The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus Models.

Transcription

1 The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus Models. Nancy Levenson (UK) Jose Miguel Rodríguez Espinosa (IAC) Almudena Alonso Herrero (CSIC) Andrés Asensio Ramos (IAC) James Radomski (Gemini) Chris Packham (UF) Scott Fisher (Gemini) Charles Telesco (UF)

2 Introduction Seyfert galaxies : Seyfert 1 & Seyfert 2 => Unification Model Seyfert 1 : Permitted lines widths ~ 104 km/s (BLR) Permitted & forbidden lines widths ~ 500 km/s (NLR) Seyfert 2 : Permitted & forbidden lines widths ~ 500 km/s (NLR) Molecular torus = key piece of the unification scheme not resolved yet! Urry and Padovani (1995)

3 Unified Model : The Torus Torus dust grains absorb optical & UV photons from the central engine, re-radiating them in the IR, peaking at mid- IR (7-26 µm). Compact-torus models : uniform dust density distribution (e.g., Pier & Krolik 1992, 1993; Granato & Danese 1994; Efstathiou & Rowan-Robinson 1995; Granato et al. 1997). Pier & Krolik (1992) Pier & Krolik (1993)

4 Compact vs clumpy models Compact-torus models predict cool material responsible for far-ir emission located far from the central engine. Tori of ~ 100 pc scale!!! - Incompatible with observations. Circinus : R < 2 pc (Packham et al. 2005) Centaurus A : R < 1.6 pc (Radomski et al. 2008) Problems reproducing the observed SEDs of AGN groups (Alonso- Herrero et al. 2003). Not able to reproduce the observed intensities of the silicate bands in Type 1 and 2 Seyferts (Roche et al. 1991). Fail in reproducing the large optical depths along the LOS revealed from X-ray observations (Simpson et al. 1994). Clumpy torus models solve those problems (Krolik & Begelman (1988) => Nenkova et al. 2002; Dullemond & Van Bemmel 2005; Fritz et al. 2006; Elitzur & Shlosman 2006; Ballantyne et al. 2006).

5 Clumpy Dusty Torus Models Dust distributed in clumps instead of homogeneusly filling the torus volume (Nenkova et al. 2008a,b; Hönig et al. 2006; Schartmann et al. 2008, 2009).

6 Isolation of the torus emission Reprocessed radiation from the torus re-emitted in the infrared. Infrared range (particularly the mid-ir) key to constrain the parameters of torus models. Goal: isolation of the torus emission. Large aperture data (e.g. ISO, Spitzer, IRAS) contaminated with circunnuclear stellar emission. High-spatial resolution infrared observations (e.g., CanariCam, T-ReCS, Michelle) key to isolate the nonstellar nuclear emission = torus emission.

7 Our work New ground-based subarcsecond resolution mid-ir imaging data for 18 nearby Seyfert galaxies. Unresolved mid-infrared fluxes through PSF subtraction. Compilation of near-ir nuclear fluxes from the literature of similar resolutions as our mid-ir data. Construction of SEDs that the AGN dominates, relatively uncontaminated by starlight, representative of the torus emission. SED fitting with the Nenkova et al. (2008a,b) clumpy models, trying to constrain the torus parameters.

8 The sample 12 Sy2, 2 Sy1.9, one Sy1.8, 2 Sy1.5 and one Sy1.

9 Mid-IR observations Mid-IR imaging obtained with three instruments: OSCIR at CTIO (0.183 /pixel) OSCIR at Gemini North (0.089 /pixel) T-ReCS at Gemini South (0.089 /pixel) Michelle at Gemini North ( /pixel) All objects observed at the N (8-10 µm) and Q (~18 µm) bands.

10 NGC3081 (Sy2) at Si2 (8.8 µm) and Qa (18.3 µm) T-ReCS filters.

11 PSF subtraction PSF stars observed before and after the science object observation (e.g. NGC 4388 Sy2).

12 Average Sy2 SED Combination of 7 pure Sy2 SEDs to construct an average template (CenA, Circinus, IC5063, Mrk573, NGC1386, and NGC3081). Composite objects and seeing-limited near-ir data excluded.

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14 Comparison with intermediate-type Seyferts Sy2 SEDs are steeper than those of intermediate-type Seyferts. Average Sy2 template => α = 3.1 +/- 0.9 Agreement with Sy1.8 and Sy1.9 => α = 2.0 +/- 0.4 Alonso-Herrero et Sy1.5 => α = 1.6 +/- 0.3 al. (2003) IR slopes correlated with Seyfert type, but we find a variety of SED shapes => contrary to early models predictions (that also predict α > 4 for Sy2). Clumpy torus models seem the most indicated to reproduce our SEDs.

15 SED Fitting with the Clumpy models: the Clumpy Database Asensio Ramos & Ramos Almeida (2009, ApJ, 696, 2075) developed a code based on Bayesian inference to fit the clumpy models of the Kentucky database. Machine learning techniques based on PCA decomposition + Neural networks to approximate the Clumpy Database (6 parameters-based models). Solution to the Clumpy Database degeneracy Possibility of interpolating within the database Result of the fit = probability distribution functions for each parameter Working on simultaneous fit of both SED + spectrum

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17 Circinus Mid-IR data from T-ReCS/Gemini (Packham et al. 2005) T-ReCS Q T-ReCS N NACO M NACO L Near-IR data from NACO/VLT (Prieto et al. 2004) NACO J

18 σ = width of the angular distribution of clouds Y = torus radial extent (R o /R d ) N 0 = number of clouds along equatorial plane q = index of the radial density profile Τv = optical depth of a single cloud i = inclination angle of the torus Circinus σ N 0 q i τv Av

19 Results from Sy2 modeling Number of clouds is within N 0 =[5,15]. Width of the angular distrib. of clouds is within σ=[50º,75º]. High values of the inclination angle of the torus (i>40º). Relatively low values of the optical depth per cloud (τ V <100). The radial extent of the torus (Y) results unconstrained from the fits => SED fitting poorly constrain the torus size. The outer torus contains the coolest material => high angular resolution measurements at λ > 15 µm are needed to reveal significant variations in Y.

20 Results from Intermediate-type Seyfert modelling For Sy1.5 AGN contribution must be added = torus + AGN + extinction law to fit the near-ir excess. Intermediate type fits result in lower N 0 than Sy2 (N 0 = [1,7]) and lower σ = [25º,50º]. Low values of the inclination angle are found for Sy1.5 (i < 50º). The 10 µm silicate feature appears in shallow emission or absent.

21 Results from Intermediate-type Seyfert modelling Silicate feature predicted in shallow emission

22 Predictions from the Models: AGN Luminosities Vertical shift applied in the fitting => AGN intrinsic luminosity Integration of the whole SED => torus bolometric luminosity Estimation of the fraction of AGN luminosity reprocessed by the torus. Sources with large width tori and with high number of clouds are more efficient reprocessing the radiation = Sy2. Seyfert 2 galaxies => f = 0.6 +/- 0.3 Intermediate-types => f = 0.4 +/- 0.3

23 Predictions from the Models: AGN Luminosities AGN intrinsic luminosity => allows to calculate the outer radius of the torus (R o ) by fixing Y = 15. R o = Y x R d = 15 x 0.4 x (L AGN / ) 0.5 pc, if T sub = 1500 K. We find tori to be confined to scales less than 5 pc.

24 Conclusions Clumpy models reproduce the high spatial resolution SEDs, implying that our nuclear fluxes are dominated by nonstellar emission coming from the torus. Near- to mid-ir SED fitting poorly constrains the radial extent of the torus. We find the number of clouds along equatorial rays within the interval N 0 =[5,15], and edge-on geometries more probable than face-on views for Sy2. The fitted models predict the 10 µm silicate feature in shallow absorption for most of Sy2 and in shallow emission or absernt for most of intermediate-type Seyferts.

25 Conclusions The values of N 0 and σ resulting from the fits of intermediatetype Seyferts are lower than those of Sy2. The inclination angles of Sy1.5 tori are low (i < 50º). From the derived values of bolometric AGN luminosities and torus luminosities, Sy2 seem to reprocess the nuclear radiation more efficiently than intermediate-type Seyferts. Are Type-1 tori intrinsically different than those of Type-2??? => first indication of this possibility supported by Moshe s comparison plot. According to the AGN intrinsic luminosities derived from the models, we find tori to be confined to scales less than 5 pc.

26 The future CanariCam A comparable sample of Type 1 and 2 Seyferts needs to be observed in the mid-ir with high angular resolution to compare their tori properties properly = CanariCam. Near-IR high-res. observations (e.g., NICMOS/HST) in at least two filters (J and K) will be requested. We have the machinery to fit the infrared SEDs with the clumpy models (BayesClumpy). Simultaneous fits of SED + CanariCam spectra will constrain even more the model parameters = crucial test for the unification models.