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Paper: Diagnosis of the IMF in the Universe using C, N Abundances
Volume: 445, Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants
Page: 549
Authors: Tsujimoto, T.; Bekki, K.
Abstract: Recently-determined C, N, and O abundances in the most metal-poor damped Lyman-alpha systems (DLAs) are compared with those of extremely metal-poor stars in the Galactic halo as well as extragalactic H II regions to unravel nucleosynthesis and enrichment in the early Universe. These comparisons reveal a puzzling feature showing a relatively high C/O ratio and a low N/O ratio in DLAs, which is theoretically hard to interpret. Here we propose that these elemental features are evidence that in metal-poor DLAs, the initial mass function (IMF) has a cut-off at the upper-mass end, around 20 – 25 M, and thus lacks massive stars that provide the nucleosynthesis products, resulting in the low C/O and high N/O ratios. In contrast, we find that some metal-rich extragalactic H II regions in local disk galaxies appear to have a top-heavy IMF. This suggests that the IMFs are likely to be different even among disk galaxies. Besides, there are earlier claims that high-z early-type galaxies possess a top-heavy IMF. Accordingly, we claim a non-universal IMF from the high to low redshift Universe.
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