J/ApJ/958/167ivo://CDS.VizieR/J/ApJ/958/167CDSFu S.W.Weisz D.R.Starkenburg E.Martin N.Savino A.,Boylan-Kolchin M.Cote P.Dolphin A.E.Ji A.P.Longeard N.,Mateo M.L.Patel E.Sandford N.R.2026-02-23T08:47:38Z2026-02-23T09:04:07ZCDS support team

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

cds-question@unistra.frdwarf-galaxieshst-photometrymetallicitytwo-color-diagramsvisible-astronomyWe present uniformly measured stellar metallicities of 463 stars in 13 Milky Way (MW) ultra-faint dwarf galaxies (UFDs; M_V_=-7.1 to -0.8) using narrowband CaHK (F395N) imaging taken with the Hubble Space Telescope. This represents the largest homogeneous set of stellar metallicities in UFDs, increasing the number of metallicities in these 13 galaxies by a factor of 5 and doubling the number of metallicities in all known MW UFDs. We provide the first well-populated MDFs for all galaxies in this sample, with <[Fe/H]> ranging from -3.0 to -2.0dex, and {sigma}_[Fe/H]_ ranging from 0.3-0.7dex. We find a nearly constant [Fe/H]~-2.6 over 3 decades in luminosity (~10^2^-10^5^L_{sun}_), suggesting that the mass-metallicity relationship does not hold for such faint systems. We find a larger fraction (24%) of extremely metal-poor ([Fe/H]{<}-3) stars across our sample compared to the literature (14%), but note that uncertainties in our most metal-poor measurements make this an upper limit. We find 19% of stars in our UFD sample to be metal-rich ([Fe/H]{>}-2), consistent with the sum of literature spectroscopic studies. MW UFDs are known to be predominantly >13Gyr old, meaning that all stars in our sample are truly ancient, unlike metal-poor stars in the MW, which have a range of possible ages. Our UFD metallicities are not well matched to known streams in the MW, providing further evidence that known MW substructures are not related to UFDs. We include a catalog of our stars to encourage community follow-up studies, including priority targets for ELT-era observations.2023ApJ...958..167Fhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/958/167CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/hst : HST Archived Exposures Catalog (STScI, 2007)J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006)J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009)J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)J/ApJ/756/79 : Optical phot. in 3 Local Group dwarf galaxies (Sand+, 2012)J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)J/ApJ/767/134 : Abund. of red giant stars in UFD galaxies (Vargas+, 2013)J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)J/ApJ/790/73 : Abundances of RGBs in M31 satellites (Vargas+, 2014)J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)J/AJ/149/153 : Abund. of red giants in 10 GCs (Meszaros+, 2015)J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015)J/AJ/151/82 : The 4 brightest red giants in Ret 2 (Roederer+, 2016)J/ApJ/819/53 : Magellan/M2FS sp. of Tucana 2 and Grus 1 (Walker+, 2016)J/MNRAS/472/2963 : Metallicities of Pristine stars (Youakim+, 2017)J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)J/ApJ/863/25 : Magellan obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)J/ApJ/852/99 : Abund. of 3 metal-poor stars in Hor I (Nagasawa+, 2018)J/MNRAS/490/2241 : Spectroscopy of Pristine EMP star candidates (Aguado+, 2019)J/A+A/623/A129 : New satellites of the LMC search (Fritz+, 2019)J/ApJ/870/83 : Abund. in the UFD galaxies GruI & TriII (Ji+, 2019)J/ApJS/247/7 : Narrowband Ca phot. for dSph galaxies (Han+, 2020)J/ApJ/889/27 : Abundances of 11 stars in Carina II and III (Ji+, 2020)J/A+A/640/A25 : Metal-poor stars limb-darkening coeff. (Karovicova+, 2020)J/MNRAS/491/356 : Sagittarius II study with Pristine (Longeard+, 2020)J/MNRAS/497/1236 : Chemo-dynamics of outer halo dwarf stars (Monty+, 2020)J/ApJ/892/137 : Spectroscopy of Grus II, Tuc IV and Tuc V (Simon+, 2020)J/MNRAS/492/3241 : The Pristine survey. IX. (Venn+, 2020)J/ApJ/906/96 : Dwarfs gal. in DC Justice League Simu. (Applebaum+, 2021)J/ApJ/916/81 : Grus I and Indus II deep DES photometry (Cantu+, 2021)J/ApJ/909/192 : HST/ACS photometry of Eridanus II (Gallart+, 2021)J/ApJ/914/123 : Gaia DR2 and EDR3 stars with sp. follow-up (Ibata+, 2021)J/ApJ/920/92 : VLT Sp. of Ultra-faint Dwarf Galaxies (Jenkins+, 2021)J/ApJ/908/18 : HST stellar photometry of Eridanus II (Simon+, 2021)J/MNRAS/516/2348 : Sp. of metal-poor stars in Bootes I (Longeard+, 2022)J/AJ/165/100 : Stellar param. and abundances in Reticulum II (Ji+, 2023)J/ApJS/267/18 : Abundance measurements in M15 RGB stars (Sandford+, 2023)J/ApJ/944/43 : HST/ACS stellar photometry for Reticulum II (Simon+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/958/167https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/958/167http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/958/167https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/958/167https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/958/167http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/958/167GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/958/167/ufdgal (Observational properties of the ultra-faint dwarf (UFD) galaxies (Table 1) and metallicity distribution function measurements (Table 2))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/958/167/ufdgal?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/958/167/ufdgal?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/958/167/ufdgal?GETtext/xml+votable180.050000true56.0878-43.53320.005555555555555556Cone search capability for table J/ApJ/958/167/table4 (Metallicity measurements of all stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/958/167/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/958/167/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/958/167/table4?GETtext/xml+votable180.050000true56.099955-43.545433060.005555555555555556Cone search capability for table J/ApJ/958/167/table5 (*EMP star candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/958/167/table5?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/958/167/table5?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/958/167/table5?GETtext/xml+votable180.050000true56.123845-43.529983890.005555555555555556Cone search capability for table J/ApJ/958/167/table6 (*Metal-rich ([Fe/H]{>}-2.0) stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/958/167/table6?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/958/167/table6?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/958/167/table6?GETtext/xml+votable180.050000true56.10574111-43.529386110.0055555555555555566/4419 5939 5945 10769 11655 24652 33257 33626-33627 33685 33720 34366 46089 46169 46279 462902.3657755224268815e-19 5.0765930186045485e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/958/167?format=asciiOpticaldefaultJ/ApJ/958/167/ufdgalObservational properties of the ultra-faint dwarf (UFD) galaxies (Table 1) and metallicity distribution function measurements (Table 2)r_m-MFlag on m-M (1)meta.ref;pos.framecharFoV[0.41/8.25] On-sky size in relation to the HST/WFC3 FoVphys.sizefloatExp1[3120/9481] Exposure time of the F395N imagestime.duration;obs.exposureintExp2[730/7644] Exposure time of the F475Wimagestime.duration;obs.exposureintExp3[4605/28580] Exposure time of the F606W image (2)stime.duration;obs.exposureintExp4[4605/20860] Exposure time of the F814W image (2)stime.duration;obs.exposureintF395N[25/26] HST/WFC3 F395N magnitude where F395N S/N=5magphot.mag;em.opt.UfloatSimbadNameSimbad column added by the CDSmeta.idcharnullableNEDNED column added by the CDSmeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameGalaxy namemeta.id;meta.maincharVMag[-7.1/-0.8] Absolute V-band magnitudemagphys.magAbs;em.opt.Vfloatrh[0.315/6.3] Half-light radiusarcminphys.angSize;srcfloate_rh[0.03/1]? rh uncertaintyarcminstat.error;phys.angSize;srcfloatnullabler_rhFlag on rh (1)meta.ref;pos.framecharm-M[16.8/22.8] Distance modulusmagphot.mag.distModfloate_m-M[0.04/0.4] m-M uncertaintymagstat.error;phot.mag.distModfloatF475W[25/26] HST/WFC3 F475W magnitude where F395N S/N=5magphot.mag;em.opt.BfloatUFDAbbreviated galaxy name as in tables 4-6; column added by CDSmeta.idcharprimary[Fe/H][-3.05/-2.03] Abundance [Fe/H]phys.abund.Fefloate_[Fe/H][0.06/0.34] Lower uncertainty on [Fe/H]stat.error;stat.min;phys.abund.FefloatE_[Fe/H][0.06/0.26] Upper uncertainty on [Fe/H]stat.error;stat.max;phys.abund.FefloatSig[0.26/0.72] {sigma}_[Fe/H]_ measurementstat.fit.goodnessfloate_Sig[0.08/0.28] Lower uncertainty on Sigstat.error;stat.min;stat.fit.goodnessfloatE_Sig[0.08/0.44] Upper uncertainty on Sigstat.error;stat.max;stat.fit.goodnessfloatNs[6/76] Number of stars used to make the measurementmeta.numberintNemp[0/17] Number of stars with [Fe/H]{<}-3meta.numberintNmr[1/21] Number of stars with [Fe/H]{>}-2meta.numberint_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/ApJ/958/167/table4Metallicity measurements of all starsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintUFDGalaxymeta.id.parentcharStarID[0/82] Star identifier within UFDmeta.id;meta.mainintEMP1: EMP star candidate (link to Table 5)meta.codeintnullableMR1: MR star (link to Table 6)meta.codeintnullableRAJ2000[35.6/355.1] Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[-63.3/64.6] Declination (J2000)degpos.eq.dec;meta.mainF814W[18/24.1] Apparent magnitude in HST/ACS F814W filtermagphot.mag;em.opt.Ifloate_F814W[0/0.02] Uncertainty on F814Wmagstat.error;phot.mag;em.opt.IfloatF606W[18.6/24.5] Apparent magnitude in HST/ACS F606W filtermagphot.mag;em.opt.Rfloate_F606W[0.001/0.02] Uncertainty on F606Wmagstat.error;phot.mag;em.opt.RfloatF475W[19.3/25] Apparent magnitude in HST/WFC3 F475W filtermagphot.mag;em.opt.Bfloate_F475W[0.002/0.07] Uncertainty on F475Wmagstat.error;phot.mag;em.opt.BfloatF395N[19.9/25.3] Apparent magnitude in HST/WFC3 F395N filtermagphot.mag;em.opt.Ufloate_F395N[0.006/0.2] Uncertainty on F395Nmagstat.error;phot.mag;em.opt.UfloatV-I[0.8/1.94] F475W-F814W color indexmagphot.color;em.opt.V;em.opt.Ifloate_V-I[0.002/0.07] Uncertainty on V-Imagstat.error;phot.color;em.optfloatCaHK[-1.8/-0.68] CaHK color index, defined as F395N-F475W-1.5(F475W-F814W)magphot.mag;arith.difffloate_CaHK[0.007/0.2] Uncertainty on CaHKmagstat.error;phot.mag;arith.difffloat[Fe/H][-4/-0.95] Metallicity in units of dexphys.abund.Z;arith.ratiofloatE_[Fe/H][0.04/0.81]? Upper uncertainty on [Fe/H] (1)stat.error;stat.maxfloatnullablee_[Fe/H][0.03/1.1]? Lower uncertainty on [Fe/H], all negative values (1)stat.error;phys.abund.Fefloatnullable[Fe/H]err[0.2/1] Error floor adopted for star in units of dex (2)stat.error;phys.abund.FefloatNotesAdditional measurement notes (i.e. constrained vs unconstrained measurements, EMP star candidates)meta.notecharJ/ApJ/958/167/table5*EMP star candidatesUFDGalaxymeta.id.parentchare_CaHK[0.007/0.2] Uncertainty on CaHKmagstat.error;phot.mag;arith.difffloat[Fe/H][-4/-3] Metallicity in units of dexphys.abund.Z;arith.ratiofloatE_[Fe/H][0.09/0.8]? Upper uncertainty on [Fe/H]stat.error;stat.maxfloatnullablee_[Fe/H][0.1/0.63]? Lower uncertainty on [Fe/H], all negative valuesstat.error;phys.abund.Fefloatnullable[Fe/H]err[0.2/1] Error floor adopted for star in units of dexstat.error;phys.abund.FefloatNotesAdditional measurement notes (i.e. constrained vs unconstrained measurements, EMP star candidates)meta.notecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintStarID[0/81] Star Identifier within UFDmeta.id;meta.mainintRAJ2000[43.8/355.1] Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[-63.3/64.6] Declination (J2000)degpos.eq.dec;meta.mainF814W[18.5/24.1] Apparent magnitude in HST/ACS F814W filtermagphot.mag;em.opt.Ifloate_F814W[0.001/0.02] Uncertainty on F814Wmagstat.error;phot.mag;em.opt.IfloatF606W[19.2/24.4] Apparent magnitude in HST/ACS F606W filtermagphot.mag;em.opt.Rfloate_F606W[0.001/0.02] Uncertainty on F606Wmagstat.error;phot.mag;em.opt.RfloatF475W[19.8/24.9] Apparent magnitude in HST/WFC3 F475W filtermagphot.mag;em.opt.Bfloate_F475W[0.002/0.05] Uncertainty on F475Wmagstat.error;phot.mag;em.opt.BfloatF395N[20.3/25] Apparent magnitude in HST/WFC3 F395N filtermagphot.mag;em.opt.Ufloate_F395N[0.006/0.2] Uncertainty on F395Nmagstat.error;phot.mag;em.opt.UfloatV-I[0.8/1.8] F475W-F814W color indexmagphot.color;em.opt.V;em.opt.Ifloate_V-I[0.002/0.05] Uncertainty on V-Imagstat.error;phot.color;em.optfloatCaHK[-1.76/-0.89] CaHK color index, defined as F395N-F475W-1.5(F475W-F814W)magphot.mag;arith.difffloatJ/ApJ/958/167/table6*Metal-rich ([Fe/H]{>}-2.0) starsUFDGalaxymeta.id.parentcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintStarID[0/70] Star identifier within UFDmeta.id;meta.mainintRAJ2000[35.6/355] Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[-63.3/64.6] Declination (J2000)degpos.eq.dec;meta.mainF814W[18/23.7] Apparent magnitude in HST/ACS F814W filtermagphot.mag;em.opt.Ifloate_F814W[0.001/0.02] Uncertainty on F814Wmagstat.error;phot.mag;em.opt.IfloatF606W[18.6/24.2] Apparent magnitude in HST/ACS F606W filtermagphot.mag;em.opt.Rfloate_F606W[0.001/0.02] Uncertainty on F606Wmagstat.error;phot.mag;em.opt.RfloatF475W[19.3/24.7] Apparent magnitude in HST/WFC3 F475W filtermagphot.mag;em.opt.Bfloate_F475W[0.002/0.05] Uncertainty on F475Wmagstat.error;phot.mag;em.opt.BfloatF395N[20/25.15] Apparent magnitude in HST/WFC3 F395N filtermagphot.mag;em.opt.Ufloate_F395N[0.006/0.11] Uncertainty on F395Nmagstat.error;phot.mag;em.opt.UfloatV-I[0.8/1.9] F475W-F814W color indexmagphot.color;em.opt.V;em.opt.Ifloate_V-I[0.003/0.05] Uncertainty on V-Imagstat.error;phot.color;em.optfloatCaHK[-1.23/-0.68] CaHK color index, defined as F395N-F475W-1.5(F475W-F814W)magphot.mag;arith.difffloate_CaHK[0.01/0.12] Uncertainty on CaHKmagstat.error;phot.mag;arith.difffloat[Fe/H][-1.99/-0.95] Metallicity in units of dexphys.abund.Z;arith.ratiofloatE_[Fe/H][0.05/0.5]? Upper uncertainty on [Fe/H]stat.error;stat.maxfloatnullablee_[Fe/H][0.03/1.1]? Lower uncertainty on [Fe/H], all negative valuesstat.error;phys.abund.Fefloatnullable[Fe/H]err[0.2/0.3] Error floor adopted for star in units of dexstat.error;phys.abund.FefloatNotesAdditional measurement notes (i.e. constrained vs unconstrained measurements, EMP star candidates)meta.notechar