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熱い銀河間媒質における欠落しているバリオンの観測
F Nicastro1,2, J Kaastra3, Y Krongold4
1Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Roma, Rome, Italy. fabrizio.nicastro@oa-roma.inaf.it.
Nature
|June 22, 2018
まとめ
宇宙のバリオン物質の30~40%を占める 欠けているバリオンを 温かい銀河間媒介で発見しました クワザールスペクトルの高度にイオン化された酸素 (O VII) 吸収器の観測は,銀河が豊富な領域にその存在を確認している.
科学分野:
- 宇宙学と天体物理学
- 銀河間媒体の研究
- バリオン・センサス
背景:
- ビッグバン核合成の予測と比較して観測されたバリオンの30〜40%の赤字は,古くからの宇宙学的パズルです.
- 理論的なモデルは,これらの欠けているバリオンは,銀河間の熱い,薄いガスである温かい熱い銀河間媒質 (WHIM) に存在することを示唆しています.
- WHIMの検出は,水素が主にイオン化しているため,紫外線スペクトルの信号対ノイズ比が低いため,困難です.
研究 の 目的:
- 熱い銀河間媒体の 欠落したバリオンの存在を 検出し確認する
- 熱い銀河間媒体の性質と位置をX線スペクトルで調べる
主な方法:
- 赤道偏移 > 0.4 のクエーザーの高信号比X線スペクトルの分析.
- WHIMのトレーサとして,高度にイオン化された酸素 (O VII) から吸収する特徴の特定.
- 吸収器の変動性と関連する冷吸収の評価により,他の起源 (例えば,クエーザー出流,銀河間ISM) を排除する.
主要な成果:
- クエーザーのX線スペクトルで2つのO VII吸収器が検出され,熱い,イオン化されたガスの存在を示しています.
- 吸収剤は2年間にわたって変化を示せず,局所的な源を除外して,関連する冷却吸収がなかった.
- O VIIシステムは,WHIMの予測とシミュレーションと一致する,銀河の過密度が高い地域で見つかりました.
結論:
- 観測されたO VII吸収体は,温かい銀河間媒質に起因し,その存在の強力な証拠を提供している.
- この発見は WHIMの赤字のバリオン物質を特定することで 長い間存在していたバリオンの問題を解決しました
- この発見は宇宙構造の形成と 宇宙におけるバリオン物質の分布の 数値シミュレーションを検証しています
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