The Astrophysical Journal (Jan 2023)
Timing the r-process Enrichment of the Ultra-faint Dwarf Galaxy Reticulum II
- Joshua D. Simon,
- Thomas M. Brown,
- Burçin Mutlu-Pakdil,
- Alexander P. Ji,
- Alex Drlica-Wagner,
- Roberto J. Avila,
- Clara E. Martínez-Vázquez,
- Ting S. Li,
- Eduardo Balbinot,
- Keith Bechtol,
- Anna Frebel,
- Marla Geha,
- Terese T. Hansen,
- David J. James,
- Andrew B. Pace,
- M. Aguena,
- O. Alves,
- F. Andrade-Oliveira,
- J. Annis,
- D. Bacon,
- E. Bertin,
- D. Brooks,
- D. L. Burke,
- A. Carnero Rosell,
- M. Carrasco Kind,
- J. Carretero,
- M. Costanzi,
- L. N. da Costa,
- J. De Vicente,
- S. Desai,
- P. Doel,
- S. Everett,
- I. Ferrero,
- J. Frieman,
- J. García-Bellido,
- M. Gatti,
- D. W. Gerdes,
- D. Gruen,
- R. A. Gruendl,
- J. Gschwend,
- G. Gutierrez,
- S. R. Hinton,
- D. L. Hollowood,
- K. Honscheid,
- K. Kuehn,
- N. Kuropatkin,
- J. L. Marshall,
- J. Mena-Fernández,
- R. Miquel,
- A. Palmese,
- F. Paz-Chinchón,
- M. E. S. Pereira,
- A. Pieres,
- A. A. Plazas Malagón,
- M. Raveri,
- M. Rodriguez-Monroy,
- E. Sanchez,
- B. Santiago,
- V. Scarpine,
- I. Sevilla-Noarbe,
- M. Smith,
- E. Suchyta,
- M. E. C. Swanson,
- G. Tarle,
- C. To,
- M. Vincenzi,
- N. Weaverdyck,
- R. D. Wilkinson
Affiliations
- Joshua D. Simon
- ORCiD
- Observatories of the Carnegie Institution for Science , 813 Santa Barbara Steet, Pasadena, CA 91101, USA
- Thomas M. Brown
- ORCiD
- Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
- Burçin Mutlu-Pakdil
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Department of Physics and Astronomy, Dartmouth College , 6127 Wilder Laboratory, Hanover, NH 03755, USA
- Alexander P. Ji
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA
- Alex Drlica-Wagner
- ORCiD
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Department of Astronomy and Astrophysics, University of Chicago , Chicago, IL 60637, USA; Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- Roberto J. Avila
- Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
- Clara E. Martínez-Vázquez
- ORCiD
- Gemini Observatory, NSF’s NOIRLaboratory , 670 N. A’ohoku Place, Hilo, HI 96720, USA
- Ting S. Li
- ORCiD
- Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada
- Eduardo Balbinot
- Kapteyn Astronomical Institute, University of Groningen , Landleven 12, 9747 AD Groningen, The Netherlands
- Keith Bechtol
- ORCiD
- Department of Physics, University of Wisconsin–Madison , Madison, WI 53706, USA
- Anna Frebel
- ORCiD
- Department of Physics & Kavli Institute for Astrophysics and Space Research , Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Joint Institute for Nuclear Astrophysics—Center for Evolution of the Elements , East Lansing, MI 48824, USA
- Marla Geha
- ORCiD
- Department of Astronomy, Yale University , 52 Hillhouse Avenue, New Haven, CT 06520, USA
- Terese T. Hansen
- ORCiD
- Department of Astronomy, Stockholm University , AlbaNova University Centre, SE-106 91 Stockholm, Sweden
- David J. James
- Center for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA
- Andrew B. Pace
- ORCiD
- McWilliams Center for Cosmology, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
- M. Aguena
- ORCiD
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
- O. Alves
- ORCiD
- Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA
- F. Andrade-Oliveira
- Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA
- J. Annis
- ORCiD
- Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- D. Bacon
- ORCiD
- Institute of Cosmology and Gravitation, University of Portsmouth , Portsmouth, PO1 3FX, UK
- E. Bertin
- ORCiD
- CNRS, UMR 7095, Institut d’Astrophysique de Paris , F-75014 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, UMR 7095, Institut d’Astrophysique de Paris , F-75014 Paris, France
- D. Brooks
- ORCiD
- Department of Physics & Astronomy, University College London , Gower Street, London, WC1E 6BT, UK
- D. L. Burke
- ORCiD
- Kavli Institute for Particle Astrophysics & Cosmology, P.O. Box 2450, Stanford University , Stanford, CA 94305, USA; SLAC National Accelerator Laboratory , Menlo Park, CA 94025, USA
- A. Carnero Rosell
- ORCiD
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil; Instituto de Astrofisica de Canarias , E-38205 La Laguna, Tenerife, Spain; Universidad de La Laguna , Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain
- M. Carrasco Kind
- ORCiD
- Center for Astrophysical Surveys, National Center for Supercomputing Applications , 1205 West Clark Street, Urbana, IL 61801, USA; Department of Astronomy, University of Illinois at Urbana-Champaign , 1002 W. Green Street, Urbana, IL 61801, USA
- J. Carretero
- ORCiD
- Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology , Campus UAB, E-08193 Bellaterra (Barcelona) Spain
- M. Costanzi
- ORCiD
- Astronomy Unit, Department of Physics, University of Trieste , via Tiepolo 11, I-34131 Trieste, Italy; INAF-Osservatorio Astronomico di Trieste , via G.B. Tiepolo 11, I-34143 Trieste, Italy; Institute for Fundamental Physics of the Universe , Via Beirut 2, I-34014 Trieste, Italy
- L. N. da Costa
- ORCiD
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
- J. De Vicente
- ORCiD
- Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
- S. Desai
- ORCiD
- Department of Physics, IIT Hyderabad , Kandi, Telangana 502285, India
- P. Doel
- Department of Physics & Astronomy, University College London , Gower Street, London, WC1E 6BT, UK
- S. Everett
- Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- I. Ferrero
- ORCiD
- Institute of Theoretical Astrophysics, University of Oslo , P.O. Box 1029 Blindern, NO-0315 Oslo, Norway
- J. Frieman
- Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- J. García-Bellido
- ORCiD
- Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid , E-28049 Madrid, Spain
- M. Gatti
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, PA 19104, USA
- D. W. Gerdes
- ORCiD
- Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA; Department of Astronomy, University of Michigan , Ann Arbor, MI 48109, USA
- D. Gruen
- ORCiD
- University Observatory , Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, D-81679 Munich, Germany
- R. A. Gruendl
- ORCiD
- Center for Astrophysical Surveys, National Center for Supercomputing Applications , 1205 West Clark Street, Urbana, IL 61801, USA; Department of Astronomy, University of Illinois at Urbana-Champaign , 1002 W. Green Street, Urbana, IL 61801, USA
- J. Gschwend
- ORCiD
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil; Observatório Nacional , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
- G. Gutierrez
- Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- S. R. Hinton
- ORCiD
- School of Mathematics and Physics, University of Queensland , Brisbane, QLD 4072, Australia
- D. L. Hollowood
- ORCiD
- Santa Cruz Institute for Particle Physics , Santa Cruz, CA 95064, USA
- K. Honscheid
- Center for Cosmology and Astro-Particle Physics, The Ohio State University , Columbus, OH 43210, USA; Department of Physics, The Ohio State University , Columbus, OH 43210, USA
- K. Kuehn
- ORCiD
- Australian Astronomical Optics, Macquarie University , North Ryde, NSW 2113, Australia; Lowell Observatory , 1400 Mars Hill Road, Flagstaff, AZ 86001, USA
- N. Kuropatkin
- ORCiD
- Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- J. L. Marshall
- ORCiD
- George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University , College Station, TX 77843, USA
- J. Mena-Fernández
- ORCiD
- Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
- R. Miquel
- ORCiD
- Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology , Campus UAB, E-08193 Bellaterra (Barcelona) Spain; Institució Catalana de Recerca i Estudis Avançats , E-08010 Barcelona, Spain
- A. Palmese
- Department of Astronomy, University of California , Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
- F. Paz-Chinchón
- ORCiD
- Center for Astrophysical Surveys, National Center for Supercomputing Applications , 1205 West Clark Street, Urbana, IL 61801, USA; Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge, CB3 0HA, UK
- M. E. S. Pereira
- ORCiD
- Hamburger Sternwarte, Universität Hamburg , Gojenbergsweg 112, D-21029 Hamburg, Germany
- A. Pieres
- ORCiD
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil; Observatório Nacional , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
- A. A. Plazas Malagón
- ORCiD
- Department of Astrophysical Sciences, Princeton University , Peyton Hall, Princeton, NJ 08544, USA
- M. Raveri
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, PA 19104, USA
- M. Rodriguez-Monroy
- Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
- E. Sanchez
- ORCiD
- Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
- B. Santiago
- Laboratório Interinstitucional de e-Astronomia—LIneA , Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil; Instituto de Física, UFRGS , Caixa Postal 15051, Porto Alegre, RS—91501-970, Brazil
- V. Scarpine
- Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USA
- I. Sevilla-Noarbe
- ORCiD
- Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
- M. Smith
- ORCiD
- School of Physics and Astronomy, University of Southampton , Southampton, SO17 1BJ, UK
- E. Suchyta
- Computer Science and Mathematics Division, Oak Ridge National Laboratory , Oak Ridge, TN 37831, USA
- M. E. C. Swanson
- ORCiD
- Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, CA 94720, USA
- G. Tarle
- ORCiD
- Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA
- C. To
- ORCiD
- Center for Cosmology and Astro-Particle Physics, The Ohio State University , Columbus, OH 43210, USA
- M. Vincenzi
- Institute of Cosmology and Gravitation, University of Portsmouth , Portsmouth, PO1 3FX, UK; School of Physics and Astronomy, University of Southampton , Southampton, SO17 1BJ, UK
- N. Weaverdyck
- ORCiD
- Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA; Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, CA 94720, USA
- R. D. Wilkinson
- Department of Physics and Astronomy, Pevensey Building, University of Sussex , Brighton, BN1 9QH, UK
- DOI
- https://doi.org/10.3847/1538-4357/aca9d1
- Journal volume & issue
-
Vol. 944,
no. 1
p. 43
Abstract
The ultra-faint dwarf galaxy Reticulum II (Ret II) exhibits a unique chemical evolution history, with ${72}_{-12}^{+10}$ % of its stars strongly enhanced in r -process elements. We present deep Hubble Space Telescope photometry of Ret II and analyze its star formation history. As in other ultra-faint dwarfs, the color–magnitude diagram is best fit by a model consisting of two bursts of star formation. If we assume that the bursts were instantaneous, then the older burst occurred around the epoch of reionization, forming ∼80% of the stars in the galaxy, while the remainder of the stars formed ∼3 Gyr later. When the bursts are allowed to have nonzero durations, we obtain slightly better fits. The best-fitting model in this case consists of two bursts beginning before reionization, with approximately half the stars formed in a short (100 Myr) burst and the other half in a more extended period lasting 2.6 Gyr. Considering the full set of viable star formation history models, we find that 28% of the stars formed within 500 ± 200 Myr of the onset of star formation. The combination of the star formation history and the prevalence of r -process-enhanced stars demonstrates that the r -process elements in Ret II must have been synthesized early in its initial star-forming phase. We therefore constrain the delay time between the formation of the first stars in Ret II and the r -process nucleosynthesis to be less than 500 Myr. This measurement rules out an r -process source with a delay time of several Gyr or more, such as GW170817.
Keywords
