Astronomers release most complete ultraviolet-light survey of nearby galaxies

The most comprehensive, high-resolution ultraviolet-light survey of nearby star-forming galaxies.

These six images represent the variety of star-forming regions in nearby galaxies. The galaxies are part of the Hubble Space Telescope's Legacy ExtraGalactic UV Survey (LEGUS), the sharpest, most comprehensive ultraviolet-light survey of star-forming galaxies in the nearby universe. The six images consist of two dwarf galaxies (UGC 5340 and UGCA 281) and four large spiral galaxies (NGC 3368, NGC 3627, NGC 6744, and NGC 4258). The images are a blend of ultraviolet light and visible light from Hubble's Wide Field Camera 3 and Advanced Camera for Surveys. Credits: NASA/ESA/LEGUS team
These six images represent the variety of star-forming regions in nearby galaxies. The galaxies are part of the Hubble Space Telescope's Legacy ExtraGalactic UV Survey (LEGUS), the sharpest, most comprehensive ultraviolet-light survey of star-forming galaxies in the nearby universe. The six images consist of two dwarf galaxies (UGC 5340 and UGCA 281) and four large spiral galaxies (NGC 3368, NGC 3627, NGC 6744, and NGC 4258). The images are a blend of ultraviolet light and visible light from Hubble's Wide Field Camera 3 and Advanced Camera for Surveys. Credits: NASA/ESA/LEGUS team

By merging data from new Hubble observations with archival Hubble images for 50 star-forming spiral and dwarf galaxies in the local universe, an international team of astronomers at NASA is releasing the most comprehensive, high-resolution ultraviolet-light survey of nearby star-forming galaxies. This is a vast and broad asset for understanding the complexities of star development and cosmic system advancement.

The project, called the Legacy ExtraGalactic UV Survey (LEGUS), has amassed star catalogs for each of the LEGUS galaxies and cluster catalogs for 30 of the galaxies, as well as images of the galaxies themselves.

Survey leader Daniela Calzetti of the University of Massachusetts, Amherst said, “There has never before been a star cluster and a stellar catalog that included observations in ultraviolet light. Ultraviolet light is a major tracer of the youngest and hottest star populations, which astronomers need to derive the ages of stars and get a complete stellar history. The synergy of the two catalogs combined offers an unprecedented potential for understanding star formation.”

Elena Sabbi of the Space Telescope Science Institute in Baltimore, Maryland said, “Much of the light we get from the universe comes from stars, and yet we still don’t understand many aspects of how stars form. This is even key to our existence — we know life wouldn’t be here if we didn’t have a star around.”

The exploration group precisely chose the LEGUS focuses from among 500 galaxies, compiled in ground-based reviews, situated between 11 million and 58 million light-years from Earth. Scientists chose the galaxies based on their mass, star-formation rate, and abundances of components that are heavier than hydrogen and helium. The inventory of ultraviolet objects gathered by NASA’s Galaxy Evolution Explorer (GALEX) shuttle additionally helped lay the way for the Hubble study.

In order to capture visible and ultraviolet-light images of the galaxies, scientists took help of Hubble’s Wide Field Camera 3 and the Advanced Camera. They also captured most massive young stars and star clusters.

The data suggest that star cluster catalogs contain about 8,000 young clusters whose ages range from 1 million to roughly 500 million years old. These stellar groupings are as much as 10 times more enormous than the biggest bunches found in our Milky Way cosmic system.

The star catalogs include around 39 million stars that are no less than five times more enormous than our Sun. Stars in the noticeable light pictures are between 1 million and a few billion years of age; the most youthful stars, those between 1 million and 100 million years of age, sparkle conspicuously in bright light.

Sabbi said, “We also are offering computer models to help astronomers interpret the data in the star and cluster catalogs. Researchers, for example, can investigate how star formation occurred in one specific galaxy or a set of galaxies. They can correlate the properties of the galaxies with their star formation. They can derive the star-formation history of the galaxies. The ultraviolet-light images may also help astronomers identify the progenitor stars of supernovas found in the data.”

Calzetti said, “When we look at a spiral galaxy, we usually don’t just see a random distribution of stars. It’s a very orderly structure, whether it’s spiral arms or rings, and that’s particularly true with the youngest stellar populations. On the other hand, there are multiple competing theories to connect the individual stars in individual star clusters to these ordered structures.”

“By seeing galaxies in very fine detail — the star clusters — while also showing the connection to the larger structures, we are trying to identify the physical parameters underlying this ordering of stellar populations within galaxies. Getting the final link between gas and star formation is key for understanding galaxy evolution.”

Team member Linda Smith of the European Space Agency (ESA) and the Space Telescope Science Institute added: “We’re looking at the effects of the environment, particularly with star clusters, and how their survival is linked to the environment around them.”

Sabbi said, “Webb observations would be complementary to the LEGUS views. The space observatory will penetrate dusty stellar cocoons to reveal the infrared glow of infant stars, which cannot be seen in visible- and ultraviolet-light images. Webb will be able to see how star formation propagates over a galaxy. If you have information on the gas properties, you can really connect the points and see where, when, and how star formation happens.”

According to scientists, the discovery could help astronomers interpret views of galaxies in the distant universe, where the ultraviolet glow from young stars is stretched to infrared wavelengths due to the expansion of space.

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