A Carbon-enhanced Lyman Limit System: Signature of the First Generation of Stars?

Abstract

We present the study of a Lyman limit system (LLS) at $z_{\mathrm{abs}}$ = 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.

10 pages, 5 figures. Accepted for publication in ApJ

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• Towards ultra metal-poor DLAs: linking the chemistry of the most metal-poor DLA to the first stars
• Metal-Poor Stars Observed with the Southern African Large Telescope II. An Extended Sample
• A survey of extremely metal-poor gas at cosmic noon: evidence of elevated [O/Fe]