SMC west halo: a slice of the galaxy that is being tidally stripped?
  Star clusters trace age and metallicity gradients
  (ABRIDGED) The evolution and structure of the Magellanic Clouds is presently
under debate. The classical scenario where both the Large and Small Magellanic
Clouds (LMC, SMC) are orbiting the Milky Way has been challenged by an
alternative where the LMC and SMC are in their first close passage to our
Galaxy. Detailed studies of stellar populations in the galaxies should
constrain the proposed scenarios. In particular, the west halo of the SMC was
recently characterized with radial trends in age and metallicity which
indicates tidal disruption. We increase the sample of star clusters in the west
halo of the SMC with homogeneous age, metallicity, and distance derivations, to
determine better age and metallicity gradients. Comparisons of observed and
synthetic V,(B-V) colour-magnitude diagrams are used to derive parameters for
west halo star clusters. We derived age and metallicity for the reference
cluster NGC 152 compatible with literature parameters. Age and metallicity
gradients are confirmed in the west halo: 2.6 +/- 0.6 Gyr/deg and -0.19 +/-
0.09 dex/deg, respectively. Age-metallicity relation for the west halo has low
dispersion in metallicity and it is compatible with a burst model of chemical
enrichment. All WH clusters seem to follow the same predicted stellar
distribution, with exception of AM-3 that should belong to the counter-bridge.
Bruck 6 is only 130 +/- 40 Myr old and it could have been formed during a
recent tidal interaction of the SMC-LMC. We suggest that it is crucial to split
the SMC cluster population in groups: main body, wing/bridge, counter-bridge
and west halo. This is the way to analyse the complex star formation and
dynamical history of our neighbour. In particular we show that west halo has
clear age and metallicity gradients and age-metallicity relation, also
compatible with the dynamical model of tidal influence of the LMC over the SMC.
