A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream

TL;DR

This study uses high-resolution spectroscopy to analyze the chemical abundance variations of s-process elements and titanium in Sagittarius dwarf galaxy stars and its tidal stream, revealing insights into chemical evolution and galaxy contribution to the Milky Way halo.

Contribution

It provides detailed chemical abundance measurements along the Sagittarius stream, showing how satellite galaxy stars contribute to the Milky Way halo and comparing Sagittarius' chemical evolution to other dwarf galaxies.

Findings

Sagittarius stream stars have abundance patterns similar to the LMC, shifted in metallicity.

Chemical evolution of Sagittarius is more rapid than other dwarf galaxies.

Stars farther along the stream show halo-like chemical signatures.

Abstract

We present high-resolution spectroscopic measurements of the abundances of titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on the basis of position and radial velocity. The majority of these stars show peculiar abundance patterns compared to those of nominal Milky Way (MW) stars. The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC) and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from the other dSphs; these relative shifts reflect the faster and/or more efficient chemical evolution of Sgr compared to the other satellites, and show that Sgr has had an enrichment history more like the LMC than the other dSphs. By tracking the evolution of the abundance patterns along the Sgr stream we can follow the time variation of the chemical make-up of dSph stars donated to the MW halo by Sgr. This evolution demonstrates that while the bulk of the stars currently in the Sgr dSph are quite unlike those of the MW halo, an increasing number of stars farther along the Sgr stream have abundances like MW halo stars, a trend that shows clearly how the MW halo could have been contributed by present day satellite galaxies even if the present chemistry of those satellites is now different from typical halo field stars. Finally, we analyze the chemical abundances of a moving group of M giants among the Sgr leading arm stars at the North Galactic Cap, but having radial velocities unlike the infalling Sgr leading arm debris there. Through use of "chemical fingerprinting", we conclude that these northern hemisphere M giants also are Sgr stars, likely trailing arm debris overlapping the leading arm in the north.