Bibcode
González-Martín, O.; Rodríguez-Espinosa, J. M.; Díaz-Santos, T.; Packham, C.; Alonso-Herrero, A.; Esquej, P.; Ramos-Almeida, C.; Mason, R.; Telesco, C.
Bibliographical reference
Astronomy and Astrophysics, Volume 553, id.A35, 16 pp.
Advertised on:
5
2013
Journal
Citations
76
Refereed citations
72
Description
Context. The unified model of active galactic nuclei (AGN) claims that
the properties of AGN depend on the viewing angle of the observer with
respect to a toroidal distribution of dust surrounding the nucleus. Both
the mid-infrared (MIR) attenuation and continuum luminosity are expected
to be related to dust associated with the torus. Therefore, isolating
the nuclear component is essential for studying the MIR emission of AGN.
Aims: This work is aimed at studying the MIR emission of AGN with
the highest spatial resolution available to date, isolating its
contribution from extended emission. We would like to address three
fundamental questions: (1) how important is the AGN contribution to the
MIR spectrum; (2) where dust attenuation arises; and (3) how does
spatial resolution affect these issues. Methods: We compiled all
the T-ReCS spectra (Gemini Observatory) available in the N-band for 22
AGN: 5 Type-1 and 17 Type-2 AGN. The high angular resolution of the
T-ReCS spectra allowed us to probe physical regions of 57 pc (median).
We used a novel pipeline called RedCan capable of producing flux- and
wavelength-calibrated spectra for the CanariCam (GTC) and T-ReCS
(Gemini) instruments. We measured the fine-structure [S IV] at 10.5
μm and the PAH at 11.3 μm line strengths, together with the
silicate absorption/emission features. We also compiled Spitzer/IRS
spectra to understand how spatial resolution influences the results. We
complemented our sample with the results of 19 VISIR/VLT spectra
(Paranal Observatory) and 20 nearby, highly obscured AGN (NH
> 1.5 × 1024 cm-2) Spitzer spectra. Results: The 11.3 μm PAH feature is only clearly detected in the
nuclear spectra of two AGN, while it is more common in the Spitzer data.
For those two objects, the AGN emission in NGC 7130 accounts for more
than 80% of the MIR continuum at 12 μm, while in the case of NGC 1808
the AGN does not dominate the MIR emission. This is confirmed by the
correlation between the MIR and X-ray continuum luminosities. The [S IV]
emission line at 10.5 μm, which is believed to originate in the
narrow line region, is detected in most AGN. We have found an
enhancement of the optical depth at 9.7 μm (τ9.7) in
the high-angular resolution data for higher values of NH.
Clumpy torus models reproduce the observed values only if the
host-galaxy properties are taken into account.
Appendix A is available in electronic form at http://www.aanda.org
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