z ~ 1.5早型星系的空间分辨颜色和恒星星族性质
Spatially Resolved Colors and Stellar Population Properties in Early-Type Galaxies at z ~ 1.5
摘要：
本文给出了11个早型星系（ETGs）在1.0<z_spec<1.9时的F850 LP-F160 W颜色梯度。在有效半径R_e内，在约70%的样品中检测到显著的负F850 LP-F160 W颜色梯度，剩余的30%具有平坦的颜色轮廓。在R>R_e处扩展分析，我们发现具有负F850 LP-F160 W颜色梯度的高z ETG的分数上升到100%。对于每个星系，我们调查的径向颜色变化的起源与技术的基础上匹配的空间分辨的颜色和全球光谱能量分布（SED）的复合恒星星族模型的预测。事实上，我们发现，恒星星族的年龄是唯一的参数，其径向变化单独可以完全解释所观察到的颜色梯度和全球SED的一半的星系在我们的样本（6 ETG），而不需要任何其他恒星星族的径向变化的属性。对于这六个ETG中的四个，纯金属丰度变化也可以再现检测到的颜色梯度。尽管如此，恒星形成时间尺度的径向变化，低质量到高质量恒星和尘埃的丰度对观测到的颜色梯度的微小贡献不能完全排除。对于剩下的一半样本，我们的分析表明，一个更复杂的情况下，更多的属性的恒星星族需要同时变化，以产生观察到的颜色梯度和全球SED。我们的研究结果表明，尽管我们的星系的平均年龄很年轻（<3-4 Gyr），但它们的恒星含量已经表现出显着的差异。我们已经讨论了我们的结果的框架内最广泛接受的星系形成的情况下，并得出结论，他们都不能令人满意地解释所观察到的颜色梯度分布和高Z ETG的空间分辨的内容。
英文摘要：
We present F850LP-F160W color gradients for 11 early-type galaxies (ETGs) at 1.0<z_spec<1.9. Significant negative F850LP-F160W color gradients have been detected in ~70% of our sample within the effective radius R_e, the remaining 30% having a flat color profile. Extending the analysis at R>R_e we have found that the fraction of high-z ETGs with negative F850LP-F160W color gradients rises up to 100%. For each galaxy, we investigate the origin of the radial color variation with a technique based on the matching of both the spatially resolved color and the global spectral energy distribution (SED) to predictions of composite stellar population models. In fact, we find that the age of the stellar populations is the only parameter whose radial variation alone can fully account for the observed color gradients and global SEDs for half of the galaxies in our sample (6 ETGs), without the need of radial variation of any other stellar population property. For four out of these six ETGs, a pure metallicity variation can also reproduce the detected color gradients. Nonetheless, a minor contribution to the observed color gradients from radial variation of star-formation time scale, abundance of low-to-high mass stars and dust cannot be completely ruled out. For the remaining half of the sample, our analysis suggests a more complex scenario whereby more properties of the stellar populations need to simultaneously vary to generate the observed color gradients and global SED. Our results show that, despite the young mean age of our galaxies (<3-4 Gyr), they already exhibit significant differences among their stellar content. We have discussed our results within the framework of the widest accepted scenarios of galaxy formation and conclude that none of them can satisfactorily account for the observed distribution of color gradients and for the spatially resolved content of high-z ETGs.
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