Dense molecular clouds in the SN2008fp host galaxy
  (abridged) We use observations of interstellar absorption features, such as
atomic and molecular lines as well as diffuse interstellar bands (DIBs),
towards SN2008fp to study the physical properties of extra-galactic diffuse
interstellar clouds in the host galaxy, ESO428-G14. The properties of the
intervening dust are investigated via spectropolarimetry. The spectra of
SN2008fp reveal a complex of diffuse atomic clouds at radial velocities in line
with the systematic velocities of the host galaxy (~1700 km/s). A translucent
(A_V ~ 1.5 mag) cloud is detected at a heliocentric velocity of 1770 km/s This
cold dense cloud is rich in dense atomic gas tracers, molecules, as well as
diffuse interstellar bands. We have detected both C2 and C3 for the first time
in a galaxy beyond the Local Group. The CN (0,0) band line ratios are used to
derive an in-situ measurement of the cosmic background radiation temperature in
an external galaxy; this gives an excitation temperature of T = 2.9 +- 0.3 K.
The interstellar polarization law deviates significantly from what is observed
in the Galaxy, indicating substantial differences in the composition or size
distribution of dust grains in the SN2008fp host galaxy. C2 is used to probe
the cold diffuse ISM density and temperature. The lack of variability in the
extra-galactic absorption line profiles over a period of one month implies that
the absorbing material is not circumstellar and thus not affected directly by
the SN event. Also it shows that there are no significant density variation in
the small-scale structure of the molecular cloud down to 100 AU.
