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 LEGUS survey combines new Hubble observations with archival Hubble images for 50 nearby star-forming spiral and dwarf galaxies, offering a large and extensive resource for understanding the complexities of star formation and galaxy evolution. Astronomers are releasing the 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 catalogs provide detailed information on young, massive stars and star clusters, and how their environment affects their development.
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.
All of the galaxies are undergoing vigorous star and star-cluster formation. One of the goals of LEGUS is to sample star-forming regions across each galaxy. Because the galaxies are relatively close to Earth, Hubble can resolve individual stars.
The most intense and most recent star birth in the dwarf galaxies is concentrated away from the center. In UGC 5340, a pocket of rapid star birth appears in the lower right corner, and may have been triggered by a gravitational interaction with an unseen companion galaxy. Star formation is present across the entire body of UGC 5340, and the relatively young stars are responsible for the galaxy's blue-white color.
In UGCA 281, two giant star clusters appear brilliant white and are swaddled by greenish hydrogen gas clouds. These clusters are responsible for most of the recent star formation in UGCA 281; the rest of the galaxy is comprised of older stars and appears redder in color than UGC 5340. The reddish objects in the images of the dwarf galaxies are background galaxies that appear through these diffuse objects.
In the spiral galaxies, a wave of star formation is occurring along the dark filaments that make up the spiral arms. The fledgling stars illuminate the surrounding hydrogen gas, making the stars appear pink. Star birth begins at the inner spiral arms and moves outward. The milky white regions in the center of these galaxies represent the glow of countless numbers of stars.
The star clusters in these galaxies range in age from 1 million to roughly 500 million years old. These stellar groupings are as much as 10 times more massive than the largest clusters seen in our Milky Way galaxy.
The galaxies' stars that can be detected in the images range from the size of our Sun to more than 100 times our Sun's mass. They are between 1 million and several billion years old.
The six galaxies are between 19 million and 42 million light-years from Earth.
They were observed between January 2014 and July 2014.