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Abstract We present results on the properties of extreme gas outflows in massive (M*∼ 1011M⊙), compact, starburst (star formation rate, SFR∼ 200M⊙yr−1) galaxies atz= 0.4–0.7 with very high star formation surface densities (ΣSFR∼ 2000M⊙yr−1kpc−2). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies, we identify outflows with maximum velocities of 820–2860 km s−1. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T∼ 104K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies’ star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong Mgiiabsorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of ∼50–2200M⊙yr−1, assuming a fiducial outflow size of 5 kpc, and mass loading factors ofη∼ 5 for most of the sample. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution.
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This content will become publicly available on May 22, 2027
Resolving the Unresolved Galactic Winds in Multiphase Models. I. Methodology and Application
Abstract Galactic winds shape galaxy evolution; however, the outflowing gas is complex: it consists of multiple ionization phases, and its properties vary spatially. Therefore, methods that combine high-fidelity observations with state-of-the-art galactic-wind models are limited. Here we investigate methods for fitting the column density profiles derived from high-quality outflow observations with the multiphase, multiscale wind model from D. B. Fielding & G. L. Bryan. We identify three key outflow parameters: the initial hot-phase mass-loading factor (ηM,hot,0), the initial cool-phase mass-loading factor (ηM,cool,0), and the initial cool-cloud mass (Mcl,0). We obtain good fits (reducedχ2 < 1.5) for most galaxies, with tight constraints onηM,cool,0and moderate constraints on the other two parameters. We find the inferredηM,cool,0andηM,hot,0are mostly of order unity, with significant scatter. The constraints onηM,hot,0suggest that the interaction between the cool and hot phases allow us to indirectly constrain the properties of the hot wind from cool-outflow observations. The model also predicts various radial trends. First, for all galaxies, the cool-phase outflow velocity increases rapidly between 1 and 2r50, then reaches a plateau, wherer50is the half-light radius of the galaxy. Second, most galaxies exhibit increasingηM,cooland decreasingηM,hotwith radius, with a few showing the reverse trends. These results should be interpreted as effective, model-conditional constraints but are consistent with other recent multiphase simulations and observations. This highlights that the velocity–radius mapping encoded in UV absorption profiles enables recovery of outflow spatial structures from spatially integrated spectra. Our method paves the way for future broad parameter studies and guides updates of outflow simulations in future work.
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- PAR ID:
- 10694816
- Publisher / Repository:
- ApJ
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 1003
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 155
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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