Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ −3) Regime

Abstract

In this work, we study the phase-space and chemical properties of the Sagittarius (Sgr) stream, the tidal tails produced by the ongoing destruction of the Sgr dwarf spheroidal (dSph) galaxy, focusing on its very metal-poor (VMP; [Fe/H] 200 VMP stars. We find the leading arm ( b > 0°) of the Sgr stream to be more metal-poor, by ∼0.2 dex, than the trailing one ( b 2 Gyr ago) have present-day phase-space properties similar to lower metallicity stream stars. Conversely, those stripped more recently ( −1) members of the stream. Such correlation between kinematics and chemistry can be explained by the existence of a dynamically hotter, less centrally concentrated, and more metal-poor population in Sgr dSph prior to its disruption, implying that this galaxy was able to develop a metallicity gradient before its accretion. Finally, we identified several carbon-enhanced metal-poor ([C/Fe] > +0.7 and [Fe/H] ≤ −1.5) stars in the Sgr stream, which might be in tension with current observations of its remaining core where such objects are not found.

Keywords

• Stellar streams
• Dwarf galaxies
• CEMP stars
• Galactic archaeology
• Milky Way stellar halo
• Stellar kinematics