GD-1 Stellar Stream and Cocoon in the DESI Early Data Release
Monica Valluri (for the DESI Collaboration,), Parker Fagrelius (for the DESI Collaboration,), Sergey. E. Koposov (for the DESI Collaboration,), Ting S. Li (for the DESI Collaboration,), Oleg Y. Gnedin (for the DESI Collaboration,), Eric F. Bell (for the DESI Collaboration,), Raymond G. Carlberg (for the DESI Collaboration,), Andrew P. Cooper (for the DESI Collaboration,), Jessia N. Aguilar (for the DESI Collaboration,), Carlos Allende Prieto (for the DESI Collaboration,), Vasily Belokurov (for the DESI Collaboration,), Leandro Beraldo e Silva (for the DESI Collaboration,), David Brooks (for the DESI Collaboration,), Amanda Bystr"om (for the DESI Collaboration,), Todd Claybaugh (for the DESI Collaboration,), Kyle Dawson (for the DESI Collaboration,), Arjun Dey (for the DESI Collaboration,), Peter Doel (for the DESI Collaboration,), Jaime E. Forero-Romero (for the DESI Collaboration,), Enrique Gazta~naga (for the DESI Collaboration,), Satya Gontcho A Gontcho (for the DESI Collaboration,), Klaus Honscheid (for the DESI Collaboration,), T . Kisner (for the DESI Collaboration,), Anthony Kremin (for the DESI Collaboration,), A. Lambert (for the DESI Collaboration,), Martin Landriau (for the DESI Collaboration,), L. Le Guillou (for the DESI Collaboration,), Michael E. Levi (for the DESI Collaboration,), Axel de la Macorra (for the DESI Collaboration,), Mark Manera (for the DESI Collaboration,), Paul Martini (for the DESI Collaboration,), Gustavo E. Medina (for the DESI Collaboration,), Aaron Meisner (for the DESI Collaboration,), Ramon Miquel (for the DESI Collaboration,), John Moustakas (for the DESI Collaboration,), Adam D. Myer (for the DESI Collaboration,), Joan Najita (for the DESI Collaboration,), Claire Poppett (for the DESI Collaboration,), Francisco Prada (for the DESI Collaboration,), Mehdi Rezaie (for the DESI Collaboration,), Graziano Rossi (for the DESI Collaboration,), Alex H. Riley (for the DESI Collaboration,), Eusebio Sanchez (for the DESI Collaboration,), David Schlegel (for the DESI Collaboration,), Michael Schubnell (for the DESI Collaboration,), David Sprayberry (for the DESI Collaboration,), Gregory Tarl’e (for the DESI Collaboration,), Guillaume Thomas (for the DESI Collaboration,), Benjamin A. Weaver (for the DESI Collaboration,), Risa H. Wechsler (for the DESI Collaboration,), Rongpu Zhou (for the DESI Collaboration,), Hu Zou (for the DESI Collaboration,)
arXiv:2407.06336v1 Announce Type: new
Abstract: We present ~ 126 new spectroscopically identified members of the GD-1 tidal stream obtained with the 5000-fiber Dark Energy Spectroscopic Instrument (DESI). We confirm the existence of a “cocoon” which is broad (FWHM~2.932deg~460pc) and kinematically hot (velocity dispersion, sigma~5-8km/s) component that surrounds a narrower (FWHM~0.353deg~55pc) and colder (sigma~ 2.2-2.6km/s) thin stream component (based on a median per star velocity precision of 2.7km/s). The cocoon extends over at least a ~ 20deg segment of the stream observed by DESI. The thin and cocoon components have similar mean values of [Fe/H]: -2.54+/- 0.04dex and -2.45+/-0.06dex 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 is 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 these. In the first two cases the velocity dispersion and mean metallicity are consistent with the parent dwarf galaxy having a halo mass of ~0^9msun. Future DESI spectroscopy and detailed modeling may enable us to distinguish between these possible origins.arXiv:2407.06336v1 Announce Type: new
Abstract: We present ~ 126 new spectroscopically identified members of the GD-1 tidal stream obtained with the 5000-fiber Dark Energy Spectroscopic Instrument (DESI). We confirm the existence of a “cocoon” which is broad (FWHM~2.932deg~460pc) and kinematically hot (velocity dispersion, sigma~5-8km/s) component that surrounds a narrower (FWHM~0.353deg~55pc) and colder (sigma~ 2.2-2.6km/s) thin stream component (based on a median per star velocity precision of 2.7km/s). The cocoon extends over at least a ~ 20deg segment of the stream observed by DESI. The thin and cocoon components have similar mean values of [Fe/H]: -2.54+/- 0.04dex and -2.45+/-0.06dex 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 is 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 these. In the first two cases the velocity dispersion and mean metallicity are consistent with the parent dwarf galaxy having a halo mass of ~0^9msun. Future DESI spectroscopy and detailed modeling may enable us to distinguish between these possible origins.

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