The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger?
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2025
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| author | Aganze, Christian Chandra, Vedant Wechsler, Risa H. Li, Ting S. Koposov, Sergey E. Silva, Leandro Beraldo Carrillo, Andreia Riley, Alexander H. Valluri, Monica Gnedin, Oleg Y. Heiger, Mairead Rockosi, Constance Carlberg, Raymond Byström, Amanda Kizhuprakkat, Namitha Lambert, Mika Kim, Bokyoung Toledo, Gustavo Medina Prieto, Carlos Allende Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd T. Cooper, Andrew P. de la Macorra, Axel Dey, Arjun Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya A. Gutierrez, Gaston Ishak, Mustapha Kisner, Theodore Kremin, Anthony Lahav, Ofer Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Palanque-Delabrouille, Nathalie Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schubnell, Michael Sprayberry, David Tarlé, Gregory Weaver, Benjamin A. Zou, Hu |
| author_facet | Aganze, Christian Chandra, Vedant Wechsler, Risa H. Li, Ting S. Koposov, Sergey E. Silva, Leandro Beraldo Carrillo, Andreia Riley, Alexander H. Valluri, Monica Gnedin, Oleg Y. Heiger, Mairead Rockosi, Constance Carlberg, Raymond Byström, Amanda Kizhuprakkat, Namitha Lambert, Mika Kim, Bokyoung Toledo, Gustavo Medina Prieto, Carlos Allende Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd T. Cooper, Andrew P. de la Macorra, Axel Dey, Arjun Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya A. Gutierrez, Gaston Ishak, Mustapha Kisner, Theodore Kremin, Anthony Lahav, Ofer Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Palanque-Delabrouille, Nathalie Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schubnell, Michael Sprayberry, David Tarlé, Gregory Weaver, Benjamin A. Zou, Hu |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_11687 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger? Aganze, Christian Chandra, Vedant Wechsler, Risa H. Li, Ting S. Koposov, Sergey E. Silva, Leandro Beraldo Carrillo, Andreia Riley, Alexander H. Valluri, Monica Gnedin, Oleg Y. Heiger, Mairead Rockosi, Constance Carlberg, Raymond Byström, Amanda Kizhuprakkat, Namitha Lambert, Mika Kim, Bokyoung Toledo, Gustavo Medina Prieto, Carlos Allende Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd T. Cooper, Andrew P. de la Macorra, Axel Dey, Arjun Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya A. Gutierrez, Gaston Ishak, Mustapha Kisner, Theodore Kremin, Anthony Lahav, Ofer Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Palanque-Delabrouille, Nathalie Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schubnell, Michael Sprayberry, David Tarlé, Gregory Weaver, Benjamin A. Zou, Hu Astrophysics of Galaxies Solar and Stellar Astrophysics 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. |
| title | The Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger? |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2504.11687 |