Chemical Properties and Sagittarius-induced Dynamical Perturbations of the GD-1 Stream

Abstract

In this study, we investigate the chemical properties of the GD-1 stream using cross-matched, data-driven elemental abundances. The results reveal no clear $α$-knee in the [Mg/Fe]-[Fe/H] plane, and strong abundance consistency between the thin stream and cocoon, supporting a common origin. The absence of multiple-population signatures (e.g., C-N anti-correlation) suggests a low-mass progenitor. Using a test-particle simulation with the particle spray method and including perturbations from the Sagittarius (Sgr) dwarf galaxy, it shows that Sgr does not significantly heat the stream to form the cocoon, but modifies the intrinsic $φ_2$ distribution, in agreement with observations. The trailing arm narrowly distributed across the width of the stream, while the leading arm is more diffuse, indicating that major fraction of cocoon stars are present towards the leading arm. Sgr also drags more stream particles moving toward the Galactic center, producing an excess at $V_{\text{GSR}}<0$, consistent with data. Our study confirms the Sgr has a non-negligible dynamical influence on the GD-1 stream. Other heating mechanisms (e.g., dark matter sub-halo encounters and pre-stripping process inside the parent halo) remain to be considered, and higher-resolution spectroscopy is needed to further constrain chemical abundances.

Figures (9)

• Figure 1: The distribution of the sample in $\phi_1$–$\phi_2$ coordinates (orange dots), with two spur stars marked as red stars. The red line indicates the main track fitted by a cubic spline with five knots (green pentagons) located at [$-80$,$-1.8$], [$-60$,$-0.5$], [$-40$,$-0.2$], [$-20$,$0.0$], and [$-10$,$-0.4$], adjusted following Valluri2025. The black dashed line represents the track obtained by Li2018 using polynomial fitting for comparison. The diffuse "cocoon" structure is also labeled in the figure.
• Figure 2: The posterior distributions of the five parameters. Note that $f_c + f_s = 1$ and the median values of parameters are used to calculate the possibility of membership.
• Figure 3: Left panel: the [Mg/Fe]–[Fe/H] distribution of the GD-1 stream, with Mg abundances cross-matched from Zhang2024 and Liu2025. The black error bar represents the median uncertainties of the sample. Middle panel: 1000 Monte Carlo realizations of the median [Mg/Fe] trends. Right panel: the Pearson correlation coefficient for each realization, with the 16th, 50th, and 84th percentiles of the coefficients indicated.
• Figure 4: The KDE plots for the stream (blue) and cocoon (orange) stars among six elements. The p-values in the first row are the KS test results without uncertainties, and the p-values in the second row are the results considering Gaussian perturbations with an uncertainty of 0.2 dex.
• Figure 5: The distributions of GD-1 member stars, considering only the abundances from Zhang2024, are shown for the C-N, C-O, and Mg-Al relations. The red line represents a linear fit obtained from 1,000 bootstrap re-samplings, and the orange shaded area corresponds to the 16th and 84th percentiles of the distribution. Both Spearman and Pearson correlation coefficients, along with their p-values, are indicated, as well as the sample size. The samples in the second row are further restricted by an error cut requiring errors to be $<0.15$ dex.