Kinematic and metallicity properties od the Aquarius dwarf galaxy from
  FORS2 MXU spectroscopy
  Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to
have interacted with the large LG spirals, and therefore environmental effects
should not be the main drivers of their evolution. We aim to provide insight
into the internal mechanisms shaping LG dwarf galaxies by increasing our
knowledge of the internal properties of isolated systems. We focus on the
evolved stellar component of the Aquarius dwarf, whose kinematic and
metallicity properties have only recently started to be explored. We have
obtained spectroscopic data in the the near-infrared CaII triplet lines region
with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars, to
derive line-of-sight velocities and [Fe/H] of the individual RGB stars. We have
derived a systemic velocity of $-142.2^{+1.8}_{-1.8}$ km s$^{-1}$, in agreement
with previous measurements from both the HI gas and stars. The internal
kinematics of Aquarius appears to be best modelled by a combination of random
motions (l.o.s. velocity dispersion of $10.3^{+1.6}_{-1.3}$ km s$^{-1}$) and
linear rotation (with a gradient $-5.0^{+1.6}_{-1.9}$ km s$^{-1}$
arcmin$^{-1}$) along a P.A.=$139_{-27}^{+17}$ deg, consistent with the optical
projected major axis. This rotation signal is significantly misaligned or even
counter-rotating to that derived from the HI gas. We also find the tentative
presence of a mild negative metallicity gradient and indications that the
metal-rich stars have a colder velocity dispersion than the metal-poor ones.
This work represents a significant improvement with respect to previous
measurements of the RGB stars of Aquarius, as it doubles the number of member
stars studied in the literature. We speculate that the misaligned rotation
between the HI gas and evolved stellar component might have been the result of
recent accretion of HI gas or re-accretion after gas-loss due to internal
stellar feedback.
