The SINS/zC-SINF survey of z~2 galaxy kinematics: Outflow properties

TL;DR

This study analyzes the properties of galactic outflows at z~2 using AO data, revealing correlations with star formation surface density, galaxy mass, and orientation, and proposing a pressure balance model for wind break-out.

Contribution

It provides new insights into the outflow mechanisms at high redshift, linking outflow strength to galaxy properties and introducing a simple pressure balance model for wind break-out.

Findings

Strong outflows occur above a star formation surface density threshold of 1 Msun yr^-1 kpc^-2.

Mass loading factors and outflow velocities are comparable or greater in high-mass SFGs.

Outflowing gas has a density of 10-100 cm^-3, lower than star-forming gas.

Abstract

Based on SINFONI Ha, [NII] and [SII] AO data of 30 z \sim 2 star-forming galaxies (SFGs) from the SINS and zcSINF surveys, we find a strong correlation of the Ha broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 Msun yr^-1 kpc^-2. Above this threshold, we find that SFGs with logm_\ast>10 have similar or perhaps greater wind mass loading factors (eta = Mdotout/SFR) and faster outflow velocities than lower mass SFGs. This trend suggests that the majority of outflowing gas at z \sim 2 may derive from high-mass SFGs, and that the z \sim 2 mass-metallicity relation is driven more by dilution of enriched gas in the galaxy gas reservoir than by the efficiency of outflows. The mass loading factor is also correlated with the SFR and inclination, such that more star-forming and face-on galaxies launch more powerful outflows. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius (\sim a few kpc). 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. Using the ratio of the [SII] doublet in a broad and narrow component, we find that outflowing gas has a density of \sim10-100 cm^-3, significantly less than that of the star forming gas (600 cm^-3).