J/ApJ/838/11ivo://CDS.VizieR/J/ApJ/838/11doi:10.26093/cds/vizier.18380011CDSSimon J.D.Li T.S.Drlica-Wagner A.Bechtol K.Marshall J.L.,James D.J.Wang M.Y.Strigari L.Balbinot E.Kuehn K.Walker A.R.,Abbott T.M.C.Allam S.Annis J.Benoit-Levy A.Brooks D.,Buckley-Geer E.Burke D.L.Carnero Rosell A.Carrasco Kind M.,Carretero J.Cunha C.E.D'Andrea C.B.da Costa L.N.Depoy D.L.,Desai S.Doel P.Fernandez E.Flaugher B.Frieman J.,Garcia-Bellido J.Gaztanaga E.Goldstein D.A.Gruen D.Gutierrez G.,Kuropatkin N.Maia M.A.G.Martini P.Menanteau F.Miller C.J.,Miquel R.Neilsen E.Nord B.Ogando R.Plazas A.A.Romer A.K.,Rykoff E.S.Sanchez E.Santiago B.Scarpine V.Schubnell M.,Sevilla-Noarbe I.Smith R.C.Sobreira F.Suchyta E.Swanson M.E.C.,Tarle G.Whiteway L.Yanny B.(the DES Collaboration)2019-02-04T11:08:13Z2017-11-27T14:56:48ZCDS support team

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

cds-question@unistra.frgalaxiesspectroscopyradial-velocityline-intensitiesmetallicityinfrared-photometryvisible-astronomybroad-band-photometryWe present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Tucana III (Tuc III). We identify 26 member stars in Tuc III from which we measure a mean radial velocity of v_hel_=-102.3+/-0.4(stat.)+/-2.0(sys.)km/s, a velocity dispersion of 0.1_-0.1_^+0.7^km/s, and a mean metallicity of [Fe/H]=-2.42_-0.08_^+0.07^. The upper limit on the velocity dispersion is {sigma}<1.5km/s at 95.5% confidence, and the corresponding upper limit on the mass within the half-light radius of Tuc III is 9.0x10^4^M_{sun}_. We cannot rule out mass-to-light ratios as large as 240M_{sun}_/L_{sun}_ for Tuc III, but much lower mass-to-light ratios that would leave the system baryon-dominated are also allowed. We measure an upper limit on the metallicity spread of the stars in Tuc III of 0.19dex at 95.5% confidence. Tuc III has a smaller metallicity dispersion and likely a smaller velocity dispersion than any known dwarf galaxy, but a larger size and lower surface brightness than any known globular cluster. Its metallicity is also much lower than those of the clusters with similar luminosity. We therefore tentatively suggest that Tuc III is the tidally stripped remnant of a dark matter-dominated dwarf galaxy, but additional precise velocity and metallicity measurements will be necessary for a definitive classification. If Tuc III is indeed a dwarf galaxy, it is one of the closest external galaxies to the Sun. Because of its proximity, the most luminous stars in Tuc III are quite bright, including one star at V=15.7 that is the brightest known member star of an ultra-faint satellite.2017ApJ...838...11Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/838/11CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVII/195 : Globular Clusters in the Milky Way (Harris, 1996)J/AJ/124/1144 : Orbits of 171 single-lined spectroscopic bin. (Latham, 2002)J/AJ/132/85 : Equivalent width of 33 metal-poor RHB (Preston+, 2006)J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006)J/A+A/465/357 : Stroemgren photometry in the Draco dSph galaxy (Faria+, 2007)J/ApJ/663/960 : Radial velocities of Leo I stars (Sohn+, 2007)J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)J/ApJ/743/167 : Radial velocities and membership in Pal 13 (Bradford+, 2011)J/MNRAS/418/1526 : Dark matter in dSph galaxies (Charbonnier+, 2011)J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)J/AJ/142/22 : Heavy-element dispersion in M92 (Roederer+, 2011)J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013)J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)J/ApJ/801/74 : Dark matter profiles in dwarf galaxies (Geringer-Sameth+, 2015)J/ApJ/803/63 : gr photometry of stars in Kim 2 (Kim+, 2015)J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/838/11https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/838/11http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/838/11https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/838/11https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/838/11http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/838/11GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/838/11/table2 (Velocity and metallicity measurements for Tucana III (106 unique stars))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/838/11/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/838/11/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/838/11/table2?GETtext/xml+votable180.050000true358.58958-59.575610.0055555555555555566/46144 46145https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/838/11?format=asciiInfraredOpticaldefaultJ/ApJ/838/11/table2Velocity and metallicity measurements for Tucana III (106 unique stars)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDESSource identifier (JHHMMSS.ss+DDMMSS.s) (1)meta.id;meta.maincharNmNumber of measurements for this star (see Note (1))meta.numberintnullableMJDModified Julian Date of the observationdtime.epochfloatRAJ2000Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.maingmag[16/22] DES dereddened g band magnitude (2)magphot.mag;em.opt.Bfloatrmag[15/22] DES dereddened r band magnitude (2)magphot.mag;em.opt.RfloatS/N[2.5/181] Signal to Noise ratiostat.snrfloatHRV[-218/356] Heliocentric radial velocitykm/sspect.dopplerVeloc;pos.heliocentricfloate_HRV[1/12] Uncertainty in HRVkm/sstat.errorfloatEW[0.9/8]? CaT Equivalent width; Angstroms0.1nmspect.line.eqWidthfloatnullablee_EW[0.3/2]? Uncertainty in EW0.1nmstat.error;spect.line.eqWidthfloatnullable[Fe/H][-2.8/-1.9]? Metallicitylog(Sun)phys.abund.Zfloatnullablee_[Fe/H][0.1/0.5]? Uncertainty in [Fe/H]log(Sun)stat.error;phys.abund.FefloatnullableMm[0/1] Membership code (1=member (26 unique sources); 0=not a member)meta.code.memberintSimbadSimbad column added by the CDSmeta.ref.urlchar