The outer disc in shambles: blind detection of Monoceros and ACS with Gaia's astrometric sample

Abstract

The astrometric sample of Gaia allows us to study the outermost Galactic disc, the halo and their interface. It is precisely at the very edge of the disc where the effects of external perturbations are expected to be the most noticeable. Our goal is to detect the kinematic substructure present in the halo and at the edge of the Milky Way (MW) disc, and provide observational constraints on their phase-space distribution. We download, one HEALpix at a time, the proper motion histogram of distant stars, to which we apply a Wavelet Transformation to reveal the significant overdensities. We then analyse the large coherent structures that appear in the sky. We reveal a sharp yet complex anticentre dominated by Monoceros (MNC) and the Anticentre Stream (ACS) in the north, which we find with an intensity comparable to the Magellanic clouds and the Sagittarius stream, and by MNC south and TriAnd at negative latitudes. Our method allows us to perform a morphological analysis of MNC and ACS, both spanning more than 100${}^{\circ }$ in longitude, and to provide a high purity sample of giants with which we track MNC down to latitudes as low as $\sim$5${}^{\circ }$. Their colour-magnitude diagram is consistent with extended structures at a distance of $\sim$10-11 kpc originated in the disc, with a very low ratio of RR Lyrae over M giants, and kinematics compatible with the rotation curve at those distances or only slightly slower. We present a precise characterisation of MNC and ACS, two previously known structures that our method reveals naturally, allowing us to detect them without limiting ourselves to a particular stellar type and, for the first time, using only kinematics. Our results allow future studies to model their chemo-dynamics and evolution, thus constraining some of the most influential processes that shaped the MW.

Submitted to Astronomy and Astrophysics. Online material available upon acceptance

References in corpus (32)

• scikit-image: Image processing in Python
• The Gaia mission
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Outer structure of the Galactic warp and flare: explaining the Canis Major over-density
• Rings and Radial Waves in the Disk of the Milky Way
• Hunting for open clusters in \textit{Gaia} DR2: $582$ new OCs in the Galactic disc
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
• The Proper Motion of Sagittarius A*: III. The Case for a Supermassive Black Hole
• Substructure in Tidal Streams; Tributaries in the Anticenter Ring
• Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals
• A Multi-Band Catalog of 10978 Star Clusters, Associations and Candidates in the Milky Way
• Empirical photometric calibration of the Gaia Red Clump: colours, effective temperature and absolute magnitude
• Galactic halo stellar structures in the Triangulum-Andromeda region
• The Complex Structure of Stars in the Outer Galactic Disk as revealed by Pan-STARRS1
• An all-sky proper motion map of the Sagittarius stream using Gaia DR2
• On the Origin of Dynamically Cold Rings Around the Milky Way
• A panoramic landscape of the Sagittarius stream in Gaia DR2 revealed with the STREAMFINDER spyglass
• Full 5D characterisation of the Sagittarius stream with Gaia DR2 RR Lyrae
• The AAT/WFI survey of the Monoceros Ring and Canis Major Dwarf galaxy: I. from l = (193 - 276)o
• A Gaia early DR3 mock stellar catalog: Galactic prior and selection function
• The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia
• Gaia-DR2 extended kinematical maps. Part II: Dynamics in the Galactic disk explaining radial and vertical velocities
• The imprints of the Galactic bar on the thick disk with RAVE
• Empirical completeness assessment of the Gaia DR2, Pan-STARRS 1 and ASAS-SN-II RR Lyrae catalogues
• The velocity distribution in the solar neighbourhood from the LAMOST pilot survey
• On the Origin of the Monoceros Ring - I: Kinematics, proper motions, and the nature of the progenitor
• Cartography of Triangulum-Andromeda using SDSS stars
• The Reduced Proper Motion selected halo: methods and description of the catalogue
• A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars

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• The Pristine survey -- XVI. The metallicity of 26 stellar streams around the Milky Way detected with the STREAMFINDER in Gaia EDR3
• The Sagittarius stream in Gaia eDR3 and the origin of the bifurcations
• A self-consistent dynamical model of the Milky Way disc adjusted to Gaia data
• Kinematics beats dust: unveiling nested substructure in the perturbed outer disc of the Milky Way
• The Panchromatic Hubble Andromeda Treasury XX: The Disk of M31 is Thick
• RR Lyrae stars trace the Milky Way warp
• A Dwarf Galaxy Debris Stream Associated with Palomar 1 and the Anticenter Stream
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity