J/ApJ/908/18ivo://CDS.VizieR/J/ApJ/908/18doi:10.26093/cds/vizier.19080018CDSSimon J.D.Brown T.M.Drlica-Wagner A.Li T.S.Avila R.J.Bechtol K.,Clementini G.Crnojevic D.Garofalo A.Geha M.Sand D.J.Strader J.,Willman B.2022-09-30T23:28:51Z2022-07-27T08:39:56ZCDS support team

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

cds-question@unistra.frgalaxiesglobular-star-clustershst-photometryvisible-astronomyWe present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf galaxy EridanusII (EriII). EriII, which has an absolute magnitude of MV=-7.1, is located at a distance of 339kpc, just beyond the virial radius of the Milky Way. We determine the star formation history of EriII and measure the structure of the galaxy and its star cluster. We find that a star formation history consisting of two bursts, constrained to match the spectroscopic metallicity distribution of the galaxy, accurately describes the EriII stellar population. The best-fit model implies a rapid truncation of star formation at early times, with >80% of the stellar mass in place before z~6. A small fraction of the stars could be as young as 8Gyr, but this population is not statistically significant; Monte Carlo simulations recover a component younger than 9Gyr only 15% of the time, where they represent an average of 7{+/-}4% of the population. These results are consistent with theoretical expectations for quenching by reionization. The HST depth and angular resolution enable us to show that EriII's cluster is offset from the center of the galaxy by a projected distance of 23{+/-}3pc. This offset could be an indication of a small (~50-75pc) dark matter core in EriII. Moreover, we demonstrate that the cluster has a high ellipticity of 0.31_-0.06_^+0.05^ and is aligned with the orientation of EriII within 3{deg}{+/-}6{deg}, likely due to tides. The stellar population of the cluster is indistinguishable from that of EriII itself.2021ApJ...908...18Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/908/18CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/337 : Gaia DR1 (Gaia Collaboration, 2016)II/357 : The Dark Energy Survey (DES) Data Release 1 (Abbott+, 2018)I/345 : Gaia DR2 (Gaia Collaboration, 2018)VII/195 : Globular Clusters in the Milky Way (Harris, 1996)VII/202 : Globular Clusters in the Milky Way (Harris, 1997)J/AJ/130/1693 : HST-ACS observations of 5 globular clusters (Brown+, 2005)J/AJ/129/2714 : JHK photometry of M92 variable stars (Del Principe+, 2005)J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)J/ApJ/756/108 : HST VI photometry of variable stars in LeoT (Clementini+, 2012)J/AJ/148/83 : Spectroscopy in NGC 2360, NGC 3680, and NGC 5822 (Sales+, 2014)J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)J/ApJ/808/16 : The Cannon, new approach to determine abundances (Ness+, 2015)J/ApJ/829/26 : Variable stars in field of Andromeda XXV. III. (Cusano+, 2016)J/A+A/612/A26 : Deep HI observations of Leo T with WSRT (Adams+, 2018)J/ApJ/863/25 : Deep Magellan/Megacam obs. 4 MWsatellites (Mutlu-Pakdil+, 2018)J/ApJ/885/53 : Spectroscopy & HST photometry galaxy LeoV (Mutlu-Pakdil+, 2019)J/ApJ/875/77 : Proper motions of MW satellites with Gaia & DES (Pace+, 2019)J/ApJ/875/L13 : DECam r and i magnitudes in the Fornax 6 cluster (Wang+, 2019)J/ApJ/893/47 : Milky Way satellite census. I. DES & PS1 (Drlica-Wagner+, 2020)J/A+A/635/A107 : Spectroscopy of the Eri 2 cluster (Zoutendijk+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/908/18https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/908/18http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/908/18https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/908/18https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/908/18http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/908/18GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/908/18/table1 (Eri II stellar photometry)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/908/18/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/908/18/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/908/18/table1?GETtext/xml+votable180.050000true56.06650389-43.567203060.0055555555555555566/343662.3657755224268815e-19 3.5452907792336973e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/908/18?format=asciiOpticaldefaultJ/ApJ/908/18/table1Eri II stellar photometryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID[1/27299] Internal index numbermeta.id;meta.mainintRAJ2000[56.04/56.14] Right Ascension (J2000)degpos.eq.ra;meta.mainindexedDEJ2000[-43.57/-43.4] Declination (J2000)degpos.eq.dec;meta.mainindexedF606mag[18.8/31.2] HST/ACS F606W filter magnitude; STMAGmagphot.mag;em.opt.Rfloate_F606mag[0.004/0.6] Uncertainty in F606magmagstat.error;phot.magfloate_F814mag[0.004/0.6] Uncertainty in F814magmagstat.error;phot.magfloatF814mag[18.6/31.6] HST/ACS F814W filter magnitude; STMAGmagphot.mag;em.opt.IfloatFlag[0/2047] Photometry flag (1)meta.code.errorint