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Chemical variations and star formation histories of damped Lya systems

机译：阻尼LYA系统的化学变化和星形成历史

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Thanks to the comprehensive sets of elemental abundances in eleven damped Lya systems (DLAs) at zabs = 1 7 - 2.5, we were able for the first time to study in detail the abundance patterns of a wide range of elements, the chemical variations in the interstellar medium, the star formation, and the age of galaxies outside the Local Group Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they are very uniform, showing low RMS dispersions up to only 2-3 times higher than the statistical errors, for the majority of elements. The gas-phase abundance patterns of interstellar medium clouds within the DLA galaxies detected along the velocity profiles show on the other hand a high dispersion in several abundance ratios, indicating that variations in the gas phase, whatever their origin, are more confined to clouds within the DLA galaxies than to integrated profiles. The analysis of the cloud-to-cloud chemical variations within seven individual DLAs revealed that five of them show statistically significant variations, higher than 0 2 dex at more than 3cr, The sources of these variations are both differential dust depletion and ionisation effects, however no evidence for variations due to different star formation histories was highlighted. These results place important constraints on scenarios of galaxy formation within the CDM hierarchical theory. The DLA abundance pattern comparison with chemical evolution models indicate that the DLAs may either be associated with the outer regions of spiral galaxies or with dwarf irregular galaxies both characterised by star formation histories with low star formation efficiencies. They may be very young galaxies with ages between 20 - 250 Myr, but also galaxies with ages longer than 1 Gyr, Their star formation rates per unit area are moderate, between -3,2 < logSFR < -1.4 M0 yr"1 kpc"2.
机译：由于ZABS = 1 7 - 2.5的11个阻尼LYA系统（DLAS）综合元素丰富套装综合性大量，我们首次能够详细研究各种元素的丰富模式，化学变化星际培养基，明星形成，以及本地组外的星系年龄比较了这些高射频星系的气相丰度比，我们发现它们非常均匀，显示出低于高于2-3倍的低RMS分散量统计错误，对于大多数元素。沿着速度剖面检测到的DLA星系内的星间型云的气相丰度模式在另一方面，若干丰度比呈高分子，表明气相中的变化，无论它们的起源如何更局限于内部云DLA Galaxies比集成的档案。在七个单独DLA内的云到云化学变化的分析显示，其中五种显示出统计学上显着的变化，高于0 2 dex，这些变化的来源是差动粉尘耗尽和电离效应，但是没有突出显示由于不同星形形成历史导致的变化的证据。这些结果对CDM层次理论内的星系形成的情景来说是重要的限制。与化学进化模型的DLA丰度模式比较表明DLA可以与螺旋星系的外部区域或矮化不规则星系相关，其特征在于具有低星形形成效率的星形成历史。它们可能是20 - 250 myr之间的年龄的年轻星系，但也是长度超过1gyl的星系，每单位面积的星形成率温和，在-3,2

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