The Dust and Molecular Gas in the Brightest Cluster Galaxy in MACS
  1931.8-2635
  We present new ALMA observations of the molecular gas and far-infrared
continuum around the brightest cluster galaxy (BCG) in the cool-core cluster
MACS 1931.8-2635. Our observations reveal $1.9 \pm 0.3 \times 10^{10}$
M$_{\odot}$ of molecular gas, on par with the largest known reservoirs of cold
gas in a cluster core. We detect CO(1-0), CO(3-2), and CO(4-3) emission from
both diffuse and compact molecular gas components that extend from the BCG
center out to $\sim30$ kpc to the northwest, tracing the UV knots and H$\alpha$
filaments observed by HST. Due to the lack of morphological symmetry, we
hypothesize that the $\sim300$ km s$^{-1}$ velocity of the CO in the tail is
not due to concurrent uplift by AGN jets, rather we may be observing the
aftermath of a recent AGN outburst. The CO spectral line energy distribution
suggests that molecular gas excitation is influenced by processes related to
both star formation and recent AGN feedback. Continuum emission in Bands 6 and
7 arises from dust and is spatially coincident with young stars and nebular
emission observed in the UV and optical. We constrain the temperature of
several dust clumps to be $\lesssim 10$ K, which is too cold to be directly
interacting with the surrounding $\sim 4.8$ keV intracluster medium (ICM). The
cold dust population extends beyond the observed CO emission and must either be
protected from interacting with the ICM or be surrounded by local volumes of
ICM that are several keV colder than observed by Chandra.
