Suzaku Detection of Thermal X-Ray Emission Associated with the Western
  Radio Lobe of Fornax A
  We present the results of X-ray mapping observations of the western radio
lobe of the Fornax A galaxy, using the X-ray Imaging Spectrometer (XIS) onboard
the Suzaku satellite with a total exposure time of 327 ks. The purpose of this
study is to investigate the nature and spatial extent of the diffuse thermal
emission around the lobe by exploiting the low and stable background of the
XIS. The diffuse thermal emission had been consistently reported in all
previous studies of this region, but its physical nature and relation to the
radio lobe had not been examined in detail. Using the data set covering the
entire western lobe and the central galaxy NGC 1316, as well as comparison sets
in the vicinity, we find convincingly the presence of thermal plasma emission
with a temperature of ~1 keV in excess of conceivable background and
contaminating emission (cosmic X-ray background, Galactic halo, intra-cluster
gas of Fornax, interstellar gas of NGC 1316, and the ensemble of point-like
sources). Its surface brightness is consistent with having a spherical
distribution peaking at the center of the western lobe with a projected radius
of ~12 arcmin. If the volume filling factor of the thermal gas is assumed to be
unity, its estimated total mass amounts to ~10^{10} M_sun, which would be
~10^{2} times that of the central black hole and comparable to that of the
current gas mass of the host galaxy. Its energy density is comparable to or
larger than those in the magnetic field and non-thermal electrons responsible
for the observed radio and X-ray emission.
