Satellite group infall into the Milky Way: exploring the Crater-Leo case with new HST proper motions

Abstract

Context. Within $\Lambda$ Cold Dark Matter ($\Lambda$CDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3-5 members rather than individually. It was also suggested that this might be the reason behind the origin of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and also identical orbital planes and directions. Aims. Looking at observations of Milky Way satellites, the dwarf galaxies Leo II, IV, V, Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested "Crater-Leo group" shows a coherent distance gradient and all these objects align along a great circle on the sky. We use proper motion data to investigate whether the phase-space distribution of the members of the proposed group are indeed consistent with group infall. Methods. To further investigate this possibility, we use Gaia Data Release 3 (DR3) and new Hubble Space Telescope (HST) proper motions, $({\mu }_{\alpha \ast },{\mu }_{\delta })=(-0.1921\pm 0.0514,-0.0686\pm 0.0523)$ mas yr${}^{-1}$ for Leo IV and $({\mu }_{\alpha \ast },{\mu }_{\delta })=(0.1186\pm 0.1943,-0.1183\pm 0.1704)$ mas yr${}^{-1}$ for Leo V, to derive accurate orbital properties for the proposed group objects. In addition, we explore other possible members of this putative association. Results. Leo II, Leo IV, and Crater 1 show orbital properties consistent with those we predict from assuming group infall. However, our results suggest that Crater II was not accreted with the rest of the objects. If confirmed with increasingly accurate proper motions in the future, the Crater-Leo objects appear to constitute the first identified case of a cosmologically expected, typical group infall event, as opposed to the highly hierarchical Magellanic Cloud system.

Accepted for publication in A&A on 23-04-2024. 20 pages, 18 figures, 5 tables

References in corpus (30)

• Array Programming with NumPy
• galpy: A Python Library for Galactic Dynamics
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• Small Dwarf Galaxies Within Larger Dwarfs: Why Some Are Luminous While Most Go Dark
• Leo V: A Companion of a Companion of the Milky Way Galaxy
• Associations of Dwarf Galaxies
• Infall of substructures onto a Milky Way-like dark halo
• Two Planes of Satellites in the Centaurus A Group
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2
• A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus
• ATLAS lifts the Cup: Discovery of a New Milky Way satellite in Crater
• Kinematics of Antlia 2 and Crater 2 from The Southern Stellar Stream Spectroscopic Survey (S5)
• Reflex motion in the Milky Way stellar halo resulting from the Large Magellanic Cloud infall
• The Leo IV dwarf spheroidal galaxy: color-magnitude diagram and pulsating stars
• HST Proper Motions of NGC 147 and NGC 185: Orbital Histories and Test of Dynamically Coherent Andromeda Satellite Plane
• Testing the two planes of satellites in the Centaurus Group
• The binary fraction of stars in dwarf galaxies: the case of Leo II
• The evolved stars of Leo II dSph galaxy from near-infrared UKIRT/WFCAM observations
• The Clustering of Orbital Poles Induced by the LMC: Hints for the Origin of Planes of Satellites
• Proper Motion of the Leo II Dwarf Galaxy Based On Hubble Space Telescope Imaging
• Dynamical model of the Milky Way using APOGEE and Gaia data
• A DECam View of the Diffuse Dwarf Galaxy Crater II: Variable Stars
• On the Effect of the Large Magellanic Cloud on the Orbital Poles of Milky Way Satellite Galaxies
• Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
• A DECam View of the Diffuse Dwarf Galaxy Crater II: The Colour-Magnitude Diagram

Cited by in corpus (7)

• A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Galaxy with DELVE Early Data Release 3
• The satellite galaxy plane of NGC 4490 in light of ΛCDM - Sparsity of similarly extreme analogs and a possible role of satellite pairs
• Dwarf Galaxies in the MATLAS Survey: The satellite system of NGC474 under scrutiny with MUSE
• An LBT view of the co-rotating group of galaxies around NGC 2750: Deep imaging and new satellite candidates
• Testing a proposed "planarity" tool for studying satellite systems: On the alleged consistency of Milky Way satellite galaxy planes with $\Lambda$CDM
• The long-term stability of the Vast Polar Structure and its connection to a possible previous passage of the LMC
• Investigating the origin of the Milky Way streams. A revised look at their orbital pole distribution in light of precession effects