Issue |
A&A
Volume 651, July 2021
|
|
---|---|---|
Article Number | A91 | |
Number of page(s) | 22 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202040043 | |
Published online | 21 July 2021 |
The dust-gas AGN torus as constrained from X-ray and mid-infrared observations
1
Instituto de Radioastronomía y Astrofísica (IRyA-UNAM), 3-72 (Xangari), 8701 Morelia, Mexico
e-mail: d.esparza@irya.unam.mx
2
Instituto de Astronomía (IA-UNAM), Mexico
3
Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n 18008, Granda, Spain
4
Instituto de Astrofísica de Canarias (IAC), C/Vía Líctea, s/n, 38205 La Laguna, Spain
5
Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Spain
6
Department of Physics, University of Oxford, Oxford OX1 3RH, UK
Received:
1
December
2020
Accepted:
20
April
2021
Context. In recent decades, several multiwavelength studies have been dedicated to exploring the properties of the obscuring material in active galactic nuclei (AGN). Various models have been developed to describe the structure and distribution of this material and constrain its physical and geometrical parameters through spectral fitting techniques. However, questions around the way in which torus mid-infrared (mid-IR) and X-ray emission are related remain unanswered.
Aims. In this work, we aim to study whether the dust continuum at mid-IR and gas reflection at X-rays have the same distribution in a sample of AGN.
Methods. We carefully selected a sample of 36 nearby AGN with NuSTAR and Spitzer spectra available that satisfy the following criteria: (1) the AGN component dominates the mid-IR spectra (i.e., the stellar and interstellar medium components contribute less than 50% to the spectrum), and (2) the reflection component contributes significantly to the X-ray spectrum. Furthermore, we discarded the sources whose reflection component could be produced by ionized material in the disk. We derived the properties of the nuclear dust and gas through a spectral fitting, using models developed for mid-IR and X-ray wavelengths assuming smooth and clumpy distributions for this structure.
Results. We find that a combination of smooth and clumpy distributions of gas and dust, respectively, is preferred for ∼80% of sources with good spectral fits according to the Akaike criterion. However, considering extra information about each individual source, such as the absorption variability, we find that ∼50% of our sources are best described by a clumpy distribution of both dust and gas. The remaining ∼50% of our sources can still be explained with a smooth distribution of gas and a clumpy distribution of dust. Furthermore, we explored the torus dust-to-gas ratio, finding that it is [0.01–1] times that of the interstellar medium.
Conclusions. The results presented in this paper suggest that the distribution of the gas and dust in AGN is complex. We find at least six scenarios to explain the observed properties of our sample. In these scenarios, three gas–dust distribution combinations are possible: clumpy–clumpy, smooth–smooth, and smooth–clumpy. Most of them are in agreement with the notion that gas could also be located in the dust-free region, which is consistent with the dust-to-gas ratio found.
Key words: galaxies: active / galaxies: Seyfert / X-rays: galaxies / infrared: galaxies
© ESO 2021
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