Higher-resolution optical spectra of M * < 10 10 M ⊙ galaxies reveal outflow signatures unresolved by the SDSS
Year: 2026
Type: article
Abstract: Galactic outflows are predicted to be ubiquitous in low-mass galaxies, but observational evidence is lacking. Both a low signal-to-noise ratio and a low spectral resolution can severely hamper the detection of galactic outflows, especially in small galaxies that have intrinsically narrow spectral lines. In an effort to overcome these issues, we obtained new, medium-high resolution (FWHM inst ∼ 50 − 110 km/s) optical spectra of 52 local star-forming galaxies (0.01 < z < 0.03) with stellar masses 10 8.5 < M * /[ M ⊙ ]< 10 10 , using the TNG/DOLORES and NTT/EFOSC2 instruments. Our parent sample consists of galaxies from the Sloan Digital Sky Survey (SDSS) with available heterodyne single-dish molecular (i.e., CO) line data. The targets of this study are selected among those that, based on the comparison between CO line widths, SDSS spectral resolution, and corresponding SDSS-based H α line widths, have a high chance of being unresolved by SDSS spectroscopy. Our new, medium-high resolution spectra reveal overall narrower H α and [OIII] λ 5007 lines, with signs of asymmetries and broad wings that are absent in the SDSS spectra of the same galaxies. This confirms our hypothesis that SDSS spectroscopy does not resolve the narrow emission lines of low- M * galaxies, which hinders the detection of outflows. We identify outflow signatures in ∼30% of our targets based on the H α line spectra. Assuming a typical bi-conical outflow geometry, this detection rate is consistent with theoretical predictions of ubiquitous outflows in the low-mass regime. The outflow incidence is enhanced (∼60%) for galaxies with above average star-formation rates (SFR) for the sample (SFR > 10 −0.74 M ⊙ /yr). We estimate ionized gas mass outflow rates ranging from ∼0.1 − 50 × 10 −3 M ⊙ /yr (mean ∼20 × 10 −3 M ⊙ /yr) and corresponding mass loading factors between 0.03 and 0.14 (mean ∼0.07) for the sample.
Source: Astronomy and Astrophysics
Institutions: University of Oslo, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, University of Bologna, Brera Astronomical Observatory, Armagh Observatory & Planetarium, Max Planck Institute for Radio Astronomy, University College London, Osservatorio Astronomico di Padova
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, U.S. Department of Energy, Alfred P. Sloan Foundation, Yale University, Vanderbilt University, Princeton University, Ohio State University, Harvard University, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Portsmouth, New Mexico State University, York University, European Commission, Office of Science, College of Engineering, Michigan State University, HORIZON EUROPE Framework Programme, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory
OpenAlex ID: W7152000613