J/ApJ/808/95ivo://CDS.VizieR/J/ApJ/808/95doi:10.26093/cds/vizier.18080095CDSSimon J.D.Drlica-Wagner A.Li T.S.Nord B.Geha M.Bechtol K.,Balbinot E.Buckley-Geer E.Lin H.Marshall J.Santiago B.,Strigari L.Wang M.Wechsler R.H.Yanny B.Abbott T.Bauer A.H.,Bernstein G.M.Bertin E.Brooks D.Burke D.L.Capozzi D.,Carnero Rosell A.Carrasco Kind M.D'Andrea C.B.da Costa L.N.,Depoy D.L.Desai S.Diehl H.T.Dodelson S.Cunha C.E.Estrada J.,Evrard A.E.Neto A.F.Fernandez E.Finley D.A.Flaugher B.Frieman J.,Gaztanaga E.Gerdes D.Gruen D.Gruendl R.A.Honscheid K.James D.,Kent S.Kuehn K.Kuropatkin N.Lahav O.Maia M.A.G.March M.,Martini P.Miller C.J.Miquel R.Ogando R.Romer A.K.Roodman A.,Rykoff E.S.Sako M.Sanchez E.Schubnell M.Sevilla I.Smith R.C.,Soares-Santos M.Sobreira F.Suchyta E.Swanson M.E.C.Tarle G.,Thaler J.Tucker D.Vikram V.Walker A.R.Wester W.,(the DES Collaboration)2018-01-05T08:56:14Z2015-12-17T08:38:30ZCDS support team

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

cds-question@unistra.frmetallicityradial-velocitygalaxiesspectroscopyWe present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8+/-0.5km/s and a velocity dispersion of 3.3+/-0.7km/s. The mass-to-light ratio of Ret II within its half-light radius is 470+/-210M_{sun}_/L_{sun}_, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3dex in metallicity, with a dispersion of 0.28+/-0.09dex, and we identify several extremely metal-poor stars with [Fe/H]<-3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H]=-2.65+/-0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is log_10_(J)=18.8+/-0.6GeV^2^/cm^5^ within 0.2{deg}, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.2015ApJ...808...95Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/808/95CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/eso : ESO Science Archive Catalog (ESO, 1991-2015)I/324 : The Initial Gaia Source List (IGSL) (Smart, 2013)J/ApJ/801/74 : Dark matter profiles in dwarf gal. (Geringer-Sameth+, 2015)J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)J/ApJ/767/134 : Abundances of red giant stars in UFD gal. (Vargas+, 2013)J/ApJ/757/83 : The Blanco Cosmology Survey (BCS) (Desai+, 2012)J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)J/MNRAS/418/1526 : Dark matter in dSph galaxies (Charbonnier+, 2011)J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)J/MNRAS/326/959 : Empirical calibration of the NIR Ca triplet (Cenarro+ 2001)http://archive.eso.org/cms/eso-data.html : ESO data archivehttp://www.darkenergysurvey.org/ : Dark Energy Survey home pagehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/808/95https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/808/95http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/808/95https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/808/95https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/808/95http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/808/95GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/808/95/table1 (Velocity and metallicity measurements)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/808/95/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/808/95/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/808/95/table1?GETtext/xml+votable180.050000true53.42377-54.002010.0055555555555555566/33626 33627https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/808/95?format=asciiOpticaldefaultJ/ApJ/808/95/table1Velocity and metallicity measurementsMmCode membershipmeta.code.membercharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintInstInstrument ("MF2S", "GIRAFFE" or "GMOS")meta.id;instrcharDESStar identifier (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharRAJ2000Right ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.maingmag[16.4/21.3] g-band magnitude (1)magphot.mag;em.opt.Bfloatrmag[15.6/21] r-band magnitude (1)magphot.mag;em.opt.RfloatVel[-25.2/311.1] Velocitykm/sphys.veloc;pos.heliocentricfloate_Vel[0.9/8.3]? Velocity uncertaintykm/sstat.errorfloatnullableEW1[0.9/7]? Giraffe equivalent widthspect.line.eqWidthfloatnullablee_EW1[0.1/0.6]? EW1 uncertaintystat.errorfloatnullable[Fe/H]1[-3.4/-2]? Giraffe metallicityphys.abund.Zfloatnullablee_[Fe/H]1[0.1/0.6]? [Fe/H]1 uncertaintystat.error;phys.abund.FefloatnullableEW2[1.1/4.7]? GMOS equivalent widthspect.line.eqWidthfloatnullablee_EW2[0.2/0.6]? EW2 uncertaintystat.errorfloatnullable[Fe/H]2[-3.2/-2.8]? GMOS metallicityphys.abund.Zfloatnullablee_[Fe/H]2[0.1/0.4]? [Fe/H]2 uncertaintystat.error;phys.abund.FefloatnullableIGSLDisplay sources within 0.5" from the Initial Gaia Source List (Smart, 2013, I/324)meta.ref.urlintnullableSimbadSimbad column added by the CDSmeta.ref.urlchar