Gaps in the GD-1 Star Stream

TL;DR

This study analyzes the GD-1 star stream to identify and characterize density gaps, finding results consistent with dark matter sub-halo predictions, and providing insights into the distribution of sub-halos within the Milky Way.

Contribution

It introduces a gap-filtering technique based on simulations to quantify and analyze density variations in the GD-1 stream, supporting dark matter sub-halo models.

Findings

Detected 8±3 significant gaps in GD-1 stream.

Gap distribution aligns with dark matter sub-halo encounter predictions.

Fewer narrow gaps than cold stream models predict, indicating sub-halos below 10^6 M_sun are less common.

Abstract

GD-1 is a long, thin, Milky Way star stream that has readily visible density variations along its length. We quantify the locations, sizes and statistical significance of the density structure, i.e. gaps, using a set of scaled filters. The shapes of the filters are based on the gaps that develop in simulations of dark matter sub-halos crossing a star stream. The high Galactic latitude 8.4 kpc long segment of GD-1 that we examine has 8+/-3 gaps of 99% significance or greater, with the error estimated on the basis of tests of the gap-filtering technique. The cumulative distribution of gaps more than 3 times the width of the stream is in good agreement with predictions for dark matter sub-halo encounters with cold star streams. The number of gaps narrower than 3 times the width of the GD-1 stream falls well below the cold stream prediction which is taken into account for the gap creation rate integrated over all sizes. Simple warm stream simulations scaled to GD-1 show that the falloff in gaps is expected for sub-halos below a mass of 10^6 M_sun. The GD-1 gaps requires 100 sub-halos >10^6 M_sun within 30 kpc, the apocenter of GD-1 orbit. These results are consistent with LCDM sub-halo predictions but further improvements in stream signal-to-noise and gap modeling will be welcome.