Properties of dusty tori in active galactic nuclei - II. Type 2 AGN
  (abridged) This paper is the second part of a work investigating the
properties of dusty tori in AGN by means of multi-component SED fitting. It
focuses on low luminosity, low redshift (z < 0.25) AGN selected among emission
line galaxies as well as X-ray, radio and mid-infrared selected type 2 AGN
samples from the literature. The available multi-band photometry covers the
spectral range from the u-band up to 160 um. The observed SED of each object is
fit to a set of multi-component models comprising a stellar component, a high
optical depth torus and cold emission from a starburst (SB). The contribution
of the various components (stars, torus, SB) is reflected in the position of
the objects on the IRAC colour diagram. The comparison of type 1 (as derived
from Hatziminaoglou et al. 2008) and type 2 AGN properties is broadly
consistent with the Unified Scheme. The estimated ratio between type 2 and type
1 objects is about 2-2.5:1. The AGN accretion-to-infrared luminosity ratio is
an indicator of the obscuration of the AGN since it scales down with the
covering factor. We find evidence supporting the receding torus paradigm, with
the estimated fraction of obscured AGN decreasing with increasing optical
luminosity over four orders of magnitude. The average star formation rates are
of ~ 10, 40 and 115 Mo/yr for the low-z, type 2 and quasar samples,
respectively; but this might simply reflect observational biases, as our
quasars are one to two orders of magnitude more luminous than the type 2 AGN.
For the majority of objects with 70 and/or 160 um detections an SB component
was needed in order to reproduce the data points, implying that the
far-infrared emission in AGN arises mostly from star formation; moreover, the
SB-to-AGN luminosity ratio shows a slight trend with increasing luminosity.
