The SINS/zC-SINF Survey of z ~ 2 Galaxy Kinematics: Outflow Properties

Abstract

Using SINFONI Hα, [N ii], and [S ii] AO data of 27 z ∼ 2 star-forming galaxies (SFGs) from the SINS and zC-SINF surveys, we explore the dependence of outflow strength (via the broad flux fraction) on various galaxy parameters. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius (∼a few kpc). Decomposition of the [S ii] doublet into broad and narrow components suggests that this outflowing gas probably has a density of ∼10–100 cm−3, less than that of the star-forming gas (600 cm−3). There is a strong correlation of the Hα broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 M☉ yr−1 kpc−2. Above this threshold, we find that SFGs with log m* > 10 have similar or perhaps greater wind mass-loading factors (η = $\dot{M}_{\rm out}$/SFR) and faster outflow velocities than lower mass SFGs, suggesting that the majority of outflowing gas at z ∼ 2 may derive from high-mass SFGs. The mass-loading factor is also correlated with the star formation rate (SFR), galaxy size, and inclination, such that smaller, more star-forming, and face-on galaxies launch more powerful outflows. We propose that the observed threshold for strong outflows and the observed mass loading of these winds can be explained by a simple model wherein break-out of winds is governed by pressure balance in the disk.