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arXiv 1903.08705astro-ph.GA
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$\mathrm{z\sim1}$星系的分光光度红移和用WFIRST和Euclid预言数密度

Spectrophotometric redshifts for $\mathrm{z\sim1}$ galaxies and predictions for number densities with WFIRST and Euclid

Bhavin A. Joshi, Seth Cohen, Rogier A. Windhorst, Rolf Jansen, Norbert Pirzkal, Nimish P. Hathi

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16 pages, 8 figures. Accepted for publication in ApJ
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摘要：

利用哈勃空间望远镜（{ \it HST}）的棱镜数据和测光方法，研究了4000 nm/Balmer折点红移的精度。棱镜光谱来自探测演化和再电离光谱（PEARS）勘测，其中使用高级勘测相机（ACS）上的G800 L棱镜使用{ \it HST}。测光数据来自3D-HST合作的多个调查（特别是CANDELS和3D-HST）的成像汇编。我们证明了分光光度红移（SPZ）通常能使光度红移的精度提高$\sim$ 17- 60\ %。我们的SPZ方法是一个基于模板拟合的例程，通过协方差矩阵形式主义的棱镜光谱内的相邻点之间的相关数据，也占沿色散方向的星系形态。我们表明，SPZ的鲁棒性直接关系到D4000测量的保真度。我们还估计了基于连续谱的红移的准确性，即，对于不包含强发射线的星系，仅基于棱镜数据（$σ^{\rm NMAD}_{Δz/(1+z)}{\lesssim}0.06$）。鉴于未来的空间为基础的天文台，如WFIRST和欧几里得将花费大量的时间在无狭缝光谱观测，我们估计数密度与$\ | \mathrm{Δz/(1+z_{s})} \ | \leq 0.02$的对象。我们预测$\sim$ 700- 4400星系/度$^2$的星系与D4000 $>$ 1.1和$\ | \mathrm{Δz/(1+z_{s})} \ | \leq 0.02$的极限深度$i_{AB}$ =24马格。这是\emph{especially}重要的，在缺乏一个伴随的丰富的光度数据集，如现有的一个为坎德尔领域，未来观测的红移精确度将仅依赖于像4000埃/巴耳末突变这样的特征的存在，或者棱栅光谱中发射线的存在。

英文摘要：

We investigate the accuracy of 4000Å/Balmer-break based redshifts by combining Hubble Space Telescope ({\it HST}) grism data with photometry. The grism spectra are from the Probing Evolution And Reionization Spectroscopically (PEARS) survey with {\it HST} using the G800L grism on the Advanced Camera for Surveys (ACS). The photometric data come from a compilation by the 3D-HST collaboration of imaging from multiple surveys (notably CANDELS and 3D-HST). We show evidence that spectrophotometric redshifts (SPZs) typically improve the accuracy of photometric redshifts by $\sim$17--60\%. Our SPZ method is a template fitting based routine which accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism and also accounts for galaxy morphology along the dispersion direction. We show that the robustness of the SPZ is directly related to the fidelity of the D4000 measurement. We also estimate the accuracy of continuum-based redshifts, i.e., for galaxies that do not contain strong emission lines, based on the grism data alone ($σ^{\rm NMAD}_{Δz/(1+z)}{\lesssim}0.06$). Given that future space-based observatories like WFIRST and Euclid will spend a significant fraction of time on slitless spectroscopic observations, we estimate number densities for objects with $\ | \mathrm{Δz/(1+z_{s})} \ | \leq 0.02$. We predict $\sim$700--4400 galaxies/degree$^2$ for galaxies with D4000$>$1.1 and $\ | \mathrm{Δz/(1+z_{s})} \ | \leq 0.02$ to a limiting depth of $i_{AB}$=24 mag. This is \emph{especially} important in the absence of an accompanying rich photometric dataset like the existing one for the CANDELS fields, where redshift accuracy from future surveys will rely only on the presence of a feature like the 4000Å/Balmer breaks or the presence of emission lines within the grism spectra.

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