Segue 1 - A Compressed Star Formation History Before Reionization
  Segue 1 is the current best candidate for a "first galaxy", a system which
experienced only a single short burst of star formation and has since remained
unchanged. Here we present possible star formation scenarios which can explain
its unique metallicity distribution. While the majority of stars in all other
ultra-faint dwarfs (UFDs) are within 0.5 dex of the mean [Fe/H] for the galaxy,
5 of the 7 stars in Segue 1 have a spread of $\Delta$[Fe/H] $>0.8$ dex. We show
that this distribution of metallicities canot be explained by a gradual
build-up of stars, but instead requires clustered star formation. Chemical
tagging allows the separate unresolved delta functions in abundance space to be
associated with discrete events in space and time. This provides an opportunity
to put the enrichment events into a time sequence and unravel the history of
the system. We investigate two possible scenarios for the star formation
history of Segue 1 using Fyris Alpha simulations of gas in a $10^7$ M$_\odot$
dark matter halo. The lack of stars with intermediate metallicities $-3<$
[Fe/H] $<-2$ can be explained either by a pause in star formation caused by
supernova feedback, or by the spread of metallicities resulting from one or two
supernovae in a low-mass dark matter halo. Either possibility can reproduce the
metallicity distribution function (MDF), as well as the other observed
elemental abundances. The unusual MDF and the low luminosity of Segue 1 can be
explained by it being a first galaxy that originated with
$M_{\rm{vir}}\sim10^7$~M$_\odot$ at $z\sim10$.
