Searching for the GD-1 Stream Progenitor in Gaia DR2 with Direct N-body Simulations

Abstract

We perform a large suite of direct N-body simulations aimed at revealing the location of the progenitor, or its remnant, of the GD-1 stream. Data from \gaia\ DR2 reveals the GD-1 stream extends over $\approx 100^{\circ }$, allowing us to determine the stream's leading and trailing ends. Our models suggest the length of the stream is consistent with a dynamical age of between 2-3 Gyr and the exact length, width and location of the GD-1 stream correspond to the stream's progenitor being located between $-30^{\circ }<{\varphi }_{1,\mathrm{pro}}<-45^{\circ }$ in the standard GD-1 coordinate system. The model stream density profiles reveal that intact progenitors leave a strong over-density, recently-dissolved progenitors appear as gaps in the stream as escaped stars continue to move away from the remnant progenitor's location, and long-dissolved progenitors leave no observational signature on the remaining stream. Comparing our models to the GD-1 stream yields two possible scenarios for its progenitor's history: a) the progenitor reached dissolution approximately 500 Myr ago during the cluster's previous perigalactic pass and is both located at and responsible for the observed gap at ${\varphi }_1=-40^{\circ }$ or b) the progenitor reached dissolution over 2.5 Gyr ago, the fully-dissolved remnant is at $-30^{\circ }<{\varphi }_1<-45^{\circ }$, and an observational signature of its location no longer exists. That the dissolved progenitor is in the range $-30^{\circ }<{\varphi }_1<-45^{\circ }$ implies that density fluctuations outside of this range, e.g., a deep gap at ${\varphi }_1\approx -20^{\circ }$, are likely produced by compact baryonic or dark-matter perturbers.

arXiv comment9 pages, 5 figures, Accepted for publication in MNRAS

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