Properties of Galactic Outflows Driven by Starburst at Cosmic Noon: Insights from Hydrodynamical Simulations

TL;DR

This study uses high-resolution, 3D hydrodynamical simulations of 14 isolated low-mass disk galaxies at cosmic noon to investigate starburst-driven, multiphase galactic winds. The simulations reproduce a wide range of wind properties over $\sim$20–30 Myr, with outflow velocities from $\sim50$ to $1000\,\mathrm{km\,s^{-1}}$, mass outflow rates of $\sim0.3$–$20\,M_\odot\,\mathrm{yr}^{-1}$, and total mass loading factors $\eta_{\mathrm M}$ spanning $\sim0.24$–$6.26$, where the cool phase dominates the mass budget. Mass loading declines with increasing stellar mass and increases with SFR, but strong time- and radius-dependence complicates simple scaling; observational comparisons are further affected by differing wind definitions and measurement radii. The cool and warm phases align broadly with observations of ionized winds at cosmic noon, though systematic offsets with some studies persist, partly due to methodology. The results emphasize the need for larger, consistently analyzed samples and standardized wind measurements to robustly map outflow scaling relations and their role in galaxy evolution.

Abstract

We investigate starburst-driven galactic outflows in low-mass galaxies ($9.0 < \log(M_*/M_\odot) < 10.0$) at cosmic noon using high-resolution 3D hydrodynamical simulations based on a framework that can reproduce the multiphase outflows in M82. The simulations produce starbursts lasting 20-30 Myr, with peak star formation rates of 2-68 M$_\odot \,\rm{yr}^{-1}$. Outflow properties vary strongly with time, radial distance to galaxy center, stellar mass, and gas fraction, exhibiting velocities of 50-1000 $\,\rm{km\,s}^{-1}$, mass outflow rates of 0.3-20 M$_\odot \,\rm{yr}^{-1}$, and mass loading factors, $η_\mathrm{M}$, of 0.24-6.26. The cool phase ($8000 < T \le 2 \times 10^4$ K) dominates the outflow, and properties of the cool and warm phases are broadly consistent with observations. At $M_*= 10^{9.5}\,M_\odot$, average $η_\mathrm{M}$ for the total, cool, and warm phases are $\sim$1.2, 0.75, and 0.25, respectively. The mass loading factor decreases with increasing galaxy stellar mass, but increases with star formation rate. Given strong temporal and spatial evolution, scaling slopes from limited samples should be treated with caution. Our total $η_\mathrm{M}$ values are higher than FIRE-2 by 0.06 dex but lower than EAGLE and TNG50 by 0.50 and 0.84 dex. Accounting for methodological differences in outflow measurement reduces these gaps to 0.2-0.4 dex, suggesting that part of the discrepancy between observations and simulations reported in the literature may arise from inconsistent definitions and measurement methods, though differences in individual phases persist. Larger observational and simulation samples, together with consistent methods for measuring outflow properties, are required to draw robust conclusions about the scaling relations of galactic outflows.

Figures (13)

• Figure 1: Evolution of the gas disk and stellar particle distribution in face and edge-on views for Z1F70D at t = 5, 10, 20, and 30 Myr. The first and third rows display the evolution of the gas component, while the second and fourth rows show the spatial distribution of stellar particles over a 10 Myr interval.
• Figure 2: Top: The time evolution of the star formation rate (SFR) for each simulation is shown. Solid lines denote simulations labeled 'Z1', corresponding to models with initial conditions representative of galaxies at $z\sim1$, while dashed lines indicate the 'Z2' simulations. Bottom: Radial surface density profiles of stars formed at 30 Myr. Simulations with an initial gas fraction of $85\%$ show a modest secondary peak at approximately 1.5 kpc.
• Figure 3: Face-on and edge-on views of the distribution of star particles formed during the starburst. The color indicates the age of particle. Note that the mass of each stellar particle is 4 and $8 \times 10^4$ M$_\odot$ in the 'Z1' and 'Z2' simulations.
• Figure 4: Face-on and edge-on galaxies outflows of the 'Z1' models at t = 30 Myr. From left to right, the panels show: (1) the face-on projected gas density, (2) the face-on temperature distribution, (3) the edge-on projected gas density, and (4) the edge-on temperature distribution. Simulations with higher initial gas fraction generate more spatially extended outflows with wider opening angles and more pronounced multi-phase structures.
• Figure 5: Same as Figure \ref{['fig:z1_530']} but for a direct comparison of projected gas density between Z1F70D and Z1F70DG. In order to compare the effects of the gas return process on galactic outflows under the same initial conditions.