The energetics of starburst-driven outflows at z ∼ 1 from KMOS

Journal article

We present an analysis of the gas outflow energetics from KMOS observations of ∼ 529 main-sequence star-forming galaxies at z ∼ 1 using broad, underlying H α and forbidden lines of [N II] and [S II]. Based on the stacked spectra for a sample with median star-formation rates and stellar masses of SFR = 7 M⊙   yr−1 and M⋆ = (1.0 ± 0.1) × 1010 M⊙, respectively, we derive a typical mass outflow rate of M˙wind = 1–4 M⊙ yr−1 and a mass loading of M˙wind / SFR = 0.2–0.4. By comparing the kinetic energy in the wind with the energy released by supernovae, we estimate a coupling efficiency between the star formation and wind energetics of ϵ ∼  0.03. The mass loading of the wind does not show a strong trend with star-formation rate over the range ∼ 2–20 M⊙ yr−1, although we identify a trend with stellar mass such that dM / dt / SFR ∝ M0.26±0.07⋆⁠. Finally, the line width of the broad H α increases with disc circular velocity with a sub-linear scaling relation FWHMbroad ∝ v0.21 ± 0.05. As a result of this behaviour, in the lowest mass galaxies (M⋆ ≲ 1010 M⊙), a significant fraction of the outflowing gas should have sufficient velocity to escape the gravitational potential of the halo whilst in the highest mass galaxies (M⋆ ≳ 1010 M⊙) most of the gas will be retained, flowing back on to the galaxy disc at later times.

Authors: Swinbank, A; Harrison, C; Tiley, A; Johnson, H; Smail, I

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 487
• Issue: 1
• Pages: 381–393
• Publication date: 2019-05-09
• Acceptance date: 2019-05-02
• DOI: 10.1093/mnras/stz1275
• EISSN: 1365-2966
• ISSN: 0035-8711
• Keywords: ISM: evolution; galaxies: kinematics and dynamics; galaxies: high-redshift; galaxies: structure; FFR; galaxies: evolution; galaxies: formation