Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey

Abstract

We report the discovery of a new star cluster, DES 3, in the constellation of Indus, and deeper observations of the previously identified satellite DES J0222.7$-$5217 (Eridanus III). DES 3 was detected as a stellar overdensity in first-year Dark Energy Survey data, and confirmed with deeper photometry from the 4.1 metre Southern Astrophysical Research (SOAR) telescope. The new system was detected with a relatively high significance and appears in the DES images as a compact concentration of faint blue point sources. We determine that DES 3 is located at a heliocentric distance of $\sim 76\mathrm{kpc}$ and it is dominated by an old ($\simeq 9.8\mathrm{Gyr}$) and metal-poor ($[Fe/H]\simeq -1.88$) population. While the age and metallicity values of DES 3 are similar to globular clusters, its half-light radius ($r_{\mathrm{h}}\sim 6.5\mathrm{pc}$) and luminosity ($M_V\sim -1.9$) are more indicative of faint star clusters. Based on the apparent angular size, DES 3, with a value of $r_{\mathrm{h}}\sim 0.{}^{\prime }3$, is among the smallest faint star clusters known to date. Furthermore, using deeper imaging of DES J0222.7$-$5217 taken with the SOAR telescope, we update structural parameters and perform the first isochrone modeling. Our analysis yields the first age ($\simeq 12.6\mathrm{Gyr}$) and metallicity ($[Fe/H]\simeq -2.01$) estimates for this object. The half-light radius ($r_{\mathrm{h}}\sim 10.5\mathrm{pc}$) and luminosity ($M_V\sim -2.7$) of DES J0222.7$-$5217 suggest that it is likely a faint star cluster. The discovery of DES 3 indicates that the census of stellar systems in the Milky Way is still far from complete, and demonstrates the power of modern wide-field imaging surveys to improve our knowledge of the Galaxy's satellite population.

arXiv comment11 pages, 9 figures, 3 tables

References in corpus (58)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• emcee: The MCMC Hammer
• The Sloan Digital Sky Survey: Technical Summary
• On the variation of the Initial Mass Function
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The observed properties of dwarf galaxies in and around the Local Group
• The Dark Energy Camera
• Accurate masses for dispersion-supported galaxies
• The SDSS View of the Palomar-Green Bright Quasar Survey
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• A comprehensive Maximum Likelihood analysis of the structural properties of faint Milky Way satellites
• The Origin of the Magellanic Stream and Its Leading Arm
• Assessing the Milky Way Satellites Associated with the Sagittarius Dwarf Spheroidal Galaxy
• The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics and Data Release
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater
• "Galaxy," Defined
• Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo
• Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• A Magellanic Origin of the DES Dwarfs
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• Farthest Neighbor: The Distant Milky Way Satellite Eridanus II
• Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic Stellar History
• A New Faint Milky Way Satellite Discovered in the Pan-STARRS1 3 pi Survey
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Horologium II: a Second Ultra-faint Milky Way Satellite in the Horologium Constellation
• An Optical Catalog of Galaxy Clusters Obtained from an Adaptive Matched Filter Finder Applied to SDSS DR6
• The population of Milky Way satellites in the LambdaCDM cosmology
• The discovery of two extremely low luminosity Milky Way globular clusters
• Do globular clusters possess Dark Matter halos? A case study in NGC 2419
• Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1
• At the survey limits: discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data
• Nearest Neighbor: The Low-Mass Milky Way Satellite Tucana III
• A new distant Milky Way globular cluster in the Pan-STARRS1 3π survey
• A New Catalog of Globular Clusters in the Milky Way
• An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey
• Identifying true satellites of the Magellanic Clouds
• Discovery of a Faint Outer Halo Milky Way Star Cluster in the Southern Sky
• A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
• The predicted luminous satellite populations around SMC and LMC-mass galaxies - A missing satellite problem around the LMC?
• Magellan/M2FS Spectroscopy of the Reticulum 2 Dwarf Spheroidal Galaxy
• Searches for New Milky Way Satellites from the First Two Years of Data of the Subaru/Hyper Suprime-Cam Survey: Discovery of Cetus~III
• The Dark Energy Survey Data Processing and Calibration System
• Gaia 1 and 2. A pair of new Galactic star clusters
• The halo+cluster system of the Galactic globular cluster NGC1851
• A Hero's Little Horse: Discovery of a Dissolving Star Cluster in Pegasus
• A new Milky Way halo star cluster in the Southern Galactic Sky
• Digging deeper into the Southern skies: a compact Milky-Way companion discovered in first-year Dark Energy Survey data
• The Discovery of an Ultra-Faint Star Cluster in the Constellation of Ursa Minor
• Absolute Ages and Distances of 22 GCs using Monte Carlo Main-Sequence Fitting
• Segue 3: An Old, Extremely Low luminosity Star Cluster in the Milky Way's Halo
• The LMC geometry and outer stellar populations from early DES data
• Portrait of a Dark Horse: a Photometric and Spectroscopic Study of the Ultra-faint Milky Way Satellite Pegasus III
• Kim 3: an Ultra-faint Star Cluster in the Constellation of Centaurus
• Physical properties of star clusters in the outer LMC as observed by the Dark Energy Survey

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• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
• Proper motions of Milky Way Ultra-Faint satellites with $Gaia$ DR2 $\times$ DES DR1
• An extended halo around an ancient dwarf galaxy
• Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus
• Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey
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• Robust velocity dispersion and binary population modeling of the ultra-faint dwarf galaxy Reticulum II
• A faint halo star cluster discovered in the Blanco Imaging of the Southern Sky Survey
• Modelling the Milky Way. I -- Method and first results fitting the thick disk and halo with DES-Y3 data
• A Deeper Look at DES Dwarf Galaxy Candidates: Grus I and Indus II
• First evidence of a stripped star cluster from the Small Magellanic Cloud
• The emergence of globular clusters and globular-cluster-like dwarfs
• DELVE Milky Way Satellite Galaxy Census I: Satellite Population and Survey Selection Function in DES, DELVE, and Pan-STARRS
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