Physical Properties, Baryon Content, and Evolution of the Lyα Forest: New Insights from High-Resolution Observations at z ≲ 0.4
Physical Properties, Baryon Content, and Evolution of the Lyα Forest: New Insights from High-Resolution Observations at z ≲ 0.4
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DOI：
10.1086/511749
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发表时间：
2006-12
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通讯作者：
N. Lehner;B. Savage;P. Richter;K. Sembach;T. Tripp;B. P. W. U. O. N. Dame;U. Wisconsin;U. Bonn;Space Telescope Science Institute;U. O. Massachusetts
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作者：
N. Lehner;B. Savage;P. Richter;K. Sembach;T. Tripp;B. P. W. U. O. N. Dame;U. Wisconsin;U. Bonn;Space Telescope Science Institute;U. O. Massachusetts
我们对z = 0.4的Lyα森林进行了研究，由此得出结论：宇宙中至少有20%的重子位于由宽Lyα吸收体示踪的高电离气体中。用窄Lyα吸收体探测的冷光电离低z星系际介质（IGM）中含有约30%的重子。我们进一步发现，宽与窄Lyα吸收体的比率在z = 0.4时比在1.5 <$z = 3.6时高，这意味着大部分低红移宇宙更热和/或运动学上更受干扰。我们的基础上，这些结论与FUSE和HST STIS E140 M紫外阶梯光谱仪观察到的七个类星体的分析。我们的样品有341个H I吸收体，总的未阻塞红移路径为2.064。对于log N <$13.2，观测到的吸收体总体是完整的，具有柱密度分布f（N）<$N。对于窄吸收体（B ≤ 40 km s-1），β = 1.76 ± 0.06。多普勒参数B在低红移处的分布表明有两种分布：窄（B ≤ 40 km s-1）和宽（B > 40 km s-1）的Lyα吸收体（分别称为NLA和BLA）。NLA和一些BLA探测冷（T ~ 104 K）光电离IGM。BLA还探测温热IGM（T = 105-106 K）的高度电离气体。B的分布在z = 0.4时比在1.5 μ z = 3.6时具有更显著的高速尾部，这导致低z时的中值和平均b值比高z时高15%-30%。在z = 0.4时BLA与NLA的数密度比在1.5 z = 3.6时高约3倍。
We present a study of the Lyα forest at z ≲ 0.4, from which we conclude that at least 20% of the total baryons in the universe are located in the highly ionized gas traced by broad Lyα absorbers. The cool photoionized low-z intergalactic medium (IGM) probed by narrow Lyα absorbers contains about 30% of the baryons. We further find that the ratio of broad to narrow Lyα absorbers is higher at z ≲ 0.4 than at 1.5 ≲ z ≲ 3.6, implying that a larger fraction of the low-redshift universe is hotter and/or more kinematically disturbed. We base these conclusions on an analysis of seven QSOs observed with both FUSE and the HST STIS E140M ultraviolet echelle spectrograph. Our sample has 341 H I absorbers with a total unblocked redshift path of 2.064. The observed absorber population is complete for log N ≳ 13.2, with a column density distribution f(N) ∝ N. For narrow (b ≤ 40 km s-1) absorbers, β = 1.76 ± 0.06. The distribution of the Doppler parameter b at low redshift implies two populations: narrow (b ≤ 40 km s-1) and broad (b > 40 km s-1) Lyα absorbers (referred to as NLAs and BLAs, respectively). Both the NLAs and some BLAs probe the cool (T ~ 104 K) photoionized IGM. The BLAs also probe the highly ionized gas of the warm-hot IGM (T ≃ 105-106 K). The distribution of b has a more prominent high-velocity tail at z ≲ 0.4 than at 1.5 ≲ z ≲ 3.6, which results in median and mean b-values that are 15%-30% higher at low z than at high z. The ratio of the number density of BLAs to NLAs at z ≲ 0.4 is a factor of ~3 higher than at 1.5 ≲ z ≲ 3.6.