Modeling GD-1 Gaps in a Milky-Way Potential

TL;DR

This paper investigates the density gaps in the GD-1 star stream to test dark matter sub-halo predictions, using filters and simulations to analyze gap distributions and their origins in a Milky Way-like potential.

Contribution

It introduces a method to characterize and measure stream gaps, and uses simulations to link large gaps to dark matter sub-halos in the galaxy's halo.

Findings

Density variations are three times higher than expected from star count variance.

Large gaps (>1 kpc) are consistent with sub-halos at predicted abundance.

Small gaps are mostly noise, while large gaps indicate sub-halo interactions.

Abstract

The GD-1 star stream is currently the best available for identifying density fluctuations, "gaps", along its length as a test of the LCDM prediction of large numbers of dark matter sub-halos orbiting in the halo. Density variations of some form are present, since the variance of the density along the stream is three times that expected from the empirically estimated variation in the filtered mean star counts. The density variations are characterized with filters that approximate the shape of sub-halo gravitationally induced stream gaps. The filters locate gaps and measures their amplitude, leading to a measurement of the distribution of gap widths. To gain understanding of the factors influencing the gap width distribution, a suite of collisionless n-body simulations for a GD-1 like orbit in a Milky Way-like potential provides a dynamically realistic statistical prediction of the gap distribution. The simulations show that every location in the stream has been disturbed to some degree by a sub-halo. The small gaps found via the filtering are largely noise. Larger gaps, those longer than 1 kpc, or 10 degrees for GD-1, are the source of the excess variance. The suite of stream simulations shows that sub-halos at the predicted inner halo abundance or possibly somewhat higher can produce the required large sale density variations.