Bibcode
González-Martín, Omaira; Masegosa, Josefa; Hernán-Caballero, Antonio; Márquez, Isabel; Ramos-Almeida, C.; Alonso-Herrero, Almudena; Aretxaga, Itziar; Rodriguez-Espinosa, J. M.; Acosta-Pulido, J. A.; Hernández-García, Lorena; Esparza-Arredondo, Donaji; Martínez-Paredes, Mariela; Bonfini, Paolo; Pasetto, Alice; Dultzin, Deborah
Bibliographical reference
The Astrophysical Journal, Volume 841, Issue 1, article id. 37, 19 pp. (2017).
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5
2017
Journal
Citations
26
Refereed citations
24
Description
Several authors have claimed that less luminous active galactic nuclei
(AGNs) are not capable of sustaining a dusty torus structure. Thus, a
gradual resizing of the torus is expected when the AGN luminosity
decreases. Our aim is to examine mid-infrared observations of local AGNs
of different luminosities for the gradual resizing and disappearance of
the torus. We applied the decomposition method described by
Hernán-Caballero et al. to a sample of ∼100 Spitzer/IRS
spectra of low-luminosity AGNs and powerful Seyferts in order to
decontaminate the torus component from other contributors. We have also
included Starburst objects to ensure secure decomposition of the
Spitzer/IRS spectra. We have used the affinity propagation (AP) method
to cluster the data into five groups within the sample according to
torus contribution to the 5–15 μm range ({C}{torus})
and bolometric luminosity ({L}{bol}). The AP groups show a
progressively higher torus contribution and an increase of the
bolometric luminosity from Group 1 ({C}{torus}∼ 0 % and
{log}({L}{bol})∼ 41) up to Group 5
({C}{torus}∼ 80 % and {log}({L}{bol})∼
44). We have fitted the average spectra of each of the AP groups to
clumpy models. The torus is no longer present in Group 1, supporting its
disappearance at low luminosities. We were able to fit the average
spectra for the torus component in Groups 3 ({C}{torus}∼
40 % and {log}({L}{bol})∼ 42.6), 4
({C}{torus}∼ 60 % and {log}({L}{bol})∼
43.7), and 5 to Clumpy torus models. We did not find a good fitting to
Clumpy torus models for Group 2 ({C}{torus}∼ 18 % and
{log}({L}{bol})∼ 42). This might suggest a different
configuration and/or composition of the clouds for Group 2, which is
consistent with the different gas content seen in Groups 1, 2, and 3,
according to detections of {{{H}}}2 molecular lines. Groups
3, 4, and 5 show a trend of decreasing torus width (which leads to a
likely decrease of the geometrical covering factor), although we cannot
confirm it with the present data. Finally, Groups 3, 4, and 5 show an
increase of the outer radius of the torus for higher luminosities,
consistent with a resizing of the torus according to AGN luminosity.
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