Asymmetric metallicity patterns in the stellar velocity space with RAVE
Antoja, Teresa; Kordopatis, Georges, 1985-; Helmi, A. (Amina), 1970-; Monari, Giacomo, 1984-; Famaey, Benoit; Wyse, Rosemary F. G.; Grebel, Eva K.; Steinmetz, Matthias, 1966-; Bland-Hawthorn, J. (Joss); Gibson, Brad K.; Bienaymé, Olivier; Navarro, Julio F. (Julio Fernando); Parker, Quentin A.; Reid, Warren A. (Warren Alfred); Seabroke, George; Siebert, Arnaud, 1974-; Siviero, Alessandro; Zwitter, Tomaž
EA Milne Centre for Astrophysics
Galaxy: kinematics and dynamics; Galaxy: structure; Galaxy: disk; Galaxy: evolution
- ©ESO 2017
Context. The chemical abundances of stars encode information on their place and time of origin. Stars formed together in e.g. a cluster, should present chemical homogeneity. Also disk stars influenced by the effects of the bar and the spiral arms might have distinct chemical signatures depending on the type of orbit that they follow, e.g. from the inner versus outer regions of the MilkyWay.
Aims. We explore the correlations between velocity and metallicity and the possible distinct chemical signatures of the velocity overdensities of the local Galactic neighbourhood.
Methods. We use the large spectroscopic survey RAVE and the Geneva Copenhagen Survey. We compare the metallicity distribution of regions in the velocity plane (vR, vφ) with that of their symmetric counterparts (−vR, vφ).We expect similar metallicity distributions if there are no tracers of a sub-population (e.g., a dispersed cluster, accreted stars), if the disk of the Galaxy is axisymmetric, and if the orbital effects of the bar and the spiral arms are weak.
Results. We find that the metallicity-velocity space of the solar neighbourhood is highly patterned. A large fraction of the velocity plane shows differences in the metallicity distribution when comparing symmetric vR regions. The typical differences in the median metallicity are of 0.05 dex with statistical significant of at least 95% confidence, and with values up to 0.6 dex. Stars moving with low azimuthal velocity vφ and outwards in the Galaxy have on average higher metallicity than those moving inwards. These include stars in the Hercules and Hyades moving groups and other velocity branch-like structures. For higher vφ, the stars moving inwards have higher metallicity than those moving outwards. We have also discovered a positive gradient in vφ with respect to metallicity at high metallicities, a part from the two known positive and negative gradients for the thin and thick disks.# Conclusions. The most likely interpretation of the metallicity asymmetry is that it is mainly due to the orbital effects of the Galactic bar and the radial metallicity gradient of the disk. We present a simulation that supports this idea.
- The University of Hull
- Peer reviewed
- 1 MB