The Origin of the 300 km s‑1 Stream near Segue 1

Fu, Sal Wanying; Simon, Joshua D.; Shetrone, Matthew; Bovy, Jo; Beers, Timothy C.; Fernández-Trincado, J. G.; Placco, Vinicius M.; Zamora, Olga; Allende Prieto, Carlos; García-Hernández, D. A. et al.
Bibliographical reference

The Astrophysical Journal, Volume 866, Issue 1, article id. 42, 14 pp. (2018).

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We present a search for new members of the 300 km s‑1 stream (300S) near the dwarf galaxy Segue 1 using wide-field survey data. We identify 11 previously unknown bright stream members in the APOGEE-2 and SEGUE-1 and 2 spectroscopic surveys. Based on the spatial distribution of the high-velocity stars, we confirm for the first time that this kinematic structure is associated with a 24°-long stream seen in SDSS and Pan-STARRS imaging data. The 300S stars display a metallicity range of ‑2.17 < [Fe/H] <‑1.24, with an intrinsic dispersion of {0.21}-0.09+0.12 dex. They also have chemical abundance patterns similar to those of Local Group dwarf galaxies, as well as that of the Milky Way halo. Using the open-source code galpy to model the orbit of the stream, we find that the progenitor of the stream passed perigalacticon about 70 Myr ago, with a closest approach to the Galactic center of about 4.1 kpc. Using Pan-STARRS DR1 data, we obtain an integrated stream luminosity of 4 × 103 L ⊙. We conclude that the progenitor of the stream was a dwarf galaxy that is probably similar to the satellites that were accreted to build the present-day Milky Way halo.
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