The Detection of Silicate Emission from Quasars at 10 and 18 Microns

Hao, Lei; Spoon, H. W. W.; Sloan, G. C.; Marshall, J. A.; Armus, L.; Tielens, A. G. G. M.; Sargent, B.; Bemmel, I. M. van; Charmandaris, V.; Weedman, D. W.; Houck, J. R.

doi:10.1086/431227

Cited by 188 publications

(248 citation statements)

References 29 publications

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“…Fig. 1 in Hao et al 2005). The measurement on 2007 Feb. 07 has a relatively steep, increasing spectrum and flux values consistent with the Spitzer spectrum at the long wavelength end.…”

Section: C 273supporting

confidence: 68%

“…5 from 2007 Feb. 28 and 2007 Jun. 28 as well as the spectrum in Hao et al 2005Hao et al from 2004 Jan. 06) show variations of less than 10% and are also consistent with the VISIR and TIMMI2 photometries. Hence we see no evidence for any significant variability during our observations.…”

Section: C 273supporting

confidence: 67%

“…Indeed, for most AGN, including the sources of the snapshot survey, a silicate absorption or emission feature is present in high signal to noise Spitzer spectra, even if the signature is very weak (see e.g. Hao et al 2005;Weedman et al 2005;Buchanan et al 2006). The MIDI spectra presented here only show indications for silicate absorption or emission for three sources of the snapshot survey: MCG-05-23-016 (feature in absorption, Seyfert 2 galaxy), Mrk 1239 (feature in emission, Seyfert 1.5 galaxy) and 3C 273 (also in emission, type 1 quasar).…”

Section: Spectral Featuresmentioning

confidence: 99%

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Parsec-scale dust distributions in Seyfert galaxies

Tristram¹,

Raban

Meisenheimer

et al. 2009

A&A

113

106

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Aims. The emission of warm dust dominates the mid-infrared spectra of active galactic nuclei (AGN). Only interferometric observations provide the necessary angular resolution to resolve the nuclear dust and to study its distribution and properties. The investigation of dust in AGN cores is hence one of the main science goals for the MID-infrared Interferometric instrument MIDI at the VLTI. As the first step, the feasibility of AGN observations was verified and the most promising sources for detailed studies were identified. Methods. This was carried out in a "snapshot survey" with MIDI using Guaranteed Time Observations. In the survey, observations were attempted for 13 of the brightest AGN in the mid-infrared which are visible from Paranal. Results. The results of the three brightest, best studied sources have been published in separate papers. Here we present the interferometric observations for the remaining 10, fainter AGN. For 8 of these, interferometric measurements could be carried out. Size estimates or limits on the spatial extent of the AGN-heated dust were derived from the interferometric data of 7 AGN. These indicate that the dust distributions are compact, with sizes on the order of a few parsec. The derived sizes roughly scale with the square root of the luminosity in the mid-infrared, s ∝ √ L MIR , with no clear distinction between type 1 and type 2 objects. This is in agreement with a model of nearly optically thick dust structures heated to T ∼ 300 K. For three sources, the 10 μm feature due to silicates is tentatively detected either in emission or in absorption. Conclusions. The faint AGN of the snapshot survey are at the sensitivity limit of observations with MIDI. Thus, the data set presented here provides a good insight into the observational difficulties and their implications for the observing strategy and data analysis. Based on the results for all AGN studied with MIDI so far, we conclude that in the mid-infrared the differences between individual galactic nuclei are greater than the generic differences between type 1 and type 2 objects.

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“…Fig. 1 in Hao et al 2005). The measurement on 2007 Feb. 07 has a relatively steep, increasing spectrum and flux values consistent with the Spitzer spectrum at the long wavelength end.…”

Section: C 273supporting

confidence: 68%

Section: C 273supporting

confidence: 67%

Section: Spectral Featuresmentioning

confidence: 99%

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Parsec-scale dust distributions in Seyfert galaxies

Tristram¹,

Raban

Meisenheimer

et al. 2009

A&A

113

106

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“…For a silicate temperature of 260 K -consistent with the range found for other quasars (e.g. Hao et al 2005) -the simulated spectrum reproduces the observed strengths of the 9.7 and 18 μm features.…”

Section: Silicate Emissionsupporting

confidence: 83%

TheSpitzerdiscovery of a galaxy with infrared emission solely due to AGN activity

Hony

Kemper

Woods

et al. 2011

A&A

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Aims. We present an analysis of a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of which the infrared (IR) emission is entirely dominated by emission associated with the active galactic nucleus. Methods. We present the 5−37 μm Spitzer/IRS spectrum and broad wavelength spectral energy distribution (SED) of SAGE1CJ053634.78-722658.5, an IR point-source detected by Spitzer/SAGE. The source was observed in the SAGE-Spec program and was included to determine the nature of sources with deviant IR colours. The spectrum shows a redshifted (z = 0.14 ± 0.005) silicate emission feature with an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic hydrocarbon (PAH) emission bands. We compare the source with models of emission from dusty tori around AGNs. We present a diagnostic diagram that will help to identify similar sources based on Spitzer/MIPS and Herschel/PACS photometry. Results. The SED of SAGE1CJ053634.78-722658.5 is peculiar because it lacks far-IR emission due to cold dust and a clear stellar counterpart. We find that the SED and the IR spectrum can be understood as emission originating from the inner ∼10 pc around an accreting black hole. There is no need to invoke emission from the host galaxy, either from the stars or from the interstellar medium, although a possible early-type host galaxy cannot be excluded based on the SED analysis. The hot dust around the accretion disk gives rise to a continuum, which peaks at 4 μm, whereas the strong silicate features may arise from optically thin emission of dusty clouds within ∼10 pc around the black hole. The weak PAH emission does not appear to be linked to star formation, as star formation templates strongly over-predict the measured far-IR flux levels. Conclusions. The SED of SAGE1CJ053634.78-722658.5 is rare in the local universe but may be more common in the more distant universe. The conspicuous absence of host-galaxy IR emission places limits on the far-IR emission arising from the dusty torus alone.

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“…For type 1 AGN, the situation is less clear. Early reports of the silicate emission feature in a number of quasars discussed that the central wavelength might be shifted towards longer wavelengths (Hao et al 2005;Siebenmorgen et al 2005;Sturm et al 2005). Recently Nikutta et al (2009) suggested that radiative transfer effects might cause the silicate emission feature in AGN to shift towards longer wavelengths.…”

Section: The N-band Silicate Feature In Agn At High Spatial Resolutionmentioning

confidence: 99%

The dusty heart of nearby active galaxies

Hoenig

Kishimoto

Gandhi

et al. 2010

A&A

154

135

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In a series of papers, we aim at stepping towards characterizing physical properties of the AGN dust torus by combining IR highspatial resolution observations with 3D clumpy torus models. In this first paper, we present mid-IR imaging and 8−13 μm lowresolution spectroscopy of nine type 1 and ten type 2 AGN. The observations were carried out with the VLT/VISIR mid-IR imager and spectrograph and can be considered the largest currently available mid-infrared spectro-photometric data set of AGN at spatial resolution < ∼ 100 pc. These data resolve scales at which the emission from the dust torus dominates the overall flux, and emission from the host galaxy (e.g. star-formation) is resolved out in most cases. The silicate absorption features are moderately deep and emission features, if seen at all, are shallow. The strongest silicate emission feature in our sample shows some notable shift of the central wavelength from the expected 9.7 μm (based on ISM extinction curves) to ∼10.5 μm. We compare the observed mid-IR luminosities of our objects to AGN luminosity tracers (X-ray, optical and [O iii] luminosities) and find that the mid-IR radiation is emitted quite isotropically. In two cases, IC 5063 and MCG-3-34-64, we find evidence for extended dust emission in the narrow-line region. We confirm the correlation between observed silicate feature strength and Hydrogen column density, which was recently found in Spitzer data at lower spatial resolution. In a further step, our 3D clumpy torus model has been used to interpret the data. We show that the strength of the silicate feature and the mid-IR spectral index α can be used to get reasonable constraints on the radial dust distribution of the torus and the average number of clouds N 0 along an equatorial line-of-sight in clumpy torus models. The mid-IR spectral index α is almost exclusively determined by the radial dust distribution power-law index a, while the silicate feature depth mostly depends on N 0 and the torus inclination. A comparison of model predictions to our type 1 and type 2 AGN reveals that average parameters of a = −1.0 ± 0.5 and N 0 = 5 − 8 are typically seen in the presented sample, which means that the radial dust distribution is rather shallow. As a proof-of-concept of this method, we compared the model parameters derived from α and the silicate feature strength to more detailed studies of full IR SEDs and interferometry and found that the constraints on a and N 0 are consistent. Finally, we may have found evidence that the radial structure of the torus changes from low to high AGN luminosities towards steeper dust distributions, and we discuss implications for the IR size-luminosity relation.

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The Detection of Silicate Emission from Quasars at 10 and 18 Microns

Cited by 188 publications

References 29 publications

Parsec-scale dust distributions in Seyfert galaxies

Parsec-scale dust distributions in Seyfert galaxies

TheSpitzerdiscovery of a galaxy with infrared emission solely due to AGN activity

The dusty heart of nearby active galaxies

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