Radial measurements of IMF-sensitive absorption features in two massive ETGs
Radial measurements of IMF-sensitive absorption features in two massive ETGs
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DOI：
10.1093/mnras/stx3199
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发表时间：
2016-12
影响因子：
4.8
通讯作者：
S. Vaughan;R. Davies;S. Zieleniewski;R. Houghton
中科院分区：
文献类型：
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作者：
S. Vaughan;R. Davies;S. Zieleniewski;R. Houghton
我们对两个大质量早期类型星系NGC1277和IC843的恒星初始质量函数(IMF)敏感吸收特征进行了径向测量。利用牛津短波积分场谱图(SWIFT)，我们获得了NaI0.82和FeH0.99指数的分辨测量，其中发现这两个星系在~0.4A的NaI吸收和平坦的FeH剖面上都显示出强烈的梯度。我们发现这些测量可以用IMF的径向梯度、[Na/Fe]和[Fe/H]的适当丰度梯度或两者的组合来解释，而我们的数据无法打破这种简并。我们还使用全谱拟合从每个物体的积分光谱中推断全局性质，得到了与IC843中的Salpeter一致的单峰IMF斜率(x=2.27±0.17)，但比NGC1277中的Salpeter更陡峭(x=2.69±0.11)，尽管它们的FeH等效宽度相似。我们独立地对FeH特征的强度进行了拟合，并与EMILES和CvD12恒星布居库进行了比较，找到了模型之间的一致性。用这种方法计算的IMF值与NGC1277谱拟合值吻合较好(xCvD=2.5 9+0.2 5-0.48，Xe-Miles=2.77±0.31)，但与IC843的一致性较差，单用FeH得到的IMF值比全谱拟合法得到的斜率更陡(χCVD=2.5 7+0.30-0.4 1，χE-Miles=2.72±0.2 5)。这项工作突出了大波长覆盖对于打破丰度和IMF变化之间的简并性的重要性，如果在没有其他光谱信息的情况下使用Wing-Ford波段作为IMF指数，可能会产生疑问。
We make radial measurements of stellar initial mass function (IMF) sensitive absorption features in the two massive early-type galaxies NGC 1277 and IC 843. Using the Oxford Short Wavelength Integral Field specTrogaph (SWIFT), we obtain resolved measurements of the Na I 0.82 and FeH 0.99 indices, amongst others, finding both galaxies show strong gradients in Na I absorption combined with flat FeH profiles at ~0.4 A. We find these measurements may be explained by radial gradients in the IMF, appropriate abundance gradients in [Na/Fe] and [Fe/H], or a combination of the two, and our data are unable to break this degeneracy. We also use full spectral fitting to infer global properties from an integrated spectrum of each object, deriving a unimodal IMF slope consistent with Salpeter in IC 843 (x = 2.27 ± 0.17) but steeper than Salpeter in NGC 1277 (x = 2.69 ± 0.11), despite their similar FeH equivalent widths. Independently, we fit the strength of the FeH feature and compare to the EMILES and CvD12 stellar population libraries, finding agreement between the models. The IMF values derived in this way are in close agreement with those from spectral fitting in NGC 1277 (xCvD= 2.59+0.25-0.48, xE-MILES= 2.77 ± 0.31), but are less consistent in IC 843, with the IMF derived from FeH alone leading to steeper slopes than when fitting the full spectrum (χCvD= 2.57+0.30-0.41,χE-MILES= 2.72 ± 0.25). This work highlights the importance of a large wavelength coverage for breaking the degeneracy between abundance and IMF variations, and may bring into doubt the use of the Wing-Ford band as an IMF index if used without other spectral information.