The CO emission in the Taffy Galaxies (UGC 12914/5) at 60pc
  resolution-I: The battle for star formation in the turbulent Taffy Bridge
  We present ALMA observations at a spatial resolution of 0.2 arcsec (60 pc) of
CO emission from the Taffy galaxies (UGC 12914/5). The observations are
compared with narrow-band Pa$\alpha$, mid-IR, radio continuum and X-ray
imaging, plus optical spectroscopy. The galaxies have undergone a recent
head-on collision, creating a massive gaseous bridge which is known to be
highly turbulent. The bridge contains a complex web of narrow molecular
filaments and clumps. The majority of the filaments are devoid of star
formation, and fall significantly below the Kennicutt-Schmidt relationship for
normal galaxies, especially for the numerous regions undetected in Pa$\alpha$
emission. Within the loosely connected filaments and clumps of gas we find
regions of high velocity dispersion which appear gravitationally unbound for a
wide range of likely values of $X_{\rm CO}$. Like the "Firecracker" region in
the Antennae system, they would require extremely high external dynamical or
thermal pressure to stop them dissipating rapidly on short crossing timescales
of 2-5~Myrs. We suggest that the clouds may be transient structures within a
highly turbulent multi-phase medium which is strongly suppressing star
formation. Despite the overall turbulence in the system, stars seem to have
formed in compact hotspots within a kpc-sized extragalactic HII region, where
the molecular gas has a lower velocity dispersion than elsewhere, and shows
evidence for a collision with an ionized gas cloud. Like the shocked gas in the
Stephan's Quintet group, the conditions in the Taffy bridge shows how difficult
it is to form stars within a turbulent, multi-phase, gas.
