Hints of a disrupted binary dwarf galaxy in the Sagittarius stream

ABSTRACT In this work, we look for evidence of a non-unity mass ratio binary dwarf galaxy merger in the Sagittarius stream. Simulations of such a merger show that, upon merging with a host, particles from the less massive galaxy will often mostly be found in the extended stream and less so in the central remnant. Motivated by these simulations, we use the Apache Point Observatory Galactic Evolution Experiment Data Release 17 chemical data from approximately 1100 stars in both the Sagittarius remnant and stream to look for evidence of contamination from a second dwarf galaxy. We separate the Sagittarius data into its remnant and stream and compare the Mg/Fe content of the two populations. In particular, we select Mg/Fe to search for hints of unique star formation histories among our sample stars. Comparing the stream and remnant populations, we find regions that have distinct Mg/Fe distributions for fixed Fe/H, in addition to distinct chemical tracks in Mg/Fe–Fe/H abundance space. We show that there are large regions of the tracks for which the probability of the two samples being drawn from the same distribution is very low (p 0.05). Furthermore, we show that the two tracks can be fit with unique star formation histories using simple, one-zone galactic chemical evolution models. While more work must be done to discern whether the hypothesis presented here is true, our work hints at the possibility that Sagittarius may consist of two dwarf galaxy progenitors.