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

doi:10.3847/1538-4357/aca9d1

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. BaconE. 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

^*Corresponding author for this work

Australian Astronomical Optics

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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.

Original language	English
Article number	43
Pages (from-to)	1-10
Number of pages	10
Journal	The Astrophysical Journal
Volume	944
Issue number	1
DOIs	https://doi.org/10.3847/1538-4357/aca9d1
Publication status	Published - 10 Feb 2023

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Copyright the Author(s) 2023. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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Simon, J. D., Brown, T. M., Mutlu-Pakdil, B., Ji, A. P., Drlica-Wagner, A., Avila, R. J., Martínez-Vázquez, C. E., Li, T. S., Balbinot, E., Bechtol, K., Frebel, A., Geha, M., Hansen, T. T., James, D. J., Pace, A. B., Aguena, M., Alves, O., Andrade-Oliveira, F., Annis, J., ... Wilkinson, R. D. (2023). Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II. The Astrophysical Journal, 944(1), 1-10. Article 43. https://doi.org/10.3847/1538-4357/aca9d1

@article{7064029f3df344e7a2ea7dd9d9756075,

title = "Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II",

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.",

author = "Simon, \{Joshua D.\} and Brown, \{Thomas M.\} and Bur{\c c}in Mutlu-Pakdil and Ji, \{Alexander P.\} and Alex Drlica-Wagner and Avila, \{Roberto J.\} and Mart{\'i}nez-V{\'a}zquez, \{Clara E.\} and Li, \{Ting S.\} and Eduardo Balbinot and Keith Bechtol and Anna Frebel and Marla Geha and Hansen, \{Terese T.\} and James, \{David J.\} and Pace, \{Andrew B.\} and M. Aguena and O. Alves and F. Andrade-Oliveira and J. Annis and D. Bacon and E. Bertin and D. Brooks and Burke, \{D. L.\} and Rosell, \{A. Carnero\} and Kind, \{M. Carrasco\} and J. Carretero and M. Costanzi and \{da Costa\}, \{L. N.\} and \{De Vicente\}, J. and S. Desai and P. Doel and S. Everett and I. Ferrero and J. Frieman and J. Garc{\'i}a-Bellido and M. Gatti and Gerdes, \{D. W.\} and D. Gruen and Gruendl, \{R. A.\} and J. Gschwend and G. Gutierrez and Hinton, \{S. R.\} and Hollowood, \{D. L.\} and K. Honscheid and K. Kuehn and N. Kuropatkin and Marshall, \{J. L.\} and J. Mena-Fern{\'a}ndez and R. Miquel and A. Palmese and F. Paz-Chinch{\'o}n and Pereira, \{M. E. S.\} and A. Pieres and Malag{\'o}n, \{A. A.Plazas\} and M. Raveri and M. Rodriguez-Monroy and E. Sanchez and B. Santiago and V. Scarpine and I. Sevilla-Noarbe and M. Smith and E. Suchyta and Swanson, \{M. E. C.\} and G. Tarle and C. To and M. Vincenzi and N. Weaverdyck and Wilkinson, \{R. D.\}",

note = "Copyright the Author(s) 2023. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.",

year = "2023",

month = feb,

day = "10",

doi = "10.3847/1538-4357/aca9d1",

language = "English",

volume = "944",

pages = "1--10",

journal = "The Astrophysical Journal",

issn = "0004-637X",

publisher = "American Astronomical Society",

number = "1",

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Simon, JD, Brown, TM, Mutlu-Pakdil, B, Ji, AP, Drlica-Wagner, A, Avila, RJ, Martínez-Vázquez, CE, Li, TS, Balbinot, E, Bechtol, K, Frebel, A, Geha, M, Hansen, TT, James, DJ, Pace, AB, Aguena, M, Alves, O, Andrade-Oliveira, F, Annis, J, Bacon, D, Bertin, E, Brooks, D, Burke, DL, Rosell, AC, Kind, MC, Carretero, J, Costanzi, M, da Costa, LN, De Vicente, J, Desai, S, Doel, P, Everett, S, Ferrero, I, Frieman, J, García-Bellido, J, Gatti, M, Gerdes, DW, Gruen, D, Gruendl, RA, Gschwend, J, Gutierrez, G, Hinton, SR, Hollowood, DL, Honscheid, K, Kuehn, K, Kuropatkin, N, Marshall, JL, Mena-Fernández, J, Miquel, R, Palmese, A, Paz-Chinchón, F, Pereira, MES, Pieres, A, Malagón, AAP, Raveri, M, Rodriguez-Monroy, M, Sanchez, E, Santiago, B, Scarpine, V, Sevilla-Noarbe, I, Smith, M, Suchyta, E, Swanson, MEC, Tarle, G, To, C, Vincenzi, M, Weaverdyck, N & Wilkinson, RD 2023, 'Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II', The Astrophysical Journal, vol. 944, no. 1, 43, pp. 1-10. https://doi.org/10.3847/1538-4357/aca9d1

TY - JOUR

T1 - Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II

AU - Simon, Joshua D.

AU - Brown, Thomas M.

AU - Mutlu-Pakdil, Burçin

AU - Ji, Alexander P.

AU - Drlica-Wagner, Alex

AU - Avila, Roberto J.

AU - Martínez-Vázquez, Clara E.

AU - Li, Ting S.

AU - Balbinot, Eduardo

AU - Bechtol, Keith

AU - Frebel, Anna

AU - Geha, Marla

AU - Hansen, Terese T.

AU - James, David J.

AU - Pace, Andrew B.

AU - Aguena, M.

AU - Alves, O.

AU - Andrade-Oliveira, F.

AU - Annis, J.

AU - Bacon, D.

AU - Bertin, E.

AU - Brooks, D.

AU - Burke, D. L.

AU - Rosell, A. Carnero

AU - Kind, M. Carrasco

AU - Carretero, J.

AU - Costanzi, M.

AU - da Costa, L. N.

AU - De Vicente, J.

AU - Desai, S.

AU - Doel, P.

AU - Everett, S.

AU - Ferrero, I.

AU - Frieman, J.

AU - García-Bellido, J.

AU - Gatti, M.

AU - Gerdes, D. W.

AU - Gruen, D.

AU - Gruendl, R. A.

AU - Gschwend, J.

AU - Gutierrez, G.

AU - Hinton, S. R.

AU - Hollowood, D. L.

AU - Honscheid, K.

AU - Kuehn, K.

AU - Kuropatkin, N.

AU - Marshall, J. L.

AU - Mena-Fernández, J.

AU - Miquel, R.

AU - Palmese, A.

AU - Paz-Chinchón, F.

AU - Pereira, M. E. S.

AU - Pieres, A.

AU - Malagón, A. A.Plazas

AU - Raveri, M.

AU - Rodriguez-Monroy, M.

AU - Sanchez, E.

AU - Santiago, B.

AU - Scarpine, V.

AU - Sevilla-Noarbe, I.

AU - Smith, M.

AU - Suchyta, E.

AU - Swanson, M. E. C.

AU - Tarle, G.

AU - To, C.

AU - Vincenzi, M.

AU - Weaverdyck, N.

AU - Wilkinson, R. D.

N1 - Copyright the Author(s) 2023. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2023/2/10

Y1 - 2023/2/10

N2 - 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.

AB - 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.

UR - https://www.scopus.com/pages/publications/85148014531

U2 - 10.3847/1538-4357/aca9d1

DO - 10.3847/1538-4357/aca9d1

M3 - Article

AN - SCOPUS:85148014531

SN - 0004-637X

VL - 944

SP - 1

EP - 10

JO - The Astrophysical Journal

JF - The Astrophysical Journal

IS - 1

M1 - 43

ER -

Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II

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