GD-1 Stellar Stream and Cocoon in the DESI Early Data Release

GD-1 Stellar Stream and Cocoon in the DESI Early Data Release

We present  ∼115 new spectroscopically identified members of the GD-1 tidal stream observed with the 5000-fiber Dark Energy Spectroscopic Instrument (DESI). We confirm the existence of a “cocoon,” which is a broad (FWHM ∼ 2 $\mathop{.}\limits^{\unicode{x000b0}}$ 932 ∼ 460 pc) and kinematically hot (...

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Main Authors: M. Valluri, P. Fagrelius, S. E. Koposov, T. S. Li, Oleg Y. Gnedin, E. F. Bell, R. G. Carlberg, A. P. Cooper, J. Aguilar, S. Ahlen, C. Allende Prieto, V. Belokurov, L. Beraldo e Silva, D. Brooks, A. Byström, T. Claybaugh, K. Dawson, A. Dey, P. Doel, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, J. Han, K. Honscheid, T. Kisner, A. Kremin, A. Lambert, M. Landriau, L. Le Guillou, M. E. Levi, A. de la Macorra, M. Manera, P. Martini, G. E. Medina, A. Meisner, R. Miquel, J. Moustakas, A. D. Myers, J. Najita, C. Poppett, F. Prada, M. Rezaie, G. Rossi, A. H. Riley, E. Sanchez, D. Schlegel, M. Schubnell, D. Sprayberry, G. Tarlé, G. Thomas, B. A. Weaver, R. H. Wechsler, R. Zhou, H. Zou
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
Subjects:
Atomic spectroscopy
Spectroscopy
Milky Way dark matter halo
Dark matter
Stellar streams
Milky Way dynamics
Online Access:https://doi.org/10.3847/1538-4357/ada690
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Summary:We present  ∼115 new spectroscopically identified members of the GD-1 tidal stream observed with the 5000-fiber Dark Energy Spectroscopic Instrument (DESI). We confirm the existence of a “cocoon,” which is a broad (FWHM ∼ 2 $\mathop{.}\limits^{\unicode{x000b0}}$ 932 ∼ 460 pc) and kinematically hot (velocity dispersion, σ  ∼ 5–8 km s ^−1 ) component that surrounds a narrower (FWHM ∼ 0 $\mathop{.}\limits^{\unicode{x000b0}}$ 353 ∼ 55 pc) and colder [( σ  = 3.09 ± 0.76 km s ^−1 )] thin stream component (based on a median per star velocity precision of 2.7 km s ^−1 ). The cocoon extends over at least a 30 ^∘ segment of the stream observed by DESI. The thin and cocoon components have similar mean values of [Fe/H]: −2.54 ± 0.04 dex and −2.47 ± 0.06 dex, suggestive of a common origin. The data are consistent with the following scenarios for the origin of the cocoon. The progenitor of the GD-1 stream was an accreted globular cluster (GC) and: (a) the cocoon was produced by pre-accretion tidal stripping of the GC while it was still inside its parent dwarf galaxy; (b) the cocoon comprises debris from the parent dwarf galaxy; (c) an initially thin GC tidal stream was heated by impacts from dark subhalos in the Milky Way; (d) an initially thin GC stream was heated by a massive Sagittarius dwarf galaxy; or a combination of some of these. Future DESI spectroscopy and detailed modeling may enable us to distinguish between these possible origins.
ISSN:1538-4357

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