ACS LCID项目。III。鲸鱼座dSph星系的恒星形成历史：一个再电离后的化石
The ACS LCID project. III. The star formation history of the Cetus dSph galaxy: a post-reionization fossil
摘要：
我们使用深HST/ACS观测计算鲸鱼座矮球状（dSph）星系的恒星形成历史（SFH）。我们的测光达到低于最古老的主序关闭，这使我们能够估计的年龄和持续时间的主要情节恒星形成的鲸鱼座。这可以很好地近似为一个单一的事件，在大约12+/-0.5 Gyr之前达到峰值，持续时间不超过1.9+/-0.5 Gyr（FWHM）。我们的解决方案还表明，在过去的8个Gyr期间，鲸鱼座基本上没有恒星形成。这使得鲸鱼座的SFH可以与最古老的银河系dSphs相媲美。考虑到鲸鱼座目前被隔离在本星系群的外围边缘，这意味着鲸鱼座在大多数银河系矮卫星的形态-银河系中心距离关系中是一个明显的异常值。我们的研究结果还表明，在宇宙被再电离很久之后，鲸鱼座在z ~ 1继续形成恒星，并且在鲸鱼座的SFH中没有再电离时代的明确标志。我们简要地讨论了这些结果的矮星系演化模型的影响。最后，我们提出了一个全面的帐户的数据减少和分析策略所采用的所有星系的LCID（本地宇宙学从孤立的矮）项目。我们采用两种不同的测光代码（DAOPHOT/ALLFRAME和DOLPHOT），三种不同的SFH重建代码（IAC-流行/MinnIAC，匹配，COLE），和两个恒星演化库（BaSTI和Padova/Girardi），允许详细评估的建模和观测的不确定性。
英文摘要：
We use deep HST/ACS observations to calculate the star formation history (SFH) of the Cetus dwarf spheroidal (dSph) galaxy. Our photometry reaches below the oldest main sequence turn-offs, which allows us to estimate the age and duration of the main episode of star formation in Cetus. This is well approximated by a single episode that peaked roughly 12+/-0.5 Gyr ago and lasted no longer than about 1.9+/-0.5 Gyr (FWHM). Our solution also suggests that essentially no stars formed in Cetus during the past 8 Gyrs. This makes Cetus' SFH comparable to that of the oldest Milky Way dSphs. Given the current isolation of Cetus in the outer fringes of the Local Group, this implies that Cetus is a clear outlier in the morphology-Galactocentric distance relation that holds for the majority of Milky Way dwarf satellites. Our results also show that Cetus continued forming stars through z ~ 1, long after the Universe was reionized, and that there is no clear signature of the epoch of reionization in Cetus' SFH. We discuss briefly the implications of these results for dwarf galaxy evolution models. Finally, we present a comprehensive account of the data reduction and analysis strategy adopted for all galaxies targeted by the LCID (Local Cosmology from Isolated Dwarfs) project. We employ two different photometry codes (DAOPHOT/ALLFRAME and DOLPHOT), three different SFH reconstruction codes (IAC-pop/MinnIAC, MATCH, COLE), and two stellar evolution libraries (BaSTI and Padova/Girardi), allowing for a detailed assessment of the modeling and observational uncertainties.
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