在红移7的极度贫金属气体
Robert A Simcoe1, Peter W Sullivan, Kathy L Cooksey
1MIT-Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Building 37, Room 664L, Cambridge, Massachusetts 02139, USA. simcoe@space.mit.edu
Nature
|December 11, 2012
概括
早期宇宙的观测显示了极低的重元素丰度,这表明原始条件持续的时间比预期的要长. 这一发现提供了关于第一个恒星的形成和宇宙化学丰富的见解.
科学领域:
- 宇宙微波背景和早期宇宙研究
- 天体物理化学和核合成
- 银河系的形成和进化
背景情况:
- 在天体物理环境中,重元素的丰度通常在0.001到太阳值的2倍之间.
- 以前的低丰度测量来自银河系光环恒星和类星体吸收系统,红移z=3.
- 从大爆炸后的十亿年开始,当早期的恒星合成元素时,直接的丰富度测量以前是不可用的.
研究的目的:
- 报告来自早期宇宙的直接丰富度测量,特别是大爆炸后的第一十亿年内.
- 为了研究气体在红移z=7.04时的化学成分,相应的年龄为7.72亿年.
- 为了限制重元素的丰富性,并评估早期宇宙的电离和化学丰富状态.
主要方法:
- 在红移z = 7.04的类星体光谱中观察和重元素的吸收.
- 分析光谱数据以检测和量化金属 (比重的元素) 的存在.
- 基于吸收特征的气体特性建模,考虑重力绑定和扩散无绑定场景.
主要成果:
- 在z = 7.04.04处检测出一个大的中性柱.
- 没有相应的金属吸收,表明化学含量少于1/10,000 (绑定) 或1/1000 (不绑定) 的太阳水平.
- 观察到的条件表明,在z ≈ 7的这个区域,宇宙可能没有完全离子化或化学丰富.
结论:
- 在这个早期的宇宙时代,气体的化学含量明显低于预期.
- 如果气体是星系间的,这意味着缺乏广泛的再电离和化学丰富,z ≈ 7.
- 如果这种气体位于原星系内,那么它的少量就表明它是由于低效的冷却导致未被观测到的第三种群恒星形成的可行地点.
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