Discovery of distant RR Lyrae stars in the Milky Way using DECam
  We report the discovery of distant RR Lyrae stars, including the most distant
known in the Milky Way, using data taken in the $g-$band with the Dark Energy
Camera as part of the High cadence Transient Survey (HiTS; 2014 campaign). We
detect a total of 173 RR Lyrae stars over a ~120 deg^2 area, including both
known RR Lyrae and new detections. The heliocentric distances d_H of the full
sample range from 9 to >200 kpc, with 18 of them beyond 90 kpc. We identify
three sub-groups of RR Lyrae as members of known systems: the Sextans dwarf
spheroidal galaxy, for which we report 46 new discoveries, and the ultra-faint
dwarf galaxies Leo IV and Leo V. Following an MCMC methodology, we fit
spherical and ellipsoidal profiles of the form rho(R) ~ R^n to the radial
density distribution of RR Lyrae in the Galactic halo. The best fit corresponds
to the spherical case, for which we obtain a simple power-law index of
n=-4.17^{+0.18}_{-0.20}, consistent with recent studies made with samples
covering shorter distances. The pulsational properties of the outermost RR
Lyrae in the sample (d_H>90 kpc) differ from the ones in the halo population at
closer distances. The distribution of the stars in a Period-Amplitude diagram
suggest they belong to Oosterhoff-intermediate or Oosterhoff II groups, similar
to what is found in the ultra-faint dwarf satellites around the Milky Way. The
new distant stars discovered represent an important addition to the few
existing tracers of the Milky Way potential in the outer halo.
