Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis

Hansen, T. T.; Marshall, J. L.; Simon, J. D.; Li, T. S.; Bernstein, R. A.; Pace, A. B.; Ferguson, P.; Nagasawa, D. Q.; Kuehn, K.; Carollo, D.; Geha, M.; James, D.; Walker, A.; Diehl, H. T.; Aguena, M.; Allam, S.; Avila, S.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Costanzi, M.; Da Costa, L. N.; Desai, S.; De Vicente, J.; Doel, P.; Eckert, K.; Eifler, T. F.; Everett, S.; Ferrero, I.; Frieman, J.; Garcia-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Hinton, S. R.; Hollowood, D. L.; Honscheid, K.; Kuropatkin, N.; Maia, M. A. G.; March, M.; Miquel, R.; Palmese, A.; Paz-Chinchon, F.; Plazas, A. A.; Sanchez, E.; Santiago, B.; Scarpine, V.; Serrano, S.; Smith, M.; Soares-Santos, M.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Varga, T. N.; Wilkinson, R. (2020): Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis. In: Astrophysical Journal, Vol. 897, No. 2, 183

Abstract

We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass (M) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of ther-process elements in this star matches the scaledr-process pattern of the solar system andr-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites ofr-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the alpha andr-process element enrichment of the galaxy favors a neutron star merger as the origin of ther-process elements in Grus II.

• Item Type: Journal article
• Faculties: Physics
• Subjects: 500 Science > 530 Physics
• ISSN: 0004-637X
• Language: English