J/ApJ/887/19ivo://CDS.VizieR/J/ApJ/887/19doi:10.26093/cds/vizier.18870019CDSPrice-Whelan A.M.Nidever D.L.Choi Y.Schlafly E.F.Morton T.,Koposov S.E.Belokurov V.2022-05-31T12:59:16Z2021-06-08T11:43:08ZCDS support team

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

cds-question@unistra.frstellar-associationsinfrared-photometryvisible-astronomybroad-band-photometrymagellanic-cloudsmilky-way-galaxyWe report the discovery of a young ({tau}~117Myr), low-mass (M~1200M_{sun}_), metal-poor ([Fe/H]~-1.14) stellar association at a heliocentric distance D~28.7kpc, placing it far into the Milky Way (MW) halo. At its present Galactocentric position (R,z)~(23,15)kpc, the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic Cloud system, but is located ~60{deg} from the Large Magellanic Cloud center on the other side of the MW disk. If the cluster is colocated with HI gas in the stream, we directly measure the distance to the leading arm of the Magellanic stream. The measured distance is inconsistent with Magellanic stream model predictions that do not account for ram pressure and gas interaction with the MW disk. The estimated age of the cluster is consistent with the time of last passage of the leading arm gas through the Galactic midplane; we therefore speculate that this star formation event was triggered by its last disk midplane passage. Most details of this idea remain a puzzle: the Magellanic stream has low column density, the MW disk at large radii has low gas density, and the relative velocity of the leading arm and MW gas is large. However it formed, the discovery of a young stellar cluster in the MW halo presents an interesting opportunity for study. This cluster was discovered with Gaia astrometry and photometry alone, but follow-up DECam photometry was crucial for measuring its properties.2019ApJ...887...19Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/887/19CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)VII/195 : Globular Clusters in the Milky Way (Harris, 1996)VII/202 : Globular Clusters in the Milky Way (Harris, 1997)I/345 : Gaia DR2 (Gaia Collaboration, 2018)J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)J/A+A/547/A12 : Leading arm Magellanic Cloud Catalog (Venzmer+, 2012)J/A+A/564/A125 : AGN Torus model comparison of AGN in the CDFS (Buchner+, 2014)J/MNRAS/442/1680 : Red giants in SMC. Abundances (Dobbie+, 2014)J/ApJ/792/43 : Detected sources in the Magellanic Stream region (For+, 2014)J/ApJ/795/64 : Exoplanet physical parameters (Foreman-Mackey+, 2014)J/MNRAS/471/4571 : Magellanic Inter-Cloud Project. III (Carrera+, 2017)J/AJ/154/199 : Survey of the MAgellanic Stellar History (Nidever+, 2017)J/A+A/616/A10 : Open clusters GaiaDR2 HR diagrams (Gaia Collaboration, 2018)J/A+A/619/A180 : GaiaDR2 photometric sensitivity curves (Maiz Apellaniz+, 2018)J/AJ/156/18 : APOGEE DR14: companions of evolved stars (Price-Whelan+, 2018)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/887/19https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/887/19http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/887/19https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/887/19https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/887/19http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/887/19GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/887/19/decam (DECam photometry and sky positions for point sources in the observed DECam field)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/887/19/decam?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/887/19/decam?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/887/19/decam?GETtext/xml+votable180.050000true178.34160194-28.622051110.005555555555555556Cone search capability for table J/ApJ/887/19/gaia (Gaia DR2 data and membership probabilities computed for all stars in the cluster region)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/887/19/gaia?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/887/19/gaia?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/887/19/gaia?GETtext/xml+votable180.050000true184.79962522605-34.971638341920.0055555555555555564/1539 1542 1545 1548-1550 5/6151 6155 6162 6174 6176-6177 6179 6188-6189 6191 6204 6288 6/24599 24603 24615 24619 24640 24642-24643 24652 24654-24655 24688 24690-24691 24700 24702-24703 24712-24713 24740-24741 24761 24763 24820 24824 24960 24962 24968 25109 25156 383591.9867573869263685e-19 4.621782916333392e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/887/19?format=asciiOpticalInfrareddefaultJ/ApJ/887/19/decamDECam photometry and sky positions for point sources in the observed DECam fieldrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameName of the source (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharRAJ2000[177.5/180.1] Right ascension (J2000) (ra)degpos.eq.ra;meta.mainindexedDEJ2000[-30.5/-28.5] Declination (J2000) (dec)degpos.eq.dec;meta.mainindexedgmag[13.14/22] DECam g-band magnitude (g)magphot.mag;em.opt.Bfloate_gmag[0.0012/0.5] Uncertainty on the gmag (g_err)magstat.error;phot.magfloatimag[12.84/22] DECam i-band magnitude (i)magphot.mag;em.opt.Ifloate_imag[0.0015/0.5] Uncertainty on the imag (i_err)magstat.error;phot.magfloatSeq[54/54108] Running sequence number (id)meta.idintCont[0/1] Control mask (control_mask) (1)meta.codeintCl[0/1] Cluster mask (cluster_mask) (1)meta.codeintMm[0/1] Member mask (member_mask) (2)meta.code.memberintJ/ApJ/887/19/gaiaGaia DR2 data and membership probabilities computed for all stars in the cluster regionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaGaia DR2 identifier (source_id)meta.id;meta.mainRA_ICRS[173.5/185.5] Barycentric right ascension (ICRS) at Ep=2015.5 (ra)degpos.eq.ra;meta.mainDE_ICRS[-35/-23] Barycentric declination (ICRS) at Ep=2015.5 (dec)degpos.eq.dec;meta.mainpmRA[-96.3/22.6] Gaia proper motion in right ascension (pmRA*cosDE) (pmra)mas/yrpos.pm;pos.eq.rafloatpmDE[-54.4/29.1] Gaia proper motion in declination (pmdec)mas/yrpos.pm;pos.eq.decfloatGmag[9.3/20.9] Gaia G-band mean magnitude (G0 )magphot.mag;stat.mean;em.optfloatBPmag[9.39/21.27] Gaia BP-band mean magnitude (BP0)magphot.mag;stat.mean;em.opt.BfloatRPmag[9.1/21.3] Gaia RP-band mean magnitude (RP0)magphot.mag;stat.mean;em.opt.RfloatMm[0/1] Membership probability (member_prob)stat.probabilityfloat_RA.icrsRight ascension (ICRS) at Epoch=J2000, proper motions taken into accountdegpos.eq.ranullableindexed_DE.icrsDeclination (ICRS) at Epoch=J2000, proper motions taken into accountdegpos.eq.decnullableindexed