SC Connecticut News

A series of recent studies has provided new insights into the Milky Way's satellite galaxies. These studies, part of the Satellites Around Galactic Analogs (SAGA) Survey, offer a comparison between our galaxy and others in the universe.

Since 2012, the SAGA Survey has examined 101 galaxies similar to the Milky Way, identifying hundreds of smaller satellite galaxies orbiting them. This research contributes to understanding galaxy formation and evolution.

Three new studies accepted for publication in The Astrophysical Journal indicate that while most Milky Way satellites have stopped forming stars, many systems studied by SAGA still show star formation. However, the number of observable Milky Way satellites aligns with those in other systems surveyed by SAGA.

"The Milky Way’s satellite population is a unique combination of small satellites containing only older stars, and its two largest satellites, which are actively forming new stars," said Marla Geha, a professor at Yale University and co-founder of the SAGA Survey alongside Yao-Yuan Mao from the University of Utah and Risa Wechsler from Stanford University.

The recent studies mark the final release of data from the SAGA Survey following earlier releases in 2017 and 2021. "Our work is similar to character development in a movie," Geha noted. "The SAGA Survey results help us construct a backstory for the Milky Way."

One study highlights 378 satellite galaxies across 101 larger systems with confirmed satellites ranging from zero to 13 per system compared to four observable for the Milky Way. While about 60 known satellites exist around our galaxy, most are too faint for SAGA detection.

Another study suggests that systems with more massive satellite galaxies tend to have more overall satellites. It also finds that closer satellite galaxies are more likely to have their star formation quenched due to environmental factors.

A third study uses these findings to refine theoretical models of galaxy formation. It predicts that quenched galaxies should also be found in isolated environments—a hypothesis testable through future spectroscopic surveys.

Researchers believe these studies will enhance understanding of dark matter halos' role in galaxy evolution. Dark matter halos contain dense patches where all galaxies form; smaller ones can become satellites if caught by a larger host's gravitational pull.

The way low-mass galaxies fall into such gravity wells may depend on factors beyond just mass—possibly involving environmental aspects around each galaxy as well.

The National Science Foundation and Heising-Simons Foundation supported this research using data from numerous public and private sky surveys along with specialized instruments.