MAMMOTH-Subaru V.宇宙变化对$z=2.2-2.3$上Ly $α$光度函数的影响
MAMMOTH-Subaru V. Effects of Cosmic Variance on Ly$α$ Luminosity Functions at $z=2.2-2.3$
摘要：
在观测小体积的高z宇宙时，宇宙方差给星系数密度特性带来了很大的不确定性，这种不确定性在观测天文学中产生了星系数$σ_{g}$的场间方差。这种不确定性显著影响了Lya发射体（LAEs）的亮度函数（LF）测量。对于大多数以前的Lya LF研究，$σ_{g}$通常是从宇宙学模拟的预测中采用的，但几乎没有得到观测的证实。测量宇宙方差需要大量的样本，超过了大多数天文仪器的能力。在这项研究中，我们展示了一种观测方法来测量宇宙方差贡献的$z\approx2.2$ Lya LF。使用Subaru/Hyper Suprime-Cam（HSC）的窄带和宽带观测LAE候选者，具有8个独立的字段，使总调查区域$\simeq11.62$ deg $^2$和共动体积为$\simeq8.71\times10^6$ Mpc $^3$。这八个领域是使用MAMMOTH项目选择的。我们报告了一个最佳拟合Schechter函数，参数$α=-1.75$（固定），$L_{Lyα}^{*}=5.18_{-0.40}^{+0.43} \times 10^{42}$ erg s $^{-1}$和$ϕ_{Lya}^{*}=4.87_{-0.55}^{+0.54}\times10^{-4}$ Mpc $^{-3}$的整体Lya LF。裁剪出的区域，可以偏差的宇宙方差测量后，我们计算$σ_{g}$，通过采样LAE内的多个点上分配的字段图像。研究了$σ_{g}$和调查体积$V$之间的关系，拟合出一个简单的幂律：$σ_g=k\times(\frac{V_{\rm eff}}{10^5 {\rm Mpc}^3})^β$。我们发现最佳拟合值的$-1.209_{-0.106}^{+0.106}$的$β$和$0.986_{-0.100}^{+0.108}$的k。我们比较我们的测量与模拟预测，发现LAEs的宇宙方差可能比一般的恒星形成星系。
英文摘要：
Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-z Universe with a small volume, such uncertainties produce the field-to-field variance of galaxy number $σ_{g}$ in observational astronomy. This uncertainty significantly affects the Luminosity Functions (LF) measurement of Lya Emitters (LAEs). For most previous Lya LF studies, $σ_{g}$ is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for $z\approx2.2$ Lya LFs. The LAE candidates are observed using narrowband and broadband of the Subaru/Hyper Suprime-Cam (HSC), with 8 independent fields, making the total survey area $\simeq11.62$deg$^2$ and a comoving volume of $\simeq8.71\times10^6$Mpc$^3$. These eight fields are selected using the project of MAMMOTH. We report a best-fit Schechter function with parameters $α=-1.75$ (fixed), $L_{Lyα}^{*}=5.18_{-0.40}^{+0.43} \times 10^{42}$erg s$^{-1}$ and $ϕ_{Lya}^{*}=4.87_{-0.55}^{+0.54}\times10^{-4}$Mpc$^{-3}$ for the overall Lya LFs. After clipping out the regions that can bias the cosmic variance measurements, we calculate $σ_{g}$, by sampling LAEs within multiple pointings assigned on the field image. We investigate the relation between $σ_{g}$ and survey volume $V$, and fit a simple power law: $σ_g=k\times(\frac{V_{\rm eff}}{10^5 {\rm Mpc}^3})^β$. We find best-fit values of $-1.209_{-0.106}^{+0.106}$ for $β$ and $0.986_{-0.100}^{+0.108}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs might be larger than that of general star-forming galaxies.
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