The Pristine Survey - VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime

K. Youakim*, E. Starkenburg, N. F. Martin, G. Matijevič, D. S. Aguado, C. Allende Prieto, A. Arentsen, P. Bonifacio, R. G. Carlberg, J. I. González Hernández, V. Hill, G. Kordopatis, C. Lardo, J. F. Navarro, P. Jablonka, R. Sánchez Janssen, F. Sestito, G. F. Thomas, K. Venn

*Corresponding author for this work

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13 Citations (Scopus)

Abstract

The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ( [Fe/H] < -3),and currently consists of over 4 million FGK-type stars over a sky area of ∼ 2500 deg^2. We focus our analysis on a subsample of ∼80 000main-sequence turn-off stars with heliocentric distances between 6 and20 kpc, which we take to be a representative sample of the inner halo.The resulting metallicity distribution function (MDF) has a peak at[Fe/H] =-1.6, and a slope of Δ(LogN)/Δ [Fe/H] = 1.0 ±0.1 in the metallicity range of -3.4 < [Fe/H] < -2.5. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low-latitude field in the anticentre direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4for [Fe/H] < -2.5 and 1.5 for [Fe/H] < -3, suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.
Original languageEnglish
Pages (from-to)4986-5002
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume492
Issue number4
DOIs
Publication statusPublished - Mar-2020
Externally publishedYes

Keywords

  • stars: abundances
  • Galaxy: abundances
  • Galaxy: evolution
  • Galaxy: formation
  • Galaxy: halo
  • galaxies: dwarf

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