J/A+A/665/A57ivo://CDS.VizieR/J/A+A/665/A57doi:10.26093/cds/vizier.36650057CDSLovdal S.S.Ruiz-Lara T.Koppelman H.H.Matsuno T.Dodd E.Helmi A.2024-10-18T20:01:00Z2022-09-13T08:06:02ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmilky-way-galaxystellar-associationsvisible-astronomyMerger debris is expected to populate the stellar haloes of galaxies. In the case of the Milky Way, this debris should be apparent as clumps in a space defined by the orbital integrals of motion of the stars. Our aim is to develop a data-driven and statistics-based method for finding these clumps in integrals-of-motion space for nearby halo stars and to evaluate their significance robustly. We used data from Gaia EDR3, extended with radial velocities from ground-based spectroscopic surveys, to construct a sample of halo stars within 2.5kpc from the Sun. We applied a hierarchical clustering method that makes exhaustive use of the single linkage algorithm in three-dimensional space defined by the commonly used integrals of motion energy E, together with two components of the angular momentum, L_z_ and L_perp_. To evaluate the statistical significance of the clusters, we compared the density within an ellipsoidal region centred on the cluster to that of random sets with similar global dynamical properties. By selecting the signal at the location of their maximum statistical significance in the hierarchical tree, we extracted a set of significant unique clusters. By describing these clusters with ellipsoids, we estimated the proximity of a star to the cluster centre using the Mahalanobis distance. Additionally, we applied the HDBSCAN clustering algorithm in velocity space to each cluster to extract subgroups representing debris with different orbital phases. Our procedure identifies 67 highly significant clusters (>3{sigma}), containing 12% of the sources in our halo set, and 232 subgroups or individual streams in velocity space. In total, 13.8% of the stars in our data set can be confidently associated with a significant cluster based on their Mahalanobis distance. Inspection of the hierarchical tree describing our data set reveals a complex web of relations between the significant clusters, suggesting that they can be tentatively grouped into at least six main large structures, many of which can be associated with previously identified halo substructures, and a number of independent substructures. This preliminary conclusion is further explored in a companion paper, in which we also characterise the substructures in terms of their stellar populations. Our method allows us to systematically detect kinematic substructures in the Galactic stellar halo with a data-driven and interpretable algorithm. The list of the clusters and the associated star catalogue are provided in two tables in electronic format.2022A&A...665A..57Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/665/A57CatalogResearchIsServedByTAP VizieR generic servicerelated-tohttps://github.com/SofieLovdal/IOM_clustering :https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/665/A57https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/665/A57http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/665/A57https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/665/A57https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/665/A57http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/665/A57GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/665/A57/table1Spatial location and extent of the extracted clustersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLabel[1/68] Cluster labelmeta.idintsigni[3.01/13.17] Statistical significance according to Eq. 3stat.valuedoubleNorig[12/2137] Number of original members according to the single linkage proceduremeta.numberintmu0[-0.95/0.8] Mean energy, Ephys.energydoubleSimbadSimbad column added by the CDSmeta.ref.urlcharNDcut[9/3032] Number of stars for which this cluster is the closest, considering at most a Mahalanobis distance of 2.13meta.numberintmu1[-0.99/0.42] Mean perpendicular momentum, Lperpphys.angMomentumdoublemu2[-0.64/0.86] Mean angular momentum in z-direction, Lzphys.angMomentumdoublesigma00[0.00/0.03] Variance in Estat.variancedoublesigma01[-0.01/0.01] Covariance between E and Lperpstat.covariancedoublesigma02[-0.01/0.01] Covariance between E and Lzstat.covariancedoublesigma11[0.00/0.02] Variance in Lperpstat.variancedoublesigma12[-0.01/0.01] Covariance between Lperp and Lzstat.covariancedoublesigma22[0.00/0.01] Variance in Lzstat.variancedoubleJ/A+A/665/A57/table2Halo star catalogue with corresponding cluster labelsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaEDR3Gaia EDR3 source_idmeta.id;meta.mainx[-2.5/2.5] x-coordinatepos.cartesian.xdoubley[-2.46/2.48] y-coordinatepos.cartesian.ydoublez[-2.46/2.5] z-coordinatepos.cartesian.zdoublevx[-571/498] x-component of velocity vectorkm/sphys.veloc;pos.cartesian.xdoublevy[-779/272] y-component of velocity vectorkm/sphys.veloc;pos.cartesian.ydoublevz[-525/516] z-component of velocity vectorkm/sphys.veloc;pos.cartesian.zdoubleE[-169824/-69] Energykm**2.s**-2phys.energydoubleLperp[0/4287] Perpendicular angular momentumkpc.km/sphys.angMomentumdoubleLz[-4504/4588] Angular momentum in z-directionkpc.km/sphys.angMomentumdoublesigniSignificance of the cluster corresponding to Labelorigstat.fit.goodnessdoubleLabelorig[0/68] Cluster label according to the original single linkage assignmentmeta.idintLabelDcut[0/68] Closest cluster according to a Mahalanobis distance of at least 2.13meta.idintDMahalanobis distance to the cluster corresponding to Labelorigpos.distancedouble