ALMA observations of cold molecular gas filaments trailing rising radio
  bubbles in PKS0745-191
  We present ALMA observations of the CO(1-0) and CO(3-2) line emission tracing
filaments of cold molecular gas in the central galaxy of the cluster
PKS0745-191. The total molecular gas mass of 4.6 +/- 0.3 x 10^9 solar masses,
assuming a Galactic X_{CO} factor, is divided roughly equally between three
filaments each extending radially 3-5 kpc from the galaxy centre. The emission
peak is located in the SE filament roughly 1 arcsec (2 kpc) from the nucleus.
The velocities of the molecular clouds in the filaments are low, lying within
+/-100 km/s of the galaxy's systemic velocity. Their FWHMs are less than 150
km/s, which is significantly below the stellar velocity dispersion. Although
the molecular mass of each filament is comparable to a rich spiral galaxy, such
low velocities show that the filaments are transient and the clouds would
disperse on <10^7 yr timescales unless supported, likely by the indirect effect
of magnetic fields. The velocity structure is inconsistent with a merger origin
or gravitational free-fall of cooling gas in this massive central galaxy. If
the molecular clouds originated in gas cooling even a few kpc from their
current locations their velocities would exceed those observed. Instead, the
projection of the N and SE filaments underneath X-ray cavities suggests they
formed in the updraft behind bubbles buoyantly rising through the cluster
atmosphere. Direct uplift of the dense gas by the radio bubbles appears to
require an implausibly high coupling efficiency. The filaments are coincident
with low temperature X-ray gas, bright optical line emission and dust lanes
indicating that the molecular gas could have formed from lifted warmer gas that
cooled in situ.
