宽质量范围内红序星系的像差比：镁、钙、碳和氮的“X平面”
Abundance ratios in red-sequence galaxies over a wide mass range: The "X-planes" for magnesium, calcium, carbon and nitrogen
摘要：
本文分析了后发座星系团和沙普利超星系团中147个红序星系的轻元素Mg、Ca、C和N相对于Fe的丰度比。样本的光度范围为6等，从巨大的椭圆星系到M^*+4的矮星。我们利用广泛的质量范围调查系统的趋势，在丰度比Mg/Fe，Ca/Fe，C/Fe和N/Fe。我们发现，这些比率中的每一个都可以很好地建模，使用形式[X/Fe] = a0 + a1 log sigma + a2 [Fe/H]的双参数关系，其中sigma是速度分散。分析这些“X-平面”揭示了丰度模式的新结构，超越了传统的单参数（例如Mg/Fe-σ）相关性。α元素Mg和Ca的X-平面表明与速度弥散正相关，同时与Fe/H反相关（即a1>0和a2<0）。与传统的X/Fe-sigma关系相比，考虑这两种效应大大减少了分散。对于C和N，恢复了与速度弥散的类似相关性，但没有额外的Fe/H依赖性（即a1>0和a2~0）。X/Fe对两个参数的明确依赖性表明，至少有两个物理过程在设定丰度模式。Mg/Fe和Ca/Fe的Fe/H依赖性，在固定的西格玛，可能是由于不同的恒星形成的持续时间，从星系到星系。C和N没有相应的Fe/H依赖性，这与这些元素在低质量恒星中产生是一致的。在Fe/H固定的情况下，元素Mg、C和N的σ增加相似，Ca的σ增加略浅。这种趋势模式不能仅仅用恒星形成时间尺度随西格玛的系统变化来解释。
英文摘要：
We analyse the abundance ratios of the light elements Mg, Ca, C and N, relative to Fe, for 147 red-sequence galaxies in the Coma cluster and the Shapley Supercluster. The sample covers a six-magnitude range in luminosity, from giant ellipticals to dwarfs at M^*+4. We exploit the wide mass range to investigate systematic trends in the abundance ratios Mg/Fe, Ca/Fe, C/Fe and N/Fe. We find that each of these ratios can be well modelled using two-parameter relations of the form [X/Fe] = a0 + a1 log sigma + a2 [Fe/H], where sigma is the velocity dispersion. Analysing these "X-planes" reveals new structure in the abundance patterns, beyond the traditional one-parameter (e.g. Mg/Fe-sigma) correlations. The X-planes for the alpha elements, Mg and Ca, indicate a positive correlation with velocity dispersion, and simultaneously an anti-correlation with Fe/H (i.e. a1>0 and a2<0). Taking both effects into account dramatically reduces the scatter, compared to the traditional X/Fe-sigma relations. For C and N, a similar correlation with velocity dispersion is recovered, but there is no additional dependence on Fe/H (i.e. a1>0 and a2~0). The explicit dependence of X/Fe on two parameters is evidence that at least two physical processes are at work in setting the abundance patterns. The Fe/H dependence of Mg/Fe and Ca/Fe, at fixed sigma, may result from different durations of star formation, from galaxy to galaxy. The absence of corresponding Fe/H dependence for C and N is consistent with these elements being generated in lower-mass stars. The increase with sigma, at fixed Fe/H, is similar for elements Mg, C and N, and slightly shallower for Ca. This pattern of trends cannot be explained solely by a systematic variation of star-formation time-scale with sigma.
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