The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most
  metal-poor populations in the inner Milky Way
  Metal-poor stars are important tools for tracing the early history of the
Milky Way, and for learning about the first generations of stars. Simulations
suggest that the oldest metal-poor stars are to be found in the inner Galaxy.
Typical bulge surveys, however, lack low metallicity ([Fe/H] < -1.0) stars
because the inner Galaxy is predominantly metal-rich. The aim of the Pristine
Inner Galaxy Survey (PIGS) is to study the metal-poor and very metal-poor (VMP,
[Fe/H] < -2.0) stars in this region. In PIGS, metal-poor targets for
spectroscopic follow-up are selected from metallicity-sensitive CaHK photometry
from the CFHT. This work presents the ~250 deg^2 photometric survey as well as
intermediate-resolution spectroscopic follow-up observations for ~8000 stars
using AAOmega on the AAT. The spectra are analysed using two independent tools:
ULySS with an empirical spectral library, and FERRE with a library of synthetic
spectra. The comparison between the two methods enables a robust determination
of the stellar parameters and their uncertainties. We present a sample of 1300
VMP stars -- the largest sample of VMP stars in the inner Galaxy to date.
Additionally, our spectroscopic dataset includes ~1700 horizontal branch stars,
which are useful metal-poor standard candles. We furthermore show that PIGS
photometry selects VMP stars with unprecedented efficiency: 86%/80%
(lower/higher extinction) of the best candidates satisfy [Fe/H] < -2.0, as do
80%/63% of a larger, less strictly selected sample. We discuss future
applications of this unique dataset that will further our understanding of the
chemical and dynamical evolution of the innermost regions of our Galaxy.
