J/A+A/645/A69ivo://CDS.VizieR/J/A+A/645/A69doi:10.26093/cds/vizier.36450069CDSKoppelman H.H.Helmi A.2021-09-10T07:41:48Z2021-01-15T07:08:53ZCDS support team

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

cds-question@unistra.frmilky-way-galaxystellar-distanceproper-motionsThe Gaia mission has provided the largest ever astrometric chart of the Milky Way. Using it to map the Galactic halo is helpful for disentangling its merger history. The identification of halo stars in Gaia DR2 with reliable distance estimates requires special methods because such stars are typically farther away and scarce. We applied the reduced proper motion (RPM) method to identify halo main sequence stars on the basis of Gaia photometry and proper motions. Using the colour-absolute-magnitude relation for this type of star, we calculated photometric distances. Our selection results in a set of 10^7^ tentative main sequence halo stars with typical distance uncertainties of 7% and with median velocity errors of 20km/s. The median distance of our sample is ~4.4kpc, with the faintest stars located at ~16kpc. The spatial distribution of the stars in our sample is centrally concentrated. A visual inspection of the mean velocities of stars on the sky reveals large-scale patterns as well as clear imprints of the GD-1 stream and tentative hints of the Jhelum and Leiptr streams. Incompleteness and selection effects limit our ability to interpret the patterns reliably as well as to identify new substructures. We define a pseudo-velocity space by setting the line-of-sight velocities of our sample stars to zero. In this space, we recover several known structures such as the footprint of Gaia-Enceladus (i.e. the Gaia-Sausage) as well as the Helmi Streams and some other retrograde substructures (Sequoia, Thamnos). We show that the two-point velocity correlation function reveals significant clustering on scales smaller than 100km/s of a similar amplitude as found for the 6D Gaia halo sample. This clumping of stars in velocity space might hint at the presence of nearby streams that are predominantly phase-mixed. A spectroscopic follow-up of our halo main sequence sample is bound to yield unprecedented views of Galactic history and dynamics. In future Gaia data releases, the level of systematics will be reduced and the astrometry will be more precise, which will allow for the identification of more substructures at larger distances.2021A&A...645A..69Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/645/A69CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)I/349 : StarHorse, Gaia DR2 photo-astrometric distances (Anders+, 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39754-39755 39757-39759 39920-39921 39933-39935 40616-40617 41468-41470 41580-41582 41588-41590 41592 41628-41630 41644-41646 41648-41649 41664-41666 41668 41694-41695 41705-41707 41732-41734 41741 41748-41750 41752-41753 41761 41790-41793 41796-41797 41808 41823 41830-41831 41833-41835 41841-41843 41863 41865-41867 42152-42153 42156 42160-42162 42164 42188-42189 42196-42198 42200 42235 42300-42301 42344-42345 42348-42349 42360 42368 42407 42409-42411 42417-42419 42423 42467 42470-42471 42482 42507 42510-42511 42567 42577-42582 42752 42755 42956-42958 42980 42982 43008-43009 43023 43030-43031 43033-43035 43045-43047 43051https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/645/A69?format=asciidefaultJ/A+A/645/A69/catalogReduced proper motion (RPM) catalogrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR2Gaia DR2 source_idmeta.id;meta.mainindexedE(B-V)Reddening E(B-V) (from Schlegel et al., 1998ApJ...500..525S)magphot.color.excessdoubleAvAv extinction (from E(B-V))magphys.absorptiondoubleRUWEGaia DR2 RUWE parametermeta.code.qualdoubleHgReduced proper motion (see Eq.5)magphys.magAbsdoubleDistPhotPhotometric distancekpcpos.distancedoublee_DistPhotPhotometric distance uncertaintykpcstat.errordoubleExtfracFraction of full extinctionphys.absorption;arith.ratiodoubleRA_ICRSGaia DR2 right ascension (ICRS) at Ep=2015.5 (1)degpos.eq.ra;meta.mainindexedDE_ICRSGaia DR2 declination (ICRS) at Ep=2015.5 (1)degpos.eq.dec;meta.mainindexed_RA.icrsRight ascension (ICRS) at Epoch=J2015.5 (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)degpos.eq.ranullableindexed_DE.icrsDeclination (ICRS) at Epoch=J2015.5 (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)degpos.eq.decnullableindexed