A NASA-backed study in The Astrophysical Journal says dwarf galaxies retain only a small fraction of the oxygen their stars make, pointing to stronger supernova-driven winds than models predict.
NASA said on November 2 that researchers using the Hubble Space Telescope have found that 37 nearby dwarf galaxies hold far less oxygen than simulations predict. The results appear in a paper published in The Astrophysical Journal as part of the Galaxies Losing Oxygen via Winds (GLOW) project, funded by NASA and the National Science Foundation. The dwarf galaxies studied contain from a few thousand to hundreds of millions of stars, and were chosen because their masses fall in the range where theory expects increasing amounts of oxygen to be expelled.
The team combined archival Hubble optical imaging, which resolves individual stars and reveals star-formation histories, with data from NASA's retired Spitzer Space Telescope and the ground-based Very Large Array and Australian Telescope Compact Array. Oxygen was used as a tracer because it is the most abundant element after hydrogen and helium, is relatively easy to detect, and its production in stars is well understood. According to the study, galactic winds driven by supernovae appear to remove oxygen from low-mass galaxies more effectively than current models assume, so dwarf galaxies keep only a small fraction of what their stars produce.
Researchers say it remains unclear whether the missing oxygen sits in the diffuse gas halo around these galaxies, known as the circumgalactic medium, or has been ejected entirely into intergalactic space. Principal investigator Kristen Wingfield McQuinn said the work helps show how much galaxies enrich the space between them. She hopes to use the Nancy Grace Roman Space Telescope to find even fainter, lower-mass galaxies, then follow up with Hubble and the James Webb Space Telescope, while co-investigator Grace Telford plans detailed Hubble observations of the massive stars involved.
