The Virgo Overdensity Explained

Abstract

We suggest that the Virgo Overdensity (VOD) of stars in the stellar halo is the result of a radial dwarf galaxy merger that we call the Virgo Radial Merger. Because the dwarf galaxy passed very near to the Galactic center, the debris has a large range of energies but nearly zero $L_z$ angular momentum. The debris appears to extend from 5 to 50 kpc from the Sun in the Virgo region. We connect different parts of this merger debris to the Perpendicular and Parallel Streams (the Virgo Stellar Stream is associated with either or both of these streams), the Hercules-Aquila Cloud (HAC), and possibly the Eridanus Phoenix Overdensity (EriPhe). This radial merger can explain the majority of the observed moving groups of RR Lyrae and blue horizontal branch stars that have previously been identified in Virgo. This merger also produces debris in the Solar neighborhood similar to that identified as the Gaia-Enceladus or it Gaia-sausage merger. Orbits are provided for components of the Virgo Radial Merger progenitor and for debris that appears to be related to the Cocytos Stream, which was also recovered in the Virgo region.

17 pages, 5 figures, submitted to AAS Interstellar Matter and the Local Universe corridor

References in corpus (43)

• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• Gaia Data Release 2: The astrometric solution
• The VizieR database of Astronomical Catalogues
• galpy: A Python Library for Galactic Dynamics
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• Co-formation of the Galactic disc and the stellar halo
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• Gaia Data Release 2: Catalogue validation
• The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: IV. Modeling the Sagittarius Tidal Tails
• Four New Stellar Debris Streams in the Galactic Halo
• The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 kpc and Other Over-Densities in the Outer Halo
• The Cold Dark Matter Halos of Local Group Dwarf Spheroidals
• The Hercules-Aquila Cloud
• Spectroscopy of QUEST RR Lyrae Variables: the new Virgo Stellar Stream
• The shape of the Galactic halo with $Gaia$ DR2 RR Lyrae. Anatomy of an ancient major merger
• The Orbit of the Orphan Stream
• The Overdensity in Virgo, Sagittarius Debris, and the Asymmetric Spheroid
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• La Silla QUEST RR Lyrae Star Survey: Region I
• An Orbit Fit for the Grillmair Dionatos Cold Stellar Stream
• Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2
• Spectroscopy of Bright QUEST RR Lyrae Stars: Velocity Substructures toward Virgo
• Exploring the Virgo Stellar Stream with SEKBO Survey RR Lyrae Stars
• Proper Motions in Kapteyn Selected Area 103: A Preliminary Orbit for the Virgo Stellar Stream
• Discovery of a Stellar Overdensity in Eridanus-Phoenix in the Dark Energy Survey
• Update on the Nature of Virgo Overdensity
• The Origin of the Virgo Stellar Substructure
• A comprehensive view of the Virgo Stellar Stream
• A Photometric Metallicity Estimate of the Virgo Stellar Overdensity
• Stellar over-densities in the halo: the extent of the Virgo over-density
• Hubble Space Telescope Proper Motions of Individual Stars in Stellar Streams: Orphan, Sagittarius, Lethe, and the New "Parallel" Stream
• Disentangling the Virgo Overdensity with RR Lyrae stars
• Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density
• A Spatial Characterization of the Sagittarius Dwarf Galaxy Tidal Tails
• Main Sequence Star Populations in the Virgo Overdensity Region
• A Magellanic origin for the Virgo substructure
• A tangle of stellar streams in the north Galactic cap
• Fitting the density substructure of the stellar halo with MilkyWay@home
• An Orbit Fit to Likely Hermus Stream Stars

Cited by in corpus (19)

• Streams, substructures and the early history of the Milky Way
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• Galactic potential constraints from clustering in action space of combined stellar stream data
• Local RR Lyrae Stars: native and alien
• The Local Stellar Halo is Not Dominated by a Single Radial Merger Event
• Distant Echoes of the Milky Way's Last Major Merger
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia
• Linking nearby stellar streams to more distant halo overdensities
• Kinematics and Metallicity of Red Giant Branch Stars in the Northeast Shelf of M31
• High-Resolution Chemical Abundances of the Nyx Stream
• Revealing the Milky Way's Most Recent Major Merger with a Gaia EDR3 Catalog of Machine-Learned Line-of-Sight Velocities
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity
• Mapping Milky Way Halo Substructure using Stars in the Extended Blue Tail of the Horizontal Branch
• Stellar halo striations from assumptions of axisymmetry
• Multi-wavelength observations of the Galactic X-ray binaries IGR J20155+3827 and Swift J1713.4-4219
• GSE vs. LMC: reshaping of radially biased stellar haloes by satellites
• A Tilt in the Dark Matter Halo of the Galaxy