EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with $M_{\ast }=10^4-10^7{M}_{\odot }$: Weak Feedback in Low-Mass Galaxies?

Abstract

We study emission line profiles of 21 nearby low-mass ($M_{\ast }=10^4-10^7{M}_{\odot }$) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star-formation rates of $\mathrm{sSFR}\sim 100-1000{\mathrm{Gyr}}^{-1}$ that are well above the star-formation main sequence and its extrapolation. We identify broad-line components of H$\alpha$ and [OIII]$\lambda 5007$ emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The board-line components have moderately large line widths of $\sim 100$ km s${}^{-1}$. We estimate the maximum outflow velocities $v_{\max }$ and obtain values of $\simeq 60-200$ km s${}^{-1}$, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of $v_{\max }$ with star-formation rates, stellar masses, and circular velocities, extend down into this low-mass regime. Broad- to narrow-line flux ratios BNRs are generally found to be smaller than those of massive galaxies. The small $v_{\max }$ and BNRs suggest that the mass loading factors $\eta$ can be as small as 0.1 - 1 or below, in contrast to the large $\eta$ of energy-driven outflows predicted by numerical simulations.

22 pages, 11 figures, Accepted for publication by ApJ

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• EMPRESS. V. Metallicity Diagnostics of Galaxies over 12+log(O/H)=~6.9-8.9 Established by a Local Galaxy Census: Preparing for JWST Spectroscopy
• Shaken, not blown: the gentle baryonic feedback of nearby starburst dwarf galaxies
• The evolution of CNO elements in galaxies
• EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations
• New Ionization Models and the Shocking Nitrogen Excess at z > 5
• EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs
• EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies
• An Escaping Outflow in a Galaxy with an Intermediate-mass Black Hole
• Extreme Metallicity Dwarf Galaxies in IllustrisTNG
• Higher resolution optical spectra of $M_{\ast }<10^{10}{M}_{\odot }$ galaxies reveal outflow signatures unresolved by the SDSS