Anatomy of a blazar in the (sub-)millimeter: ALMA Observations of PKS
  0521-365
  We aim at analyzing the (sub-)millimeter emission in a nearby blazar, PKS
0521-365 , to study the synchrotron and thermal emission in the different
components detected at low frequency. We analyze the archive public data of the
ALMA Cycle 0 where PKS 0521-365 is used as a calibrator. A total of 13 projects
with 23 dataset is analyzed in band 3, 6 and 7 and combined. The whole set of
data is combined and wavelet filtered to obtain a deep image reaching a dynamic
range of 47000. The individual emission flux is measured at different date over
a period of 11 months in various components. Finally we analyze the Spectral
Energy Distribution (SED) in each different component, including the radio jet
and counter jet. The point sources detected in the field follow a similar
distribution to previous studies. The blazar flux shows large variation
especially in band 3. Different components are observed: core, radio jet and
newly detected counter jet, Hot Spot (HS) and a disky structure roughly
perpendicular to the jet. The HS emission is formed by a point source
surrounded by an extended emission. The viewing angle of the jet is about 30
with a Doppler factor of 1.6$. The HS is at a distance of 19 kpc from the
center. The SED analysis shows a strong variation of the core spectral index,
especially in band 3. The two components in the radio jet have roughly a flat
spectral index in band 6 and 7. Using these ALMA data the different weak and
extended components are detected. The analysis of both jets constrains the
geometrical distance of the HS to the center. The SED presents a different
shape in time and frequency for each component. Finally a new structure is
detected roughly perpendicular to the radio jet and a thermal emission origin
is currently favoured. Further observations at higher spatial resolution are
needed to confirm that hypothesis.
