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
摘要： Gravitational waves (GWs) from the compact binary coalescences can be used as standard sirens to explore the cosmic expansion history. In the next decades, it is anticipated that we could obtain the multi-band GW standard siren data (from nanohertz to a few hundred hertz), which are expected to play an important role in cosmological parameter estimation. In this work, we give for the first time the joint constraints on cosmological parameters using the future multi-band GW standard siren observations. We simulate the multi-band GW standard sirens based on the SKA-era pulsar timing array (PTA), the Taiji observatory, and the Cosmic Explorer (CE) to perform cosmological analysis. In the $\Lambda$CDM model, we find that the joint PTA+Taiji+CE data could provide a tight constraint on the Hubble constant with a $0.5\%$ precision. Moreover, PTA+Taiji+CE could break the cosmological parameter degeneracies generated by CMB, especially in the dynamical dark energy models. When combining the PTA+Taiji+CE data with the CMB data, the constraint precisions of $\Omega_{\rm m}$ and $H_0$ are $1.0\%$ and $0.3\%$, meeting the standard of precision cosmology. The joint CMB+PTA+Taiji+CE data give $\sigma(w)=0.028$ in the $w$CDM model and $\sigma(w_0)=0.11$ and $\sigma(w_a)=0.32$ in the $w_0w_a$CDM model, which are comparable with or close to the latest constraint results by the CMB+BAO+SN. In conclusion, it is worth expecting to use the future multi-band GW observations to explore the nature of dark energy and measure the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Measurements of time-delay cosmography of lensed quasars can provide an independent probe to explore the expansion history of the late-time Universe. In this paper, we employ the time-delay cosmography measurements from seven lenses (here abbreviated as the TD data) to constrain interacting dark energy (IDE) models. We mainly focus on the scenario of vacuum energy (with $w=-1$) interacting with cold dark matter, and consider four typical cases of the interaction form $Q$. When the TD data alone are employed, we find that the IDE models with $Q\propto \rho_{\rm de}$ seem to have an advantage in relieving the $H_{0}$ tension between the cosmic microwave background (CMB) and TD data. When the TD data are added to the CMB$+$BAO$+$SN$+H_0$ data, we find that: (i) the coupling parameter $\beta$ in all the considered IDE models is positive within 1$\sigma$ range, implying a mild preference for the case of cold dark matter decaying into dark energy; (ii) the IDE model with $Q = \beta H_{0} \rho_{\rm c}$ slightly relieves the $S_8$ tension, but the other considered IDE models further aggravate this tension; (iii) the Akaike information criteria of the IDE models with $Q \propto \rho_{\rm c}$ are lower than that of the $\Lambda$CDM model, indicating that these IDE models are more preferred by the current mainstream data. We conclude that the considered IDE models have their own different advantages when the TD data are employed, and none of them can achieve good scores in all aspects.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.
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