TWO DISTINCT RED GIANT BRANCH POPULATIONS IN THE GLOBULAR CLUSTER NGC 2419 AS TRACERS OF A MERGER EVENT IN THE MILKY WAY
- Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of)
- Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
- Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720 (United States)
Recent spectroscopic observations of the outer halo globular cluster (GC) NGC 2419 show that it is unique among GCs, in terms of chemical abundance patterns, and some suggest that it was originated in the nucleus of a dwarf galaxy. Here we show, from the Subaru narrowband photometry employing a calcium filter, that the red giant branch (RGB) of this GC is split into two distinct subpopulations. Comparison with spectroscopy has confirmed that the redder RGB stars in the hk[=(Ca–b) – (b – y)] index are enhanced in [Ca/H] by ∼0.2 dex compared to the bluer RGB stars. Our population model further indicates that the calcium-rich second generation stars are also enhanced in helium abundance by a large amount (ΔY = 0.19). Our photometry, together with the results for other massive GCs (e.g., ω Cen, M22, and NGC 1851), suggests that the discrete distribution of RGB stars in the hk index might be a universal characteristic of this growing group of peculiar GCs. The planned narrowband calcium photometry for the Local Group dwarf galaxies would help to establish an empirical connection between these GCs and the primordial building blocks in the hierarchical merging paradigm of galaxy formation.
- OSTI ID:
- 22364133
- Journal Information:
- Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 778; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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