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The Star Formation History of the Universe over the Past Eight Billion Years.

机译：过去八十年来宇宙的恒星形成历史。

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摘要

How galaxies such as our own Milky Way formed and evolved remains a mystery. There are two general approaches in galaxy formation and evolution studies. One is to infer formation histories via archaeological investigations of galaxies at low redshift, in the local Universe. The other is to study galaxy formation and evolution in action by observing faint distant galaxies, the ancestors of local galaxies, in the more distant and younger Universe, at higher redshift.;I employ the first approach to study the formation of elliptical galaxies, the most massive galaxies in the Universe. I investigate the stellar content of 1923 elliptical galaxies, the largest high-fidelity sample in the local Universe, as a function of stellar mass and environment. I infer their star formation histories, finding that isolated low-mass elliptical galaxies formed their stars slightly later than their counterparts in galaxy clusters.;I measure the cosmic star formation rate (SFR) density at redshift z ∼ 1, when the Universe was eight billion years younger. The cosmic SFR density measures how many stars are being formed per unit volume of the Universe. I show that galaxies were more actively forming stars eight billion years ago than they are at present, by roughly an order of magnitude. The reason why galaxies are so much less active at present remains unknown, partly due to the small sample size of distant galaxies observed previously.;To improve the sample size, we have completed a new galaxy survey, the Prism Multi-object Survey (PRIMUS). We have observed ∼ 120, 000 galaxies spanning distances from the local Universe to redshift z ∼ 1. We specifically targeted fields with existing multi-wavelength data in the X-ray, ultraviolet, optical, and infrared. The large sample and multi-wavelength data allow precise statistical studies of galaxy evolution since z ∼1. As a preliminary result from PRIMUS, I show that 15% of galaxies that appear to lack star formation in the optical actually show star formation when observed in the infrared. The overall contribution of these obscured star-forming galaxies to the cosmic SFR density is not negligible (about 10%).
机译：像我们自己的银河系这样的星系如何形成和演化仍然是一个谜。在星系形成和演化研究中有两种通用方法。一种是通过对当地宇宙中低红移的星系进行考古调查来推断形成历史。另一种方法是在更高的红移下，通过观察更遥远和更年轻的宇宙中微弱的遥远星系（本地星系的祖先）来研究星系的形成和演化。我采用第一种方法研究椭圆形星系的形成，即宇宙中最庞大的星系。我研究了1923个椭圆星系的恒星含量，这是当地宇宙中最大的高保真度样本，与恒星质量和环境有关。我推断出它们的恒星形成历史，发现孤立的低质量椭圆形星系的形成恒星比其星系团中的恒星形成的恒星稍晚。;当宇宙八时，我测量了红移z〜1时宇宙恒星形成率（SFR）密度。十亿岁宇宙SFR密度衡量每单位体积宇宙中正在形成多少颗恒星。我证明，在八十亿年前，星系比现在更活跃地形成恒星，大约一个数量级。目前尚不清楚星系活动度如此之低的原因尚不明确，部分原因是先前观察到的遥远星系的样本量较小。为了提高样本量，我们完成了一项新的星系调查，Prism Multi-Object Survey（PRIMUS） ）。我们已经观测到从本地宇宙到红移z〜1的大约120，000个星系。我们专门针对具有现有多波长数据的X射线，紫外，光学和红外领域。自z〜1以来，大量的样本和多波长数据允许对星系演化进行精确的统计研究。作为PRIMUS的初步结果，我证明了在光学中似乎缺少恒星形成的星系中有15％在红外中观察时实际上显示出恒星形成。这些模糊的恒星形成星系对宇宙SFR密度的总体贡献不可忽略（约10％）。

著录项

  • 作者

    Zhu, Guangtun.;

  • 作者单位

    New York University.;

  • 授予单位 New York University.;
  • 学科 Physics Astrophysics.;Physics General.;Physics Astronomy and Astrophysics.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 259 p.
  • 总页数 259
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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