Tucson Standard

A team of astronomers led by David Sand from the University of Arizona Steward Observatory has discovered three faint and ultra-faint dwarf galaxies near NGC 300, a galaxy located approximately 6.5 million light-years from Earth. These newly identified galaxies, named Sculptor A, B, and C, provide an opportunity to study small galaxies and understand why their star formation ceased billions of years ago.

Sand shared these findings at the 245th Meeting of the American Astronomical Society in National Harbor, Maryland. The research is published in The Astrophysical Journal Letters.

Ultra-faint dwarf galaxies are the faintest known type of galaxy, containing only a few hundred to thousands of stars compared to the Milky Way's hundreds of billions. Their small size and diffuse nature make them difficult to detect among brighter celestial bodies. Most discoveries have been made near the Milky Way, but its gravitational forces and hot gases can strip away gas from these dwarf galaxies, affecting their evolution.

The three ultra-faint dwarf galaxies found by Sand's team reside in a space isolated from larger objects' influence. They contain only very old stars, supporting theories that star formation was halted early in cosmic history.

"Small galaxies like these are remnants from the early universe," Sand stated. "They help us understand what conditions were like when the first stars and galaxies formed."

The discovery required manual searching through images taken for the DECam Legacy Survey (DECaLS), part of the DESI Legacy Imaging Surveys. Sand recounted finding them during casual searches while watching TV during the pandemic.

The Sculptor galaxies are among the first ultra-faint dwarf galaxies discovered in an environment free from large structures' influence. Further investigation used Gemini South telescope data showing they lack gas and contain old stars, suggesting early cessation of star formation.

"This is exactly what we would expect for such tiny objects," Sand explained. He noted that their isolation means nearby massive galaxies could not have removed their gas.

Potential explanations include high-energy ultraviolet photons during the Epoch of Reionization or supernova explosions pushing out gas within these dwarfs.

Dwarf galaxies may offer insights into studying the early universe as they connect current galactic structures with early cosmological formations.

"We don't know how strong or uniform this reionization effect was," said Sand. More discoveries like Sculptor could clarify this process using machine learning tools for faster identification.

Funding for this work came from the National Science Foundation (NSF). The Gemini Observatory is managed by AURA under an NSF cooperative agreement on behalf of several international partners.