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THE GAIA-ESO SURVEY: METAL-RICH BANANAS in the BULGE

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Williams, AA 
Evans, NW 
Molloy, M 
Kordopatis, G 
Smith, MC 

Abstract

We analyse the kinematics of ∼2000 giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region −10∘≲≲10∘ and −11∘≲b≲−3∘. We find distinct kinematic trends in the metal rich ([M/H]>0) and metal poor ([M/H]<0) stars in the data. The velocity dispersion of the metal-rich stars drops steeply with latitude, compared to a flat profile in the metal-poor stars, as has been seen previously. We argue that the metal-rich stars in this region are mostly on orbits that support the boxy-peanut shape of the bulge, which naturally explains the drop in their velocity dispersion profile with latitude. The metal rich stars also exhibit peaky features in their line-of-sight velocity histograms, particularly along the minor axis of the bulge. We propose that these features are due to stars on resonant orbits supporting the boxy-peanut bulge. This conjecture is strengthened through the comparison of the minor axis data with the velocity histograms of resonant orbits generated in simulations of buckled bars. The 'banana' or 2:1:2 orbits provide strongly bimodal histograms with narrow velocity peaks that resemble the Gaia-ESO metal-rich data.

Description

Keywords

galaxies: general, galaxies: kinematics and dynamics, Galaxy: bulge

Journal Title

Astrophysical Journal Letters

Conference Name

Journal ISSN

2041-8205
2041-8213

Volume Title

824

Publisher

American Astronomical Society
Sponsorship
Science and Technology Facilities Council (ST/L006553/1)
Science and Technology Facilities Council (ST/N000927/1)
European Research Council (320360)
Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012.” The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the European Science Foundation (ESF) through the GREAT Research Network Programme.