Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy
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}_{...
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2025-01-01
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| author | 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 |
| author_facet | 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 |
| author_sort | W. Cerny |
| collection | DOAJ |
| description | 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. |
| format | Article |
| id | doaj-art-86590f0070da4f43bb6a3601c6836f3d |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-86590f0070da4f43bb6a3601c6836f3d2025-01-23T11:38:11ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01979216410.3847/1538-4357/ad8ebaDiscovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite GalaxyW. Cerny0https://orcid.org/0000-0003-1697-7062A. Chiti1https://orcid.org/0000-0002-7155-679XM. Geha2https://orcid.org/0000-0002-7007-9725B. Mutlu-Pakdil3https://orcid.org/0000-0001-9649-4815A. Drlica-Wagner4https://orcid.org/0000-0001-8251-933XC. Y. Tan5https://orcid.org/0000-0003-0478-0473M. Adamów6https://orcid.org/0000-0002-6904-359XA. B. Pace7https://orcid.org/0000-0002-6021-8760J. D. Simon8https://orcid.org/0000-0002-4733-4994D. J. Sand9https://orcid.org/0000-0003-4102-380XA. P. Ji10https://orcid.org/0000-0002-4863-8842T. S. Li11https://orcid.org/0000-0002-9110-6163A. K. Vivas12https://orcid.org/0000-0003-4341-6172E. F. Bell13https://orcid.org/0000-0002-5564-9873J. L. Carlin14https://orcid.org/0000-0002-3936-9628J. A. Carballo-Bello15https://orcid.org/0000-0002-3690-105XA. Chaturvedi16https://orcid.org/0000-0001-5143-1255Y. Choi17https://orcid.org/0000-0003-1680-1884A. Doliva-Dolinsky18https://orcid.org/0000-0001-9775-9029O. Y. Gnedin19https://orcid.org/0000-0001-9852-9954G. Limberg20https://orcid.org/0000-0002-9269-8287C. E. Martínez-Vázquez21https://orcid.org/0000-0002-9144-7726S. Mau22https://orcid.org/0000-0003-3519-4004G. E. Medina23https://orcid.org/0000-0003-0105-9576M. Navabi24https://orcid.org/0000-0001-9438-5228N. E. D. Noël25https://orcid.org/0000-0002-8282-469XV. M. Placco26https://orcid.org/0000-0003-4479-1265A. H. Riley27https://orcid.org/0000-0001-5805-5766I. U. Roederer28https://orcid.org/0000-0001-5107-8930G. S. Stringfellow29https://orcid.org/0000-0003-1479-3059C. R. Bom30https://orcid.org/0000-0003-4383-2969P. S. Ferguson31https://orcid.org/0000-0001-6957-1627D. J. James32https://orcid.org/0000-0001-5160-4486D. Martínez-Delgado33P. Massana34https://orcid.org/0000-0002-8093-7471D. L. Nidever35https://orcid.org/0000-0002-1793-3689J. D. Sakowska36https://orcid.org/0000-0002-1594-1466L. Santana-Silva37https://orcid.org/0000-0003-3402-6164N. F. Sherman38https://orcid.org/0000-0001-5399-0114E. J. Tollerud39https://orcid.org/0000-0002-9599-310XDELVE CollaborationDepartment of Astronomy, Yale University , New Haven, CT 06520, USA ; william.cerny@yale.eduDepartment of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USADepartment of Astronomy, Yale University , New Haven, CT 06520, USA ; william.cerny@yale.eduDepartment of Physics and Astronomy, Dartmouth College , Hanover, NH 03755, USADepartment 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, USAKavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Physics, University of Chicago , Chicago, IL 60637, USACenter for Astrophysical Surveys , National Center for Supercomputing Applications, 1205 West Clark St., Urbana, IL 61801, USAMcWilliams 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, USAObservatories of the Carnegie Institution for Science , 813 Santa Barbara St., Pasadena, CA 91101, USADepartment of Astronomy/Steward Observatory , 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065, USADepartment of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USADepartment of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, CanadaCerro Tololo Inter-American Observatory/NSF NOIRLab , Casilla 603, La Serena, ChileDepartment of Astronomy, University of Michigan , Ann Arbor, MI 48109, USARubin Observatory/AURA , 950 North Cherry Avenue, Tucson, AZ 85719, USAInstituto de Alta Investigación , Universidad de Tarapacá, Casilla 7D, Arica, ChileDepartment of Physics, University of Surrey , Guildford, GU2 7XH, UKNSF NOIRLab , 950 N. Cherry Avenue, Tucson, AZ 85719, USADepartment 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, USADepartment of Astronomy, University of Michigan , Ann Arbor, MI 48109, USAKavli 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, BrazilInternational Gemini Observatory/NSF NOIRLab , 670 N. A’ohoku Place, Hilo, HI 96720, USADepartment 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, USADepartment of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, CanadaDepartment of Physics, University of Surrey , Guildford, GU2 7XH, UKDepartment of Physics, University of Surrey , Guildford, GU2 7XH, UKNSF NOIRLab , 950 N. Cherry Avenue, Tucson, AZ 85719, USAInstitute for Computational Cosmology, Department of Physics, Durham University , South Road, Durham, DH1 3LE, UKDepartment of Physics, North Carolina State University , Raleigh, NC 27695, USACenter for Astrophysics and Space Astronomy, University of Colorado , 389 UCB, Boulder, CO 80309-0389, USACentro Brasileiro de Pesquisas Físicas , Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ, BrazilDepartment of Physics, University of Wisconsin-Madison , Madison, WI 53706, USAASTRAVEO LLC , P.O. Box 1668, Gloucester, MA 01931, USA; Applied Materials Inc. , 35 Dory Road, Gloucester, MA 01930, USACentro 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, SpainNSF NOIRLab , Casilla 603, La Serena, ChileNSF 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, USADepartment of Physics, University of Surrey , Guildford, GU2 7XH, UKCentro Brasileiro de Pesquisas Físicas , Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ, BrazilInstitute for Astrophysical Research, Boston University , 725 Commonwealth Avenue, Boston, MA 02215, USASpace Telescope Science Institute , 3700 San Martin Dr., Baltimore, MD 21218, USAWe 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.https://doi.org/10.3847/1538-4357/ad8ebaDwarf galaxiesMilky Way GalaxyLocal Group |
| spellingShingle | 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 Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy The Astrophysical Journal Dwarf galaxies Milky Way Galaxy Local Group |
| title | Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy |
| title_full | Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy |
| title_fullStr | Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy |
| title_full_unstemmed | Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy |
| title_short | Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy |
| title_sort | discovery and spectroscopic confirmation of aquarius iii a low mass milky way satellite galaxy |
| topic | Dwarf galaxies Milky Way Galaxy Local Group |
| url | https://doi.org/10.3847/1538-4357/ad8eba |
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