A closer look at the spur, blob, wiggle, and gaps in GD-1

The GD-1 stream is one of the longest and coldest stellar streams discovered to date, and one of the best objects for constraining the dark matter properties of the Milky Way. Using data from Gaia DR2, we study the proper motions (PMs), distance, morphology, and density of the stream to uncover small-scale perturbations. The PM cleaned data show a clear distance gradient across the stream, ranging from 7 to 12 kpc. However, unlike earlier studies that found a continuous gradient, we uncover a distance minimum at φ1 ≈ −40 deg, after which the distance increases again. We can reliably trace the stream between −85 < φ1 <15 deg, showing an even further extent to GD-1 beyond the earlier extension of Price-Whelan and Bonaca. We constrain the stream track and density using a Boolean matched filter approach and find three large under densities and significant residuals in the stream track lining up with these gaps. The gaps are located at φ1 = −36, −20, and −3 deg, with the gap at −3 deg being surrounded by a clear sinusoidal wiggle. We argue that this wiggle is due to a perturbation since it has the wrong orientation to come from a progenitor. We compute a total initial stellar mass of the stream segment of 1.58 ± 0.07 × 104 M⊙. With the extended view of the spur in this work, we argue that the spur may be unrelated to the adjacent gap in the stream. Finally, we show that an interaction with the Sagittarius dwarf can create features similar to the spur.