One of the principal systematic constraints on the Epoch of Reionisation (EoR) experiment is the accuracy of the foreground calibration model. Recent results have shown that highly accurate models of extended foreground sources, and including models for sources in both the primary beam and its sidelobes, are necessary for reducing foreground power. To improve the accuracy of the source models for the EoR fields observed by the Murchison Widefield Array (MWA), we conducted the MWA Long Baseline Epoch of Reionisation Survey (LoBES). This survey consists of multi-frequency observations of the main MWA EoR fields and their eight neighbouring fields using the MWA Phase II extended array. We present the results of the first half of this survey centred on the MWA EoR0 observing field (centred at RA(J2000) 0 h, Dec(J2000) -27 deg). This half of the survey covers an area of 3069 degrees$^2$, with an average rms of 2.1 mJy beam$^{-1}$. The resulting catalogue contains a total of 80824 sources, with 16 separate spectral measurements between 100 and 230 MHz, and spectral modelling for 78$\%$ of these sources. Over this region we estimate that the catalogue is 90$\%$ complete at 32 mJy, and 70$\%$ complete at 10.5~mJy. The overall normalised source counts are found to be in good agreement with previous low-frequency surveys at similar sensitivities. Testing the performance of the new source models we measure lower residual rms values for peeled sources, particularly for extended sources, in a set of MWA Phase I data. The 2-dimensional power spectrum of these data residuals also show improvement on small angular scales -- consistent with the better angular resolution of the LoBES catalogue. It is clear that the LoBES sky models improve upon the current sky model used by the Australian MWA EoR group for the EoR0 field.
The redshifted cosmological 21 cm signal emitted by neutral hydrogen during the first billion years of the universe is much fainter relative to other galactic and extragalactic radio emissions, posing a great challenge towards detection of the signal. Therefore, precise instrumental calibration is a vital prerequisite for the success of radio interferometers such as the Murchison Widefield Array (MWA), which aim for a 21 cm detection. Over the previous years, novel calibration techniques targeting the power spectrum paradigm of EoR science have been actively researched and where possible imple…
The detection of redshifted hyperfine line of neutral hydrogen (HI) is the most promising probe of the Epoch of Reionization (EoR). We report an analysis of 55 hours of Murchison Widefield Array (MWA) Phase II drift scan EoR data. The data correspond to a central frequency $ν_0 = 154.24 \, \rm MHz$ ($z\simeq 8.2$ for the redshifted HI hyperfine line) and bandwidth $B = 10.24 \, \rm MHz$. As one expects greater system stability in a drift scan, we test the system stability by comparing the extracted power spectra from data with noise simulations and show that the power spectra for the cleanest …
We use the latest multi-redshift ($z=6.5-8.7$) upper limits on the 21-cm signal from the Murchison Widefield Array (MWA) to explore astrophysical models which are inconsistent with the data. These upper limits are achieved using 298 h of carefully excised data over four observing seasons. To explore these upper limits in the context of reionisation astrophysics, we use 21CMMC. We then connect the disfavoured regions of parameter space to existing observational constraints on reionisation such as high-$z$ galaxy ultra-violet (UV) luminosity functions, background UV photoionisation rate, interga…
The Murchison Widefield Array Phase III upgrade: Sensitivity Doubled, Number of Baselines Quadrupled, Flexibility Enhanced, and EoR Observations Optimised
International Centre for Radio Astronomy Research, Curtin University（国际射电天文研究中心，科廷大学）；Curtin Institute for Data Science, Curtin University（科廷数据科学研究所，科廷大学）；SKA Observatory（平方公里阵列巡天望远镜观测站）；Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)（三维全天空天体物理学卓越中心 (ASTRO 3D)）
We investigate the contribution of extended radio sources such as Centaurus A, and Galactic supernova remnants (SNRs) to our ability to detect the statistical $21\,\rm{cm}$ signal from the Epoch of Reionisation (EoR) with the Murchison Widefield Array (MWA). These sources are typically ignored because they are in highly attenuated parts of the MWA primary beam, however in aggregate these sources have apparent flux densities of $10\,\rm{Jy}$ on angular scales we expect to detect the $21\,\rm{cm}$ signal. We create bespoke multi-component 2D Gaussian models for Galactic SNRs and for Centaurus A,…
SKA-Low simulations for a cosmic dawn/epoch of reionisation deep field
SKA Observatory（SKA天文台）；Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学学院乔德雷尔银行天体物理学中心）；Department of Physics and Astronomy, University of Pennsylvania（宾夕法尼亚大学物理与天文学系）；LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université（巴黎天文台卢克斯实验室，PSL研究大学，法国国家科学研究中心，索邦大学）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；INAF – Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学校物理实验室，PSL大学，法国国家科学研究中心，索邦大学，巴黎大学）；International Centre for Radio Astronomy Research, Curtin University（科廷大学国际射电天文研究中心）；ARC Centre of Excellence for All-Sky Astrophysics in 3D（ARC三维全天体物理学卓越中心）
Preparing for the first detection of the cosmic 21-cm signal from large-scale interferometer experiments requires rigorous testing of the data analysis and reduction pipelines. To validate that these pipelines do not erroneously remove or add features that can mimic the cosmic signal (e.g. from side-lobes or large-scale power leakage), we require reionisation simulations larger than the experiments primary field of view. For an experiment such as the MWA, with a field of view of $\sim25^{2}$ deg.$^{2}$, this would require a simulation of several Gpcs, which is currently infeasible. To overcome…
We present a broadband map of polarized diffuse emission at 167-198 MHz developed from data from the Murchison Widefield Array (MWA). The map is designed to improve visibility simulation and precision calibration for 21 cm Epoch of Reionization (EoR) experiments. It covers a large swath - 11,000 sq. deg. - of the Southern Hemisphere sky in all four Stokes parameters and captures emission on angular scales of 1 to 9 degrees. The band-averaged diffuse structure is predominantly unpolarized but has significant linearly polarized structure near RA = 0 h. We evaluate the accuracy of the map by comb…
Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation
我们应用贝叶斯统计，通过Multinest算法对不同的再电离场景进行模型选择。首先，我们恢复了21 CMMC的结果，用于21 cmFAST模型的参数估计。我们继续测试几个玩具模型的时代的Reionisation（EoR）定义的对比形态和规模。我们发现，LOFAR观测不太可能允许模型选择，即使有很长的集成时间。HERA需要61个偶极子在1080小时内进行相同的分析，并与具有217个偶极子的SKA相当。我们发现SKA只需要324小时的观察就可以最终区分我们的模型。一旦模型选择是可以实现的，观察先验的分析进行发现，中性分数检查在特定的红移添加很少或没有推论。我们在一个模型内区分基准参数或区分星系与一个常数与幂律质光比的水平模型选择的困难。最后，我们探索使用Savage-Dickey密度比来显示参数Rmfp在21 cm FAST内的冗余。
Stations of dipole antennas for SKA1-Low will comprise 256 elements spread over an area with a diameter of 38~m. We consider the effect of residual unsubtracted sources well outside of the main beam for differing numbers of unique station configurations, in the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD), both in simulation and with theoretical considerations. We find that beam sidelobes imprint power that renders the cosmological signal unobservable over a range of scales unless compact sources are subtracted beyond θ_Z=30 degrees from zenith, and that station apodization will likely…
Current attempts to measure the 21cm Power Spectrum of neutral hydrogen during the Epoch of Reionization are limited by systematics which produce measured upper limits above both the thermal noise and the expected cosmological signal. These systematics arise from a combination of observational, instrumental, and analysis effects. In order to further understand and mitigate these effects, it is instructive to explore different aspects of existing datasets. One such aspect is the choice of observing field. To date, MWA EoR observations have largely focused on the EoR0 field. In this work, we pre…
21cm Intensity Mapping (IM) has been proposed about 15 years ago as a cost effective method to carry out cosmological surveys and to map the 3D distribution of matter in the universe, over a large range of post EoR redshifts, from z=0 to z=6. Since then a number of pathfinder instruments have been built, such as CHIME or Tianlai. Several other ones will be commissioned in the next few years (HIRAX, CHORD, BINGO), while even larger arrays, with several thousand antennae are being considered for the next generation experiments. We will briefly review the 21cm cosmology of the Epoch of Reionisati…
