Stellar chemo-kinematics of the Cetus dwarf spheroidal galaxy
  In order to minimize environmental effects and gain an insight into the
internal mechanisms that shape the properties of the early-type dwarf systems,
we study one of the few isolated dwarf spheroidal galaxies (dSphs) of the Local
Group (LG): Cetus. We obtained VLT/FORS2 spectra ($R\sim2600$) in the region of
the nIR CaII triplet lines for 80 candidate red giant branch stars. The
analysis yielded line-of-sight velocities and metallicities ([Fe/H]) for 54
bona fide member stars. The kinematic analysis shows that Cetus is a mainly
pressure-supported ($\sigma_v = 11.0_{-1.3}^{+1.6}$ km/s),
dark-matter-dominated system ($M_{1/2}/L_V = 23.9_{-8.9}^{+9.7}
M_\odot/L_\odot$) with no significant signs of internal rotation. We find Cetus
to be a metal-poor system with a significant [Fe/H] spread (median [Fe/H] =
-1.71 dex, median-absolute-deviation = 0.49 dex), as expected for its stellar
mass. We report the presence of a mild metallicity gradient compatible with
those found in other dSphs of the same luminosity; we trace the presence of a
stellar population gradient also in the spatial distribution of stars in
different evolutionary phases in ancillary SuprimeCam photometric data. There
are tentative indications of two chemo-kinematically distinct sub-populations,
with the more metal-poor stars showing a hotter kinematics than the
metal-richer ones. Furthermore, the photometric dataset reveals the presence of
a foreground population that most likely belongs to the Sagittarius stream.
This study represents a first comprehensive analysis of Cetus chemo-kinematic
properties. Our results add Cetus to the growing scatter in stellar-dark matter
halo properties in low-mass galactic systems. The presence of a metallicity
gradient akin to those found in similar systems inhabiting different
environments may hint at metallicity gradients in LG early-type dwarfs being
driven by internal mechanisms.
