Timing the r-process Enrichment of the Ultra-faint Dwarf Galaxy Reticulum II Academic Article uri icon

abstract

  • 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 colormagnitude 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.

published proceedings

  • ASTROPHYSICAL JOURNAL

altmetric score

  • 14.13

author list (cited authors)

  • Simon, J. D., Brown, T. M., Mutlu-Pakdil, B., Ji, A. P., Drlica-Wagner, A., Avila, R. J., ... Wilkinson, R. D.

citation count

  • 0

complete list of authors

  • Simon, Joshua D||Brown, Thomas M||Mutlu-Pakdil, Burcin||Ji, Alexander P||Drlica-Wagner, Alex||Avila, Roberto J||Martinez-Vazquez, Clara E||Li, Ting S||Balbinot, Eduardo||Bechtol, Keith||Frebel, Anna||Geha, Marla||Hansen, Terese T||James, David J||Pace, Andrew B||Aguena, M||Alves, O||Andrade-Oliveira, F||Annis, J||Bacon, D||Bertin, E||Brooks, D||Burke, DL||Rosell, A Carnero||Kind, M Carrasco||Carretero, J||Costanzi, M||da Costa, LN||De Vicente, J||Desai, S||Doel, P||Everett, S||Ferrero, I||Frieman, J||Garcia-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-Fernandez, J||Miquel, R||Palmese, A||Paz-Chinchon, F||Pereira, MES||Pieres, A||Malagon, AA Plazas||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

publication date

  • February 2023