PEARS巡天中的早型星系：探测中等红移的恒星星族
Early-type galaxies in the PEARS survey: Probing the stellar populations at moderate redshift
摘要：
利用PEARS计划中的HST/ACS无缝棱晶光谱，我们研究了GOODS南北场中形态选择的早型星系的恒星星族。样本-从（v2.0）HST/ACS图像的视觉分类中提取，并限制红移z>0.4 -包括228个星系（F775 W <24 ABmag），z约为1.3，320弧分2，中值红移zM=0.75。这项工作大大增加了我们以前在HUDF中GRAPES巡天的样本（18个星系超过~11弧分2; Pasquali et al. 2006 b）。棱镜数据使我们能够将样品分为“红色”和“蓝色”光谱，后者占总数的15%。三个不同的网格模型参数化的恒星形成的历史被用来适应低分辨率的光谱。在样本的红移范围内-对应于5到10 Gyr之间的宇宙年龄-我们发现恒星质量和平均年龄之间有很强的相关性，而年龄的 ** 分布 **（由分布的RMS定义）大约为1 Gyr，并且与恒星质量无关。最佳拟合参数表明，它是形成时代，而不是形成时标，最好的相关性在早期类型的星系的质量。这一结果--以及最近观测到的大质量星系数量密度缺乏演化--激发了对绕过蓝云中任何相位的（大质量）星系形成通道的需求，正如Dekel等人（2009）的模拟所建议的那样。
英文摘要：
Using HST/ACS slitless grism spectra from the PEARS program, we study the stellar populations of morphologically selected early-type galaxies in the GOODS North and South fields. The sample - extracted from a visual classification of the (v2.0) HST/ACS images and restricted to redshifts z>0.4 - comprises 228 galaxies (F775W<24 ABmag) out to z~1.3 over 320 arcmin2, with a median redshift zM=0.75. This work significantly increases our previous sample from the GRAPES survey in the HUDF (18 galaxies over ~11 arcmin2; Pasquali et al. 2006b). The grism data allow us to separate the sample into `red' and `blue' spectra, with the latter comprising 15% of the total. Three different grids of models parameterising the star formation history are used to fit the low-resolution spectra. Over the redshift range of the sample - corresponding to a cosmic age between 5 and 10 Gyr - we find a strong correlation between stellar mass and average age, whereas the **spread** of ages (defined by the RMS of the distribution) is roughly ~1 Gyr and independent of stellar mass. The best-fit parameters suggest it is formation epoch and not formation timescale, that best correlates with mass in early-type galaxies. This result - along with the recently observed lack of evolution of the number density of massive galaxies - motivates the need for a channel of (massive) galaxy formation bypassing any phase in the blue cloud, as suggested by the simulations of Dekel et al. (2009).
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
