DOE OSTI · 3229485
Characterizing the GD-1 Stream with DESI DR2 Data: Thin Stream and Hot Cocoon
Abstract
GD-1 is among the longest, coldest stellar streams in the Milky Way, making it an ideal target for probing dark matter substructure through dynamical heating. We present a catalog of 608 spectroscopically confirmed GD-1 members from the first three years of Dark Energy Spectroscopic Instrument (DESI) observations. This constitutes the largest homogeneous spectroscopic sample of GD-1, doubling the number of members previously available only through heterogeneous compilations combining multiple surveys with different systematics. Using these data, we derive updated stream tracks in sky position, proper motion, and radial velocity that extend over $100^\circ$ of the stream. We apply a Gaussian mixture model to decompose the stream into a dynamically cold thin component ($Ï_V = 2.49\pm 0.28$ km s$^{-1}$, width $= 0.23\pm0.01^\circ$) and a kinematically hot cocoon ($Ï_V = 6.13\pm0.75$ km s$^{-1}$, width $= 2.18\pm0.17^\circ$). The cocoon contains $\sim30\%$ of members and its velocity dispersion is consistent with $\sim11$ Gyr of heating by cold dark matter subhalos. We also detect a large proper motion dispersion ($41.36\pm4.98$ km s$^{-1}$) along the stream direction in the cocoon component. This feature indicates a significant line-of-sight distance spread in the cocoon, and its origin will be further explored in a forthcoming paper. These measurements demonstrate the power of DESI spectroscopy for characterizing the multi-component phase-space structure of stellar streams and constraining small-scale dark matter substructure.
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Jarvis, Emma [Toronto U.] (ORCID:0009000656127336), Li, Ting S. [Toronto U.] (ORCID:0000000291106163), Koposov, Sergey E. [Edinburgh U., Inst. Astron.; Cambridge U.] (ORCID:000000032644135X), Carlberg, Raymond G. [Toronto U.] (ORCID:0000000276670081), Valluri, Monica [U. Michigan, Dept. Astron.] (ORCID:0000000262572341), Mohammed, Nasser [Toronto U.] (ORCID:0009000812240382), Aguilar, J. [LBL, Berkeley], Ahlen, S. [Boston U.] (ORCID:0000000160987247), Allende Prieto, Carlos [IAC, La Laguna; Laguna U., Tenerife] (ORCID:000000020084572X), Beraldo e Silva, Beraldo Silva, Leandro [Rio de Janeiro Observ.] (ORCID:0000000207401507), Bianchi, D. [Milan U.; Brera Observ.] (ORCID:0000000197120006), Brooks, D. [University Coll. London], Byström, Amanda [Edinburgh U., Inst. Astron.] (ORCID:0000000256898791), Claybaugh, T. [LBL, Berkeley], Cooper, A. P. [Taiwan, Natl. Tsing Hua U.] (ORCID:000000018274158X), Cuceu, A. [LBL, Berkeley] (ORCID:0000000221690595), de la Macorra, A. [UNAM, Mexico] (ORCID:0000000217691640), Dey, Arjun [Natl. Solar Observ., Tucson] (ORCID:0000000249284003), Dey, Biprateep [Toronto U., Astron. Dept.; Pittsburgh U.] (ORCID:0000000256657912), Doel, P. [University Coll. London], Forero-Romero, J. E. [Andes U., Bogota] (ORCID:0000000228903725), Gaztañaga, E. [Barcelona, IEEC; Portsmouth U., ICG; ICE, Bellaterra] (ORCID:0000000196320815), Gnedin, Oleg Y. [Michigan U.; KEK, Tsukuba; Hiroshima Shudo U.] (ORCID:0000000198529954), Gontcho A. Gontcho, Satya [Virginia U.] (ORCID:000000033142233X), Gutierrez, G. [Fermilab], Honscheid, K. [Chicago U., KICP; Ohio State U.] (ORCID:0000000265502023), Joyce, R. [Natl. Solar Observ., Tucson] (ORCID:0000000302015241), Kehoe, R. [Southern Methodist U.], Kisner, T. [LBL, Berkeley] (ORCID:0000000335107134), Kizhuprakkat, Namitha [Taiwan, Natl. Tsing Hua U.] (ORCID:0000000308538887), Kremin, A. [LBL, Berkeley] (ORCID:0000000163567424), Lambert, Mika [UC, Santa Cruz] (ORCID:0000000225278899), Landriau, M. [LBL, Berkeley] (ORCID:0000000318388528), Le Guillou, L. [LPNHE, Paris] (ORCID:0000000171788868), Medina, Gustavo E. [Toronto U.] (ORCID:0000000301059576), Meisner, A. [Natl. Solar Observ., Tucson] (ORCID:0000000211257384), Miquel, R. [ICREA, Barcelona; Barcelona, IFAE], Nadathur, S. [Portsmouth U., ICG] (ORCID:0000000190703102), Najita, Joan [Natl. Solar Observ., Tucson] (ORCID:000000025758150X), Palanque-Delabrouille, N. [IRFU, Saclay; LBL, Berkeley] (ORCID:000000033188784X), Percival, W. J. [Waterloo U.; Perimeter Inst. Theor. Phys.] (ORCID:0000000206445727), Prada, F. [Granada U., Theor. Phys. Astrophys.] (ORCID:0000000171458674), Pérez-Ràfols, I. [Barcelona, Polytechnic U.] (ORCID:0000000169790125), Qiu, Tian [SKLPPC, Shanghai; Shanghai Jiaotong U.; Shanghai Jiao Tong U.; KLPAC, Shanghai] (ORCID:0000000249002088), Riley, Alexander H. [Lund U.] (ORCID:0000000158055766), Rockosi, Constance M. [UC, Santa Cruz] (ORCID:0000000266677028), Rossi, G. [Sejong U.], Sanchez, E. [Madrid, CIEMAT] (ORCID:0000000296468198), Sandford, Nathan [Toronto U.] (ORCID:0000000273933595), Schlafly, E. F. [Baltimore, Space Telescope Sci.] (ORCID:0000000235697421), Schlegel, D. [LBL, Berkeley], Silber, J. [LBL, Berkeley] (ORCID:0000000234610320), Sprayberry, D. [Natl. Solar Observ., Tucson], Tarlé, G. [Michigan U.; KEK, Tsukuba; Hiroshima Shudo U.] (ORCID:0000000317040781), Weaver, B. A. [Natl. Solar Observ., Tucson], Zhou, R. [LBL, Berkeley] (ORCID:0000000153814372), Zou, H. [Beijing Observ.] (ORCID:0000000266843997). 2026-04-22. Characterizing the GD-1 Stream with DESI DR2 Data: Thin Stream and Hot Cocoon. https://www.osti.gov/biblio/3229485
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