X-ray and infrared diagnostics of nearby active galactic nuclei with
  MAXI and AKARI
  Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far
infrared wavelengths, with Monitor of All-sky X-ray Image (MAXI) and the
Japanese infrared observatory AKARI, respectively. Among the X-ray sources
listed in the second release of the MAXI all-sky X-ray source catalog, 100 ones
are currently identified as a non-blazar-type active galactic nucleus. These
include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1
and 27 type-2 objects. The AKARI all-sky survey point source catalog was
searched for their mid- and far-infrared counterparts at 9, 18, and 90 $\mu$m.
As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2
ones) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV)
and infrared luminosities of these objects were investigated, together with
their color information. Adopting the canonical photon index, $\Gamma = 1.9$,
of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness
ratio between the 3-4 and 4-10 keV ranges derived with MAXI was roughly
converted into the absorption column density. After the X-ray luminosity was
corrected for absorption from the estimated column density, the well-known
X-ray-to-infrared luminosity correlation was confirmed at least in the
Compton-thin regime. In contrast, NGC 1365, only one Compton-thick object in
the MAXI catalog, was found to deviate from the correlation toward a
significantly lower X-ray luminosity by nearly an order of magnitude. It was
verified that the relation between the X-ray hardness below 10 keV and
X-ray-to-infrared color acts as an effective tool to pick up Compton-thick
objects. The difference in the infrared colors between the type-1 and type-2
Seyfert galaxies and its physical implication on the classification and
unification of active galactic nuclei were briefly discussed.
