Mining and mapping the first generations of stars with the Pristine CaH&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 deg^2, 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.