- Peng, Zixuan;
- Martin, Crystal L;
- Chen, Zirui;
- Fielding, Drummond B;
- Xu, Xinfeng;
- Heckman, Timothy;
- Ramambason, Lise;
- Li, Yuan;
- Carr, Cody;
- Hu, Weida;
- Chen, Zuyi;
- Scarlata, Claudia;
- Henry, Alaina
Abstract:
We study the physical origins of outflowing cold clouds in a sample of 14 low-redshift dwarf (M
* ≲ 1010
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] λ5007 and Hα. The maximum velocities (
v
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
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
max
≳
1000
km
s
−
1
) in nine out of 14 star-forming dwarf galaxies, comparable to active galactic nucleus–driven winds.