标题： 仙女座的深度光度测量揭示了潮汐流和球状群体之间的惊人相似性 显示英文标题

标题： Deep Photometry of Andromeda Reveals Striking Similarities in the Tidal Stream and Spheroid Populations

摘要： 我们为仙女座星系（M31）的巨型潮汐流中的一个区域绘制了颜色-亮度图（CMD）。这些由哈勃太空望远镜上的高级勘测相机拍摄的观测数据，在V~30星等处达到50%的完备性，并深入到最老主序点以下1个星等。流与先前球状晕CMD之间的显著相似性表明它们具有非常相似的年龄和金属丰度分布，但这一结果仍是个谜；我们推测了这种结果可能的解释，但指出没有一种解释是毫无问题的。正如预期的那样，由于与仙女座星系相互作用引发的恒星形成爆发，流CMD中并没有明显的多重拐点。这两个区域的恒星形成持续了大约60亿年，达到了相对较高的金属丰度，并且在60亿年前基本完成。球状晕和流的密切相似性表明两者可能源自同一事件；值得进一步研究这些结构中的恒星是否是与M31相互作用的盘状星系的残余，甚至可能是由M31盘本身因相互作用而瓦解形成的。 显示英文摘要

摘要： We present a color-magnitude diagram (CMD) for a field in the giant tidal stream of the Andromeda galaxy (M31). These observations, taken with the Advanced Camera for Surveys on the Hubble Space Telescope, are 50% complete at V~30 mag, reaching 1 mag below the oldest main-sequence turnoff. Striking similarities between the stream and a previous spheroid CMD imply they have very similar age and metallicity distributions, but present something of an enigma; we speculate on possible interpretations of this result, but note that none are without problems. Distinct multiple turnoffs, as might be expected from pulses of star formation caused by interaction with Andromeda, are not apparent in the stream CMD. Star formation in both fields lasted about 6 billion years, building up to relatively high metallicities and being largely complete 6 billion years ago. The close similarity of the spheroid and stream suggests that both may have derived from the same event; it would be worth exploring to what extent stars in these structures are the remnants of a disk galaxy that interacted with M31, or even were disrupted from the M31 disk itself by the interaction.