分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from compact binary coalescences encode the absolute luminosity distances of GW sources. Once the redshifts of GW sources are known, one can use the distance-redshift relation to constrain cosmological parameters. One way to obtain the redshifts is to localize GW sources by GW observations and then use galaxy catalogs to determine redshifts from a statistical analysis of redshift information of the potential host galaxies, and such GW data are commonly referred to as dark sirens. The third-generation (3G) GW detectors are planned to work in the 2030s and will observe numerous compact binary coalescences. Using these GW events as dark sirens requires high-quality galaxy catalogs from future sky survey projects. The China Space Station Telescope (CSST) will be launched in 2024 and will observe billions of galaxies within a 17500 deg$^2$ survey area up to $z\sim 4$, providing photometric and spectroscopic galaxy catalogs. In this work, we simulate the CSST galaxy catalog and the 5-year GW data, and combine them to infer the Hubble constant ($H_0$). Our results show that the measurement precision of $H_0$ could reach better than $0.005\%$, which is an astonishing precision for the Hubble constant measurement. We conclude that the synergy between the 3G GW detectors and CSST will be of far-reaching importance in dark-siren cosmology.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Steven Cunnington
Laura Wolz
Philip Bull
Isabella P. Carucci
Keith Grainge
Melis O. Irfan
Yichao Li
Alkistis Pourtsidou
Mario G. Santos
Marta Spinelli
Jingying Wang
摘要： Blind cleaning methods are currently the preferred strategy for handling foreground contamination in single-dish HI intensity mapping surveys. Despite the increasing sophistication of blind techniques, some signal loss will be inevitable across all scales. Constructing a corrective transfer function using mock signal injection into the contaminated data has been a practice relied on for HI intensity mapping experiments. However, assessing whether this approach is viable for future intensity mapping surveys where precision cosmology is the aim, remains unexplored. In this work, using simulations, we validate for the first time the use of a foreground transfer function to reconstruct power spectra of foreground-cleaned low-redshift intensity maps and look to expose any limitations. We reveal that even when aggressive foreground cleaning is required, which causes ${>}\,50\%$ negative bias on the largest scales, the power spectrum can be reconstructed using a transfer function to within sub-percent accuracy. We specifically outline the recipe for constructing an unbiased transfer function, highlighting the pitfalls if one deviates from this recipe, and also correctly identify how a transfer function should be applied in an auto-correlation power spectrum. We validate a method that utilises the transfer function variance for error estimation in foreground-cleaned power spectra. Finally, we demonstrate how incorrect fiducial parameter assumptions (up to ${\pm}100\%$ bias) in the generation of mocks, used in the construction of the transfer function, do not significantly bias signal reconstruction or parameter inference (inducing ${<}\,5\%$ bias in recovered values).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Fast radio bursts (FRBs) can be used to measure the Hubble constant by employing the Macquart relation. However, at present, only a small number of FRB events are localized to their host galaxies with known redshifts. In this paper, we develop a Bayesian method to statistically measure the Hubble constant using unlocalized FRBs and galaxy catalog data, which makes it possible to constrain cosmological parameters by using a large number of FRB data without known redshift information. Using the six FRB events observed by ASKAP combined with the big bang nucleosynthesis result, we obtain $H_0=71.7^{+8.8}_{-7.4}$ km s$^{-1}$ Mpc$^{-1}$ in the simulation-based case and $H_0=71.5^{+10.0}_{-8.1}$ km s$^{-1}$ Mpc$^{-1}$ in the observation-based case ($68\%$ highest-density interval), assuming different host galaxy population parameters. We also estimate that in the next few years, using thousands of FRBs could achieve a $3\%$ precision on the random error of the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jingying Wang
Mario G. Santos
Philip Bull
Keith Grainge
Steven Cunnington
Jose Fonseca
Melis O. Irfan
Yichao Li
Alkistis Pourtsidou
Paula S. Soares
Marta Spinelli
Gianni Bernardi
Brandon Engelbrecht
摘要： While most purpose-built 21cm intensity mapping experiments are close-packed interferometer arrays, general-purpose dish arrays should also be capable of measuring the cosmological 21cm signal. This can be achieved most efficiently if the array is used as a collection of scanning autocorrelation dishes rather than as an interferometer. As a first step towards demonstrating the feasibility of this observing strategy, we show that we are able to successfully calibrate dual-polarisation autocorrelation data from 64 MeerKAT dishes in the L-band (856-1712 MHz, 4096 channels), with 10.5 hours of data retained from six nights of observing. We describe our calibration pipeline, which is based on multi-level RFI flagging, periodic noise diode injection to stabilise gain drifts and an absolute calibration based on a multi-component sky model. We show that it is sufficiently accurate to recover maps of diffuse celestial emission and point sources over a 10 deg x 30 deg patch of the sky overlapping with the WiggleZ 11hr field. The reconstructed maps have a good level of consistency between per-dish maps and external datasets, with the estimated thermal noise limited to 1.4 x the theoretical noise level (~ 2 mK). The residual maps have rms amplitudes below 0.1 K, corresponding to <1% of the model temperature. The reconstructed Galactic HI intensity map shows excellent agreement with the Effelsberg-Bonn HI Survey, and the flux of the radio galaxy 4C+03.18 is recovered to within 3.6%, which demonstrates that the autocorrelation can be successfully calibrated to give the zero-spacing flux and potentially help in the imaging of MeerKAT interferometric data. Our results provide a positive indication towards the feasibility of using MeerKAT and the future SKA to measure the HI intensity mapping signal and probe cosmology on degree scales and above.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The neutral hydrogen (HI) intensity mapping (IM) survey is regarded as a promising approach for cosmic large-scale structure (LSS) studies. A major issue for the HI IM survey is to remove the bright foreground contamination. A key to successfully remove the bright foreground is to well control or eliminate the instrumental effects. In this work, we consider the instrumental effect of polarization leakage and use the U-Net approach, a deep learning-based foreground removal technique, to eliminate the polarization leakage effect.In this method, the principal component analysis (PCA) foreground subtraction is used as a preprocessing step for the U-Net foreground subtraction. Our results show that the additional U-Net processing could either remove the foreground residual after the conservative PCA subtraction or compensate for the signal loss caused by the aggressive PCA preprocessing. Finally, we test the robustness of the U-Net foreground subtraction technique and show that it is still reliable in the case of existing constraint error on HI fluctuation amplitude.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The 21 cm intensity mapping (IM) technique provides us with an efficient way
to observe the cosmic large-scale structure (LSS). From the LSS data, one can
use the baryon acoustic oscillation and redshift space distortion to trace the
expansion and growth history of the universe, and thus measure the dark energy
parameters. In this paper, we make a forecast for cosmological parameter
estimation with the synergy of three 21 cm IM experiments. Specifically, we
adopt a novel joint survey strategy, FAST ($0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The 21 cm intensity mapping (IM) technique provides us with an efficient way
to observe the cosmic large-scale structure (LSS). From the LSS data, one can
use the baryon acoustic oscillation and redshift space distortion to trace the
expansion and growth history of the universe, and thus measure the dark energy
parameters. In this paper, we make a forecast for cosmological parameter
estimation with the synergy of three 21 cm IM experiments. Specifically, we
adopt a novel joint survey strategy, FAST ($0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the neutral hydrogen (HI) intensity mapping (IM) survey, the foreground contamination on the cosmological signals is extremely severe, and the systematic effects caused by radio telescopes themselves further aggravate the difficulties in subtracting foreground. In this work, we investigate whether the deep learning method, concretely the 3D U-Net algorithm here, can play a crucial role in foreground subtraction when considering the systematic effect caused by the telescope's primary beam. We consider two beam models, i.e., the Gaussian beam model as a simple case and the Cosine beam model as a sophisticated case. The traditional principal component analysis (PCA) method is employed as a comparison and, more importantly, as the preprocessing step for the U-Net method to reduce the sky map dynamic range. We find that in the case of the Gaussian beam, the PCA method can effectively clean the foreground. However, the PCA method cannot handle the systematic effect induced by the Cosine beam, and the additional U-Net method can improve the result significantly. In order to show how well the PCA and U-Net methods can recover the HI signals, we also derive the HI angular power spectra, as well as the HI 2D power spectra, after performing the foreground subtractions. It is found that, in the case of Gaussian beam, the concordance with the original HI map using U-Net is better than that using PCA by $27.4\%$, and in the case of Cosine beam, the concordance using U-Net is better than that using PCA by $144.8\%$. Therefore, the U-Net based foreground subtraction can efficiently eliminate the telescope primary beam effect and shed new light on recovering the HI power spectrum for future HI IM experiments.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Melis O. Irfan
Yichao Li
Mario G. Santos
Philip Bull
Junhua Gu
Steven Cunnington
Keith Grainge
Jingying Wang
摘要： We present and compare several methods to mitigate time-correlated (1/f) noise within the HI intensity mapping component of the MeerKAT Large Area Synoptic Survey (MeerKLASS). By simulating scan strategies, the HI signal, white and correlated noise, we assess the ability of various data processing pipelines to recover the power spectrum of HI brightness temperature fluctuations. We use MeerKAT pilot data to assess the level of 1/f noise expected for the MeerKLASS survey and use these measurements to create realistic levels of time-correlated noise for our simulations. We find the time-correlated noise component within the pilot data to be between 16 and 23 times higher than the white noise level at the scale of k = 0.04 Mpc^-1. Having determined that the MeerKAT 1/f noise is partially correlated across all the frequency channels, we employ Singular Value Decomposition (SVD) as a technique to remove 1/f noise but find that over-cleaning results in the removal of HI power at large (angular and radial) scales; a power loss of 20 per cent is seen for a 2-mode SVD clean at the scale of k = 0.04 Mpc^-1. We compare the impact of map-making using weighting by the full noise covariance (i.e. including a 1/f component), as opposed to just a simple unweighted binning, finding that including the time-correlated noise information reduces the excess power added by 1/f noise by up to 30 per cent.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The neutral hydrogen (HI) intensity mapping (IM) survey is regarded as a promising approach for cosmic large-scale structure (LSS) studies. A major issue for the HI IM survey is to remove the bright foreground contamination. A key to successfully remove the bright foreground is to well control or eliminate the instrumental effects. In this work, we consider the instrumental effect of polarization leakage and use the U-Net approach, a deep learning-based foreground removal technique, to eliminate the polarization leakage effect.In this method, the principal component analysis (PCA) foreground subtraction is used as a preprocessing step for the U-Net foreground subtraction. Our results show that the additional U-Net processing could either remove the foreground residual after the conservative PCA subtraction or compensate for the signal loss caused by the aggressive PCA preprocessing. Finally, we test the robustness of the U-Net foreground subtraction technique and show that it is still reliable in the case of existing constraint error on HI fluctuation amplitude.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Fast radio bursts (FRBs) can be used to measure the Hubble constant by employing the Macquart relation. However, at present, only a small number of FRB events are localized to their host galaxies with known redshifts. In this paper, we develop a Bayesian method to statistically measure the Hubble constant using unlocalized FRBs and galaxy catalog data, which makes it possible to constrain cosmological parameters by using a large number of FRB data without known redshift information. Using the six FRB events observed by ASKAP combined with the big bang nucleosynthesis result, we obtain $H_0=71.7^{+8.8}_{-7.4}$ km s$^{-1}$ Mpc$^{-1}$ in the simulation-based case and $H_0=71.5^{+10.0}_{-8.1}$ km s$^{-1}$ Mpc$^{-1}$ in the observation-based case ($68\%$ highest-density interval), assuming different host galaxy population parameters. We also estimate that in the next few years, using thousands of FRBs could achieve a $3\%$ precision on the random error of the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Steven Cunnington
Yichao Li
Mario G. Santos
Jingying Wang
Isabella P. Carucci
Melis O. Irfan
Alkistis Pourtsidou
Marta Spinelli
Laura Wolz
Paula S. Soares
Chris Blake
Philip Bull
Brandon Engelbrecht
José Fonseca
Keith Grainge
Yin-Zhe Ma
摘要： We present a detection of correlated clustering between MeerKAT radio intensity maps and galaxies from the WiggleZ Dark Energy Survey. We find a $7.7\sigma$ detection of the cross-correlation power spectrum, the amplitude of which is proportional to the product of the HI density fraction ($\Omega_{\rm HI}$), HI bias ($b_{\rm HI}$) and the cross-correlation coefficient ($r$). We therefore obtain the constraint $\Omega_{\rm HI} b_{\rm HI} r\,{=}\,[0.86\,{\pm}\,0.10\,({\rm stat})\,{\pm}\,0.12\,({\rm sys})]\,{\times}\,10^{-3}$, at an effective scale of $k_{\rm eff}\,{\sim}\,0.13\,h\,{\rm Mpc}^{-1}$. The intensity maps were obtained from a pilot survey with the MeerKAT telescope, a 64-dish pathfinder array to the SKA Observatory (SKAO). The data were collected from 10.5 hours of observations using MeerKAT's L-band receivers over six nights covering the 11hr field of WiggleZ, in the frequency range $1015-973\,{\rm MHz}$ (0.400$\,{<}\,z\,{<}\,$0.459 in redshift). This detection is the first practical demonstration of the multi-dish auto-correlation intensity mapping technique for cosmology. This marks an important milestone in the roadmap for the cosmology science case with the full SKAO.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from compact binary coalescences encode the absolute luminosity distances of GW sources. Once the redshifts of GW sources are known, one can use the distance-redshift relation to constrain cosmological parameters. One way to obtain the redshifts is to localize GW sources by GW observations and then use galaxy catalogs to determine redshifts from a statistical analysis of redshift information of the potential host galaxies, and such GW data are commonly referred to as dark sirens. The third-generation (3G) GW detectors are planned to work in the 2030s and will observe numerous compact binary coalescences. Using these GW events as dark sirens requires high-quality galaxy catalogs from future sky survey projects. The China Space Station Telescope (CSST) will be launched in 2024 and will observe billions of galaxies within a 17500 deg$^2$ survey area up to $z\sim 4$, providing photometric and spectroscopic galaxy catalogs. In this work, we simulate the CSST galaxy catalog and the 5-year GW data, and combine them to infer the Hubble constant ($H_0$). Our results show that the measurement precision of $H_0$ could reach better than $0.005\%$, which is an astonishing precision for the Hubble constant measurement. We conclude that the synergy between the 3G GW detectors and CSST will be of far-reaching importance in dark-siren cosmology.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Wenkai Hu
Yichao Li
Yougang Wang
Fengquan Wu
Bo Zhang
Ming Zhu
Shifan Zuo
Guilaine Lagache
Yinzhe Ma
Mario G. Santos
Xuelei Chen
摘要： We investigate the 1/f noise of the Five-hundred-meter Aperture Spherical Telescope (FAST) receiver system using drift-scan data from an intensity mapping pilot survey. All the 19 beams have 1/f fluctuations with similar structures. Both the temporal and the 2D power spectrum densities are estimated. The correlations directly seen in the time series data at low frequency $f$ are associated with the sky signal, perhaps due to a coupling between the foreground and the system response. We use Singular Value Decomposition (SVD) to subtract the foreground. By removing the strongest components, the measured 1/f noise power can be reduced significantly. With 20 modes subtraction, the knee frequency of the 1/f noise in a 10 MHz band is reduced to $1.8 \times 10^{-3}\Hz$, well below the thermal noise over 500-seconds time scale. The 2D power spectra show that the 1/f-type variations are restricted to a small region in the time-frequency space and the correlations in frequency can be suppressed with SVD modes subtraction. The residual 1/f noise after the SVD mode subtraction is uncorrelated in frequency, and a simple noise diode frequency-independent calibration of the receiver gain at 8s interval does not affect the results. The 1/f noise can be important for HI intensity mapping, we estimate that the 1/f noise has a knee frequency $(f_{k}) \sim$ 6 $\times$ 10$^{-4}$Hz, and time and frequency correlation spectral indices $(\alpha) \sim 0.65$, $(\beta) \sim 0.8$ after the SVD subtraction of 30 modes. This can bias the HI power spectrum measurement by 10 percent.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Neutral hydrogen (HI) intensity mapping (IM) survey is generally regarded as a promising tool to explore the expansion history of the universe. In this work, we investigate the capability of MeerKAT HI IM observation in interferometric mode to estimate the power spectrum and constrain cosmological parameters in typical dark energy models. Besides, a novel approach of delay spectrum is employed, which can achieve separating the weak HI signal from the foreground in the frequency space. We find that the different survey fields have a great influence on the fractional errors on power spectrum $\Delta P/P$ in a limited observational time of 10 h. With the integration time increasing from 10 h to 10000 h, $\Delta P/P$ becomes distinctly smaller until the cosmic variance begins to dominate. In the total 10000 h observation, the lower $\Delta P/P$ in low $k$ can be achieved when tracking 100 points for MeerKAT L-band and 10 points for MeerKAT UHF-band. Through simulating 10000 h HI IM survey, we obtain $\sigma(\Omega_{\rm m})=0.044$ and $\sigma(H_0)=2.8~{\rm kms^{-1}\ Mpc^{-1}}$ with MeerKAT L-band, which are worse than the results of $\sigma(\Omega_{\rm m})=0.028$ and $\sigma(H_0)=2.0~{\rm km\ s^{-1}\ Mpc^{-1}}$ with MeerKAT UHF-band in the $\Lambda$CDM model. However, in the $w$CDM and CPL models, MeerKAT shows a limited capability of constraining dark-energy equation of state, even though combined with Planck data. Our analysis is shown to be a useful guide for the near future MeerKAT observations in HI IM survey.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Fengquan Wu
Jixia Li
Shifan Zuo
Xuelei Chen
Santanu Das
John P. Marriner
Trevor M. Oxholm
Anh Phan
Albert Stebbins
Peter T. Timbie
Reza Ansari
Jean-Eric Campagne
Zhiping Chen
Yanping Cong
Qizhi Huang
Yichao Li
Tao Liu
Yingfeng Liu
Chenhui Niu
Calvin Osinga
摘要： The Tianlai Dish Pathfinder Array is a radio interferometer designed to test techniques for 21~cm intensity mapping in the post-reionization universe as a means for measuring large-scale cosmic structure. It performs drift scans of the sky at constant declination. We describe the design, calibration, noise level, and stability of this instrument based on the analysis of about $\sim 5 \%$ of 6,200 hours of on-sky observations through October, 2019. Beam pattern determinations using drones and the transit of bright sources are in good agreement, and compatible with electromagnetic simulations. Combining all the baselines, we make maps around bright sources and show that the array behaves as expected. A few hundred hours of observations at different declinations have been used to study the array geometry and pointing imperfections, as well as the instrument noise behaviour. We show that the system temperature is below 80~K for most feed antennas, and that noise fluctuations decrease as expected with integration time, at least up to a few hundred seconds. Analysis of long integrations, from 10 nights of observations of the North Celestial Pole, yielded visibilities with amplitudes of 20-30~mK, consistent with the expected signal from the NCP radio sky with $<10\,$mK precision for $1 ~\mathrm{MHz} \times 1~ \mathrm{min}$ binning. Hi-pass filtering the spectra to remove smooth spectrum signal yields a residual consistent with zero signal at the $0.5\,$mK level.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Neutral hydrogen (HI) intensity mapping (IM) survey is generally regarded as a promising tool to explore the expansion history of the universe. In this work, we investigate the capability of MeerKAT HI IM observation in interferometric mode to estimate the power spectrum and constrain cosmological parameters in typical dark energy models. Besides, a novel approach of delay spectrum is employed, which can achieve separating the weak HI signal from the foreground in the frequency space. We find that the different survey fields have a great influence on the fractional errors on power spectrum $\Delta P/P$ in a limited observational time of 10 h. With the integration time increasing from 10 h to 10000 h, $\Delta P/P$ becomes distinctly smaller until the cosmic variance begins to dominate. In the total 10000 h observation, the lower $\Delta P/P$ in low $k$ can be achieved when tracking 100 points for MeerKAT L-band and 10 points for MeerKAT UHF-band. Through simulating 10000 h HI IM survey, we obtain $\sigma(\Omega_{\rm m})=0.044$ and $\sigma(H_0)=2.8~{\rm kms^{-1}\ Mpc^{-1}}$ with MeerKAT L-band, which are worse than the results of $\sigma(\Omega_{\rm m})=0.028$ and $\sigma(H_0)=2.0~{\rm km\ s^{-1}\ Mpc^{-1}}$ with MeerKAT UHF-band in the $\Lambda$CDM model. However, in the $w$CDM and CPL models, MeerKAT shows a limited capability of constraining dark-energy equation of state, even though combined with Planck data. Our analysis is shown to be a useful guide for the near future MeerKAT observations in HI IM survey.
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