The Astrophysical Journal (Jan 2025)
Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy
- W. Cerny,
- A. Chiti,
- M. Geha,
- B. Mutlu-Pakdil,
- A. Drlica-Wagner,
- C. Y. Tan,
- M. Adamów,
- A. B. Pace,
- J. D. Simon,
- D. J. Sand,
- A. P. Ji,
- T. S. Li,
- A. K. Vivas,
- E. F. Bell,
- J. L. Carlin,
- J. A. Carballo-Bello,
- A. Chaturvedi,
- Y. Choi,
- A. Doliva-Dolinsky,
- O. Y. Gnedin,
- G. Limberg,
- C. E. Martínez-Vázquez,
- S. Mau,
- G. E. Medina,
- M. Navabi,
- N. E. D. Noël,
- V. M. Placco,
- A. H. Riley,
- I. U. Roederer,
- G. S. Stringfellow,
- C. R. Bom,
- P. S. Ferguson,
- D. J. James,
- D. Martínez-Delgado,
- P. Massana,
- D. L. Nidever,
- J. D. Sakowska,
- L. Santana-Silva,
- N. F. Sherman,
- E. J. Tollerud,
- DELVE Collaboration
Affiliations
- W. Cerny
- ORCiD
- Department of Astronomy, Yale University , New Haven, CT 06520, USA ; [email protected]
- A. Chiti
- ORCiD
- Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA
- M. Geha
- ORCiD
- Department of Astronomy, Yale University , New Haven, CT 06520, USA ; [email protected]
- B. Mutlu-Pakdil
- ORCiD
- Department of Physics and Astronomy, Dartmouth College , Hanover, NH 03755, USA
- A. Drlica-Wagner
- ORCiD
- Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- C. Y. Tan
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Physics, University of Chicago , Chicago, IL 60637, USA
- M. Adamów
- ORCiD
- Center for Astrophysical Surveys , National Center for Supercomputing Applications, 1205 West Clark St., Urbana, IL 61801, USA
- A. B. Pace
- ORCiD
- McWilliams Center for Cosmology, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213, USA; Department of Astronomy, University of Virginia , 530 McCormick Road, Charlottesville, VA 22904, USA
- J. D. Simon
- ORCiD
- Observatories of the Carnegie Institution for Science , 813 Santa Barbara St., Pasadena, CA 91101, USA
- D. J. Sand
- ORCiD
- Department of Astronomy/Steward Observatory , 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065, USA
- A. P. Ji
- ORCiD
- Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA
- T. S. Li
- ORCiD
- Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada
- A. K. Vivas
- ORCiD
- Cerro Tololo Inter-American Observatory/NSF NOIRLab , Casilla 603, La Serena, Chile
- E. F. Bell
- ORCiD
- Department of Astronomy, University of Michigan , Ann Arbor, MI 48109, USA
- J. L. Carlin
- ORCiD
- Rubin Observatory/AURA , 950 North Cherry Avenue, Tucson, AZ 85719, USA
- J. A. Carballo-Bello
- ORCiD
- Instituto de Alta Investigación , Universidad de Tarapacá, Casilla 7D, Arica, Chile
- A. Chaturvedi
- ORCiD
- Department of Physics, University of Surrey , Guildford, GU2 7XH, UK
- Y. Choi
- ORCiD
- NSF NOIRLab , 950 N. Cherry Avenue, Tucson, AZ 85719, USA
- A. Doliva-Dolinsky
- ORCiD
- Department of Physics and Astronomy, Dartmouth College , Hanover, NH 03755, USA; Department of Chemistry and Physics, University of Tampa , 401 West Kennedy Boulevard, Tampa, FL 33606, USA
- O. Y. Gnedin
- ORCiD
- Department of Astronomy, University of Michigan , Ann Arbor, MI 48109, USA
- G. Limberg
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Astronomy & Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637, USA; Departamento de Astronomia, IAG, Universidade de São Paulo , SP 05508-090, São Paulo, Brazil
- C. E. Martínez-Vázquez
- ORCiD
- International Gemini Observatory/NSF NOIRLab , 670 N. A’ohoku Place, Hilo, HI 96720, USA
- S. Mau
- ORCiD
- Department of Physics, Stanford University , 382 Via Pueblo Mall, Stanford, CA 94305, USA; Kavli Institute for Particle Astrophysics & Cosmology, P.O. Box 2450, Stanford University , Stanford, CA 94305, USA
- G. E. Medina
- ORCiD
- Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada
- M. Navabi
- ORCiD
- Department of Physics, University of Surrey , Guildford, GU2 7XH, UK
- N. E. D. Noël
- ORCiD
- Department of Physics, University of Surrey , Guildford, GU2 7XH, UK
- V. M. Placco
- ORCiD
- NSF NOIRLab , 950 N. Cherry Avenue, Tucson, AZ 85719, USA
- A. H. Riley
- ORCiD
- Institute for Computational Cosmology, Department of Physics, Durham University , South Road, Durham, DH1 3LE, UK
- I. U. Roederer
- ORCiD
- Department of Physics, North Carolina State University , Raleigh, NC 27695, USA
- G. S. Stringfellow
- ORCiD
- Center for Astrophysics and Space Astronomy, University of Colorado , 389 UCB, Boulder, CO 80309-0389, USA
- C. R. Bom
- ORCiD
- Centro Brasileiro de Pesquisas Físicas , Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ, Brazil
- P. S. Ferguson
- ORCiD
- Department of Physics, University of Wisconsin-Madison , Madison, WI 53706, USA
- D. J. James
- ORCiD
- ASTRAVEO LLC , P.O. Box 1668, Gloucester, MA 01931, USA; Applied Materials Inc. , 35 Dory Road, Gloucester, MA 01930, USA
- D. Martínez-Delgado
- Centro de Estudios de Física del Cosmos de Aragón (CEFCA) , Unidad Asociada al CSIC, Plaza San Juan 1, 44001 Teruel, Spain; ARAID Foundation , Avda. de Ranillas, 1-D, E-50018 Zaragoza, Spain
- P. Massana
- ORCiD
- NSF NOIRLab , Casilla 603, La Serena, Chile
- D. L. Nidever
- ORCiD
- NSF NOIRLab , 950 N. Cherry Avenue, Tucson, AZ 85719, USA; Department of Physics, Montana State University , P.O. Box 173840, Bozeman, MT 59717-3840, USA; NSF’s National Optical-Infrared Astronomy Research Laboratory , 950 N. Cherry Avenue, Tucson, AZ 85719, USA
- J. D. Sakowska
- ORCiD
- Department of Physics, University of Surrey , Guildford, GU2 7XH, UK
- L. Santana-Silva
- ORCiD
- Centro Brasileiro de Pesquisas Físicas , Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ, Brazil
- N. F. Sherman
- ORCiD
- Institute for Astrophysical Research, Boston University , 725 Commonwealth Avenue, Boston, MA 02215, USA
- E. J. Tollerud
- ORCiD
- Space Telescope Science Institute , 3700 San Martin Dr., Baltimore, MD 21218, USA
- DELVE Collaboration
- DOI
- https://doi.org/10.3847/1538-4357/ad8eba
- Journal volume & issue
-
Vol. 979,
no. 2
p. 164
Abstract
We present the discovery of Aquarius III, an ultra-faint Milky Way satellite galaxy identified in the second data release of the DECam Local Volume Exploration survey. Based on deeper follow-up imaging with DECam, we find that Aquarius III is a low-luminosity ( ${M}_{V}=-{2.5}_{-0.5}^{+0.3};$ ${L}_{V}={850}_{-260}^{+380}\ {L}_{\odot }$ ), extended ( ${r}_{1/2}={41}_{-8}^{+9}$ pc) stellar system located in the outer halo ( D _⊙ = 85 ± 4 kpc). From medium-resolution Keck/DEIMOS spectroscopy, we identify 11 member stars and measure a mean heliocentric radial velocity of ${v}_{\mathrm{sys}}=-{13.1}_{-0.9}^{+1.0}\ \mathrm{km}\ {{\rm{s}}}^{-1}$ for the system and place an upper limit of σ _v < 3.5 km s ^−1 ( σ _v < 1.6 km s ^−1 ) on its velocity dispersion at the 95% (68%) credible level. Based on calcium-triplet metallicities of the six brightest red giant members, we find that Aquarius III is very metal-poor ([Fe/H]= − 2.61 ± 0.21) with a statistically significant metallicity spread ( ${\sigma }_{[\mathrm{Fe}/{\rm{H}}]}={0.46}_{-0.14}^{+0.26}$ dex). We interpret this metallicity spread as strong evidence that the system is a dwarf galaxy as opposed to a star cluster. Combining our velocity measurement with Gaia proper motions, we find that Aquarius III is currently situated near its orbital pericenter in the outer halo ( r _peri = 78 ± 7 kpc) and that it is plausibly on first infall onto the Milky Way. This orbital history likely precludes significant tidal disruption from the Galactic disk, notably unlike other satellites with comparably low velocity dispersion limits in the literature. Thus, if further velocity measurements confirm that its velocity dispersion is truly below σ _v ≲ 2 km s ^−1 , Aquarius III may serve as a useful laboratory for probing galaxy formation physics in low-mass halos.
Keywords
