A Trifurcated Sagittarius Stream in the South

We identify substructure in SDSS stripes 80-86 in the southern Galactic cap using statistical photometric parallax of blue main sequence turnoff stars. By optimizing a halo model over the data using MilkyWay@home, we recover structures consistent with the Sagittarius Stream trailing tail, the Bifurcated Stream, and the Cetus Polar Stream. Analysis of the fit shape of the Sagittarius Stream suggests the existence of a previously undiscovered branch of the Stream, which lies coincident on the sky but at different distances than the main branch of the Sagittarius trailing tail. We explore potential mechanisms of generating this new trifurcated branch. We measure the flattening parameter q of the smooth stellar halo to be 0.40±0.10, which is smaller (more oblate) than the measurements in the Galactic north.