Unveiling the Origins of the Leiptr Stellar Stream: A Disrupted Ultra-Faint Dwarf Galaxy?

The study led by Kaia R. Atzberger investigates the chemical composition of the Leiptr stellar stream, which was previously thought to originate from a tidally disrupted globular cluster. Stellar streams are collections of stars that once belonged to larger structures like globular clusters or dwarf galaxies but have been torn apart by the gravitational forces of the Milky Way. By studying the chemical elements in the stars of these streams, scientists can trace their origins, helping to understand the formation and evolution of our galaxy.

Background and Motivation

Stellar streams offer a snapshot of the Milky Way's history of galactic mergers and interactions. Some streams come from globular clusters—tight, old groups of stars—while others originate from dwarf galaxies, which are smaller galaxies swallowed by the Milky Way. Distinguishing between these sources can be difficult, but chemical analysis provides clues. Leiptr was originally believed to be a globular cluster stream, but no detailed chemical studies had been done until now.

Observations

Atzberger and the team observed five candidate stars from the Leiptr stream using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. These stars were selected from a catalog generated by Gaia’s STREAMFINDER algorithm, which helps identify potential members of stellar streams based on their movements through space. One of the stars was found to be a non-member, leaving four for further analysis. The researchers focused on the chemical abundances of elements like iron (Fe), magnesium (Mg), barium (Ba), and strontium (Sr) to infer the origins of these stars.

Results

The four Leiptr stars showed some key characteristics of stars that likely belonged to a low-mass dwarf galaxy. For instance, their metallicity—a measure of how much heavier elements they contain compared to hydrogen—was low, with an average value of [Fe/H] = -2.2. Unlike globular clusters, which tend to have very uniform chemical compositions, the Leiptr stars showed variations in their metallicity and other chemical elements, supporting the idea that Leiptr is the remnant of a dwarf galaxy rather than a globular cluster.

The low abundances of alpha elements like magnesium ([α/Fe] ~ 0) and neutron-capture elements like barium and strontium (with [Ba/Fe] and [Sr/Fe] ~ -1) were especially telling. These patterns are typically found in dwarf galaxies, which undergo different processes of chemical enrichment compared to globular clusters.

Interpretation

The chemical signatures in the Leiptr stars suggest that their progenitor was a low-mass dwarf galaxy, likely in the mass range of ultra-faint dwarf galaxies. These tiny galaxies are some of the most ancient building blocks of the Milky Way and are thought to have formed during the universe’s early stages. The study adds to a growing body of evidence that many stellar streams come from such disrupted dwarf galaxies, revealing more about the galaxy’s formation history.

Conclusion

This research provides the first detailed chemical evidence that the Leiptr stellar stream likely originated from an ultra-faint dwarf galaxy. By studying more stars in the stream and gathering additional data, scientists hope to confirm this conclusion and continue piecing together the history of galactic mergers that shaped the Milky Way.

Source: Atzberger