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arXiv 1402.6566astro-ph.CO
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从星系红移巡天恢复Local Group运动

On the recovery of Local Group motion from galaxy redshift surveys

Adi Nusser, Marc Davis, Enzo Branchini

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14 pages, 7 figures
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摘要：

在全天红移巡天中，观测到的本星系群相对于宇宙微波背景的运动与基于大尺度结构引力场的线性理论预测存在着$\sim 150 km s^{-1}$差异。我们进行了各种测试，表明LG运动不能恢复到比$150-200 km s^{-1}$更好的幅度和$\approx10^\circ$内的方向。这些测试依赖于千禧年模拟中使用半解析星系形成模型确定的模拟星系目录。我们将这些结果与$K_s=11.75$双质量星系红移巡天进行了比较，该巡天提供了迄今为止最深、最宽和最完整的星系空间分布。在我们的分析中，我们使用一个新的，简洁的关系推导LG运动和整体流量的星系在红移空间的真实分布。我们的研究结果表明，不确定性的主要来源是小的有效深度的调查，如2MRS，防止适当的采样的大尺度结构超过$\sim100 h^{-1} Mpc$。为了达到$Λ$ CDM宇宙中$\approx 250 h^{-1}Mpc $的“收敛尺度”，需要更深的红移测量。更深入的调查还将减轻“凯撒火箭”的影响，在2MRS这样的调查中，凯撒火箭仍然是一个重要的不确定性来源。由于LG的安静和适度的密度环境，线性预测的纯动力学不确定性在$\sim 90 km s^{-1}$的水平上是次主导的。最后，我们表明，从线性星系偏置和散粒噪声误差的偏差提供了一个较小的贡献，总的误差预算。

英文摘要：

There is a $\sim 150 km s^{-1}$ discrepancy between the measured motion of the Local Group of galaxies (LG) with respect to the CMB and the linear theory prediction based on the gravitational force field of the large scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than $150-200 km s^{-1}$ in amplitude and within a $\approx10^\circ$ in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the $K_s=11.75$ Two-Mass Galaxy Redshift Survey, which provides the deepest, widest and most complete spatial distribution of galaxies available so far. In our analysis we use a new, concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the 2MRS that prevents a proper sampling of the large scale structure beyond $\sim100 h^{-1} Mpc$. Deeper redshift surveys are needed to reach the "convergence scale" of $\approx 250 h^{-1}Mpc $ in a $Λ$CDM universe. Deeper survey would also mitigate the impact of the "Kaiser rocket" which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of $\sim 90 km s^{-1}$. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget.

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