Large-scale star-formation-driven outflows at 1 < z < 2 in the 3D-HST survey

Abstract

We present evidence of large-scale outflows from three low-mass (log(M */M·) 9.75) star-forming (SFR>4 M ·yr-1) galaxies observed at z = 1.24, z = 1.35, and z = 1.75 in the 3D-HST Survey. Each of these galaxies is located within a projected physical distance of 60kpc around the sight line to the quasar SDSSJ123622.93+621526.6, which exhibits well-separated strong (W λ2796 r g∼ 0.8 Å) Mg II absorption systems matching precisely to the redshifts of the three galaxies. We derive the star formation surface densities from the Hα emission in the WFC3 G141 grism observations for the galaxies and find that in each case the star formation surface density well exceeds 0.1 M·yr-1kpc-2, the typical threshold for starburst galaxies in the local universe. From a small but complete parallel census of the 0.65 < z < 2.6 galaxies with H 140 ≲ 24 proximate to the quasar sight line, we detect Mg II absorption associated with galaxies extending to physical distances of 130kpc. We determine that the Wr > 0.8Å Mg II covering fraction of star-forming galaxies at 1 < z < 2 may be as large as unity on scales extending to at least 60kpc, providing early constraints on the typical extent of starburst-driven winds around galaxies at this redshift. Our observations additionally suggest that the azimuthal distribution of Wr > 0.4Å Mg II absorbing gas around star-forming galaxies may evolve from z ∼ 2 to the present, consistent with recent observations of an increasing collimation of star-formation-driven outflows with time from z 3. © 2012. The American Astronomical Society. All rights reserved.