103, page 17 of 33 gas (Inoue 2011), attenuation by dust (Calzetti et al. 2000; Charlot & Fall 2000) and re-emission of the energy at longer wavelengths (Draine & Li 2007; Casey 2012; Dale et al. 2014), active nuclei (Fritz et al. 2006; Dale et al. 2014), and the IGM (Meiksin 2006).”
• The dust covering factor in active galactic nuclei (2016, methodology): “3), while keeping the optical depth and the outer–to–inner radius ratio (Rout/Rin) constant, the shape of the resulting SED will remain exactly the same, only scaled along the flux axis (Ivezic & Elitzur 1997; Fritz et al. 2006).”
• Defining the intrinsic AGN infrared spectral energy distribution and measuring its contribution to the infrared output of composite galaxies (2011, methodology): “The range of input parameters of the former (i.e., continuous) model are given in table 1 of Fritz et al. (2006).”
• Dust covering factor, silicate emission, and star formation in luminous QSOs (2007, background): “InitialSpitzer detections of silicate emission relaxed the torus model assumptions (Fritz et al., 2006), but more detailed investigations revealed a complex scenario.”
• 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, methodology): “Besides the lack of X-ray fitting capability, CIGALE’s current AGN model (Fritz et al. 2006), which covers the UV to IR, also has some other disadvantages.”
• Luminous Infrared Galaxies with the Submillimeter Array. I. Survey Overview and the Central Gas to Dust Ratio (2008, methodology): “Fritz et al. (2006) fit the infrared spectral energy distribution with a type II AGN model; however, these model fits suggest that starburst – 33 – emission is likely the dominant component at 880 µm.”
• Dusty Star Forming Galaxies at High Redshift (2014, methodology): “…and Siebenmorgen, 2009; Nenkova et al., 2002; Dullemond and van Bemmel, 2005; Piovan et al., 2006; Nenkova et al., 2008; Takagi et al., 2003; Fritz et al., 2006; Hönig et al., 2006; Schartmann et al., 2008), but here we try to focus on the techniques which have been most commonly employed…”