分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmic microwave background (CMB), carrying the inhomogeneous information of the very early universe, is of great significance for understanding the origin and evolution of our universe. However, observational CMB maps contain serious foreground contaminations from several sources, such as galactic synchrotron and thermal dust emissions. Here, we build a deep convolutional neural network (CNN) to recover the tiny CMB signal from various huge foreground contaminations. Focusing on the CMB temperature fluctuations, we find that the CNN model can successfully recover the CMB temperature maps with high accuracy, and that the deviation of the recovered power spectrum $C_\ell$ is smaller than the cosmic variance at $\ell>10$. We then apply this method to the current Planck observation, and find that the recovered CMB is quite consistent with that disclosed by the Planck collaboration, which indicates that the CNN method can provide a promising approach to the component separation of CMB observations. Furthermore, we test the CNN method with simulated CMB polarization maps based on the CMB-S4 experiment. The result shows that both the EE and BB power spectra can be recovered with high accuracy. Therefore, this method will be helpful for the detection of primordial gravitational waves in current and future CMB experiments. The CNN is designed to analyze two-dimensional images, thus this method is not only able to process full-sky maps, but also partial-sky maps. Therefore, it can also be used for other similar experiments, such as radio surveys like the Square Kilometer Array.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Primordial B-mode detection is one of the main goals of the current and future CMB experiments. However, the weak B-mode signal is overshadowed by several Galactic polarized emissions, such as the thermal dust emission and the synchrotron radiation. Subtracting the foreground components from CMB observations is one of the key challenges in the search for primordial B-mode signal. Here, we construct a deep convolutional neural network (CNN) model, called CMBFSCNN (Cosmic Microwave Background Foreground Subtraction with CNN), which can cleanly remove various foreground components from the simulated CMB observational maps with the sensitivity of the CMB-S4 experiment. The noisy CMB Q (or U) maps are recovered with a mean absolute difference of $0.018 \pm 0.023\ \mu$K (or $0.021 \pm 0.028\ \mu$K). To remove residual instrumental noise in the foreground-cleaned map, inspired by the Needlet Internal Linear Combination method, we divide the whole data into two ``half-split maps'' which share the same sky signal but with uncorrelated noise, and perform the cross-correlation technique to reduce the instrumental noise effect at the power spectrum level. We find that the CMB EE and BB power spectra can be precisely recovered with significantly reduced noise effects. Finally, we apply this pipeline on the current Planck observations. As expected, various foregrounds have been cleanly removed on the Planck observational maps and the recovered EE and BB power spectra are in good agreement with the Planck official results.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Primordial B-mode detection is one of the main goals of the current and future CMB experiments. However, the weak B-mode signal is overshadowed by several Galactic polarized emissions, such as the thermal dust emission and the synchrotron radiation. Subtracting the foreground components from CMB observations is one of the key challenges in the search for primordial B-mode signal. Here, we construct a deep convolutional neural network (CNN) model, called CMBFSCNN (Cosmic Microwave Background Foreground Subtraction with CNN), which can cleanly remove various foreground components from the simulated CMB observational maps with the sensitivity of the CMB-S4 experiment. The noisy CMB Q (or U) maps are recovered with a mean absolute difference of $0.018 \pm 0.023\ \mu$K (or $0.021 \pm 0.028\ \mu$K). To remove residual instrumental noise in the foreground-cleaned map, inspired by the Needlet Internal Linear Combination method, we divide the whole data into two ``half-split maps'' which share the same sky signal but with uncorrelated noise, and perform the cross-correlation technique to reduce the instrumental noise effect at the power spectrum level. We find that the CMB EE and BB power spectra can be precisely recovered with significantly reduced noise effects. Finally, we apply this pipeline on the current Planck observations. As expected, various foregrounds have been cleanly removed on the Planck observational maps and the recovered EE and BB power spectra are in good agreement with the Planck official results.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Time-ordered data (TOD) from ground-based CMB experiments are generally filtered before map-making to remove or reduce the contamination from the ground and the atmospheric emissions. However, when the observation region contains strong point sources, the filtering process will result in considerable leakage around the point sources in a measured CMB map, and leave spurious polarization signals. Therefore, such signals need to be assessed and removed before CMB science exploitation. In this work, we present a new method that we call "template fitting" and can effectively remove these leakage signals in pixel domain, not only satisfying the requirement for measuring primordial gravitational waves from CMB-$B$ modes, but also avoiding time-consuming operations on TOD.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Time-ordered data (TOD) from ground-based CMB experiments are generally filtered before map-making to remove or reduce the contamination from the ground and the atmospheric emissions. However, when the observation region contains strong point sources, the filtering process will result in considerable leakage around the point sources in a measured CMB map, and leave spurious polarization signals. Therefore, such signals need to be assessed and removed before CMB science exploitation. In this work, we present a new method that we call "template fitting" and can effectively remove these leakage signals in pixel domain, not only satisfying the requirement for measuring primordial gravitational waves from CMB-$B$ modes, but also avoiding time-consuming operations on TOD.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Internal Linear Combination (ILC) is widely used to extract the cosmic microwave background (CMB) signal from multi-frequency observation maps, especially for Satellite experiments with quasi-full sky coverage. We extend ILC method to CMB polarization map analysis with a small sky patch which is especially typical for ground-based experiments, by combing ILC with a template cleaning method which can give pure $B$ map free from $EB$ leakage caused by partial sky coverage. The feature of our methods is that we do the ILC analysis on pseudo-scalar $B$ maps, and the advantage is that it totally avoids the impact of $EB$ leakage on ILC, so that it can improve the efficiency of component separation dramatically. We demonstrate our methods with mock data of a future ground-based experiment with a deep survey on a clean patch in the northern sky, and the results show that the level of foreground residual can be well controlled, it biases the tensor to scalar ratio ($r$) at the order of $10^{-3}$ which is comparable to the statistical error by noise.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
Hong Li
Si-Yu Li
Yang Liu
Yong-Ping Li
Yifu Cai
Mingzhe Li
Gong-Bo
Zhao
Cong-Zhan Liu
Zheng-Wei Li
He Xu
Di Wu
Yong-Jie Zhang
Zu-Hui
Fan
Yong-Qiang Yao
Chao-Lin Kuo
Fang-Jun Lu
Xinmin Zhang
摘要： In this paper, we will give a general introduction to the project of Ali CMB Polarization Tele-scope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many di erent institutes in China. It is the rst ground-based cosmic microwave background (CMB) polarization experiment in China and an integral part of China's Gravitational Waves Program. The main scienti c goal of AliCPT project is to probe the primor-dial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The rst stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with 3 years' observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years' observation will improve the current limit by two order of magnitude.
分类： 物理学 >> 核物理学 提交时间： 2016-09-19
摘要： The study of reionization history plays an important role in understanding the evolution of our universe. It is commonly believed that the intergalactic medium (IGM) in our universe are fully ionized today, however the reionizing process remains to be mysterious. A simple instantaneous reionization process is usually adopted in modern cosmology without direct observational evidence. However, the history of ionization fraction, xe(z) will influence cosmic microwave background (CMB) observables and constraints on optical depth τ. With the mocked future data sets based on featured reionization model, we find the bias on τ introduced by instantaneous model can not be neglected. In this paper, we study the cosmic reionization history in a model independent way, the so called principle component analysis (PCA) method, and reconstruct xe(z) at different redshift z with the data sets of Planck, WMAP 9 years temperature and polarization power spectra, combining with the baryon acoustic oscillation (BAO) from galaxy survey and type Ia supernovae (SN) Union 2.1 sample respectively. The results show that reconstructed xe(z) is consistent with instantaneous behavior, however, there exists slight deviation from this behavior at some epoch. With PCA method, after abandoning the noisy modes, we get stronger constraints, and the hints for featured xe(z) evolution could become a little more obvious.
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