Chemical Abundances in the Leiptr Stellar Stream: A Disrupted Ultra-faint Dwarf Galaxy?

TL;DR

This study analyzes the chemical composition of stars in the Leiptr stellar stream to determine its origin, suggesting it is likely a disrupted ultra-faint dwarf galaxy with very low metallicity and distinctive element abundance patterns.

Contribution

It provides the first detailed chemical abundance analysis of the Leiptr stream, indicating its progenitor was a very low-mass dwarf galaxy, possibly an ultra-faint dwarf galaxy, which is a novel insight.

Findings

Stars in Leiptr have low metallicity (~-2.2)

Chemical patterns match those of low-mass dwarf galaxies

Leiptr may be the lowest-mass dwarf galaxy stream identified

Abstract

Chemical abundances of stellar streams can be used to determine the nature of a stream's progenitor. Here we study the progenitor of the recently discovered Leiptr stellar stream, which was previously suggested to be a tidally disrupted halo globular cluster. We obtain high-resolution spectra of five red giant branch stars selected from the Gaia DR2 STREAMFINDER catalog with Magellan/MIKE. One star is a clear non-member. The remaining four stars display chemical abundances consistent with those of a low-mass dwarf galaxy: they have a low mean metallicity, $\langle{\rm[Fe/H]}\rangle = -2.2$; they do not all have identical metallicities; and they display low [$\alpha$/Fe] $\sim 0$ and [Sr/Fe] and [Ba/Fe] $\sim -1$. This pattern of low $\alpha$ and neutron-capture element abundances is only found in intact dwarf galaxies with stellar mass $\lesssim 10^5 M_\odot$. Although more data are needed to be certain, Leiptr's chemistry is consistent with being the lowest-mass dwarf galaxy stream without a known intact progenitor, possibly in the mass range of ultra-faint dwarf galaxies. Leiptr thus preserves a record of one of the lowest-mass early accretion events into the Milky Way.