The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger?

The census of stellar streams and dwarf galaxies in the Milky Way provides direct constraints on galaxy formation models and the nature of dark matter. The DESI Milky Way survey (with a footprint of 14,000$~deg{^2}$ and a depth of $r<19$ mag) delivers the largest sample of distant metal-poor stars compared to previous optical fiber-fed spectroscopic surveys. This makes DESI an ideal survey to search for previously undetected streams and dwarf galaxies. We present a detailed characterization of the Cocytos stream, which was re-discovered using a clustering analysis with a catalog of giants in the DESI year 3 data, supplemented with Magellan/MagE spectroscopy. Our analysis reveals a relatively metal-rich ([Fe/H]$=-1.3$) and thick stream (width$=1.5^\circ$) at a heliocentric distance of $\approx 25$ kpc, with an internal velocity dispersion of 6.5-9 km s$^{-1}$. The stream's metallicity, radial orbit, and proximity to the Virgo stellar overdensities suggest that it is most likely a disrupted globular cluster that came in with the Gaia-Enceladus merger. We also confirm its association with the Pyxis globular cluster. Our result showcases the ability of wide-field spectroscopic surveys to kinematically discover faint disrupted dwarfs and clusters, enabling constraints on the dark matter distribution in the Milky Way.

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ArXiv.org
Published
2025-04-16
DOI
https://doi.org/10.48550/arxiv.2504.11687
Primary Topic
Phagocytosis and Immune Regulation
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article
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article

The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger?

Andreia Carrillo, O. Lahav, D. Brooks, G. E. Medina et al.
ArXiv.org
Phagocytosis and Immune Regulation
article

The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger?

Andreia Carrillo, O. Lahav, D. Brooks, G. E. Medina, Leonardo Enzo Brito da Silva, Vedant Chandra, Ting S. Li, N. Palanque‐Delabrouille, Gregory Tarlé, Constance M. Rockosi, Laurent Le Guillou, David Sprayberry, Alexander H. Riley, D. Bianchi, Ignasi Pérez-Ràfols, Axel de la Macorra, B. A. Weaver, Martin Landriau, Mairead Heiger, J. Aguilar, Anthony Kremin, Eusebio Sanchez, Satya Gontcho A Gontcho, Oleg Y. Gnedin, Martin Lambert, Namitha Kizhuprakkat, ENRIQUE GAZTAÑAGA, R. G. Carlberg, Arjun T. Dey, Steven P. Ahlen, Andrew P. Cooper, Aaron Meisner, Sergey E. Koposov, R. Miquel, Theodore S. Kisner, Risa H. Wechsler, Christian Aganze, Amanda Byström, Monica Valluri, Mustapha Ishak, Bokyoung Kim, Carlos Prieto, Hu Zou, T. Claybaugh, Graziano Rossi, Michael Schubnell, P. Doel, J. E. Forero-Romero, Gaston Gutierrez, F. Prada
article en

Abstract

The census of stellar streams and dwarf galaxies in the Milky Way provides direct constraints on galaxy formation models and the nature of dark matter. The DESI Milky Way survey (with a footprint of 14,000$~deg{^2}$ and a depth of $r<19$ mag) delivers the largest sample of distant metal-poor stars compared to previous optical fiber-fed spectroscopic surveys. This makes DESI an ideal survey to search for previously undetected streams and dwarf galaxies. We present a detailed characterization of the Cocytos stream, which was re-discovered using a clustering analysis with a catalog of giants in the DESI year 3 data, supplemented with Magellan/MagE spectroscopy. Our analysis reveals a relatively metal-rich ([Fe/H]$=-1.3$) and thick stream (width$=1.5^\circ$) at a heliocentric distance of $\approx 25$ kpc, with an internal velocity dispersion of 6.5-9 km s$^{-1}$. The stream's metallicity, radial orbit, and proximity to the Virgo stellar overdensities suggest that it is most likely a disrupted globular cluster that came in with the Gaia-Enceladus merger. We also confirm its association with the Pyxis globular cluster. Our result showcases the ability of wide-field spectroscopic surveys to kinematically discover faint disrupted dwarfs and clusters, enabling constraints on the dark matter distribution in the Milky Way.

ArXiv.org
Boston University (US), Institució Catalana de Recerca i Estudis Avançats (ES), Fermi National Accelerator Laboratory (US), Harvard University (US), High Energy Accelerator Research Organization (JP), Universidad de La Laguna (ES), University of California, Santa Cruz (US), Institute for High Energy Physics (ES), University of Milan (IT), Durham University (GB), National Tsing Hua University (TW), Brera Astronomical Observatory (IT), Sejong University (KR), National Solar Observatory (US), Valongo Observatory (BR), Institut d'Estudis Espacials de Catalunya (ES), Kavli Institute for Particle Astrophysics and Cosmology (US), Menlo School (US), Institut Català de Ciències del Clima (ES), Laboratoire de Physique Nucléaire et de Hautes Énergies (FR), Indiana Cancer Consortium (US), Centre for Theoretical Physics and Astrophysics (UZ), Michigan United (US), Unidades Centrales Científico-Técnicas (ES), Mylan (Switzerland) (CH), National Astronomical Observatories (CN), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (ES), University College London (GB), University of Portsmouth (GB), Syracuse University (US), Universidad Nacional Autónoma de México (MX), Netherlands Institute for Radio Astronomy (NL), Universitat Politècnica de Catalunya (ES)
Phagocytosis and Immune Regulation
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