标题： 光度红移偏差来自星系演化 显示英文标题

标题： Photometric Redshift Biases from Galaxy Evolution

摘要： 提议的宇宙学巡天将利用比现有任何完整的光谱红移巡天中更微弱的星系的 photometric redshift（光谱红移），这些巡天用于训练 photo-z 方法。 我们研究了已知的微弱星系和明亮星系之间差异导致的 photo-z 偏差：更高的红移处活动星系核（AGN）活动增加，以及本质上亮度较高与较暗的早期型星系之间的金属丰度差异。 我们发现，即使平均 photometric 目标和训练集之间存在非常小的不匹配，也可能诱导出足以显著破坏推导出的宇宙学参数的 photo-z 偏差。 旧星族中约 0.003 dex 的金属丰度偏移，或者任何星系光谱受到约 0.2% 活动星系核（AGN）流量的污染，就足以在 photo-z 中引入 10^-3 的偏差。 这些结果强调了将明亮星系的行为外推到较暗星系群体的危险性，并且表明需要一个光谱训练集，该训练集涵盖 photo-z 目标的所有特性，即延伸到第 25 星等或更暗的未来巡天中将使用的星系。 显示英文摘要

摘要： Proposed cosmological surveys will make use of photometric redshifts of galaxies that are significantly fainter than any complete spectroscopic redshift surveys that exist to train the photo-z methods. We investigate the photo-z biases that result from known differences between the faint and bright populations: a rise in AGN activity toward higher redshift, and a metallicity difference between intrinsically luminous and faint early-type galaxies. We find that even very small mismatches between the mean photometric target and the training set can induce photo-z biases large enough to corrupt derived cosmological parameters significantly. A metallicity shift of ~0.003dex in an old population, or contamination of any galaxy spectrum with ~0.2% AGN flux, is sufficient to induce a 10^-3 bias in photo-z. These results highlight the danger in extrapolating the behavior of bright galaxies to a fainter population, and the desirability of a spectroscopic training set that spans all of the characteristics of the photo-z targets, i.e. extending to the 25th mag or fainter galaxies that will be used in future surveys.