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arXiv 1909.09609astro-ph.COastro-ph.GAastro-ph.HEgr-qc
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奇异速度对由引力波标准Sirens估算哈勃常数的影响

The Impact of Peculiar Velocities on the Estimation of the Hubble Constant from Gravitational Wave Standard Sirens

Constantina Nicolaou, Ofer Lahav, Pablo Lemos, William Hartley, Jonathan Braden

摘要:

在这项工作中,我们研究了系统的不确定性所产生的计算时的特殊速度估计的哈勃常数($H_0$)从引力波标准警报。我们研究了GW170817事件及其宿主星系NGC4993的奇异速度的估计,当对邻近星系进行高斯平滑时。NGC 4993是一个相对较近的星系,在$\sim 40 \ {\rm Mpc}$之外,受到特殊速度的显著影响。我们证明了一个直接依赖于估计的特殊速度值的平滑尺度的选择。我们表明,当不考虑这个系统,$\sim 200 \ {\rm km \ s ^{-1}}$在特有的速度的偏见引起的偏见$\sim 4 \ {\rm km \ s ^{-1} \ Mpc^{-1}}$的哈勃常数。我们制定了一个贝叶斯模型,该模型解释了特殊的速度对平滑尺度的依赖性,并通过边缘化这个参数,我们消除了选择平滑尺度的需要。所提出的模型产生$H_0 = 68.6 ^{+14.0}_{-8.5}~{\rm km\ s^{-1}\ Mpc^{-1}}$。我们证明,在这个模型下,一个更强大的无偏估计的哈勃常数从附近的GW源。

英文摘要:

In this work we investigate the systematic uncertainties that arise from the calculation of the peculiar velocity when estimating the Hubble constant ($H_0$) from gravitational wave standard sirens. We study the GW170817 event and the estimation of the peculiar velocity of its host galaxy, NGC 4993, when using Gaussian smoothing over nearby galaxies. NGC 4993 being a relatively nearby galaxy, at $\sim 40 \ {\rm Mpc}$ away, is subject to a significant effect of peculiar velocities. We demonstrate a direct dependence of the estimated peculiar velocity value on the choice of smoothing scale. We show that when not accounting for this systematic, a bias of $\sim 200 \ {\rm km \ s ^{-1}}$ in the peculiar velocity incurs a bias of $\sim 4 \ {\rm km \ s ^{-1} \ Mpc^{-1}}$ on the Hubble constant. We formulate a Bayesian model that accounts for the dependence of the peculiar velocity on the smoothing scale and by marginalising over this parameter we remove the need for a choice of smoothing scale. The proposed model yields $H_0 = 68.6 ^{+14.0}_{-8.5}~{\rm km\ s^{-1}\ Mpc^{-1}}$. We demonstrate that under this model a more robust unbiased estimate of the Hubble constant from nearby GW sources is obtained.

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