arXiv subjects

Peng-Ju Wu

Publications and source records attributed to Peng-Ju Wu.

23 records · Page 2Linked to original sources

arXiv2023

Null test for cosmic curvature using Gaussian process

The cosmic curvature $Ω_{K,0}$, which determines the spatial geometry of the universe, is an important parameter in modern cosmology. Any deviation from $Ω_{K,0}=0$ would have a profound impact on primordial inflation paradigm and fundamental physics. In this work, we adopt a cosmological model-independent method to test whether $Ω_{K,0}$ deviates from zero. We use the Gaussian process to reconstruct the reduced Hubble parameter $E(z)$ and the derivative of distance $D'(z)$ from observational data, and then determine $Ω_{K,0}$ with a null test relation. The cosmic chronometer (CC) Hubble data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon sample are considered. Our result is consistent with a spatially flat universe within the domain of reconstruction $0 1$, it tends to favor a closed universe. In this sense, there is still a possibility for a closed universe. We also carry out the null test of the cosmic curvature at $0<z<4.5$ using the simulated gravitational wave standard sirens, CC+BAO and redshift drift Hubble data. The result shows that in the future, with the synergy of multiple high-quality observations, we can tightly constrain the spatial geometry or exclude the flat universe.

astro-ph.CO↗

arXiv2022

Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization

The reionization process is expected to be prolonged by the small-scale absorbers (SSAs) of ionizing photons, which have been seen as Lyman-limit systems in quasar absorption line observations. We use a set of semi-numerical simulations to investigate the effects of absorption systems on the reionization process, especially their impacts on the neutral islands during the late Epoch of Reionization (EoR). Three models are studied, i.e. the extreme case of no-SSA model with a high level of ionizing background, the moderate-SSA model with a relatively high level of ionizing background, and the dense-SSA model with a low level of ionizing background. We find that while the characteristic scale of neutral regions decreases during the early and middle stages of reionization, it stays nearly unchanged at about 10 comoving Mpc during the late stage for the no-SSA and moderate-SSA models. However, in the case of weak ionizing background in the dense-SSA model, the characteristic island scale shows obvious evolution, as large islands break into many small ones that are slowly ionized. The evolutionary behavior of neutral islands during the late EoR thus provides a novel way to constrain the abundance of SSAs. We discuss the 21-cm observation with the upcoming Square Kilometre Array. The different models can be distinguished by either the 21-cm imaging or the 21-cm power spectrum measurements.

astro-ph.CO↗

arXiv2021

Prospects for measuring dark energy with 21 cm intensity mapping experiments

Using the 21 cm intensity mapping (IM) technique can efficiently perform large-scale neutral hydrogen surveys, and this method has great potential for measuring dark-energy parameters. Some 21 cm IM experiments aiming at measuring dark energy in the redshift range of $0<z<3$ have been proposed and performed, in which the typical ones using single-dish mode include e.g., BINGO, FAST, and SKA1-MID, and those using interferometric mode include e.g., HIRAX, CHIME, and Tianlai. In this work, we make a forecast for these typical 21 cm IM experiments on their capability of measuring parameters of dark energy. We find that the interferometers have great advantages in constraining cosmological parameters. In particular, the Tianlai cylinder array alone can achieve the standard of precision cosmology for the $Λ$CDM model (i.e., the precision of parameters is better than 1%). However, for constraining dynamical dark energy, we find that SKA1-MID performs very well. We show that the simulated 21 cm IM data can break the parameter degeneracies inherent in the CMB data, and CMB+SKA1-MID offers $σ(w)=0.013$ in the $w$CDM model, and $σ(w_0)=0.080$ and $σ(w_a)=0.25$ in the CPL model. Compared with CMB+BAO+SN, Tianlai can provide tighter constraints in $Λ$CDM and $w$CDM, but looser constraints (tighter than CMB+BAO) in CPL, and the combination CMB+BAO+SN+Tianlai gives $σ(w)=0.013$, $σ(w_0)=0.055$, and $σ(w_a)=0.13$. In addition, it is found that the synergy of FAST ($0<z<0.35$)+SKA1-MID ($0.35<z<0.77$)+Tianlai ($0.77<z<2.55$) offers a very promising survey strategy. Finally, we find that the residual foreground contamination amplitude has a considerable impact on constraint results. We show that in the future 21 cm IM experiments will provide a powerful probe for exploring the nature of dark energy.

astro-ph.CO↗

arXiv2021

How can gravitational-wave standard sirens and 21 cm intensity mapping jointly provide a precise late-universe cosmological probe?

In the next decades, the gravitational-wave (GW) standard siren observations and the neutral hydrogen 21-cm intensity mapping (IM) surveys, as two promising cosmological probes, will play an important role in precisely measuring cosmological parameters. In this work, we make a forecast for cosmological parameter estimation with the synergy between the GW standard siren observations and the 21-cm IM surveys. We choose the Einstein Telescope (ET) and the Taiji observatory as the representatives of the GW detection projects and choose the Square Kilometre Array (SKA) phase I mid-frequency array as the representative of the 21-cm IM experiments. In the simulation of the 21-cm IM data, we assume perfect foreground removal and calibration. We find that the synergy of the GW standard siren observations and the 21-cm IM survey could break the cosmological parameter degeneracies. The joint ET+Taiji+SKA data give $σ(H_0)=0.28\ {\rm km\ s^{-1}\ Mpc^{-1}}$ in the $Λ$CDM model, $σ(w)=0.028$ in the $w$CDM model, which are better than the results of $Planck$+BAO+SNe, and $σ(w_0)=0.077$ and $σ(w_a)=0.295$ in the CPL model, which are comparable with the results of $Planck$+BAO+SNe. In the $Λ$CDM model, the constraint precision of $H_0$ and $Ω_{\rm m}$ is less than or rather close to 1%, indicating that the magnificent prospects for precision cosmology with these two promising cosmological probes are worth expecting.

astro-ph.CO↗

arXiv2021

Prospects for Constraining Interacting Dark Energy Models with 21 cm Intensity Mapping Experiments

We forecast constraints on cosmological parameters in the interacting dark energy models using the mock data generated for neutral hydrogen intensity mapping (IM) experiments. In this work, we only consider the interacting dark energy models with energy transfer rate $Q=βHρ_{\rm c}$, and take BINGO, FAST, SKA1-MID, and Tianlai as typical examples of the 21 cm IM experiments. We find that the Tianlai cylinder array will play an important role in constraining the interacting dark energy model. Assuming perfect foreground removal and calibration, and using the Tianlai-alone data, we obtain $σ(H_0)=0.19$ km s$^{-1}$ Mpc$^{-1}$, $σ(Ω_{\rm m})=0.0033$ and $σ(σ_8)=0.0033$ in the I$Λ$CDM model, which are much better than the results of Planck+optical BAO (i.e. optical galaxy surveys). However, the Tianlai-alone data cannot provide a very tight constraint on the coupling parameter $β$ compared with Planck+optical BAO, while the Planck+Tianlai data can give a rather tight constraint of $σ(β)=0.00023$ due to the parameter degeneracies being well broken by the data combination. In the I$w$CDM model, we obtain $σ(β)=0.00079$ and $σ(w)=0.013$ from Planck+Tianlai. In addition, we also make a detailed comparison among BINGO, FAST, SKA1-MID, and Tianlai in constraining the interacting dark energy models. We show that future 21 cm IM experiments will provide a useful tool for exploring the nature of dark energy and play a significant role in measuring the coupling between dark energy and dark matter.

astro-ph.CO↗