GASP. XXII The molecular gas content of the JW100 jellyfish galaxy at
  z~0.05: does ram pressure promote molecular gas formation?
  Within the GASP survey, aimed at studying the effect of the ram-pressure
stripping on the star formation quenching in cluster galaxies, we analyze here
ALMA observations of the jellyfish galaxy JW100. We find an unexpected large
amount of molecular gas ($\sim 2.5 \times 10^{10} M_{\odot}$), 30\% of which is
located in the stripped gas tail out to $\sim$35 kpc from the galaxy center.
The overall kinematics of molecular gas is similar to the one shown by the
ionized gas, but for clear signatures of double components along the stripping
direction detected only out to 2 kpc from the disk. The line ratio $r_{21}$ has
a clumpy distribution and in the tail can reach large values ($\geq 1$), while
its average value is low (0.58 with a 0.15 dispersion). All these evidence
strongly suggest that the molecular gas in the tail is newly born from stripped
HI gas or newly condensed from stripped diffuse molecular gas. The analysis of
interferometric data at different scales reveals that a significant fraction
($\sim 40\%$) of the molecular gas is extended over large scales ($\geq 8$ kpc)
in the disk, and this fraction becomes predominant in the tail ($\sim 70\%$).
By comparing the molecular gas surface density with the star formation rate
surface density derived from the \Ha emission from MUSE data, we find that the
depletion time on 1 kpc scale is particularly large ($5-10$ Gyr) both within
the ram-pressure disturbed region in the stellar disk, and in the complexes
along the tail.
