Abstract
Recently revealed C, N, and O abundances in the most metal-poor damped
Lyman-alpha (DLA) absorbers are compared with those of extremely metal-poor
stars in the Galactic halo, as well as extragalactic H II regions, to decipher
nucleosynthesis and chemical enrichment in the early Universe. These
comparisons surprisingly identify a relatively high C/O ratio and a low N/O
ratio in DLA systems, which is hard to explain theoretically. We propose that
if these features are confirmed by future studies, this effect occurs because
the initial mass function in metal-poor DLA systems has a cut-off at the upper
mass end at around 20-25 Msun, thus lacks the massive stars that provide the
nucleosynthesis products leading to the low C/O and high N/O ratios. This
finding is a reasonable explanation of the nature of DLA systems in which a
sufficient amount of cold H I gas remains intact because of the suppression of
ionization by massive stars. In addition, our claim strongly supports a high
production rate of N in very massive stars, which might be acceptable in light
of the recent nucleosynthesis calculations with fast rotation models. The
updates of both abundance data and nucleosynthesis results will strengthen our
novel proposition that the C/O and N/O abundances are a powerful tool for
inferring the form of the initial mass function.
Description
[1103.0033] Implications of a non-universal IMF from C, N, and O abundances in very metal-poor Galactic stars and damped Lyman-alpha absorbers
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