金属が非常に少ないガスで,赤偏移は7です
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
まとめ
初期の宇宙の観測は,重元素の豊富度が非常に低いことを明らかにし,原始的な条件が予想以上に長く続いたことを示唆しています. この発見は,最初の星の形成と宇宙の化学的濃縮についての洞察を提供します.
科学分野:
- 宇宙マイクロ波の背景と初期の宇宙の研究
- 天体物理学化学と核合成
- 銀河の形成と進化について
背景:
- 天体物理学的環境における重元素の豊富さは,通常,太陽光値の0.001倍から2倍の範囲にあります.
- 以前の低富裕度測定は,赤道偏移 z = 3 で銀河のハロ星やクワザール吸収系からでした.
- 初期の恒星が元素を合成したビッグバン後の最初の10億年からの直接的な豊富度測定は,以前は利用できませんでした.
研究 の 目的:
- 初期の宇宙の,特にビッグバン後の最初の10億年の間における,直接的な豊富度測定を報告する.
- 赤い偏移 z = 7.04 でガスの化学組成を調べるため,年齢は7億7200万年.
- 重元素の豊富さを制限し,初期の宇宙のイオン化と化学的濃縮状態を評価する.
主な方法:
- クワザールスペクトルにおける水素と重元素の吸収の観測,赤道移転 z = 7.04 の場合.
- 金属 (ヘリウムより重い元素) の存在を検出および定量化するために,スペクトルデータの分析.
- 吸収特性に基づいてガスの性質をモデリングし,重力的に結合されたシナリオと拡散的に結合されていないシナリオの両方を考慮します.
主要な成果:
- z = 7.04で中性水素の大柱が検出されました.
- 対応する金属吸収の欠如は,化学物質の濃度が太陽レベルの1/10,000 (bound) または1/1000 (unbound) 未満であることを示しています.
- 観測された条件は,宇宙がz ≈ 7のこの領域で完全にイオン化または化学的に濃縮されていない可能性を示唆しています.
結論:
- この初期の宇宙時代におけるガスの化学的豊富さは,予想より著しく低い.
- ガスが銀河間である場合,それは広範な再イオン化とz ≈ 7による化学的濃縮の欠如を暗示する.
- ガスが原銀河の中に存在する場合,その少量の量は,低効率な冷却による観測されていない集団IIIの恒星の形成のための適当な場所であることを示唆しています.
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