A Relic Star Cluster in the Sextans Dwarf Spheroidal Galaxy -
  Implications for Early Star and Galaxy Formation
  We present tentative evidence for the existence of a dissolved star cluster
in the Sextans dwarf spheroidal galaxy. In a sample of six stars, we identify
three (possibly four) stars around [Fe/H] =-2.7 that are highly clustered in a
multi-dimensional chemical abundance space. The estimated initial stellar mass
of the cluster is M*,init = 1.9^+1.5_-0.9 (1.6^+1.2_-0.8)*10^5 Msol assuming a
Salpeter (Kroupa) initial mass function (IMF). If corroborated by follow-up
spectroscopy, this ancient star cluster at [Fe/H] =-2.7 is the most metal-poor
system identified to date. Inspired by this finding, we also present a new way
to interpret the cumulative metallicity functions of dwarf galaxies. From
available observational data, we speculate that the ultra-faint dwarf galaxy
population, or a significant fraction thereof, and the more luminous, classical
dwarf spheroidal population were formed in different environments and would
thus be distinct in origin.
