The Origin of the 300 km s${}^{-1}$ Stream Near Segue 1

Abstract

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${}^{\circ }$-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 $4\times 10^3$ L${}_{\odot }$. 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.

arXiv comment20 pages, 13 figures, accepted to ApJ. Updated with discussion on possible association of 300S with the Virgo Overdensity. Corrected RA range in Fig 2

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