Constraining the Contribution of Galaxies and Active Galactic Nuclei to Cosmic Reionization
Constraining the Contribution of Galaxies and Active Galactic Nuclei to Cosmic Reionization
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DOI：
10.1093/mnras/stx1754
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发表时间：
2016-02
影响因子：
4.8
通讯作者：
S. Yoshiura;K. Hasegawa;K. Ichiki;H. Tashiro;Hayato Shimabukuro;Keitaro Takahashi
中科院分区：
文献类型：
--
作者：
S. Yoshiura;K. Hasegawa;K. Ichiki;H. Tashiro;Hayato Shimabukuro;Keitaro Takahashi
了解宇宙再电离的详细过程是天体物理学和宇宙学的遗留问题之一。本文建立了一个包括高z值星系和活动星系核(AGN)贡献的宇宙再电离模型，并用该模型计算了再电离和热历史。为了保持模型的通用性和真实性，我们在观测到的宇宙恒星形成历史和观测到的亮端UV光度函数的约束下，改变了电离光子的逃逸分数f_rM ESC}$和活动星系核光度函数在高红移时的微弱端斜率α_rM HZ}$。此外，我们还模拟了活动星系核的光谱能量分布(SED)，它依赖于爱丁顿比和黑洞质量。通过将计算的再电离历史与观测到的离子{H}{i}组分和汤姆逊散射的普朗克散射光学厚度进行比较，我们发现当我们使用Giallongo等人得到的亮端光度函数时，α_(Rm)Hzt；-1.5$和$f_(Rm)ESC}<；0.15$是有利的。我们的结果表明，活动星系核占主导地位的模型，其微弱活动星系核的丰度与Giallongo等人的估计相同。只有在高z星系的贡献几乎可以忽略的情况下才允许，而星系主导的模型也是允许的。我们还发现SED的形状对热历史有很大的影响。因此，预计对IGM热状态的测量将提供有关电离源性质的有用信息。
Understanding the detailed process of cosmic reionization is one of the remaining problems in astrophysics and cosmology. Here we construct a model of cosmic reionization that includes contribution from high-$z$ galaxies and active galactic nuclei (AGNs), and calculate the reionization and thermal histories with the model. To keep the model to be general and realistic, we vary the escape fraction of ionizing photons, $f_{\rm esc}$, and the faint-end slope of the AGN luminosity function at high redshifts, $\alpha_{\rm hz}$, within the constraints from the observed cosmic star formation history and the observed bright-end UV luminosity functions at $z \leq 6$. Additionally, we model the spectral energy distribution (SED) of AGNs which depends on the Eddington ratio and the black-hole mass. By comparing the computed reionization histories with the observed \ion{H}{i} fractions and the optical depth for Thomson scattering from Planck, we find that $\alpha_{\rm hz} > -1.5$ and $f_{\rm esc} < 0.15$ are favored when we employ the bright-end luminosity function obtained by Giallongo et al. Our result suggests that an AGN-dominated model with the abundance of faint-AGNs being as large as the estimate by Giallongo et al. is allowed only if the contribution from high-z galaxies is almost negligible, while a galaxy-dominant model is also allowed. We also find that the shape of SED has a significant impact on the thermal history. Therefore it is expected that measurements of the thermal state of the IGM provide useful information on properties of ionizing sources.