Title: The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: a Test for the Clumpy Torus Models
Autor(s): Cristina Ramos Almeida, Nancy A. Levenson, Jose Miguel Rodríguez Espinosa, Almudena Alonso-Herrero,
Andrés Asensio Ramos, James T. Radomski, Chris Packham, R. Scott Fisher, and Charles Telesco.
Abstract: We present subarcsecond resolution mid-IR photometry
from 8 to 20 \micron~of eighteen Seyfert
galaxies obtained primarily from the Gemini Telescopes, representing one of the largest
compilations of mid-IR Gemini observations of Seyferts.
We construct spectral energy distributions (SEDs) with the unresolved mid-IR fluxes which are
dominated by the AGN emission. At the spatial resolution afforded by Gemini, the fluxes
are relatively uncontaminated by stellar emission. We augment
the data with near-infrared measurements from the literature at similar angular resolution.
We find that the IR SEDs of intermediate-type Seyferts are flatter and present higher 10
to 18 \micron~ratios than those of Seyfert 2 galaxies.
We fit the sample of Seyfert SEDs with clumpy dusty torus models, which
accurately reproduce the high spatial resolution measurements.
For Seyfert 2s, we find the number of clouds along equatorial rays
$N_0 = 5$--15, edge-on geometries more probable than face-on views, and
the 10 \micron~silicate feature in shallow absorption.
For the intermediate-type Seyferts, $N_0$ and the inclination angle of
the torus are lower than those of the Seyfert 2s, with the silicate feature appearing
in shallow emission or absent.
The columns of material responsible for the X-ray absorption
are larger than those inferred from the model fits,
which is consistent with hot X-ray absorbing gas located within the dust sublimation radius
whereas the mid-IR flux arises from an area farther from the accretion disc.
In the models, the outer radial extent of the torus scales with the
AGN luminosity, and we find the tori to be confined to scales less than 5 pc.