Two distinct red giant branch populations in the globular cluster NGC 2419 as tracers of a merger event in the milky way

Young Wook Lee, Sang Il Han, Seok Joo Joo, Sohee Jang, Chongsam Na, Sakurako Okamoto, Nobuo Arimoto, Dongwook Lim, Hak Sub Kim, Suk Jin Yoon

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20 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article numberL13
JournalAstrophysical Journal Letters
Volume778
Issue number1
DOIs
Publication statusPublished - 2013 Nov 20

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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