J/MNRAS/479/5343ivo://CDS.VizieR/J/MNRAS/479/5343doi:10.26093/cds/vizier.74795343CDSKoposov S.E.Walker M.G.Belokurov V.Casey A.R.Geringer-Sameth A.,Mackey D.Da Costa G.Erkal D.Jethwa P.Mateo M.Olszewski E.W.,Bailey J.I.2024-08-18T20:20:50Z2022-05-06T09:04:06ZCDS support team

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

cds-question@unistra.frgalaxiesglobular-star-clustersmagellanic-cloudsvisible-astronomyWe report the discovery of a nearby dwarf galaxy in the constellation of Hydrus, between the Large (LMC) and the Small Magellanic Clouds (SMC). Hydrus 1 is a mildly elliptical ultrafaint system with luminosity M_V_~-4.7 and size 53+/-3pc, located 28kpc from the Sun and 24kpc from the LMC. From spectroscopy of ~30 member stars, we measure a velocity dispersion of 2.7+/-0.5 km/s and find tentative evidence for a radial velocity gradient consistent with 3km/s rotation. Hydrus 1's velocity dispersion indicates that the system is dark matter dominated, but its dynamical mass-to-light ratio M/L=66^+29^_-20_ is significantly smaller than typical for ultrafaint dwarfs at similar luminosity. The kinematics and spatial position of Hydrus 1 make it a very plausible member of the family of satellites brought into the Milky Way by the Magellanic Clouds. While Hydrus 1's proximity and well-measured kinematics make it a promising target for dark matter annihilation searches, we find no evidence for significant gamma-ray emission from Hydrus 1. The new dwarf is a metal-poor galaxy with a mean metallicity [Fe/H]=-2.5 and [Fe/H] standard deviation of 0.4dex, similar to other systems of similar luminosity. {alpha} abundances of Hyi 1 members indicate that star formation was extended, lasting between 0.1 and 1Gyr, with self-enrichment dominated by supernova Ia. The dwarf also hosts a highly carbon-enhanced extremely metal-poor star with [Fe/H]~-3.2 and [C/Fe]~+3.0.2018MNRAS.479.5343Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/479/5343CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/479/5343https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/479/5343http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/479/5343https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/479/5343https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/479/5343http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/479/5343GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/479/5343/table2 (Spectroscopic measurements for individual stars with either S/N>3 or RV error less than 10km/s in the Hydrus 1 field)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/479/5343/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/479/5343/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/479/5343/table2?GETtext/xml+votable180.050000true37.69-79.360.0055555555555555566/32913 32916https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/479/5343?format=asciiOpticaldefaultJ/MNRAS/479/5343/table2Spectroscopic measurements for individual stars with either S/N>3 or RV error less than 10km/s in the Hydrus 1 fieldSimbadSimbad column added by the CDSmeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDStar identification numbermeta.id;meta.mainintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainS/NMedian signal to noise ratio of the spectraem.wl.central;stat.medianfloatHRVHeliocentric radial velocitykm/sspect.dopplerVeloc;pos.heliocentricfloate_HRVRadial velocity errorkm/sstat.errorfloatTeffEffective temperatureKphys.temperature.effectiveinte_TeffEffective temperature errorKstat.error;phys.temperature.effectiveintloggmeanMean Surface gravitylog(cm.s**-2)phys.gravity;stat.meanfloate_loggmeanMean Surface gravity errorlog(cm.s**-2)stat.errorfloat[Fe/H]Metallicityphys.abund.Zfloate_[Fe/H]Metallicity errorstat.error;phys.abund.Fefloatgmag? Not corrected for extinction g-band photometry from DECam observationsmagphot.mag;em.opt.Bfloatnullablermag? Not corrected for extinction r-band photometry from DECam observationsmagphot.mag;em.opt.Rfloatnullablelogodds? Log-odds ratios of being a Hydrus 1 member star versus being a foreground contaminant from the chemodynamical model fit (1)meta.code.memberdoublenullablee_logodds? Log-odds error (2)stat.errordoublenullable