J/ApJ/935/L17ivo://CDS.VizieR/J/ApJ/935/L17doi:10.26093/cds/vizier.19359017CDSSand D.J.Mutlu-Pakdil B.Jones M.G.Karunakaran A.Wang F.Yang J.,Chiti A.Bennet P.Crnojevic D.Spekkens K.2024-11-06T20:27:00Z2024-06-27T08:46:40ZCDS support team

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

cds-question@unistra.frdwarf-galaxiesinfrared-photometryvisible-astronomyphotometryWe report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D=1.4Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ~500kpc distant. Deep ground-based imaging resolves TucanaB into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. TucanaB has a half-light radius of 80{+/-}40pc and an absolute magnitude of M_V_=-6.9_-0.6_^+0.5^mag (L_V_=(5_-2_^+4^)x10^4^L{sun}), which is again comparable to the Milky Way's ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color-magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating logSFR_NUV_}/M{odot}/yr)<-5.4 for star formation on ~100Myr timescales. Given its isolation and physical properties, TucanaB may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.2022ApJ...935L..17Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/935/L17CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/371 : The Dark Energy Survey (DES): Data Release 2 (Abbott+, 2021)J/A+A/315/40 : Photometry of the Tuc dwarf galaxy (Saviane, 1996)J/AJ/127/2031 : Catalog of neighboring galaxies (Karachentsev+, 2004)J/ApJS/164/38 : UV & FIR properties nearby galaxies (Iglesias-Paramo+, 2006)J/ApJ/699/1742 : LCID project. I. Cetus and Tucana variables (Bernard+, 2009)J/ApJ/704/898 : Photometry of the Hercules dwarf galaxy (Sand+, 2009)J/ApJS/192/6 : A GALEX UV imaging survey of nearby galaxies (Lee+, 2011)J/AJ/144/4 : Properties of dwarf galaxies Local Group (McConnachie+, 2012)J/ApJ/756/79 : Optical photometry 3 Local Group dwarf galaxies (Sand+, 2012)J/ApJ/768/77 : Ultra-compact high velocity clouds from ALFALFA (Adams+, 2013)J/AJ/145/149 : ALFALFA discovery of Leo P. II. BVR photometry (Rhode+, 2013)J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)J/A+A/578/A61 : Galaxy groups in the 2M++ (Diaz-Gimenez+, 2015)J/ApJ/812/158 : Leo P RR Lyrae candidates & cumulative SFH (McQuinn+, 2015)J/ApJ/806/95 : A search for ultra-compact HVC counterparts (Sand+, 2015)J/ApJ/827/89 : HST imaging of Pisces A and B (Tollerud+, 2016)J/ApJ/891/144 : CFHT dwarf satellite galaxies around LV host (Carlsten+, 2020)J/ApJ/888/31 : HST/ACS observations and SFH of Antlia B (Hargis+, 2020)J/ApJ/909/211 : HST obs. of MADCASH-1 and MADCASH-2 (Carlin+, 2021)J/ApJ/916/L19 : Satellites around MW analogs from SAGA II (Karunakaran+, 2021)J/ApJ/907/85 : SAGA Survey II. Satellite systems around galaxies (Mao+, 2021)J/ApJ/913/53 : Gas content of dwarf gal within 2Mpc of the MW (Putman+, 2021)J/ApJ/908/18 : HST stellar photometry of Eridanus II (Simon+, 2021)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/935/L17https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/935/L17http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/935/L17https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/935/L17https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/935/L17http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/935/L17GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/935/L17/fig2 (The color-magnitude diagram of Tucana B from our Magellan IMACS data)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/935/L17/fig2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/935/L17/fig2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/935/L17/fig2?GETtext/xml+votable180.050000true341.7415-58.40600110.0055555555555555566/46209 46212https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/935/L17?format=asciiOpticalInfrareddefaultJ/ApJ/935/L17/fig2The color-magnitude diagram of Tucana B from our Magellan IMACS datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000[341/342] Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000[-59/-58] Declination in decimal degrees (J2000)degpos.eq.dec;meta.maingmag[21.5/27] Apparent g-band AB magnitude (1)magphot.mag;em.opt.Vfloatrmag[21/26.7] Apparent r-band AB magnitude (1)magphot.mag;em.opt.RfloatIDPanel identifier (2)meta.id;meta.mainchar