Large-Scale Star Formation-Driven Outflows at 1<z<2 in the 3D-HST Survey

TL;DR

This study provides evidence of large-scale star formation-driven outflows in low-mass galaxies at redshifts 1 to 2, revealing their extent and distribution through Mg II absorption observations aligned with quasar sight lines.

Contribution

It presents the first direct evidence linking starburst-driven outflows to Mg II absorption at these redshifts and measures the extent and covering fraction of such outflows.

Findings

Star formation surface densities exceed 0.1 M_sun/yr/kpc^2 in observed galaxies.

Mg II absorption extends up to 130 kpc from star-forming galaxies.

The Mg II covering fraction around star-forming galaxies may be nearly 100% within 60 kpc.

Abstract

We present evidence of large-scale outflows from three low-mass (log(M/M_sun)~9.75) star-forming (SFR >4 M_sun/yr) 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 60 kpc around the sight line to the quasar SDSS J123622.93+621526.6, which exhibits well-separated strong (W_r>0.8A) Mg II absorption systems matching precisely to the redshifts of the three galaxies. We derive the star formation surface densities from the H-alpha 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_sun/yr/kpc^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 130 kpc. We determine that the W_r>0.8A Mg II covering fraction of star-forming galaxies at 1<z<2 may be as large as unity on scales extending to at least 60 kpc, 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 W_r>0.4A 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.