Using the Subaru telescope, an international team of astronomers conducted deep multi-spectrum
Barnard's Galaxy (NGC 6822) is located onabout 1.63 million light years from Earth, which is very close by astronomical standards. However, it is located outside the virial radius of the Milky Way. NGC 6822 is known in the Local Group as a dwarf irregular galaxy. Its diameter is about 7,000 light-years and contains a spatially extensive system of globular clusters (GCs).
NGC 6822 can be seen from both northern andfrom the southern hemisphere. And the close proximity allows for a variety of multi-band studies ranging from optical to near-infrared (NIR) and mid-infrared (MIR). Moreover, its chemistry and apparent isolation make NGC 6822 a very interesting laboratory to study stellar pulsation and evolution.
A group of astronomers led by Maria Tantalo fromUniversity of Rome Tor Vergata in Italy carried out precise multi-band photometry of NGC 6822 using the Hyper-Suprime-Cam (HSC) on the Maunakea Subaru Telescope. The HSC data set was complemented by multi-band images obtained with the MegaPrime wide-field camera on the Canada-France Telescope -Hawaii (CFHT), from the Dark Energy Camera (DECam) on the Blanco Telescope at the Cerro Tololo Inter-American Observatory (CTIO) and the Wide Field Camera (WFC) on the Isaac Newton Telescope (INT) in La Palma.
This is the first article in a series on the studyof the stellar composition of NGC 6822 using the advantages of optical photometry collected with wide-field imagers available on 4–8 m class telescopes,” the researchers wrote.
As a result, scientists received a data setwhich cover a 2 square degree area at the center of NGC 6822 with three different photometric bands. In total, scientists performed about 40 million measurements of objects across the entire field of view. The final catalog includes more than 1 million stars with at least one measurement in two different photometric ranges.
It turned out that young, intermediate and oldthe stars in NGC 6822 exhibit different radial distributions. The old stellar population is spherically distributed and extends over larger radial distances than previously thought (about 1 degree). As for the young population, it is distinguished by a well-defined band and a disk-shaped distribution, offset from the center. This is compared to the older population.
Moreover, the study found that the richcarbon, the stars in NGC 6822 are more concentrated in the center, and their structural parameters are similar to both young and old stellar tracers.
Recall that irregular galaxies are galaxiesirregular shapes that do not fit into the Hubble sequence. They have neither a spiral nor an elliptical structure. Most often, such galaxies have a chaotic shape without a pronounced core and spiral arms.
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