Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters

Abstract

We present chemodynamical links between the present-day Milky Way halo field star population and Galactic globular clusters (GCs) using a dataset that combines information from the $Gaia$ space mission and the Sloan Digital Sky Survey (SDSS-IV, DR14). Moreover, we incorporated a sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of GC stellar populations. Using three different tagging techniques, we could successfully establish unique associations between 151 extratidal stars in the neighborhood of eight GCs. In addition, we traced the possible origin of about $62\%$ of the sample of CN-strong giants to their potential host clusters. Several of the involved GCs have been brought into connection with the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we could identify co-moving groups of stars at the same [Fe/H] with a possible cluster origin. We found strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54. Finally, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to $50.0\pm 16.7\%$ while the associations in the halo field rather imply $80.2_{-5.2}^{+4.9}\%$. We speculate that -- if proven real by spectroscopic follow-up -- the disparity between these numbers could indicate a major contribution of low-mass clusters to the overall number of stars escaped to the halo or, alternatively, point toward a strong mass loss from the first generation during early cluster dissolution. [abridged]

20 pages (+9 pages of appendices), 39 figures, 4 tables, accepted for publication in A&A

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