On the use of the number count of blue horizontal branch stars to infer the dominant building blocks of the milky way halo

Chul Chung, Young Wook Lee, Mario Pasquato

Research output: Contribution to journalArticle

4 Citations (Scopus)


The formation of the MilkyWay stellar halo is thought to be the result of merging and accretion of building blocks such as dwarf galaxies and massive globular clusters. Recently, Deason et al. suggested that the Milky Way outer halo formed mostly from big building blocks, such as dwarf spheroidal galaxies, based on the similar number ratio of blue straggler (BS) stars to blue horizontal branch (BHB) stars. Here we demonstrate, however, that this result is seriously biased by not taking into detailed consideration on the formation mechanism of BHB stars from helium-enhanced second-generation population. In particular, the high BS-to-BHB ratio observed in the outer halo fields is most likely due to a small number of BHB stars provided by globular clusters (GCs) rather than to a large number of BS stars. This is supported by our dynamical evolution model of GCs which shows preferential removal of first-generation stars in GCs. Moreover, there are a sufficient number of outer halo GCs which show very high BS-to-BHB ratio. Therefore, the BS-to-BHB number ratio is not a good indicator to use in arguing that more massive dwarf galaxies are the main building blocks of theMilkyWay outer halo. Several lines of evidence still suggest that GCs can contribute a significant fraction of the outer halo stars.

Original languageEnglish
Pages (from-to)L1-L5
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Publication statusPublished - 2016 Jan 1


All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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