The Pristine Survey – VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime
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- Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, Potsdam D-14482, Germany
- Observatoire astronomique de Strasbourg, Université de Strasbourg, 11 rue de l’Université, Strasbourg F-67000, France
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
- Instituto de Astrofísica de Canarias, Vía Láctea, La Laguna E-38205, Tenerife, Spain, Departamento de Astrofísica, Universidad de La Laguna, La Laguna E-38206, Tenerife, Spain
- GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, Meudon F-92190, France
- Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
- Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Lagrange, Bd de l’Observatoire, CS34229, Nice F-06304, France
- Laboratoire d’astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire, Institute of Physics, Versoix CH-1290, Switzerland
- Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, STN CSC, Victoria BC V8W 3P6, Canada
- GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, Meudon F-92190, France, Laboratoire d’astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire, Institute of Physics, Versoix CH-1290, Switzerland
- Royal Observatory Edinburgh, UK Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK
- Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, Potsdam D-14482, Germany, Observatoire astronomique de Strasbourg, Université de Strasbourg, 11 rue de l’Université, Strasbourg F-67000, France
- NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
ABSTRACT The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ($$ \rm [Fe/H] \lt -3$$), 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 ∼80 000 main-sequence turn-off 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 $$ \rm [Fe/H] =-1.6$$, and a slope of Δ(LogN)/$$\Delta \rm [Fe/H] = 1.0 \pm 0.1$$ in the metallicity range of $$-3.4\; \lt\; \rm [Fe/H]\; \lt -2.5$$. 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 5.4 for $$ \rm [Fe/H]\; \lt\; -2.5$$ and 1.5 for $$ \rm [Fe/H]\; \lt\; -3$$, suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1597557
- Journal Information:
- Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Vol. 492 Journal Issue: 4; ISSN 0035-8711
- Publisher:
- Oxford University PressCopyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
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