Sandage-Loeb Research Articles

Toward a direct measurement of the cosmic acceleration: The first preparation with FAST

Damped Lyman- α Absorber (DLA) of HI 21 cm system is an ideal probe to directly measure cosmic acceleration in real-time cosmology via Sandage–Loeb (SL) test. During short observations toward two DLAs in the commissioning progress of FAST, we manage to exhibit an HI 21 cm absorption feature from PKS1413+135 spectrum in one epoch with our highest resolution up to 100 Hz, preliminarily validating the frequency consistency under different resolutions and bandwidths. We make a Gaussian fitting to extract the spectral features, introduce two theoretical indicators to describe the fitted velocity uncertainty, and ultimately give a mean redshift and its constraint of z M = 0 . 24670045 ± 0 . 00000036 in accord with most literature. But our redshift error of the target is still three magnitudes higher than the level we can reach the drift signal. Though our first preparation has some flaws in time recording and diode settings, it still proves the correctness of our data process. Confined by limited observing time, we do not stretch FAST’s ability to obtain a better velocity constraint, so further researches are needed and in schedule. With fine sensitivity and improving spectral resolution, such observations in FAST could have reasonable possibility to explore cosmic acceleration in late time universe practically.

Toward a direct measurement of the cosmic acceleration: roadmap and forecast on FAST

HI absorption systems are great targets for direct measurement of the Sandage-Loeb (SL) effect throughout a wide range of redshift for ground-based radio telescopes. We demonstrate the significance of improving the accuracy of SL effect measurement in cosmological model selection. With its wide sky coverage and high sensitivity, we forecast that for 1 year of the upcoming commensal survey (CRAFTS) the FAST telescope is capable of discovering about 800 HI absorption systems thereby improving the SL measurement accuracy. Aiming to measurement the cosmic redshift drift rate at the precision of ż ∼ 10−10 decade−1, we propose combined observation mode with blind-searching and targeted observation. For a decade of consecutive targeted spectroscopic observation with the frequency resolution at a level of sub-0.1 Hz, we could detect the first-order derivative of the cosmological redshift with the expected precision.

Revisit of constraints on dark energy with Hubble parameter measurements including future redshift drift observations

We investigate whether the current Hubble parameter H(z) measurements could help improve the constraints on dark energy on the basis of the mainstream cosmological probes including the type Ia supernovae (SN) observation, the cosmic microwave background anisotropies (CMB) observation, and the baryon acoustic oscillations (BAO) observation. For the current H(z) data, we use 30 data points measured by using a differential age method. Furthermore, we also consider the future H(z) measurements based on the Sandage-Loeb (SL) test by means of the E-ELT in construction, and thus we also use 30 simulated H(z) data according to a 10-year SL test observation. In this work, we choose four typical dark energy models as examples, i.e., the ΛCDM model, the wCDM model, the αDE model, and the GCG model, to complete the analysis. We find that, when only the current H(z) data are added, the constraints on these models are not improved compared to the cases using the SN+CMB+BAO data; but when further adding the 10-year SL test data, the constraint results are tremendously improved for all the four models. Therefore, we conclude that, although the current H(z) measurements could not provide an evident improvement on the basis of the current mainstream cosmological probes, the future H(z) measurements from the SL test would have enormous potential to change the status of the Hubble parameter measurements in constraining dark energy.

Direct constraint on cosmic neutrino mass using observational Hubble parameter data

In order to explore the properties of cosmic neutrinos, i.e. sum of the neutrino mass (∑mυ) and the effective number of neutrino species (Neff), which affects the Hubble expansion rate H(z) and the power of observational Hubble parameter data (OHD) in constraining cosmological parameters under the ΛCDM model, we utilize OHD to constrain the properties of cosmic neutrinos and apply an accurate H(z) function with ∑mυ and Neff. First, we simulate new OHD beyond the existing 43 OHD. According to the predictions of measurements of H0 (the current H(z) value), baryon acoustic oscillations (BAO) peaks, Sandage-Loeb (SL) test and cosmic microwave background (CMB), we assume observational accuracy up to 2% and redshift 0 < z ≲ 5. With simulated H(z) data obtained from the fiducial model, we constrain the parameters including ∑mυ and Neff. When all parameters are set free, ∑mυ < 0.196 eV (95%) and Neff = 2.984 ± 0.826 (68%) are obtained, and when fixing Neff as the standard baseline 3.046, we attain ∑mυ < 0.240 eV (95%). These constrained results are much tighter than the ones obtained by the current OHD, which makes the prospect of OHD in constraining cosmological parameters more promising as its accuracy and quantity grow.

Effects of low anisotropy on interacting holographic and new agegraphic scalar fields models of dark energy

Abstract A spatially homogeneous and anisotropic Bianchi type I universe is studied with the interacting holographic and new agegraphic scalar fields models of dark energy. Given, the framework of the anisotropic model, both the dynamics and potential of these scalar field models according to the evolutionary behavior of both dark energy models are reconstructed. We also investigate the cosmological evolution of interacting dark energy models, and compare it with observational data and schematic diagram. In order to do so, we focus on observational determinations of the expansion history H ( z ) . Next, we evaluate effects of anisotropy on various topics, such as evolution of the growth of perturbations in the linear regime, statefinder diagnostic, Sandage–Loeb (SL) test and distance modulus from holographic and new agegraphic dark energy models and compare with the results of the standard FRW, Λ CDM and w CDM models. Our numerical result shows the effects of the interaction and anisotropy on the evolutionary behavior the new agegraphic scalar field models.

Redshift drift constraints on holographic dark energy

The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman-$\alpha$ forest of distant quasars, covering the "redshift desert" of $2\lesssim z\lesssim5$, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic dark energy models, i.e., the original holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density $\Omega_{m0}$ and the Hubble constant $H_0$ in other cosmological observations. For the considered two typical dark energy models, not only can a 30-year observation of SL test improve the constraint precision of $\Omega_{m0}$ and $h$ dramatically, but can also enhance the constraint precision of the model parameters $c$ and $\alpha$ significantly.

Redshift drift constraints on f(T) gravity

We explore the impact of the Sandage-Loeb (SL) test on the precision of cosmological constraints for $f(T)$ gravity theories. The SL test is an important supplement to current cosmological observations because it measures the redshift drift in the Lyman-$\alpha$ forest in the spectra of distant quasars, covering the "redshift desert" of $2 \lesssim z \lesssim5$. To avoid data inconsistency, we use the best-fit models based on current combined observational data as fiducial models to simulate 30 mock SL test data. We quantify the impact of these SL test data on parameter estimation for $f(T)$ gravity theories. Two typical $f(T)$ models are considered, the power-law model $f(T)_{PL}$ and the exponential-form model $f(T)_{EXP}$. The results show that the SL test can effectively break the existing strong degeneracy between the present-day matter density $\Omega_m$ and the Hubble constant $H_0$ in other cosmological observations. For the considered $f(T)$ models, a 30-year observation of the SL test can improve the constraint precision of $\Omega_m$ and $H_0$ enormously but cannot effectively improve the constraint precision of the model parameters.

Redshift drift exploration for interacting dark energy

By detecting redshift drift in the spectra of the Lyman-\(\alpha \) forest of distant quasars, the Sandage–Loeb (SL) test directly measures the expansion of the universe, covering the “redshift desert” of \(2 \lesssim z \lesssim 5\). Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of the SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (i) \(Q=\gamma H\rho _c\), (ii) \(Q=\gamma H\rho _{de}\), (iii) \(Q=\gamma H_0\rho _c\), and (iv) \(Q=\gamma H_0\rho _{de}\). The results show that for all the considered interacting dark energy models, relative to the current joint SN \(+\) BAO \(+\) CMB \(+\) \(H_0\) observations, the constraints on \(\Omega _m\) and \(H_0\) would be improved by about 60 and 30–40 %, while the constraints on w and \(\gamma \) would be slightly improved, with a 30-year observation of the SL test. We also explore the impact of the SL test on future joint geometric observations. In this analysis, we take the model with \(Q=\gamma H\rho _c\) as an example, and we simulate future SN and BAO data based on the space-based project WFIRST. We find that with the future geometric constraints, the redshift drift observations would help break the geometric degeneracies in a meaningful way, thus the measurement precisions of \(\Omega _m\), \(H_0\), w, and \(\gamma \) could be substantially improved using future probes.

Constraining the Generalized and Superfluid Chaplygin Gas Models with the Sandage-Loeb Test**Supported by the National Natural Science Foundation of China under Grants Nos 11175093, 11222545, 11435006, and 11375092, the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20124306110001, and the K.C. Wong Magna Fund of Ningbo University.

The Sandage-Loeb (SL) test is a direct measurement of the cosmic expansion by probing the redshift drifts of quasi-stellar objects in the ‘redshift desert’ of 2 < z < 5. In this work, we investigate its constraints on the unified dark energy and dark matter models including the generalized Chaplygin gas and the superfluid Chaplygin gas. In addition, type Ia supernovae (SNIa) data and the distance ratios derived from the cosmic microwave background radiation and baryon acoustic oscillation observations (CMB/BAO) are also used. We find that the mock SL data gives the tightest constraints on the model parameters and it can help to reduce the parameter regions allowed by the present SNIa+CMB/BAO by about 75% when all datasets considered are combined. Thus the SL test is a worthy and long awaited measurement to probe effectively the cosmic expanding history and the properties of dark energy.

Parameter estimation with Sandage-Loeb test

The Sandage-Loeb (SL) test directly measures the expansion rate of the universe in the redshift range of 2 ≲ z ≲ 5 by detecting redshift drift in the spectra of Lyman-α forest of distant quasars. We discuss the impact of the future SL test data on parameter estimation for the ΛCDM, the wCDM, and the w0waCDM models. To avoid the potential inconsistency with other observational data, we take the best-fitting dark energy model constrained by the current observations as the fiducial model to produce 30 mock SL test data. The SL test data provide an important supplement to the other dark energy probes, since they are extremely helpful in breaking the existing parameter degeneracies. We show that the strong degeneracy between Ωm and H0 in all the three dark energy models is well broken by the SL test. Compared to the current combined data of type Ia supernovae, baryon acoustic oscillation, cosmic microwave background, and Hubble constant, the 30-yr observation of SL test could improve the constraints on Ωm and H0 by more than 60% for all the three models. But the SL test can only moderately improve the constraint on the equation of state of dark energy. We show that a 30-yr observation of SL test could help improve the constraint on constant w by about 25%, and improve the constraints on w0 and wa by about 20% and 15%, respectively. We also quantify the constraining power of the SL test in the future high-precision joint geometric constraints on dark energy. The mock future supernova and baryon acoustic oscillation data are simulated based on the space-based project JDEM. We find that the 30-yr observation of SL test would help improve the measurement precision of Ωm, H0,and wa by more than 70%, 20%, and 60%, respectively, for the w0waCDM model.

Quantifying the impact of future Sandage-Loeb test data on dark energy constraints

The Sandage-Loeb (SL) test is a unique method to probe dark energy in the ``redshift desert'' of 2≲z≲5, and thus it provides an important supplement to the other dark energy probes.Therefore, it is of great importance to quantify how the future SL test data impact on the dark energyconstraints.To avoid the potential inconsistency in data, we use the best-fitting model based on the othergeometric measurements as the fiducial model to produce 30 mock SL test data.The 10-yr, 20-yr, and 30-yr observations of SL test are analyzed and compared in detail.We show that compared to the current combined data of type Ia supernovae, baryon acousticoscillation, cosmic microwave background, and Hubble constant, the 30-yr observation ofSL test could improve the constraint on Ωm by about 80% and the constraint onw by about 25%. Furthermore, the SL test can also improve the measurement of the possibledirect interaction between dark energy and dark matter. We show that the SL test 30-yr data couldimprove the constraint on γ by about 30% and 10% for the Q = γHρcand Q = γHρde models, respectively.

Sandage–Loeb test for the new agegraphic and Ricci dark energy models

The Sandage–Loeb (SL) test is a unique method to explore dark energy at the “redshift desert” (2≲z≲5), an era not covered by any other dark energy probes, by directly measuring the temporal variation of the redshift of quasar (QSO) Lyman-α absorption lines. In this Letter, we study the prospects for constraining the new agegraphic dark energy (NADE) model and the Ricci dark energy (RDE) model with the SL test. We show that, assuming only a ten-year survey, the SL test can constrain these two models with high significance.