GASP. VII. Gas accretion onto an isolated galaxy
  Theoretically, inflowing filaments of gas are one of the main causes of
growth for a galaxy. Nonetheless, observationally, probing ongoing gas
accretion is challenging. As part of the Gas Stripping Phenomena in galaxies
with MUSE (GASP) program, we present the analysis of a spiral galaxy at
z=0.04648 whose characteristics indeed are consistent with a scenario in which
gas accretion plays a major role. The most salient indirect parts of evidence
that support this picture are: 1) The galaxy is isolated, its position rules
out the mechanisms expected in dense environments. 2) It shows a pronounced
lopsidedness extending toward West. According to the spatially resolved star
formation history, this component was formed <6x10^8 yr ago. 3) It has many
large and elongated HII regions that are indication of a fragmentation due to
disk instability. 4) The stellar and gas kinematics are quite symmetric around
the same axis, but in the gas the locus of negative velocities shows a
convexity toward East, as if new gas has been infalling with different
orientation and velocity. 5) The metallicity distribution is inhomogeneous and
shows exceptionally steep gradients from the center toward the outskirts,
especially in the South-West side. 6) The luminosity weighted age is generally
low (~8 Gyr) and particularly low (<7 Gyr) along a trail crossing the galaxy
from South-West toward North. It might trace the path of the accreted gas.
These findings point to an inflow of gas probably proceeding from the
South-West side of the galaxy.
