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

Abstract

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.

Authors:

Youakim, K.  ^[1];

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Starkenburg, E. ^[1]; Martin, N. F. ^[2]; Matijevič, G. ^[1]; Aguado, D. S. ^[3]; Allende Prieto, C. ^[4]; Arentsen, A.  ^[1];

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Bonifacio, P.  ^[5];

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Carlberg, R. G. ^[6]; González Hernández, J. I. ^[4]; Hill, V. ^[7]; Kordopatis, G. ^[7]; Lardo, C.  ^[8];

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Navarro, J. F. ^[9]; Jablonka, P. ^[10]; Sánchez Janssen, R.  ^[11];

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Sestito, F. ^[12]; Thomas, G. F. ^[13]; Venn, K. ^[9]

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1. Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, Potsdam D-14482, Germany
2. Observatoire astronomique de Strasbourg, Université de Strasbourg, 11 rue de l’Université, Strasbourg F-67000, France
3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
4. 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
5. GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, Meudon F-92190, France
6. Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
7. Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Lagrange, Bd de l’Observatoire, CS34229, Nice F-06304, France
8. Laboratoire d’astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire, Institute of Physics, Versoix CH-1290, Switzerland
9. Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, STN CSC, Victoria BC V8W 3P6, Canada
10. 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
11. Royal Observatory Edinburgh, UK Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK
12. 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
13. NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada

Publication Date:

2020-01-16

Sponsoring Org.:

USDOE

OSTI Identifier:

1597557

Resource Type:

Published Article

Journal Name:

Monthly Notices of the Royal Astronomical Society

Additional Journal Information:

Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 492 Journal Issue: 4; Journal ID: ISSN 0035-8711

Publisher:

Oxford University Press

Country of Publication:

United Kingdom

Language:

English