The Stellar Density of the Major Substructure in the Milky Way Halo

Abstract

We develop, test, and apply a statistical photometric parallax method using main sequence turn off (MSTO) stars in the Sloan Digital Sky Survey (SDSS). We show using simulated data that if our density model is similar to the actual density distribution of our data, we can reliably determine the density model parameters of at least three major substructures in the Milky Way halo, and a smooth background component, using the computational resources available on MilkyWay@home (a twenty parameter fit). As a test for the new model, we fit the stellar density in SDSS stripe 19. After confirming that the model is working as intended on both simulated and observed SDSS stripe 19 data, we moved on to fitting stripes 10 through 23 in the SDSS north Galactic cap. We found an oblate halo with an average flattening of $0.58$. Seven streams were found in these fourteen stripes. The Sgr dwarf leading tidal tail detected in 8 stripes, with properties that are consistent with previous fits to the streams. The trailing tidal tail and the ''bifurcated'' stream were found at the previously identified distances. The Parallel Stream was traced across the sky at a distance of 15 kpc, and roughly tracks an orbit that was fit by previous authors to the Virgo Stellar Stream. A new stream, the Perpendicular Stream, was found at a distance of 15 kpc in the region of Virgo, but roughly perpendicular in orientation on the sky to the Parallel Stream. A stream possibly including the globular cluster NGC 5466 was also found at a distance between 5 and 15 kpc from the Sun.