The SINS/zC-SINF survey of z~2 galaxy kinematics: Outflow properties (1207.5897v2)

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).

Analysis of Outflow Properties in 4pt Galaxy Kinematics

The paper presented in this paper offers a detailed investigation into the dynamics and characteristics of galactic outflows in 4pt star-forming galaxies (SFGs) using data from the SINS and zC-SINF surveys. Employing SINFONI H$\alpha$ and adaptive optics (AO) across a sample of 27 galaxies, the research systematically dissects the relationship between outflow phenomena and various intrinsic galactic parameters. Critical attention is given to broad flux fractions, spatial extent of emissions, and correlations with star formation indicators.

The research identifies that outflows within these galaxies exhibit a significant connection with the star formation surface density, noting a distinct threshold around 1 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$. Above this threshold, higher stellar mass SFGs (logM$_{*}$ > 10) are shown to possess similar or even greater wind mass loading factors (denoted as $\eta$) and exhibit faster outflow velocities than their lower mass counterparts. This pattern suggests that major contributions to the outflowing gas could originate predominantly from higher mass SFGs, indicating that galaxy mass is a crucial determinant in outflow dynamics.

Furthermore, the paper underscores a pronounced spatial extension of outflows, typically reaching at least the half-light radius (approximately a few kiloparsecs). This spatial characteristic aligns with a broad FWHM of around 450 km/s, discernible across a variety of galactic scales. Additionally, the research finds that the local outflowing gas tends to have a lower density (~10-100 cm$^{-3}$) compared to the denser star-forming regions, which is consistent with diffuse wind nature.

The analysis also points to several secondary yet significant factors influencing outflows, including galaxy size, orientation, and star formation rate (SFR). Particularly, smaller, more star-forming, and face-on galaxies exhibit stronger outflows. Theoretical models proposed in the paper involve a pressure balance scenario in galactic disks, suggesting that 'break-out' conditions for winds are contingent upon surpassing certain star formation surface densities.

The implications of this work extend to our understanding of the feedback mechanisms that regulate galaxy evolution. The findings propose that massive galaxies may play a dominant role in enriching the intergalactic medium with metals and could contribute significantly to the observed mass-metallicity relationships at 4pt. This observation aligns with the need for enhanced outflows from massive SFGs to explain the dispersion in metals seen in various cosmic structures.

In conclusion, this paper provides a rigorous examination of galactic outflows, asserting that mass and star formation are pivotal in shaping the wind profiles of SFGs. Future work could explore the implications of these outflows on larger cosmic scales and assess their roles in broader galaxy evolution scenarios, potentially incorporating observations from other wavelengths and simulations to further delineate the forces driving these dynamic processes.