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.
Credits
NASA, ESA, and the LEGUS team| About The Object | |
|---|---|
| Object Name | Selection of galaxies from the Legacy Extra-Galactic Ultraviolet Survey (UGC 5340, NGC 4258, UGCA 281, NGC 3368, NGC 3627, NGC 6744) |
| Object Description | Spiral and dwarf galaxies |
| About The Data | |
| Data Description | The HST observations include those from the survey program (D. Calzetti/University of Massachusetts, Amherst) |
| Instrument | WFC3/UVIS, ACS/WFC |
| Exposure Dates | 17 August 2013 to 17 September 2014 |
| Filters | F275W, F336W, F438W, F606W, F555W, F814W |
| About The Image | |
| Color Info | These images are a composite of separate exposures acquired by the WFC3 and ACS instruments on the Hubble Space Telescope. Several filters were used to sample narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Magenta: F275W Blue: F336W+F438W Green: F555W or F606W Red: F814W |
| Compass Image |  |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
