http://arxiv.org/abs/1805.01484
Galactic-scale outflows regulate the stellar mass growth and chemical enrichment of galaxies, yet key outflow properties such as the chemical composition and mass loss rate remain largely unknown. We address these physical properties with rest-frame ultraviolet spectra of nine gravitationally lensed z=2-3 star forming galaxies taken with Keck/ESI. Using transitions spanning a range of optical depths and atomic elements, we study the kinematics, covering fractions, and composition of the interstellar medium in our sample. The interstellar medium seen in absorption is dominated by outflowing material, with typical velocities -150 km/s. Approximately 80% of the total column density is associated with a net outflow. Mass loss rates in the low ionization phase are comparable to or in excess of the star formation rate, with total outflow rates likely higher when accounting for ionized gas. Of order half of the heavy element yield from star formation is ejected in the low ionization phase, confirming that outflows play a critical role in regulating galaxy chemical evolution. Covering fractions vary and are in general non-uniform, with most galaxies having incomplete covering by the low ions across all velocities. Our sample spans an order of magnitude in column density yet ionic abundance patterns show remarkably little scatter, revealing a distinct “chemical fingerprint” of outflows. Gas phase Si abundances are significantly super-solar relative to Fe and Ni ([Si/Fe]$\gtrsim$0.4), indicating a combination of $\alpha$-enhancement and dust depletion. Derived properties are comparable to the most kinematically broad, metal-rich, and depleted DLAs at similar redshifts, suggesting that these extreme systems are associated with galactic outflows at small impact parameters. We discuss implications of the abundance patterns in z=2-3 galaxies and the role of outflows at this epoch.
T. Jones, D. Stark and R. Ellis
Mon, 7 May 18
35/39
Comments: 24 pages, 18 figures (plus appendix), submitted to ApJ