Star Formation from DLA Gas in the Outskirts of Lyman Break Galaxies at
  z~3
  We present evidence for spatially extended low surface brightness emission
around Lyman break galaxies (LBGs) in the V band image of the Hubble Ultra Deep
Field, corresponding to the z~3 rest-frame FUV light, which is a sensitive
measure of star formation rates (SFRs). We find that the covering fraction of
molecular gas at z~3 is not adequate to explain the emission in the outskirts
of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas
at high redshift is sufficient. We develop a theoretical framework to connect
this emission around LBGs to the expected emission from neutral H I gas i.e.,
damped Lyman alpha systems (DLAs), using the Kennicutt-Schmidt (KS) relation.
Working under the hypothesis that the observed FUV emission in the outskirts of
LBGs is from in situ star formation in atomic-dominated hydrogen gas, the
results suggest that the SFR efficiency in such gas at z~3 is between factors
of 10 and 50 lower than predictions based on the local KS relation. The total
SFR density in atomic-dominated gas at z~3 is constrained to be ~10% of that
observed from the inner regions of LBGs. In addition, the metals produced by in
situ star formation in the outskirts of LBGs yield metallicities comparable to
those of DLAs, which is a possible solution to the "Missing Metals" problem for
DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both
high and low redshifts has similar reduced SFR efficiencies and is consistent
with the same power law.
