Hunting for the first stars

Discovering the very first generation of stars born after the Big Bang at redshifts 10-30
is a prime driver for the next generation of astronomical facilities (e.g. ELTs, SKA, JWST).
To date no such bona fide Pop III star has been found in spite of massive efforts both at
high and low redshift over the past decades. Until recently it was believed that the first stars
were all very massive (>100Msun) but new numerical simulations suggest that fragmentation
during their formation would have led to some Pop. III stars having a mass of ~1Msun and
thus possibly have survived to the present-day.

In this talk I will present our ongoing work in finding the oldest stars in
the Galactic neighborhood, an approach often referred to as near-field cosmology.
Our approach rely on uvgriz photometry from the SkyMapper telescope
to very efficiently identify metal-poor candidates which are subsequently confirmed and
chemically characterized spectroscopically using 4-10m telescopes. Among
other noteworthy discoveries, we have found the first Galactic halo star without detectable amount
of iron ([Fe/H]<-7), which bear the nucleosynthetic fingerprints of a low-energetic core-collapse
supernova from a ~60Msun progenitor. Finally I will discuss our novel survey of
extremely metal-poor stars in the Galactic bulge, a region where the majority of the
oldest stars should now reside in. We have discovered >100 bulge stars with [Fe/H]<-3,
which on theoretical grounds are expected to have formed at z>15. If true, it
would make them the oldest known physical objects in the Universe, probing
a completely unchartered cosmic era.