Tucson Standard

A team of astronomers led by Catherine Fielder from the University of Arizona has obtained detailed images of a small galaxy, revealing features typically seen in larger galaxies. This study suggests that galaxy growth mechanisms might be more universal than previously thought.

Fielder presented these findings at the 245th meeting of the American Astronomical Society in National Harbor, Maryland. Galaxies grow by merging with smaller ones over billions of years, a process known as hierarchical assembly. While this is well-documented in large galaxies, it remains unclear how smaller galaxies like the Large Magellanic Cloud acquire mass due to their weaker gravitational pull.

The researchers used the Dark Energy Camera on the Blanco Telescope in Chile to survey 11 dwarf galaxies, including NGC 300. This galaxy's disk spans about 94,000 light-years and contains only about 2% of the Milky Way's stellar mass. "NGC 300 is an ideal candidate for such a study because of its isolated location," said Fielder.

Stellar maps created around NGC 300 revealed a vast stellar stream extending over 100,000 light-years from its center. "We consider a stellar stream a telltale sign that a galaxy has accreted mass from its surroundings," said Fielder. The team also found stars arranged in shell-like patterns and hints of a stream wrap, suggesting changes in orbit direction around NGC 300.

"We weren't sure we were going to find anything in any of these small galaxies," she noted. These features provide evidence that NGC 300 accreted something. A previously unknown metal-poor globular star cluster was also identified in the galaxy's halo.

Astronomers often use "metallicity" to gauge stellar population age since heavier elements are forged mostly in massive stars near their end stages. "The stars in the features we observed around NGC 300 are ancient and metal-poor," explained Fielder.

These findings reveal that even dwarf galaxies can build stellar halos through accretion, similar to larger galaxies' growth patterns. "NGC 300 now stands as one of the most striking examples of accretion-driven stellar halo assembly," Fielder stated.

Funding for this research was provided by the National Science Foundation.