We present new ALMA CO(2-1) observations tracing 2.2×1010
M⊙​ of molecular gas in Abell 2390's brightest cluster galaxy, where
half the gas is located in a one-sided plume extending 15 kpc out from the
galaxy centre. This molecular gas has a smooth and positive velocity gradient,
and is receding 250 km/s faster at its farthest point than at the galaxy
centre. To constrain the plume's origin, we analyse our new observations
alongside existing X-ray, optical and radio data. We consider the possibility
that the plume is jet-driven with lifting aided by jet inflated X-ray bubbles.
Alternatively, it may have formed following a gravitational disturbance. In
this case, the plume may either be a trail of gas stripped from the main galaxy
by ram pressure, or more recently cooled and infalling gas. The galaxy's star
formation and gas cooling rate suggest the lifespan of its molecular gas may be
low compared with the plume's age -- which would favour a recently cooled
plume. Molecular gas in close proximity to the active galactic nucleus is also
indicated by 250 km/s wide CO(2-1) absorption against the radio core, as well
as previously detected CO(1-0) and HI absorption. This absorption is optically
thick and has a line of sight velocity towards the galaxy centre of 200 km/s.
We discuss simple models to explain its origin.Comment: Submitted to MNRA