The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way
  bulge
  (Abridged) We analyzed the stellar parameters and radial velocities of ~1200
stars in five bulge fields as determined from the Gaia-ESO survey data (iDR1).
We use VISTA Variables in The Via Lactea (VVV) photometry to obtain reddening
values by using a semi-empirical T_eff-color calibration. From a Gaussian
decomposition of the metallicity distribution functions, we unveil a clear
bimodality in all fields, with the relative size of components depending of the
specific position on the sky. In agreement with some previous studies, we find
a mild gradient along the minor axis (-0.05 dex/deg between b=-6 and b=-10)
that arises from the varying proportion of metal-rich and metal-poor
components. The number of metal-rich stars fades in favor of the metal-poor
stars with increasing b. The K-magnitude distribution of the metal-rich
population splits into two peaks for two of the analyzed fields that intersects
the near and far branches of the X-shaped bulge structure. In addition, two
lateral fields at (l,b)=(7,-9) and (l,b)=(-10,-8) present contrasting
characteristics. In the former, the metallicity distribution is dominated by
metal-rich stars, while in the latter it presents a mix of a metal-poor
population and and a metal-intermediate one, of nearly equal sizes. Finally, we
find systematic differences in the velocity dispersion between the metal-rich
and the metal-poor components of each field. Our chemo-kinematical analysis is
consistent with a varying field-to-field proportion of stars belonging to (i) a
metal-rich boxy/peanut X-shaped component, with bar-like kinematics, and (ii) a
metal-poor more extended rotating structure with a higher velocity dispersion
that dominates far from the Galactic plane. These first GES data allow studying
the detailed spatial dependence of the Galactic bulge populations, thanks to
the analysis of individual fields with relatively high statistics.
