GD-1 Stellar Stream and Cocoon in the DESI Early Data Release
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 deg ~ 460 pc) and kinematically hot (velocity dispersion, sigma ~ 5-8 km/s) component that surrounds a narrower (FWHM~ 0.353 deg ~ 55) and colder (sigma = 3.09+/-0.76 km/s) thin stream component (based on a median per star velocity precision of 2.7 km/s). The cocoon extends over at least a 30 degree 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 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. Future DESI spectroscopy and detailed modeling may enable us to distinguish between these possible origins.
Keywords
Cite
@article{arxiv.2407.06336,
title = {GD-1 Stellar Stream and Cocoon in the DESI Early Data Release},
author = {Monica Valluri and Parker Fagrelius and Sergey. E. Koposov and Ting S. Li and Oleg Y. Gnedin and Eric F. Bell and Raymond G. Carlberg and Andrew P. Cooper and Jessia N. Aguilar and Carlos Allende Prieto and Vasily Belokurov and Leandro Beraldo e Silva and David Brooks and Amanda Byström and Todd Claybaugh and Kyle Dawson and Arjun Dey and Peter Doel and Jaime E. Forero-Romero and Enrique Gaztañaga and Satya Gontcho A Gontcho and Klaus Honscheid and T . Kisner and Anthony Kremin and A. Lambert and Martin Landriau and L. Le Guillou and Michael E. Levi and Axel de la Macorra and Mark Manera and Paul Martini and Gustavo E. Medina and Aaron Meisner and Ramon Miquel and John Moustakas and Adam D. Myer and Joan Najita and Claire Poppett and Francisco Prada and Mehdi Rezaie and Graziano Rossi and Alex H. Riley and Eusebio Sanchez and David Schlegel and Michael Schubnell and David Sprayberry and Gregory Tarlé and Guillaume Thomas and Benjamin A. Weaver and Risa H. Wechsler and Rongpu Zhou and Hu Zou},
journal= {arXiv preprint arXiv:2407.06336},
year = {2025}
}
Comments
Accepted for publication in The Astrophysical Journal. 25 pages, 13 figures 4 tables; Minor changes to velocity spline fitted to the stream resulting in a small change in new GD1 stream members