Metallicities and Physical Conditions in Star-forming Galaxies at z ~ 1.0-1.5
Metallicities and Physical Conditions in Star-forming Galaxies at z ~ 1.0-1.5
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z ~ 1.0-1.5 恒星形成星系中的金属丰度和物理条件
DOI：
10.1086/529030
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
Chung
中科院分区：
文献类型：
--
作者：
Xin Liu;A. Shapley;A. Coil;J. Brinchmann;Chung
本文研究了从DEEP 2星系红移巡天中选取的20个1.0 < z < 1.5的恒星形成星系的质量-金属丰度（M-Z）关系和H Ⅱ区的物理条件。我们发现恒星质量和样品中的气相氧丰度之间的相关性，并将其与从斯隆数字巡天（SDSS）中观察到的紫外线选择的z-102恒星形成星系和本地物体之间的相关性进行比较。这种比较，基于相同的经验丰度指标，表明M-Z关系的零点随红移而演变，在这个意义上，固定恒星质量的星系在较低的红移下变得更富含金属。对[O III]/Hβ和[N II]/Hα发射线比值的测量表明，平均而言，DEEP 2 1.0 < z < 1.5样本中的物体与附近H II区和SDSS发射线星系中观察到的激发序列有显著的偏移。为了充分理解这种偏移的原因，这也是在z 2恒星形成星系中观察到的，我们详细研究了一小部分SDSS星系，它们与DEEP 2样本具有相似的诊断比率。这些星系中的一些显示出活动星系核和/或激波活动的证据，这可能会导致它们不寻常的谱线比，并对巴耳末发射谱线的贡献约为20%。另一些则表明没有活动星系核或激波激发的证据，但其特征是电子密度和温度较高，因此星际气体压力比类似恒星质量的典型SDSS恒星形成星系更高。这些异常天体也有更高的浓度和恒星形成率表面密度，这与更高的星际压力直接相关。较高的星星形成率表面密度，星际压力，和H II区电离参数也可能是常见的高红移。当使用强线指示器来了解星系中重元素的演化时，必须考虑到这些影响。当这些影响包括在内时，M-Z关系到z = 2的推断演变比以前的估计更重要。
We present a study of the mass-metallicity (M-Z) relation and H II region physical conditions in a sample of 20 star-forming galaxies at 1.0 < z < 1.5 drawn from the DEEP2 Galaxy Redshift Survey. We find a correlation between stellar mass and gas-phase oxygen abundance in the sample and compare it with the one observed among UV-selected z ∼ 2 star-forming galaxies and local objects from the Sloan Digital Sky Survey (SDSS). This comparison, based on the same empirical abundance indicator, demonstrates that the zero point of the M-Z relationship evolves with redshift, in the sense that galaxies at fixed stellar mass become more metal-rich at lower redshift. Measurements of [O III]/Hβ and [N II]/Hα emission-line ratios show that, on average, objects in the DEEP2 1.0 < z < 1.5 sample are significantly offset from the excitation sequence observed in nearby H II regions and SDSS emission-line galaxies. In order to fully understand the causes of this offset, which is also observed in z ∼ 2 star-forming galaxies, we examine in detail the small fraction of SDSS galaxies that have similar diagnostic ratios to those of the DEEP2 sample. Some of these galaxies indicate evidence for AGN and/or shock activity, which may give rise to their unusual line ratios and contribute to Balmer emission lines at the level of ~20%. Others indicate no evidence for AGN or shock excitation yet are characterized by higher electron densities and temperatures, and therefore interstellar gas pressures, than typical SDSS star-forming galaxies of similar stellar mass. These anomalous objects also have higher concentrations and starformation rate surface densities, which are directly connected to higher interstellar pressure. Higher star formation rate surface densities, interstellar pressures, and H II region ionization parameters may also be common at high redshift. These effects must be taken into account when using strong-line indicators to understand the evolution of heavy elements in galaxies. When such effects are included, the inferred evolution of the M-Z relation out to z ∼ 2 is more significant than previous estimates.