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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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ada606 |
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| author | Zixuan Peng Crystal L. Martin Zirui Chen Drummond B. Fielding Xinfeng Xu Timothy Heckman Lise Ramambason Yuan Li Cody Carr Weida Hu Zuyi Chen Claudia Scarlata Alaina Henry |
| author_facet | Zixuan Peng Crystal L. Martin Zirui Chen Drummond B. Fielding Xinfeng Xu Timothy Heckman Lise Ramambason Yuan Li Cody Carr Weida Hu Zuyi Chen Claudia Scarlata Alaina Henry |
| author_sort | Zixuan Peng |
| collection | DOAJ |
| description | 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. |
| format | Article |
| id | doaj-art-ec5ee431fafb4d6395b975780a9e01dd |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-ec5ee431fafb4d6395b975780a9e01dd2025-08-20T03:05:39ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01981217110.3847/1538-4357/ada606Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf GalaxiesZixuan Peng0https://orcid.org/0000-0003-3467-6810Crystal L. Martin1https://orcid.org/0000-0001-9189-7818Zirui Chen2https://orcid.org/0000-0001-8755-3836Drummond B. Fielding3https://orcid.org/0000-0003-3806-8548Xinfeng Xu4https://orcid.org/0000-0002-9217-7051Timothy Heckman5https://orcid.org/0000-0001-6670-6370Lise Ramambason6https://orcid.org/0000-0002-9190-9986Yuan Li7https://orcid.org/0000-0001-8237-1515Cody Carr8https://orcid.org/0000-0003-4166-2855Weida Hu9https://orcid.org/0000-0003-3424-3230Zuyi Chen10https://orcid.org/0000-0002-2178-5471Claudia Scarlata11https://orcid.org/0000-0002-9136-8876Alaina Henry12https://orcid.org/0000-0002-6586-4446Department of Physics, Broida Hall, University of California at Santa Barbara , Santa Barbara, CA 93106, USA ; zixuanpeng@ucsb.eduDepartment of Physics, Broida Hall, University of California at Santa Barbara , Santa Barbara, CA 93106, USA ; zixuanpeng@ucsb.eduDepartment of Physics, Broida Hall, University of California at Santa Barbara , Santa Barbara, CA 93106, USA ; zixuanpeng@ucsb.eduCenter for Computational Astrophysics, Flatiron Institute , 162 Fifth Avenue, NY, NY 10010, USADepartment of Physics and Astronomy, Northwestern University , 2145 Sheridan Road, Evanston, IL 60208, USACenter for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University , Baltimore, MD 21218, USA; School of Earth and Space Exploration , Arizona State University, Tempe, AZ 85287, USAInstitut fur Theoretische Astrophysik , Zentrum für Astronomie, Universität Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg, GermanyDepartment of Physics, Broida Hall, University of California at Santa Barbara , Santa Barbara, CA 93106, USA ; zixuanpeng@ucsb.eduCenter for Cosmology and Computational Astrophysics , Institute for Advanced Study in Physics, Zhejiang University, Hangzhou 310058, People’s Republic of China; Institute of Astronomy , School of Physics, Zhejiang University, Hangzhou 310058, People’s Republic of ChinaDepartment of Physics and Astronomy , Texas A&M University, College Station, TX 77843-4242, USA; George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy , Texas A&M University, College Station, TX, USASteward Observatory , University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721, USAMinnesota Institute for Astrophysics , University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USACenter for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University , Baltimore, MD 21218, USA; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USAWe 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.https://doi.org/10.3847/1538-4357/ada606Emission line galaxiesDwarf galaxiesGalaxy winds |
| spellingShingle | Zixuan Peng Crystal L. Martin Zirui Chen Drummond B. Fielding Xinfeng Xu Timothy Heckman Lise Ramambason Yuan Li Cody Carr Weida Hu Zuyi Chen Claudia Scarlata Alaina Henry Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies The Astrophysical Journal Emission line galaxies Dwarf galaxies Galaxy winds |
| title | Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies |
| title_full | Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies |
| title_fullStr | Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies |
| title_full_unstemmed | Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies |
| title_short | Physical Origins of Outflowing Cold Clouds in Local Star-forming Dwarf Galaxies |
| title_sort | physical origins of outflowing cold clouds in local star forming dwarf galaxies |
| topic | Emission line galaxies Dwarf galaxies Galaxy winds |
| url | https://doi.org/10.3847/1538-4357/ada606 |
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