A Massive Galaxy in its Core Formation Phase Three Billion Years After
  the Big Bang
  Most massive galaxies are thought to have formed their dense stellar cores at
early cosmic epochs. However, cores in their formation phase have not yet been
observed. Previous studies have found galaxies with high gas velocity
dispersions or small apparent sizes but so far no objects have been identified
with both the stellar structure and the gas dynamics of a forming core. Here we
present a candidate core in formation 11 billion years ago, at z=2.3.
GOODS-N-774 has a stellar mass of 1.0x10^11 Msun, a half-light radius of 1.0
kpc, and a star formation rate of 90[+45-20]Msun/yr. The star forming gas has a
velocity dispersion 317+-30 km/s, amongst the highest ever measured. It is
similar to the stellar velocity dispersions of the putative descendants of
GOODS-N-774, compact quiescent galaxies at z~2 and giant elliptical galaxies in
the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however,
from the star formation rate and size of the galaxy we infer that many star
forming cores may be heavily obscured, and could be missed in optical and
near-infrared surveys.
