An international team of astronomers is taking advantage of NASA's Hubble Space Telescope's unprecedented sharpness and spectral range to publish the most comprehensive high-resolution ultraviolet light measurements of near star-forming galaxies.
The researchers combined new Hubble observations with Hubble archival images for 50 star-forming spiral and dwarf galaxies in the local universe, providing a large and extensive source for understanding the complexities of star formation and galaxy evolution. The project, called the Legacy ExtraGalactic UV Survey (LEGUS), has compiled star catalogs for each of the LEGUS galaxies and cluster catalogs for 30 of the galaxies, as well as images of the galaxies themselves. The data provides detailed information about young, massive stars and star clusters and how their environment affects their development.
"There has never been a star cluster and a stellar catalog of ultraviolet light observations," said Survey Director Daniela Calzetti of the University of Massachusetts, Amherst. "Ultraviolet light is a major tracer of the youngest and hottest star populations astronomers need to deduce the age of stars and obtain a complete star history, and the synergy of the two catalogs offers unprecedented potential for understanding star formation."  How stars form is still an annoying question in astronomy. "Much of the light we get from the universe comes from stars, and yet we still do not understand many aspects of how stars are created," said team member Elena Sabbi from the Space Telescope Science Institute, Baltimore, Maryland. "This is even the key to our existence – we know that life would not be here if we did not have a star."
The research team carefully selected the LEGUS targets from 500 galaxies assembled in ground-based elevations that are between 11 million and 58 million light-years from Earth. The team members chose galaxies based on their mass, the rate of star formation, and the abundance of elements heavier than hydrogen and helium. The catalog of ultraviolet objects collected by NASA's Galaxy Evolution Explorer (GALEX) also helped pave the way for the Hubble study.
The team used Hubble's Wide Field Camera 3 and Advanced Camera for Surveys to capture visible and ultraviolet images of galaxies and their most massive young stars and star clusters for over a year. The researchers also added archive images with visible light to provide a complete picture.
The Star Cluster catalogs contain about 8,000 young clusters whose ages range from 1 million to about 500 million years. These stellar groups are up to ten times more massive than the largest clusters in our Milky Way galaxy.
The star catalogs comprise about 39 million stars, at least five times as massive as our sun. Visible light stars are between one million and several billion years old; The youngest stars, which are between 1 million and 100 million years old, shine prominently in ultraviolet light.
The Hubble data provide all the information needed to analyze these galaxies, the researchers said. "We also offer computer models to help astronomers interpret the data in the star and cluster catalogs," said Sabbi. "For example, researchers can investigate how star formation occurs in a given galaxy or group of galaxies, correlate the properties of galaxies with their star formation, deduce the star formation history of galaxies, and help astronomers identify the precursor stars of supernovae
One of the key questions that astronomers can answer is the connection between star formation and the large structures like spiral galaxies a galaxy high.
"When we look at a spiral galaxy, we usually do not just see a random distribution of stars," said Calzetti. "It is a very ordered structure, whether it be spiral arms or rings, and this is especially true of the youngest stellar populations, but on the other hand, there are several competing theories to connect the individual stars in individual star clusters with these ordered structures."  When we see galaxies in very fine details – the star clusters – and at the same time show the connection to the larger structures, we try to identify the physical parameters that underlie this order of stellar populations within galaxies. The last link between gas and star formation is the key to understanding galaxy evolution.
Team member Linda Smith from the European Space Agency (ESA) and the Space Telescope Science Institute added, "We look at the effects of the environment, especially with star clusters, and how their survival is related to their surrounding environment. "
The LEGUS study will also help astronomers interpret views of galaxies in the distant universe where ultraviolet light is being stretched by young stars. Infrared wavelengths due to the expansion of space." The data in the star and cluster catalogs These nearby galaxies will pave the way for what we will see with the upcoming NASA observatory, the James Webb Space Telescope, the Canadian Space Agency (CSA), "said Sabbi.
Webb observations would complement LEGUS 'views : The space observatory will invade dusty star cocoons to expose the infrared glow of tiny stars not seen in images in visible and ultraviolet light. "Webb will see star formation spreading across a galaxy," Sabbi continued "If you have information about the gas properties, you can really connect the points and see where, when and how star formation happens takes place. "
Hubble covers a galaxy with star births