Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies
We study the physical origins of outflowing cold clouds in a sample of 14 low-redshift dwarf ( M _* ≲ 10 ^10 M _⊙ ) galaxies from the Cosmic Origins Spectrograph Legacy Archive Spectroscopic SurveY (CLASSY) using Keck/ESI data. Outflows are traced by broad (FWHM ∼260 km s ^−1 ) and very-broad (VB;...
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ada606 |
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| Summary: | We study the physical origins of outflowing cold clouds in a sample of 14 low-redshift dwarf ( M _* ≲ 10 ^10 M _⊙ ) galaxies from the Cosmic Origins Spectrograph Legacy Archive Spectroscopic SurveY (CLASSY) using Keck/ESI data. Outflows are traced by broad (FWHM ∼260 km s ^−1 ) and very-broad (VB; FWHM ∼1200 km s ^−1 ) velocity components in strong emission lines like [O iii ] λ 5007 and H α . The maximum velocities ( ${v}_{{\rm{\max }}}$ ) of broad components correlate positively with star formation rate, unlike the anticorrelation observed for VB components, and are consistent with superbubble models. In contrast, supernova-driven galactic wind models better reproduce the ${v}_{{\rm{\max }}}$ of VB components. Direct radiative cooling from a hot wind significantly underestimates the luminosities of both broad and VB components. A multiphase wind model with turbulent radiative mixing reduces this discrepancy to at least 1 dex for most VB components. Stellar photoionization likely provides additional energy since broad components lie in the starburst locus of excitation diagnostic diagrams. We propose a novel interpretation of outflow origins in star-forming dwarf galaxies—broad components trace expanding superbubble shells, while VB components originate from galactic winds. One-zone photoionization models fail to explain the low-ionization lines ([S ii ] and [O i ]) of broad components near the maximal starburst regime, which two-zone photoionization models with density-bounded channels instead reproduce. These two-zone models indicate anisotropic leakage of Lyman continuum photons through low-density channels formed by expanding superbubbles. Our study highlights extreme outflows ( ${v}_{{\rm{\max }}}\gtrsim 1000\,{\rm{km}}\,{{\rm{s}}}^{-1}$ ) in nine out of 14 star-forming dwarf galaxies, comparable to active galactic nucleus–driven winds. |
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| ISSN: | 1538-4357 |