title: Star formation inside a galactic outflow.
abstract: Recent observations have revealed massive galactic molecular outflows that may have the physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive 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 it to contribute substantially to the 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 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 solar masses per year. 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.
authors.affiliation: Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK.|Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: R
authors.initials: R
authors.lastname: Maiolino
authors.affiliation: Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: H R
authors.initials: HR
authors.lastname: Russell
authors.affiliation: Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: A C
authors.initials: AC
authors.lastname: Fabian
authors.affiliation: Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK.|Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: S
authors.initials: S
authors.lastname: Carniani
authors.affiliation: Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK.|Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: R
authors.initials: R
authors.lastname: Gallagher
authors.affiliation: CSIC-Departamento de Astrofisica-Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Cazzoli
authors.affiliation: CSIC-Departamento de Astrofisica-Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Arribas
authors.affiliation: Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK.|Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: F
authors.initials: F
authors.lastname: Belfiore
authors.affiliation: CSIC-Departamento de Astrofisica-Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Bellocchi
authors.affiliation: CSIC-Departamento de Astrofisica-Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Colina
authors.affiliation: INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 20125 Firenze, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Cresci
authors.affiliation: Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: W
authors.initials: W
authors.lastname: Ishibashi
authors.affiliation: INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 20125 Firenze, Italy.|Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto F.no, Firenze, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Marconi
authors.affiliation: INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 20125 Firenze, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Mannucci
authors.affiliation: INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 20125 Firenze, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Oliva
authors.affiliation: Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Sturm