Foregrounds in Wide-Field Redshifted 21 cm Power Spectra
Nithyanandan Thyagarajan, Daniel C. Jacobs, Judd D. Bowman, N. Barry, A. P. Beardsley, G. Bernardi, F. Briggs, R. J. Cappallo, P. Carroll, B. E. Corey, A. de Ol… 展开作者
Nithyanandan Thyagarajan, Daniel C. Jacobs, Judd D. Bowman, N. Barry, A. P. Beardsley, G. Bernardi, F. Briggs, R. J. Cappallo, P. Carroll, B. E. Corey, A. de Oliveira-Costa, Joshua S. Dillon, D. Emrich, A. Ewall-Wice, L. Feng, R. Goeke, L. J. Greenhill, B. J. Hazelton, J. N. Hewitt, N. Hurley-Walker, M. Johnston-Hollitt, D. L. Kaplan, J. C. Kasper, Han-Seek Kim, P. Kittiwisit, E. Kratzenberg, E. Lenc, J. Line, A. Loeb, C. J. Lonsdale, M. J. Lynch, B. McKinley, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, A. R. Neben, D. Oberoi, A. R. Offringa, S. M. Ord, Sourabh Paul, B. Pindor, J. C. Pober, T. Prabu, P. Procopio, J. Riding, A. E. E. Rogers, A. Roshi, N. Udaya Shankar, Shiv K. Sethi, K. S. Srivani, R. Subrahmanyan, I. S. Sullivan, M. Tegmark, S. J. Tingay, C. M. Trott, M. Waterson, R. B. Wayth, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams, C. Wu, J. S. B. Wyithe
Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor ~100 with negligible loss of sensitivity.
Quantifying Foreground Contamination in the Dark Ages 21 cm Power Spectrum Using an Electromagnetically Simulated Dipole Antenna Atop a Dielectric Surface
Brown University（布朗大学）；National Radio Astronomy Observatory（国家射电天文台）；University of Colorado Boulder（科罗拉多大学博尔德分校）；Lunar Resources, Inc.（月球资源公司）
Bayesian power spectrum estimation with modelling of systematic effects in delay-fringe rate space
Jodrell Bank Centre for Astrophysics, University of Manchester（曼彻斯特大学乔德雷尔银行天体物理学中心）；Department of Physics and Astronomy, University of Western Cape（西开普大学物理与天文系）；Department of Physics and Trottier Space Institute, McGill University（麦吉尔大学物理系和特罗蒂尔太空研究所）
Optimizing spectral-matching component separation for measuring CMB B-mode polarization with a satellite mission
Université Paris Cité（巴黎西岱大学）；CNRS（法国国家科学研究中心）；Astroparticule et Cosmologie（亚原子粒子与宇宙学）；ILANCE, CNRS – University of Tokyo International Research Laboratory（ILANCE，日本东京大学-法国国家科学研究中心国际研究实验室）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, The University of Tokyo（东京大学宇宙物质前沿研究所（Kavli IPMU））；Université Paris-Saclay（巴黎萨克雷大学）；IJCLab（伊夫·让勒默物理研究所）
A General Bayesian Framework for Foreground Modelling and Chromaticity Correction for Global 21cm Experiments
HI 21 cm吸收线被明亮的前景和系统失真所掩盖，这些失真是由于用于使观测耦合到这些前景的光谱不均匀性的天线的色度而产生的。我们证明，这些失真是足以掩盖21厘米的信号时，天线是不完美的消色差和简单的校正假设一个恒定的空间分布的前景功率是不足以克服它们。然后，我们提出了一个新的物理动机的方法建模的前景21厘米的实验，以适应作为前景的一部分，色彩失真。这是通过将天空划分为$N$区域并在每个区域中假设不同的均匀光谱指数来缩放底图来生成跨观测波段的模拟天空模型来完成的。然后，可以将得到的天空图与天线波束模型进行卷积，以给出由$N$区域的光谱指数参数化的前景和色度模型。我们证明，拟合此模型的不同$N$使用贝叶斯嵌套抽样算法和比较结果使用的证据允许21厘米的信号被可靠地检测到的数据中的一个相对平滑的圆锥形日志螺旋天线。我们还测试了一个更彩色圆锥形正弦天线，发现这个模型不会产生一个可靠的信号检测，但在一种方式，很容易区分从一个真正的检测。
