Widespread SiO and CH3OH emission in Filamentary Infrared Dark Clouds
  Infrared-Dark Clouds (IRDCs) are cold, dense regions of high (optical and
infrared) extinction, believed to be the birthplace of high-mass stars and
stellar clusters. The physical mechanisms leading to the formation of these
IRDCs are not completely understood and it is thus important to study their
molecular gas kinematics and chemical content to search for any signature of
the IRDCs formation process. Using the 30m-diameter antenna at the Instituto de
Radioastronom\'ia Milim\'etrica, we have obtained emission maps of dense gas
tracers (H$^{13}$CO$^{+}$ and HN$^{13}$C) and typical shock tracers (SiO and
CH$_3$OH) toward three IRDCs, G028.37+00.07, G034.43+00.24 and G034.77-00.55
(clouds C, F and G, respectively). We have studied the molecular gas kinematics
in these clouds and, consistent with previous works toward other IRDCs, the
clouds show complex gas kinematics with several velocity-coherent
sub-structures separated in velocity space by a few km s$^{-1}$. Correlated
with these complex kinematic structures, widespread (parsec-scale) emission of
SiO and CH$_3$OH is present in all the three clouds. For clouds C and F, known
to be actively forming stars, widespread SiO and CH$_3$OH is likely associated
with on-going star formation activity. However, for cloud G, which lacks either
8 $\mu$m or 24 $\mu$m sources and 4.5 $\mu$m H$_2$ shock-excited emission, the
detected widespread SiO and CH$_3$OH emission may have originated in a
large-scale shock interaction, although a scenario involving a population of
low-mass stars driving molecular outflows cannot be fully ruled out.
