The Astrophysical Journal (Jan 2023)
Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus
- W. Cerny,
- J. D. Simon,
- T. S. Li,
- A. Drlica-Wagner,
- A. B. Pace,
- C. E. Martínez-Vázquez,
- A. H. Riley,
- B. Mutlu-Pakdil,
- S. Mau,
- P. S. Ferguson,
- D. Erkal,
- R. R. Munoz,
- C. R. Bom,
- J. L. Carlin,
- D. Carollo,
- Y. Choi,
- A. P. Ji,
- V. Manwadkar,
- D. Martínez-Delgado,
- A. E. Miller,
- N. E. D. Noël,
- J. D. Sakowska,
- D. J. Sand,
- G. S. Stringfellow,
- E. J. Tollerud,
- A. K. Vivas,
- J. A. Carballo-Bello,
- D. Hernandez-Lang,
- D. J. James,
- D. L. Nidever,
- J. L. Nilo Castellon,
- K. A. G. Olsen,
- A. Zenteno,
- DELVE Collaboration
Affiliations
- W. Cerny
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA ; [email protected]; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA
- J. D. Simon
- ORCiD
- Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USA
- T. S. Li
- ORCiD
- Department of Astronomy and Astrophysics, University of Toronto , 50 St George Street, Toronto ON, M5S 3H4, Canada
- A. Drlica-Wagner
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA ; [email protected]; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- A. B. Pace
- ORCiD
- McWilliams Center for Cosmology, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
- C. E. Martínez-Vázquez
- ORCiD
- Gemini Observatory , NSF’s NOIRLab, 670 North A’ohoku Place, Hilo, HI 96720, USA; Cerro Tololo Inter-American Observatory , NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile
- A. H. Riley
- ORCiD
- George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University , College Station, TX 77843, USA; Department of Physics and Astronomy, Texas A&M University , College Station, TX 77843, USA
- B. Mutlu-Pakdil
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA ; [email protected]; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, 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
- P. S. Ferguson
- ORCiD
- Department of Physics, University of Wisconsin-Madison , Madison, WI 53706, USA
- D. Erkal
- ORCiD
- Department of Physics, University of Surrey , Guildford GU2 7XH, UK
- R. R. Munoz
- ORCiD
- Departamento de Astronomía, Universidad de Chile , Camino del Observatorio 1515, Las Condes, Santiago, Chile
- C. R. Bom
- ORCiD
- Centro Brasileiro de Pesquisas Físicas , Rua Doutor Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ, Brazil
- J. L. Carlin
- ORCiD
- Rubin Observatory/AURA , 950 North Cherry Avenue, Tucson, AZ, 85719, USA
- D. Carollo
- ORCiD
- INAF-Osservatorio Astronomico di Trieste , I-34143 Trieste, Italy
- Y. Choi
- ORCiD
- Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
- A. P. Ji
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA ; [email protected]; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA
- V. Manwadkar
- Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA
- D. Martínez-Delgado
- ORCiD
- Instituto de Astrofísica de Andalucía , CSIC, E-18080 Granada, Spain
- A. E. Miller
- ORCiD
- Leibniz-Institut für Astrophysik Potsdam (AIP) , An der Sternwarte 16, D-14482 Potsdam, Germany; Institut für Physik und Astronomie, Universität Potsdam , Haus 28, Karl-Liebknecht-Straße 24/25, D-14476 Golm (Potsdam), Germany
- N. E. D. Noël
- ORCiD
- Department of Physics, University of Surrey , Guildford GU2 7XH, UK
- J. D. Sakowska
- ORCiD
- Department of Physics, University of Surrey , Guildford GU2 7XH, UK
- D. J. Sand
- ORCiD
- Department of Astronomy/Steward Observatory , 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065, USA
- G. S. Stringfellow
- ORCiD
- Center for Astrophysics and Space Astronomy, University of Colorado , 389 UCB, Boulder, CO 80309-0389, USA
- E. J. Tollerud
- ORCiD
- Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
- A. K. Vivas
- ORCiD
- Cerro Tololo Inter-American Observatory , NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile
- J. A. Carballo-Bello
- ORCiD
- Instituto de Alta Investigación, Sede Esmeralda, Universidad de Tarapacá , Avenida Luis Emilio Recabarren 2477, Iquique, Chile
- D. Hernandez-Lang
- Ludwig-Maximilians-Universität München , Scheinerstraße 1, München, Germany
- D. J. James
- ORCiD
- ASTRAVEO, LLC, P.O. Box 1668, Gloucester, MA 01931, USA
- D. L. Nidever
- ORCiD
- Department of Physics, Montana State University , P.O. Box 173840, Bozeman, MT 59717-3840, USA; NSF’s National Optical-Infrared Astronomy Research Laboratory , 950 North Cherry Avenue, Tucson, AZ 85719, USA
- J. L. Nilo Castellon
- Departamento de Astronomía, Universidad de La Serena , Avenida Juan Cisternas 1200, La Serena, Chile; Dirección de Investigación y Desarrollo, Universidad de La Serena , Avenida Raúl Bitrán Nachary Nº 1305, La Serena, Chile
- K. A. G. Olsen
- ORCiD
- NSF’s National Optical-Infrared Astronomy Research Laboratory , 950 North Cherry Avenue, Tucson, AZ 85719, USA
- A. Zenteno
- ORCiD
- Cerro Tololo Inter-American Observatory , NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile
- DELVE Collaboration
- DOI
- https://doi.org/10.3847/1538-4357/aca1c3
- Journal volume & issue
-
Vol. 942,
no. 2
p. 111
Abstract
We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system ( ${r}_{1/2}={41}_{-6}^{+8}$ pc; M _V = −4.25 ± 0.2 mag) located at a heliocentric distance of ${90}_{-6}^{+4}\,\mathrm{kpc}$ . Based on spectra of seven nonvariable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV’s velocity dispersion, measuring ${\sigma }_{v}={3.3}_{-1.1}^{+1.7}$ km s ^−1 (after excluding three velocity outliers); this implies a mass-to-light ratio of ${M}_{1/2}/{L}_{V,1/2}={167}_{-99}^{+224}{M}_{\odot }/{L}_{\odot }$ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of [Fe/H] = $-{2.63}_{-0.30}^{+0.26}$ dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a nonzero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV’s proper motion using data from Gaia Early Data Release 3, finding ( μ _α _* , μ _δ ) = (0.33 ± 0.07, −0.21 ± 0.08) mas yr ^−1 . When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than 10 half-light radii away from the system’s centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc.
Keywords
