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 PKS 0745-191 .
The total molecular gas mass of 4.6 \pm 0.3 \times 10 ^ { 9 } \hbox { $ \thinspace M _ { \odot } $ } , assuming a Galactic X _ { \mathrm { 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 \sim 1 arcsec ( 2 kpc ) from the nucleus .
The velocities of the molecular clouds in the filaments are low , lying within \pm 100 \hbox { $ km s ^ { -1 } $ } of the galaxy ’ s systemic velocity .
Their FWHMs are less than 150 \hbox { $ km s ^ { -1 } $ } , 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 .