Mining and mapping the first generations of stars with the Pristine Ca H&K survey

I will present the first results of the Pristine survey, a Franco-Canadian photometric survey of the Milky Way halo performed with the new CaHK filter on CFHT's MegaCam. Currently covering ~3,000 deg², this survey leads to an efficient metallicity decomposition of the Milky Way halo. In particular, I will show how efficient Pristine is in selecting the metal-poor end of the metallicity distribution ([Fe/H]<-2.5) to hunt for the very rare extremely metal-poor stars (bearer of the chemical imprint of the first stars). Our spectroscopic follow-up campaign shows Pristine is very efficient at selecting very metal-poor stars from our photometry alone. A dedicated part of the survey also focuses on the enigmatic very faint (and therefore metal-poor) Milky Way dwarf galaxies found over the last decade. I will show how efficient Pristine is at isolating likely member stars and how it opens a well-needed window onto the detailed study of these systems that are often used as near-field cosmological probes.