GD-1 Stellar Stream and Cocoon in the DESI Early Data Release
Moustakas, J.;
Brooks, D.;
Doel, P.;
Honscheid, K.;
Li, T. S.;
Martini, P.;
Miquel, R.;
Sanchez, E.;
Schubnell, M.;
Allende Prieto, C.;
Belokurov, V.;
Koposov, S. E.;
Dey, A.;
Carlberg, R. G.;
Bell, E. F.;
Wechsler, R. H.;
Riley, A. H.;
Poppett, C.;
Beraldo e Silva, L.;
Schlegel, D.;
Meisner, A.;
Aguilar, J.;
Ahlen, S.;
Cooper, A. P.;
de la Macorra, A.;
Gontcho A Gontcho, S.;
Kisner, T.;
Kremin, A.;
Landriau, M.;
Le Guillou, L.;
Prada, F.;
Valluri, M.;
Zou, H.;
Manera, M.;
Najita, J.;
Dawson, K.;
Weaver, B. A.;
Gnedin, Oleg Y.;
Medina, G. E.;
Han, J.;
Zhou, R.;
Claybaugh, T.;
Gaztañaga, E.;
Rezaie, M.;
Rossi, G.;
Tarlé, G.;
Myers, A. D.;
Forero-Romero, J. E.;
Lambert, A.;
Sprayberry, D.;
Thomas, G.;
Fagrelius, P.;
Levi, M. E.;
Byström, A.
United States, United Kingdom, Canada, Taiwan, Spain, Colombia, France, Mexico, South Korea, China
Abstract
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 ∼ 2 932 ∼ 460 pc) and kinematically hot (velocity dispersion, σ ∼ 5–8 km s‑1) component that surrounds a narrower (FWHM ∼ 0 353 ∼ 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.
2025
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The Astrophysical Journal
Gaia
9
