Chemodynamics of the Milky Way

I. The first year of APOGEE data ^⋆

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), an der Sternwarte 16, 14482 Potsdam, Germany
e-mail: fanders@aip.de; cristina.chiappini@aip.de
² Technische Universität Dresden, Institut fur Kern- und Teilchenphysik, Zellescher Weg 16, 01069 Dresden, Germany
³ Laboratório Interinstitucional de e-Astronomia, – LIneA, rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
⁴ Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, 91501-970 Porto Alegre, Brazil
⁵ Universidade Federal do Rio de Janeiro, Observatório do Valongo, Ladeira do Pedro Antônio 43, 20080-090 Rio de Janeiro, Brazil
⁶ Osservatorio Astronomico di Padova – INAF, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ Observatório Nacional, rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
⁸ Observatoire de la Côte d’Azur, Laboratoire Lagrange, CNRS UMR 7923, BP 4229, 06304 Nice Cedex, France
⁹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
¹⁰ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹¹ Institut d’Astrophysique et de Géophysique, allée du 6 août 17, Bat. B5c, 4000 Liège 1 (Sart-Tilman), Belgium
¹² Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park PA 16802, USA
¹³ Institute for Gravitation and the Cosmos, The Pennsylvania State University, USA
¹⁴ National Optical Astronomy Observatory, 915 N. Cherry Ave., AZ 85719 Tucson, USA
¹⁵ JINA: Joint Institute for Nuclear Astrophysics, USA
¹⁶ Steward Observatory, University of Arizona, AZ 85721 Tucson, USA
¹⁷ Instituto de Astrofisica de Canarias, C/vía Láctea s/n, 38205, La Laguna, Tenerife, Spain
¹⁸ Apache Point Observatory and New Mexico State University, PO Box 59, Sunspot NM 88349-0059, USA
¹⁹ Department of Physics & Astronomy, Texas Christian University (TCU), PO Box 298840, Fort Worth TX 76129, USA
²⁰ Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville VA 22904-4325, USA
²¹ New Mexico State University, Box 30001/Department 4500, 1320 Frenger St., Las Cruces NM 88003, USA
²² The Ohio State University, Department of Astronomy, 4055 McPherson Laboratory, 140 West 18th Ave., Columbus OH 43210-1173, USA
²³ Department of Astronomy, University of Michigan, 1022 Dennison, 500 Church St., Ann Arbor MI 48109, USA
²⁴ Institut Utinam, Université de Franche-Comté, OSU THETA de Franche-Comté-Bourgogne, CNRS UMR6213, Besançon, France
²⁵ Astrophysics Research Institute, IC2, Liverpool Science Park, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF, UK
²⁶ McDonald Observatory, The University of Texas at Austin, Austin TX 78712, USA
²⁷ Vanderbilt University, Dept. of Physics & Astronomy, VU Station B 1807, Nashville TN 37235, USA
²⁸ Johns Hopkins University, Department of Physics and Astronomy, 3701 San Martin Drive, Baltimore MD 21210, USA

Received: 12 November 2013
Accepted: 20 January 2014

Abstract

Context. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) features the first multi-object high-resolution fiber spectrograph in the near-infrared ever built, thus making the survey unique in its capabilities: APOGEE is able to peer through the dust that obscures stars in the Galactic disc and bulge in the optical wavelength range. Here we explore the APOGEE data included as part of the Sloan Digital Sky Survey’s 10th data release (SDSS DR10).

Aims. The goal of this paper is to a) investigate the chemo-kinematic properties of the Milky Way disc by exploring the first year of APOGEE data; and b) to compare our results to smaller optical high-resolution samples in the literature, as well as results from lower resolution surveys such as the Geneva-Copenhagen Survey (GCS) and the RAdial Velocity Experiment (RAVE).

Methods. We select a high-quality (HQ) sample in terms of chemistry (amounting to around 20 000 stars) and, after computing distances and orbital parameters for this sample, we employ a number of useful subsets to formulate constraints on Galactic chemical and chemodynamical evolution processes in the solar neighbourhood and beyond (e.g., metallicity distributions – MDFs, [α/Fe] vs. [Fe/H] diagrams, and abundance gradients).

Results. Our red giant sample spans distances as large as 10 kpc from the Sun. Given our chemical quality requirements, most of the stars are located between 1 and 6 kpc from the Sun, increasing by at least a factor of eight the studied volume with respect to the most recent chemodynamical studies based on the two largest samples obtained from RAVE and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We find remarkable agreement between the MDF of the recently published local (d < 100 pc) high-resolution high-S/N HARPS sample and our local HQ sample (d < 1 kpc). The local MDF peaks slightly below solar metallicity, and exhibits an extended tail towards [Fe/H]= −1, whereas a sharper cutoff is seen at larger metallicities (the APOGEE sample shows a slight overabundance of stars with metallicities larger than ≃+0.3 with respect to the HARPS sample). Both samples also compare extremely well in an [α/Fe] vs. [Fe/H] diagram. The APOGEE data also confirm the existence of a gap in the abundance diagram. When expanding our sample to cover three different Galactocentric distance bins (inner disc, solar vicinity and outer disc), we find the high-[α/Fe] stars to be rare towards the outer zones (implying a shorter scale-length of the thick disc with respect to the thin disc), as previously suggested in the literature. Finally, we measure the gradients in [Fe/H] and [α/Fe], and their respective MDFs, over a range of 6 < R < 11 kpc in Galactocentric distance, and a 0 < z < 3 kpc range of distance from the Galactic plane. We find a good agreement with the gradients traced by the GCS and RAVE dwarf samples. For stars with 1.5 < z < 3 kpc (not present in the previous samples), we find a positive metallicity gradient and a negative gradient in [α/Fe].