Astronomers using the Hubble Space Telescope have found that dwarf galaxies retain only a small fraction of the oxygen their stars produce, while galactic winds apparently remove oxygen from low-mass galaxies more effectively than current models predict, according to a study published Monday in The Astrophysical Journal.
The findings, from the Galaxies Losing Oxygen via Winds (GLOW) project, challenge existing simulations that predicted significantly more oxygen should remain in the galaxies. "Oxygen is produced by stars, which are inside of galaxies. We know that the oxygen had to be inside of the galaxies at some point in the past, so the oxygen must have been ejected," said co-investigator Grace Telford, assistant professor in the Department of Physics and Astronomy at the University of Utah. "And to do that, you need energy from massive stars and supernova explosions to drive material out of the host galaxies and into the space between galaxies."
Dwarf galaxies are small systems containing a few thousand to hundreds of millions of stars. Oxygen, the most abundant element after hydrogen and helium, serves as a reliable tracer for how chemical elements are distributed in a galaxy because it is relatively easy to detect and its production is well understood. "It's really for practical reasons that we've chosen oxygen," said Kristen Wingfield McQuinn, GLOW principal investigator and mission head of the Science Operations Center for NASA's Nancy Grace Roman Space Telescope.
The study analyzed 37 nearby dwarf galaxies using archival optical data from Hubble along with data from NASA's retired Spitzer Space Telescope, the Very Large Array, and the Australian Telescope Compact Array. Researchers traced oxygen atoms produced by stars to understand how they are distributed across stars, gas, and dust. They found that galactic winds from supernovae are apparently more effective at removing oxygen from low-mass galaxies than current models predict.
"Oxygen is one of the primary elements formed by stars. Being able to trace how much oxygen gets made, and then how much is distributed inside and outside of galaxies, helps us understand galaxy evolution," said McQuinn. "It also helps us learn where and how much galaxies are enriching the space between galaxies, called the intergalactic medium."
The galaxies were chosen because their masses fall in the range where simulations and theory predict increasing oxygen loss, and because they are close enough for Hubble to resolve individual stars. A previous study from 2014 addressed oxygen loss in Milky Way-like galaxies, but the GLOW project extended this to low-mass galaxies across a wide range of masses and environments.
McQuinn has an approved program to use the Roman Space Telescope to find even lower-mass dwarf galaxies. Once identified, she hopes to use Hubble and the James Webb Space Telescope for deeper observations to reconstruct the galaxies' star-formation histories. Telford plans to use Hubble to study individual massive stars in these dwarf galaxies and characterize how they differ in these small galaxies.
Analysis
Why This Matters
- Oxygen loss affects how dwarf galaxies evolve and enrich the space between galaxies, influencing models of galaxy formation.
- The findings suggest current simulations underestimate the efficiency of supernova-driven winds in low-mass galaxies.
- Understanding dwarf galaxies, the most common type in the universe, helps refine theories of how larger galaxies like the Milky Way formed.
Background
Dwarf galaxies are the most common type of galaxy in the universe. Because of their low mass, they are more susceptible to losing material through supernova explosions. The GLOW project, funded by NASA and the National Science Foundation, aimed to measure how much oxygen is retained versus lost in these small systems. Previous research on Milky Way-like star-forming galaxies found they also lose a large fraction of oxygen, some of which ends up in the circumgalactic medium. The GLOW study extended this research to low-mass galaxies across a wider range of masses and environments.
What to Watch
- Future observations using the Roman Space Telescope to identify ultra-faint dwarf galaxies across a wide area of sky.
- Deeper observations with Hubble and the James Webb Space Telescope to reconstruct star-formation histories in these systems.
- Detailed studies of individual massive stars in dwarf galaxies to characterize oxygen production and ejection.
Checked
12 claims in this story checked against 1 source: 12 supported.
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- SupportedThe headline says Hubble found that dwarf galaxies hold little of their oxygen.NASA: “Researchers found that dwarf galaxies can hold onto only a small fraction of the oxygen made by their stars.”
- SupportedThe study of 37 nearby dwarf galaxies found that supernova-driven winds apparently remove oxygen more effectively than current models predict.NASA: “Galactic winds unleashed by supernovae are apparently more effective at removing oxygen from low-mass galaxies than current models predict, according to the new study.”
- SupportedHubble researchers found that dwarf galaxies retain only a small fraction of the oxygen their stars produce.NASA: “The findings show that dwarf galaxies can hold onto only a small fraction of the oxygen made by stars.”
- SupportedThe study was published Monday in The Astrophysical Journal.NASA: “In a paper published Monday in The Astrophysical Journal, researchers using Hubble studied 37 nearby dwarf galaxies”
- SupportedTelford said oxygen had been inside galaxies in the past and must have been ejected.NASA: ““Oxygen is produced by stars, which are inside of galaxies. We know that the oxygen had to be inside of the galaxies at some point in the past, so the oxygen must have been ejected,” said co-investigator Grace Telford”
- SupportedTelford said massive stars and supernova explosions provide energy to drive material out of host galaxies and into the space between galaxies.NASA: ““And to do that, you need energy from massive stars and supernova explosions to drive material out of the host galaxies and into the space between galaxies.””
- SupportedThe study analyzed 37 nearby dwarf galaxies using Hubble optical data and data from Spitzer, the Very Large Array and the Australian Telescope Compact Array.NASA: “Along with data from NASA’s retired Spitzer Space Telescope as well as the ground-based Very Large Array and Australian Telescope Compact Array, the researchers analyzed 37 nearby dwarf galaxies”
- SupportedSimulations predicted that significantly more oxygen should remain in the galaxies.NASA: “Simulations predict that significantly more oxygen, a tracer of a wider set of heavy elements, should reside in these galaxies.”
- SupportedMcQuinn said oxygen was chosen for practical reasons.NASA: ““So, it’s really for practical reasons that we’ve chosen oxygen,” said Kristen Wingfield McQuinn”
- SupportedOxygen is the most abundant element after hydrogen and helium and is a reliable indicator of how chemical elements are distributed in a galaxy because it is relatively easy to detect and its production is well understood.NASA: “Oxygen, the most abundant element after hydrogen and helium, is relatively easy to detect and measure, and its production is well understood — making it a reliable indicator of how chemical elements are distributed in a galaxy.”
- SupportedA 2014 study addressed oxygen loss in Milky Way-like galaxies, and GLOW extended that research to low-mass galaxies across a wide range of masses and environments.NASA: “A previous study from 2014 addressed this question for Milky Way-like, star-forming galaxies”
- SupportedMcQuinn has an approved Roman Space Telescope program to find lower-mass dwarf galaxies and hopes to use Hubble and Webb for deeper observations of them.NASA: “She has an approved program to use the Roman Space Telescope to find these faint and tiny systems across a wide swath of sky. Once she’s identified these galaxies, McQuinn hopes to use Hubble and NASA’s James Webb Space Telescope to get deeper observations of their stars.”
