Prolate rotation and metallicity gradient in the transforming dwarf
  galaxy Phoenix
  Transition type dwarf galaxies are thought to be systems undergoing the
process of transformation from a star-forming into a passively evolving dwarf,
which makes them particularly suitable to study evolutionary processes driving
the existence of different dwarf morphological types. Here we present results
from a spectroscopic survey of ~200 individual red giant branch stars in the
Phoenix dwarf, the closest transition type with a comparable luminosity to
"classical" dwarf galaxies. We measure a systemic heliocentric velocity V =
-21.2 km/s. Our survey reveals the clear presence of prolate rotation, which is
aligned with the peculiar spatial distribution of the youngest stars in
Phoenix. We speculate that both features might have arisen from the same event,
possibly an accretion of a smaller system. The evolved stellar population of
Phoenix is relatively metal-poor (<[Fe/H]> = -1.49+/-0.04 dex) and shows a
large metallicity spread ($\sigma_{\rm [Fe/H]} = 0.51\pm0.04$\,dex), with a
pronounced metallicity gradient of -0.13+/-0.01 dex per arcmin similar to
luminous, passive dwarf galaxies. We also report a discovery of an extremely
metal-poor star candidate in Phoenix and discuss the importance of correcting
for spatial sampling when interpreting the chemical properties of galaxies with
metallicity gradients. This study presents a major leap forward in our
knowledge of the internal kinematics of the Phoenix transition type dwarf
galaxy, and the first wide area spectroscopic survey of its metallicity
properties.
