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arXiv 1201.2373astro-ph.GA
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A779中团簇镓的年龄和金属丰度

Ages and Metallicities of Cluster Galaxies in A779 using Modified Strömgren Photometry

Yuvraj Harsha Sreedhar, Andrew P. Odell, Karl D. Rakos, Gerhard Hensler, Werner W. Zeilinger

摘要:

为了探索星系团的形成和演化,拉科斯和他的同事们引入了一种分光光度法,使用了改进的斯特伦格伦光度法。但是,随着对该项目能力的相当大的争论,我们在对三个A779数据集中六个常见星系的颜色重复性和年龄和金属丰度的重复性进行彻底测试后,重新引入了该系统。经过修改的斯特伦格伦和斯特伦格伦过滤系统之间的一致性已经被发现,以产生类似的颜色(精度为0.09 mag in(uz-vz),0.02 mag in(bz-yz)和0.03 mag in(vz-vz)),年龄和金属丰度(PCA的不确定度为0.36 Gyr和0.04 dex,GALEV模型的不确定度为0.44 Gyr和0.2 dex)。我们推断,该技术能够通过分离年龄效应和金属丰度效应来缓解年龄-金属丰度简并,但仍然不能完全打破。我们进一步扩展本文,重新研究的星系演化的低质量,动态差的A779星系团的光度(质量),密度,径向距离与估计的年龄,金属丰度,和恒星形成的历史。我们的研究结果清楚地显示了双峰的年轻,低质量,金属贫人口的平均年龄为6.7 Gyr(\pm 0.5 Gyr)和老,高质量,金属丰富的星系的平均年龄为9 Gyr(\pm 0.5 Gyr)。该方法还观测到了蓝团星系向红团的颜色演化以及缩小现象。我们的分析表明,修改后的Strömgren测光是非常适合于研究低和中z星系团,因为它是能够观察到更深的光谱红移极限,更好的空间分辨率,和窄带滤波器估计年龄和金属丰度与其他方法相比,研究恒星星族方案的不确定性较小。

英文摘要:

In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using the modified Strömgren photometry. But with the considerable debate toward the project's abilities, we re-introduce the system after a thorough testing of repeatability of colors and reproducibility of the ages and metallicities for six common galaxies in the three A779 data sets. A fair agreement has been found between the modified Strömgren and Strömgren filter systems to produce similar colors (with the precision of 0.09 mag in (uz-vz), 0.02 mag in (bz-yz), and 0.03 mag in (vz-vz)), ages and metallicities (with the uncertainty of 0.36 Gyr and 0.04 dex from the PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but still unable to completely break. We further extend this paper to re-study the evolution of galaxies in the low mass, dynamically poor A779 cluster by correlating the luminosity (mass), density, radial distance with the estimated age, metallicity, and the star formation history. Our results distinctly show the bimodality of the young, low-mass, metal-poor population with the mean age of 6.7 Gyr (\pm 0.5 Gyr) and the old, high-mass, metal-rich galaxies with the mean age of 9 Gyr (\pm 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red, and the downsizing phenomenon. Our analysis shows that the modified Strömgren photometry is very well suited for studying low- and intermediate-z clusters, as it is capable of observing deeper with better spatial resolution at spectroscopic redshift limits, and the narrowband filters estimate the age and metallicity with lesser uncertainties compared to other methods that study stellar population scenarios.

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