arXivDaily arXiv每日学术速递 周一至周五更新
arXiv周末暂无论文更新，休息一下吧，周末愉快~~
arXiv 0806.1653astro-ph
收藏

早期宇宙中富金属恒星形成的三种模式

Three Modes of Metal-Enriched Star Formation in the Early Universe

Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea, Michael L. Norman

备注：
Significant revisions made, emulateapj, 15 pages, 3 tables, 8 figures, accepted for publication in ApJ. High-res version available at: http://solo.colorado.edu/~brittons/papers/threemodes.pdf
发表信息：
Astrophys.J.691:441-451,2009
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

对星族III（Pop III）恒星形成的模拟表明，它们的质量比今天观测到的Pop II和Pop I恒星大得多。这是由于无金属气体的坍缩动力学，这是由分子氢的辐射冷却调节的。我们研究如何通过在恒星形成环境中加入金属来改变气体云的坍塌，通过在各种金属丰度下模拟预富集恒星的形成。当金属丰度低于临界金属丰度Z_cr时，坍缩过程与无金属的情况类似，只有大质量天体形成。对于金属丰度远高于Z_cr的情况，有效的冷却迅速地将气体温度降低到CMB的温度。气体不能辐射冷却到低于CMB温度，并且变得热稳定。对于高金属丰度，Z >= 10^-2.5 Zsun，这发生在气体云演化的早期，此时密度仍然相对较低。由此产生的云核几乎没有碎片，很可能形成大质量恒星。如果金属丰度不是大大高于Z_cr，云有效地冷却，但没有达到CMB温度，并分裂成多个对象发生。我们的结论是，在高红移（z >= 4）有三种不同的恒星形成模式：一种是“原始”模式，产生大质量恒星（10 s至100 s Msun），金属丰度极低（Z ≤ 10^-3.75 Zsun）; CMB调节模式，产生中等质量（10 s的Msun）的恒星，其金属丰度高（Z >= 10^-2.5 Zsun，红移z ~ 15-20）;在这两种金属丰度之间存在一种低质量（几个Msun）模式。随着宇宙年龄的增长和CMB温度的降低，低质量模式的范围扩展到更高的金属丰度，最终成为恒星形成的唯一模式。（节录）

英文摘要：

Simulations of the formation of Population III (Pop III) stars suggest that they were much more massive than the Pop II and Pop I stars observed today. This is due to the collapse dynamics of metal-free gas, which is regulated by the radiative cooling of molecular hydrogen. We study how the collapse of gas clouds is altered by the addition of metals to the star-forming environment by performing a series of simulations of pre-enriched star formation at various metallicities. For metallicities below the critical metallicity, Z_cr, collapse proceeds similarly to the metal-free case, and only massive objects form. For metallicities well above Z_cr, efficient cooling rapidly lowers the gas temperature to the temperature of the CMB. The gas is unable to radiatively cool below the CMB temperature, and becomes thermally stable. For high metallicities, Z >= 10^-2.5 Zsun, this occurs early in the evolution of the gas cloud, when the density is still relatively low. The resulting cloud-cores show little or no fragmentation, and would most likely form massive stars. If the metallicity is not vastly above Z_cr, the cloud cools efficiently but does not reach the CMB temperature, and fragmentation into multiple objects occurs. We conclude that there were three distinct modes of star formation at high redshift (z >= 4): a `primordial' mode, producing massive stars (10s to 100s Msun) at very low metallicities (Z <= 10^-3.75 Zsun); a CMB-regulated mode, producing moderate mass (10s of Msun) stars at high metallicites (Z >= 10^-2.5 Zsun at redshift z ~ 15-20); and a low-mass (a few Msun) mode existing between those two metallicities. As the universe ages and the CMB temperature decreases, the range of the low mass mode extends to higher metallicities, eventually becoming the only mode of star formation. (Abridged)

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。

↑