Radio emission from neutral hydrogen atoms in the direction of the Orion Nebula, the most nearby regions of high-mass star formation. The red colors show the 21-cm emission from hydrogen, resolved for the first time at this level of detail by observations from the Neutral Atomic Hydrogen in the Solar Neighborhood (NeAtHood) project, led by Juan Diego Soler from the University of Vienna. The cyan colors show the emission from warm interstellar dust in near-infrared light. Credit: Juan D. Soler, University of Vienna, with data from the NRAO's Jansky VLA and NASA's Wide-field Infrared Survey Explorer (WISE).
Hi-Res File New view of a familiar nebula
The Orion Nebula is perhaps the best known nebula, yet new discoveries continue to emerge from observations across all wavelengths of the electromagnetic spectrum. Long known to be a region of active star formation, astronomers using the U.S. National Science Foundation Very Large Array (NSF VLA) have resolved the emission from neutral atomic hydrogen that elucidates how the young stars in Orion are shaping their surrounding neighborhood.
A team of astronomers led by Juan D. Soler of the University of Vienna used the NSF VLA, operated by the U.S. National Science Foundation’s National Radio Astronomy Observatories (NSF NRAO), to obtain high-resolution observations of the emission from neutral hydrogen atoms (HI) at 21 centimeters wavelength. Neutral atomic hydrogen, or H I, is traced by faint radio emission at a wavelength of 21 centimeters. Mapping that emission at high angular resolution is challenging, but the NSF VLA’s interferometric design makes it possible to resolve the structure of nearby star-forming regions.The NSF VLA, therefore, proved to be the best possible instrument for the task, Soler explains. “The NSF VLA is a very unique instrument. It is fundamental, offering the best resolution that we can get in HI from the northern hemisphere. We cannot do this with any other instrument.”
A team of astronomers led by Juan D. Soler of the University of Vienna used the NSF VLA, operated by the U.S. National Science Foundation’s National Radio Astronomy Observatories (NSF NRAO), to obtain high-resolution observations of the emission from neutral hydrogen atoms (HI) at 21 centimeters wavelength. Neutral atomic hydrogen, or H I, is traced by faint radio emission at a wavelength of 21 centimeters. Mapping that emission at high angular resolution is challenging, but the NSF VLA’s interferometric design makes it possible to resolve the structure of nearby star-forming regions.The NSF VLA, therefore, proved to be the best possible instrument for the task, Soler explains. “The NSF VLA is a very unique instrument. It is fundamental, offering the best resolution that we can get in HI from the northern hemisphere. We cannot do this with any other instrument.”
Measuring the bubble directly
When Soler and his team looked deep within the Orion Nebula, they focused on a previously identified expanding bubble formed by young stars. These past observations used tracers such as CII as a proxy for the hydrogen and offered an estimate of the mass associated with star formation. Because Soler’s team was able to observe the HI directly, their data provided a more direct estimate of the bubble’s mass,improving measurements by a factor of ten. “Measuring mass is fundamental,” Soler says, “because it tells us how efficiently these newly formed stars shape their environment with wind and radiation.”
Furthermore, the data obtained by Soler’s team also map the neutral atomic hydrogen in the vast molecular clouds within the Orion Nebula. Soler describes this interrelationship: “Talking about molecular clouds without talking about HI, is like talking about islands without ever mentioning the sea. It turns out that as we’re resolving the sea, we’re finding phenomena like this bubble that are shaping and connecting those molecular clouds. We imagine them as separate objects, not as if they were islands, completely isolated; in fairness, they’re more like archipelagos.”
Furthermore, the data obtained by Soler’s team also map the neutral atomic hydrogen in the vast molecular clouds within the Orion Nebula. Soler describes this interrelationship: “Talking about molecular clouds without talking about HI, is like talking about islands without ever mentioning the sea. It turns out that as we’re resolving the sea, we’re finding phenomena like this bubble that are shaping and connecting those molecular clouds. We imagine them as separate objects, not as if they were islands, completely isolated; in fairness, they’re more like archipelagos.”
First result from NeAtHood
These results, published in Astronomy & Astrophysics, are the first within a larger project called Neutral Atomic Hydrogen in the Solar System Neighborhood (NeAtHood), which aims to continue observing other nearby molecular clouds within star-forming regions visible from the northern hemisphere to produce arcminute-resolution HI maps. Soler looks to the possibility of future observations both within this program and beyond, saying, “[The bubble] is the kind of thing that should be there, but we were not expecting to see this so clearly. So now I wonder, what other surprises are hiding in the data? And in the future, the Next-Generation VLA (ngVLA) is going to target even more distant regions in the Milky Way.”
Links: Scientific Paper
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