S 5 : Tidal Disruption in Crater 2 and Formation of Diffuse Dwarf Galaxies in the Local Group
Year: 2026
Type: article
Abstract: We present results of a spectroscopic campaign around the diffuse dwarf galaxy Crater 2 (Cra2) and its tidal tails as part of the Southern Stellar Stream Spectroscopic Survey ( S 5 ). Cra2 is a Milky Way dwarf spheroidal satellite with extremely cold kinematics, but a huge size similar to the Small Magellanic Cloud, which may be difficult to explain within collisionless cold dark matter. We identify 143 Cra2 members, of which 114 belong to the galaxy’s main body, and 29 are deemed part of its stellar stream. We confirm that Cra2 is dynamically cold (central velocity dispersion 2.5 1 − 0.30 + 0.33 km s − 1 ) and also discover a ≈7 σ velocity gradient consistent with its tidal debris track. We separately estimate the stream’s internal velocity dispersion to be 5.7 4 − 0.83 + 0.98 km s − 1 . We develop a suite of N -body simulations with both cuspy and cored density profiles on a realistic Cra2 orbit to compare with S 5 observations. We find that the velocity dispersion ratio between the Cra2 stream and galaxy ( 2.3 0 − 0.35 + 0.41 ) is difficult to reconcile with a cuspy halo with fiducial concentration and an initial mass predicted by standard stellar mass–halo mass relationships. Instead, either a cored halo with a relatively small core radius or a low-concentration cuspy model can reproduce this ratio. Despite tidal mass loss, Cra2 is metal-poor (〈[Fe/H]〉 = −2.16 ± 0.04) compared to the stellar mass–metallicity relation for its luminosity. Other diffuse dwarf galaxies similar to Cra2 in the Local Group (Antlia 2 and Andromeda 19) also challenge galaxy formation models. Finally, we discuss possible formation scenarios for Cra2, including ram-pressure stripping of a gas-rich progenitor combined with tides.
Source: The Astrophysical Journal
Authors: Guilherme Limberg, Alexander P. Ji, Ting S. Li, Denis Erkal, Sergey E. Koposov, Andrew B. Pace, Andrew P. Li, Petra Awad, Alexandra Senkevich, Joss Bland-Hawthorn, Lara Cullinane, Gary Da Costa, Alex Drlica-Wagner, Raphaël Errani, Peter S. Ferguson, Kyler Kuehn, Geraint F. Lewis, Sarah L. Martell, Jorge Peñarrubia, Nora Shipp, Yong Yang, Daniel B. Zucker
Institutions: University of Chicago, NSF-Simons AI Institute for the Sky, University of Toronto, University of Surrey, University of Cambridge, University of Edinburgh, University of Virginia, Leiden University, The University of Sydney, Leibniz Institute for Astrophysics Potsdam, Australian National University, Fermi National Accelerator Laboratory, Carnegie Mellon University, University of Washington, Lowell Observatory, UNSW Sydney, Macquarie University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, National Aeronautics and Space Administration, University of Chicago, University of Notre Dame, European Space Agency, University of New South Wales, Leibniz-Institut für Astrophysik Potsdam, Kavli Institute for Cosmological Physics, University of Chicago, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council, Leibniz-Gemeinschaft, Laboratory Directed Research and Development, Fermilab
Awards: Collaborative Research: Cosmic Shear on Extremely Large Scales with the Dark Energy Camera, G1679284459, Collaborative Research: Jump Starting LSST Proper Motion Science with 12 Years of DECam Observations, Collaborative Research: Cosmic Shear on Extremely Large Scales with the Dark Energy Camera, G2037078528, G2614460161, Metallicity Distributions of the Faintest Dwarf Galaxies, Probing dark matter distribution in the Milky Way with the DESI survey, Near Field Cosmology with Milky Way's Satellite Galaxies and Stellar Streams
OpenAlex ID: W7215039965