The Gaia-ESO survey: metal-rich bananas in the bulge

Journal Article · Mon Jun 20 04:00:00 EDT 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8205/824/2/L29· OSTI ID:22868979

Williams, Angus A.; Evans, N. W.; Gilmore, G.; Koposov, S. E; Casey, A.; Hourihane, A.; Lewis, J. ^[1]; Molloy, Matthew ^[2]; Kordopatis, Georges ^[3]; Smith, M. C.; Shen, J. ^[4]; Randich, S.; Franciosini, E. ^[5]; Bensby, T. ^[6]; Francois, P. ^[7]; Recio-Blanco, A.; Laverny, P. de ^[8]; Bayo, A. ^[9]; Carraro, G. ^[10]; others, and

---

1. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
2. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
3. Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)
4. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)
5. INAF Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Florence (Italy)
6. Lund Observatory, Dept of Astronomy and Theoretical Physics, Box 43, SE-221 00 Lund (Sweden)
7. GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, F-92190 Meudon (France)
8. Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Bvd. de l’Observatoire, CS 34229, F-06340 Nice (France)
9. Instituto de Física y Astronomía, Universidad de Valparaíso, Valparaíso (Chile)
10. European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago de Chile (Chile)

We analyze the kinematics of ∼2000 giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region −10{sup ∘}≲ℓ≲10{sup ∘} and −11{sup ∘}≲b≲−3{sup ∘}. 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.

• OSTI ID: 22868979
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 824; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DISPERSIONS
GALAXIES
GIANT STARS
METALS
ORBITS
SHAPE
SIMULATION