Astronomers using the NASA/ESA Hubble Space Telescope have completed the sharpest, most comprehensive UV-light survey of star-forming galaxies in the local Universe.
These six images represent the variety of star-forming regions in nearby galaxies. The galaxies — part of LEGUS survey — are two dwarf galaxies (UGC 5340 and UGCA 281) and four large spiral galaxies (NGC 4258, NGC 3368, NGC 3627, and NGC 6744). They are between 19 million and 42 million light-years from Earth. The images are a blend of UV and visible light from Hubble’s WFC3 and ACS instruments. Image credit: NASA / ESA / LEGUS Team.
The Hubble’s Legacy ExtraGalactic UV Survey (LEGUS) captured the details of 50 star-forming spiral and dwarf galaxies within 60 million light-years of Earth in both visible and UV light.
The LEGUS astronomers selected its targets from among 500 candidate galaxies, compiled from ground-based surveys, located between 11 million and 58 million light-years from Earth.
They chose the galaxies based on their mass, star-formation rate, and their abundances of elements heavier than hydrogen and helium.
Because of the proximity of the selected galaxies, Hubble was able to resolve them into their main components: stars and star clusters.
With the LEGUS data, gathered with Hubble’s Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS), the researchers created a catalogue with about 8,000 young clusters and it also created a star catalogue comprising about 39 million massive stars.
“The data provide detailed information on young, massive stars and star clusters, and how their environment affects their development,” the astronomers explained.
“As such, the catalogue offers an extensive resource for understanding the complexities of star formation and galaxy evolution.”
“One of the key questions the LEGUS survey may help us answer is the connection between star formation and the major structures, such as spiral arms, that make up a galaxy. These structured distributions are particularly visible in the youngest stellar populations.”
“When we look at a spiral galaxy, we usually don’t just see a random distribution of stars,” said survey leader Dr. Daniela Calzetti, an astronomer at the University of Massachusetts, Amherst.
“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.”
“We’re looking at the effects of the environment, particularly with star clusters, and how their survival is linked to the environment around them,” said team member Dr. Linda Smith, from ESA and the Space Telescope Science Institute.
“The data in the star and cluster catalogs of these nearby galaxies will help pave the way for what we see with the upcoming NASA/ESA/CSA James Webb Space Telescope (JWST),” said team member Dr. Elena Sabbi, from the Space Telescope Science Institute.
LEGUS will not only allow astronomers to understand the local Universe. It will also help interpret views of distant galaxies, where the UV light from young stars is stretched to infrared wavelengths due to the expansion of space.
