Fitting the density substructure of the stellar halo with MilkyWay@home

TL;DR

This paper introduces a method to analyze the stellar density substructures in the Milky Way halo using SDSS data, successfully identifying and characterizing major streams and overdensities, with implications for the galaxy's dark matter halo shape.

Contribution

The paper presents a novel statistical photometric parallax method applied to SDSS data, enabling detailed modeling of halo substructures with a twenty-parameter fit on MilkyWay@home.

Findings

Identified three major halo substructures, including the Sagittarius stream and Virgo Overdensity.

Measured the widths of these streams, revealing a very wide trailing tail.

Results suggest potential implications for the shape of the Milky Way's dark matter halo.

Abstract

We propose and test a method for applying statistical photometric parallax to main sequence turn off (MSTO) stars in the Sloan Digital Sky Survey (SDSS). Using simulated data, we show that if our density model is similar to the actual density distribution of our data, we can reliably determine the density model parameters of three major substructures in the Milky Way halo using the computational resources available on MilkyWay@home (a twenty parameter fit). We fit the stellar density in SDSS stripe 19 with a smooth stellar spheroid component and three major streams. One of these streams is consistent with the Sagittarius tidal stream at $21.1$ kpc away, one is consistent with the trailing tail of the Sagittarius tidal stream in the north Galactic cap at $48$ kpc away, and one is possibly part of the Virgo Overdensity at $6$ kpc away. We find the one sigma widths of these three streams to be $1.0$ kpc, $17.6$ kpc, and $6.1$ kpc, respectively. The width of the trailing tail is extremely wide ($41$ kpc full width at half maximum). This large width could have implications for the shape of the Milky Way dark matter halo. The width of the Virgo Overdensity-like structure is consistent with what we might expect for a "cloud"-like structure; analysis of additional stripes of data are needed to outline the full extent of this structure and confirm its association with the Virgo Overdensity.