From Carbon to Cobalt: Chemical Compositions and Ages of z ∼ 0.7 Quiescent Galaxies
From Carbon to Cobalt: Chemical Compositions and Ages of z ∼ 0.7 Quiescent Galaxies
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DOI：
10.3847/1538-4357/acc176
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发表时间：
2023-03
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通讯作者：
Aliza G. Beverage;M. Kriek;C. Conroy;N. Sandford;R. Bezanson;M. Franx;A. van der Wel;D. Weisz
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作者：
Aliza G. Beverage;M. Kriek;C. Conroy;N. Sandford;R. Bezanson;M. Franx;A. van der Wel;D. Weisz
我们用来自LEGA-C调查的超深静止框架光学光谱给出了位于z∼0.7时的135个大质量静止星系的元素丰度模式(C、N、Mg、Si、Ca、Ti、V、Cr、Fe、Co和Ni)。利用全光谱分层贝叶斯模型，计算了S星体的四个星速离散区(σv)的平均年龄和元素丰度(−v)，范围为15 0~2 5 0 km。由此得到的元素丰度测量结果精确到0.05度。大多数元素以及总金属丰度和恒星年龄与σv呈正相关。因此，离散度最高的星系形成得最早，也是最富金属的。我们发现在[X/Fe]和σv之间只有轻微或不显著的趋势，这表明平均恒星形成时间尺度并不强烈地依赖于速度弥散。首先，z∼0.7型静止星系的丰度模式与z∼0时惊人地相似。然而，在最低速度弥散时，z∼0.7星系比z∼0星系略微增加了N、Mg、Ti和Ni丰度比，并提前了形成红移。因此，尽管高质量静止星系的数量几乎没有进化，但低质量静止星系的数量在过去6年里显著增长。最后，z∼0和z∼0.7两个静止星系的丰度模式与基于化学演化模型的理论预测有很大的不同，这表明我们对这些星系的富集史的了解仍然非常有限。
We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies at z ∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion (σ v ) ranging from 150–250 km s−1 using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation with σ v . Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] and σ v , suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of the z ∼ 0.7 quiescent galaxies are strikingly similar to those at z ∼ 0. However, at the lowest-velocity dispersions, the z ∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than their z ∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of both z ∼ 0 and z ∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited.