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首页> 外文期刊>The Astrophysical journal >A UNIFORM ANALYSIS OF THE Lyα FOREST AT z = 0-5. Ⅴ. THE EXTRAGALACTIC IONIZING BACKGROUND AT LOW REDSHIFT
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A UNIFORM ANALYSIS OF THE Lyα FOREST AT z = 0-5. Ⅴ. THE EXTRAGALACTIC IONIZING BACKGROUND AT LOW REDSHIFT

机译：z = 0-5时的Lyα森林的均匀分析。五。低REDSHIFT的超离子电离背景。

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In Paper Ⅲ of our series, "A Uniform Analysis of the Lyα Forest at z = 0-5," we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(v_0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum-likelihood technique and the best estimates possible for each QSO's Lyman limit flux and systemic redshift, we find J(v_0) = 7.6_(-3.0)~(+9.4) x 10~(-23) erg s~(-1) cm~(-2) Hz~(-1) sr~(-1) at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z < 1 and z > 1, the values of J(v_0) found are 6.5_(-1.6)~(+3.8) x 10~(-23) erg s~(-1) cm~(-2) Hz~(-1) sr~(-1), and 1.0_(-0.2)~(+3.8) x 10~(-22) erg s~(-1) cm~(-2) Hz~(-1) sr~(-1), respectively, indicating that the mean intensity of the background is evolving over the red-shift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best-fit H Ⅰ photoionization rates are found to be 6.7 x 10~(-13) s~(-1) for all red-shifts, and 1.9 x 10~(-13) and 1.3 x 10~(-12) s~(-1) for z < 1 and z > 1, respectively. The inclusion of blazars, associated absorbers, or damped Lyα absorbers, or the consideration of a ΛCDM cosmology rather than one in which Ω_Λ = 0 has no significant effect on the results. The result obtained using radio-loud objects is not significantly different from that found using radio-quiet objects. Allowing for a variable equivalent width threshold gives a consistently larger value of J(v_0) than the constant threshold treatment, though this is found to be sensitive to the inclusion of a small number of weak lines near the QSO emission redshifts. This work confirms that the evolution of the number density of Lyα lines is driven by a decrease in the ionizing background from z ～ 2 to z ～ 0 as well as by the formation of structure in the intergalactic medium.
机译：在我们的系列论文“ z = 0-5的Lyα森林的均匀分析”的论文Ⅲ中，我们从哈勃太空望远镜（HST）上的微弱天体光谱仪（FOS）档案中提出了一套270个类星体光谱。这些光谱共有151条，产生906条谱线，适用于在低红移条件下使用邻近效应信号来测量J（v_0），即氢电离背景辐射场的平均强度。使用最大似然技术并对每个QSO的莱曼极限通量和系统红移进行最佳估计，我们发现J（v_0）= 7.6 _（-3.0）〜（+9.4）x 10〜（-23）erg s〜（ -1）cm〜（-2）Hz〜（-1）sr〜（-1）在0.03 1的行组成）时，找到的J（v_0）的值为6.5 _（-1.6）〜（+3.8）x 10〜（-23）erg s 〜（-1）cm〜（-2）Hz〜（-1）sr〜（-1）和1.0 _（-0.2）〜（+3.8）x 10〜（-22）erg s〜（-1） cm〜（-2）Hz〜（-1）sr〜（-1），分别表示背景的平均强度在此数据集的红移范围内演变。放宽假设样品光谱和背景的光谱形状相同的假设，发现所有红移的最佳拟合HⅠ光电离速率为6.7 x 10〜（-13）s〜（-1），并且z <1和z> 1分别为1.9 x 10〜（-13）和1.3 x 10〜（-12）s〜（-1）。包含大酒瓶，相关的吸收剂或阻尼的Lyα吸收剂，或者考虑使用ΛCDM宇宙学，而不是考虑其中Ω_Λ= 0不会对结果产生重大影响。使用无线电大声对象获得的结果与使用无线电无声对象发现的结果没有显着差异。尽管发现这对QSO发射红移附近包含少量弱线很敏感，但允许可变的等效宽度阈值给出的J（v_0）值始终大于恒定阈值处理。这项工作证实，Lyα线数密度的演化是由电离本底从z〜2降低到z〜0以及在银河系中间介质中形成结构驱动的。

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