Title: Star formation in a galactic outflow,
Abstract: Recent observations have revealed massive galactic molecular outflows that
may have physical conditions (high gas densities) required to form stars.
Indeed, several recent models predict that such massive galactic outflows may
ignite star formation within the outflow itself. This star-formation mode, in
which stars form with high radial velocities, could contribute to the
morphological evolution of galaxies, to the evolution in size and velocity
dispersion of the spheroidal component of galaxies, and would contribute to the
population of high-velocity stars, which could even escape the galaxy. Such
star formation could provide in-situ chemical enrichment of the circumgalactic
and intergalactic medium (through supernova explosions of young stars on large
orbits), and some models also predict that it may contribute substantially to
the global star formation rate observed in distant galaxies. Although there
exists observational evidence for star formation triggered by outflows or jets
into their host galaxy, as a consequence of gas compression, evidence for star
formation occurring within galactic outflows is still missing. Here we report
new spectroscopic observations that unambiguously reveal star formation
occurring in a galactic outflow at a redshift of 0.0448. The inferred star
formation rate in the outflow is larger than 15 Msun/yr. Star formation may
also be occurring in other galactic outflows, but may have been missed by
previous observations owing to the lack of adequate diagnostics.