A Carbon-enhanced Lyman Limit System: Signature of the First Generation
  of Stars?
  We present the study of a Lyman limit system (LLS) at $z_{\rm abs}$ = 1.5441
towards quasar J134122.50+185213.9 observed with VLT X-shooter. This is a very
peculiar system with strong C I absorption seen associated with a neutral
hydrogen column density of log $N$(H I) (cm$^{-2}$) = 18.10, too small to
shield the gas from any external UV flux. The low ionization absorption lines
exhibit a simple kinematic structure consistent with a single component. Using
CLOUDY models to correct for ionization, we find that the ionization parameter
of the gas is in the range $-$ 4.5 $<$ log $U$ $<$ $-$4.2 and the gas density
$-$1.5 $<$ log $n$(H) (cm$^{-3}$) $<$ $-$1.2. The models suggest that carbon is
overabundant relative to iron, [C/Fe] $>$ +2.2 at [Fe/H] $\sim$ $-$1.6. Such a
metal abundance pattern is reminiscent of carbon-enhanced metal-poor stars
detected in the Galaxy halo. Metal enrichment by the first generation of
supernovae provides a plausible explanation for the inferred abundance pattern
in this system.
