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

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 $\sim 2500{\mathrm{deg}}^2$. We focus our analysis on a subsample of $\sim 80000$ main sequence turnoff stars with heliocentric distances between 6 and 20 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 $\Delta$(LogN)/$\Delta [Fe/H]=1.0\pm 0.1$ 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 anticenter 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 5.4 for [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.

17 pages, 12 figures, 5 tables, accepted for publication in MNRAS

References in corpus (17)

• Two Stellar Components in the Halo of the Milky Way
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The stellar halo of the Galaxy
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• Substructure in Tidal Streams; Tributaries in the Anticenter Ring
• Diverse Stellar Haloes in Nearby Milky Way-Mass Disc Galaxies
• A New Catalog of Globular Clusters in the Milky Way
• The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge
• Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution
• The Pristine survey III: Spectroscopic confirmation of an efficient search for extremely metal-poor stars
• Pristine IX: CFHT ESPaDOnS Spectroscopic Analysis of 115 Bright Metal-Poor Candidate Stars
• The minimum metallicity of globular clusters and its physical origin -- implications for the galaxy mass-metallicity relation and observations of proto-globular clusters at high redshift
• Does SEGUE/SDSS indicate a dual Galactic halo?
• Chemical Mapping of the Milky Way With The Canada-France Imaging Survey: A Non-parametric Metallicity-Distance Decomposition of the Galaxy
• The Pristine survey II: a sample of bright stars observed with FEROS
• The "Building Blocks" of Stellar Halos

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