DOLORES reveals galactic outflows hidden in SDSS spectra of low-mass galaxies
New observations obtained using the low resolution spectrograph DOLORES installed at the Telescopio Nazionale Galileo (TNG – La Palma) together with EFOSC2 installed at the New Technology Telescope (NTT - Chile), have revealed galactic outflow signatures in low-mass star-forming galaxies that remained undetected in previous Sloan Digital Sky Survey (SDSS) data. By using the highest spectral resolution provided by the VPH grisms of DOLORES, astronomers were able to investigate 52 nearby galaxies (0.01 < z < 0.03) with stellar masses below 10^10 solar masses, uncovering subtle features hidden by the lower resolution of earlier surveys. The sample was carefully selected to include galaxies whose narrow emission lines were expected to remain unresolved in SDSS spectra, based on a comparison of CO line widths, Hα line widths, and the spectral resolution of the survey.
The new spectra show significantly narrower emission lines together with asymmetric profiles and broad wings in the Hα and [OIII] emission lines, clear indicators of gas outflows driven by stellar feedback. These signatures were not visible in the corresponding SDSS spectra, demonstrating the crucial role of higher-resolution observations in studying the physical processes shaping low-mass galaxies.
The study identified outflow signatures in approximately 30% of the observed galaxies, providing strong observational support for theoretical models that predict galactic winds to be widespread in the low-mass regime. The incidence of outflows rises to nearly 60% among galaxies with enhanced star-formation activity, highlighting the close connection between star formation and feedback processes.
These results showcase the capabilities of DOLORES in probing the kinematics of ionized gas and reveal how medium-high resolution spectroscopy can uncover phenomena that remain unresolved in large-scale surveys, opening a new window on the evolution of low-mass galaxies.
Fig.1: Example spectra obtained with TNG/DOLORES spectroscopy using the V656 and V510 grisms with a 1.0" slit.
Fig.2: The solid green line shows a linear fit to the combined SDSS resolved and high-resolution data. The blue solid line shows the linear fit to the resolved SDSS extrapolated to the SDSS unresolved regime as a dashed line. Targets without detections in CO are marked with vertical line markers on the x-axis at the position corresponding to their Hα line widths inferred from their NTT or TNG spectra. Dotted vertical lines show the approximate SDSS resolution R = 2000 (FWHM ∼ 150 km/s), and the median resolution for the sample achieved with TNG (FWHM ∼ 52 km/s) and NTT (FWHM ∼ 78 km/s) for the Hα line.