GASP XXI. Star formation rates in the tails of galaxies undergoing
  ram-pressure stripping
  Using MUSE observations from the GASP survey, we study 54 galaxies undergoing
ram-pressure stripping (RPS) spanning a wide range in galaxy mass and host
cluster mass. We use this rich sample to study how the star formation rate
(SFR) in the tails of stripped gas depends on the properties of the galaxy and
its host cluster. We show that the interplay between all the parameters
involved is complex and that there is not a single, dominant one in shaping the
observed amount of SFR. Hence, we develop a simple analytical approach to
describe the mass fraction of stripped gas and the SFR in the tail, as a
function of the cluster velocity dispersion, galaxy stellar mass,
clustercentric distance and speed in the intracluster medium. Our model
provides a good description of the observed gas truncation radius and of the
fraction of star-formation rate (SFR) observed in the stripped tails, once we
take into account the fact that the star formation efficiency in the tails is a
factor $\sim 5$ lower than in the galaxy disc, in agreement with GASP ongoing
HI and CO observations. We finally estimate the contribution of RPS to the
intracluster light (ICL) and find that the average SFR in the tails of
ram-pressure stripped gas is $\sim 0.22 M_{\odot}\,\mathrm{yr}^{-1} $ per
cluster. By extrapolating this result to evaluate the contribution to the ICL
at different epochs, we compute an integrated average value per cluster of
$\sim 4 \times 10^9 M_\odot$ of stars formed in the tails of RPS galaxies since
$z\sim 1$.
