arXiv subjects

Zong-Hong Zhu

Publications and source records attributed to Zong-Hong Zhu.

At least 127 records · Page 7Linked to original sources

arXiv2018

The First Release of the AST3-1 Point Source Catalogue from Dome A, Antarctica

The three Antarctic Survey Telescopes (AST3) aim to carry out time domain imaging survey at Dome A, Antarctica. The first of the three telescopes (AST3-1) was successfully deployed on January 2012. AST3-1 is a 500\,mm aperture modified Schmidt telescope with a 680\,mm diameter primary mirror. AST3-1 is equipped with a SDSS $i$ filter and a 10k $\times$ 10k frame transfer CCD camera, reduced to 5k $\times$ 10k by electronic shuttering, resulting in a 4.3 deg$^2$ field-of-view. To verify the capability of AST3-1 for a variety of science goals, extensive commissioning was carried out between March and May 2012. The commissioning included a survey covering 2000 deg$^2$ as well as the entire Large and Small Magellanic Clouds. Frequent repeated images were made of the center of the Large Magellanic Cloud, a selected exoplanet transit field, and fields including some Wolf-Rayet stars. Here we present the data reduction and photometric measurements of the point sources observed by AST3-1. We have achieved a survey depth of 19.3\,mag in 60 s exposures with 5\,mmag precision in the light curves of bright stars. The facility achieves sub-mmag photometric precision under stable survey conditions, approaching its photon noise limit. These results demonstrate that AST3-1 at Dome A is extraordinarily competitive in time-domain astronomy, including both quick searches for faint transients and the detection of tiny transit signals.

astro-ph.IM↗

arXiv2018

Statistical analysis with cosmic-expansion-rate measurements and two-point diagnostics

Direct measurements of Hubble parameters $H(z)$ are very useful for cosmological model parameters inference. Based on them, Sahni, Shafieloo and Starobinski introduced a two-point diagnostic $Omh^2(z_i, z_j)$ as an interesting tool for testing the validity of the $Λ$CDM model. Applying this test they found a tension between observations and predictions of the $Λ$CDM model. We use the most comprehensive compilation $H(z)$ data from baryon acoustic oscillations (BAO) and differential ages (DA) of passively evolving galaxies to study cosmological models using the Hubble parameters itself and to distinguish whether $Λ$CDM model is consistent with the observational data with statistical analysis of the corresponding $Omh^2(z_i, z_j)$ two-point diagnostics. Our results show that presently available $H(z)$ data significantly improve the constraints on cosmological parameters. The corresponding statistical $Omh^2(z_i, z_j)$ two-point diagnostics seems to prefer the quintessence with $w>-1$ over the $Λ$CDM model. Better and more accurate prior knowledge of the Hubble constant, will considerably improve the performance of the statistical $Omh^2(z_i, z_j)$ method.

astro-ph.CO↗

arXiv2018

What is parameterized $Om(z)$ diagnostics telling us in light of recent observations?

In this paper, we propose a new parametrization of $Om(z)$ diagnostics and show how the most recent and significantly improved observations concerning the $H(z)$ and SN Ia measurements can be used to probe the consistency or tension between $Λ$CDM model and observations. Our results demonstrates that $H_0$ plays a very important role in the consistency test of $Λ$CDM with the $H(z)$ data. Adopting the Hubble constant priors from \textit{Planck} 2013 and Riess (2016), one finds a considerable tension between the current $H(z)$ data and $Λ$CDM model and confirms the conclusions obtained previously by the others. However, with the Hubble constant prior taken from WMAP9, the discrepancy between $H(z)$ data and $Λ$CDM disappears, i.e., the current $H(z)$ observations still support the cosmological constant scenario. This conclusion is also supported by the results derived from the JLA SNe Ia sample. The best-fit Hubble constant from the combination of $H(z)$+JLA ($H_0=68.81^{+1.50}_{-1.49}$ km/s/Mpc) is well consistent with the results derived both by Planck 2013 and WMAP9, which is significantly different from the recent local measurement by Riess (2016).

astro-ph.CO↗

arXiv2018

Curvature from strong gravitational lensing: a spatially closed Universe or systematics?

Model-independent constraints on the spatial curvature are not only closely related to important problems such as the evolution of the Universe and properties of dark energy, but also provide a test of the validity of the fundamental Copernican principle. In this paper, with the distance sum rule in the Friedmann-Lemaître-Robertson-Walker metric, we achieve model-independent measurements of the spatial curvature from the latest type Ia supernovae and strong gravitational lensing (SGL) observations. We find that a spatially closed Universe is preferred. Moreover, by considering different kinds of velocity dispersion and subsample, we study possible factors which might affect model-independent estimations for the spatial curvature from SGL observations. It is suggested that the combination of observational data from different surveys might cause a systematic bias and the tension between the spatially flat Universe and SGL observations is alleviated when the subsample only from the Sloan Lens ACS Survey is used or a more complex treatment for the density profile of lenses is considered.

astro-ph.CO↗

arXiv2017

Multimessenger tests of the weak equivalence principle from GW170817 and its electromagnetic counterparts

The coincident detection of a gravitational-wave (GW) event GW170817 with electromagnetic (EM) signals (e.g., a short gamma-ray burst SGRB 170817A or a macronova) from a binary neutron star merger within the nearby galaxy NGC 4933 provides a new, multimessenger test of the weak equivalence principle (WEP), extending the WEP test with GWs and photons. Assuming that the arrival time delay between the GW signals from GW170817 and the photons from SGRB 170817A or the macronova is mainly attributed to the gravitational potential of the Milky Way, we demonstrate that the strict upper limits on the deviation from the WEP are $Δγ<1.4\times10^{-3}$ for GW170817/macronova and $Δγ<5.9\times10^{-8}$ for GW170817/SGRB 170817A. A much more severe constraint on the WEP accuracy can be achieved ($\sim0.9\times10^{-10}$) for GW170817/SGRB 170817A when we consider the gravitational potential of the Virgo Cluster, rather than the Milky Way's gravity. This provides the tightest limit to date on the WEP through the relative differential variations of the $γ$ parameter for two different species of particles. Compared with other multimessenger (photons and neutrinos) results, our limit is 7 orders of magnitude tighter than that placed by the neutrinos and photons from supernova 1987A, and is almost as good as or is an improvement of 6 orders of magnitude over the limits obtained by the low-significance neutrinos correlated with GRBs and a blazar flare.

astro-ph.HE↗

arXiv2017

Precision cosmology from future lensed gravitational wave and electromagnetic signals

The standard siren approach of gravitational wave cosmology appeals to the direct luminosity distance estimation through the waveform signals from inspiralling double compact binaries, especially those with electromagnetic counterparts providing redshifts. It is limited by the calibration uncertainties in strain amplitude and relies on the fine details of the waveform. The Einstein Telescope is expected to produce $10^4-10^5$ gravitational wave detections per year, $50-100$ of which will be lensed. Here we report a waveform-independent strategy to achieve precise cosmography by combining the accurately measured time delays from strongly lensed gravitational wave signals with the images and redshifts observed in the electromagnetic domain. We demonstrate that just 10 such systems can provide a Hubble constant uncertainty of $0.68\%$ for a flat Lambda Cold Dark Matter universe in the era of third generation ground-based detectors.

astro-ph.CO↗

arXiv2017

Ultra-compact structure in radio quasars as a cosmological probe: a revised study of the interaction between cosmic dark sectors

A new compilation of $120$ angular-size/redshift data for compact radio quasars from very-long-baseline interferometry (VLBI) surveys motivates us to revisit the interaction between dark energy and dark matter with these probes reaching high redshifts $z\sim 3.0$. In this paper, we investigate observational constraints on different phenomenological interacting dark energy (IDE) models with the intermediate-luminosity radio quasars acting as individual standard rulers, combined with the newest BAO and CMB observation from Planck results acting as statistical rulers. The results obtained from the MCMC method and other statistical methods including Figure of Merit and Information Criteria show that: (1) Compared with the current standard candle data and standard clock data, the intermediate-luminosity radio quasar standard rulers , probing much higher redshifts, could provide comparable constraints on different IDE scenarios. (2) The interaction between dark energy and dark matter seems to be vanishing or slightly smaller than zero. At the 68.3\% confidence level, the energy is seen transferred from dark matter to dark energy, which implies that those IDE models can not alleviate the coincidence problem or even more sever. However, the strong degeneracies between the interaction term and Hubble constant may contribute to alleviate the tension of $H_0$ between the recent Planck and HST measurements. (3) Concerning the ranking of competing dark energy models, IDE with more free parameters are substantially penalized by the BIC criterion, which agrees very well with the previous results derived from other cosmological probes.

astro-ph.CO↗

arXiv2017

Model-independent Constraints on Cosmic Curvature and Opacity

In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, $H(z)$, and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function $H(z)$ from opacity-free expansion rate measurements. Then, we integrate the $H(z)$ to obtain distance modulus $μ_{\rm H}$, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli $μ_{\rm H}$ with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate ($H_0$: global estimation, $67.74\pm 0.46~\rm km~ s^{-1} ~Mpc^{-1}$, and local measurement, $73.24\pm 1.74~\rm km~ s^{-1} ~Mpc^{-1}$) exert influence on the reconstructed $H(z)$ and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for $H_0$ matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.

astro-ph.CO↗

arXiv2017

Testing and selecting cosmological models with ultra-compact radio quasars

In this paper, we place constraints on four alternative cosmological models under the assumption of the spatial flatness of the Universe: CPL, EDE, GCG and MPC. A new compilation of 120 compact radio quasars observed by very-long-baseline interferometry, which represents a type of new cosmological standard rulers, are used to test these cosmological models. Our results show that the fits on CPL obtained from the quasar sample are well consistent with those obtained from BAO. For other cosmological models considered, quasars provide constraints in agreement with those derived with other standard probes at $1σ$ confidence level. Moreover, the results obtained from other statistical methods including Figure of Merit, $Om(z)$ and statefinder diagnostics indicate that: (1) Radio quasar standard ruler could provide better statistical constraints than BAO for all cosmological models considered, which suggests its potential to act as a powerful complementary probe to BAO and galaxy clusters. (2) Turning to $Om(z)$ diagnostics, CPL, GCG and EDE models can not be distinguished from each other at the present epoch. (3) In the framework of statefinder diagnostics, MPC and EDE will deviate from $\rmΛ$CDM model in the near future, while GCG model cannot be distinguished from $\rmΛ$CDM model unless much higher precision observations are available.

astro-ph.CO↗

arXiv2017

Ultra-compact structure in intermediate-luminosity radio quasars: building a sample of standard cosmological rulers and improving the dark energy constraints up to $z\sim 3$

In this paper, we present a new compiled milliarcsecond compact radio data set of 120 intermediate-luminosity quasars in the redshift range $0.46< z <2.76$. These quasars show negligible dependence on redshifts and intrinsic luminosity, and thus represents, in the standard model of cosmology, a fixed comoving-length of standard ruler. We implement a new cosmology-independent technique to calibrate the linear size of of this standard ruler as $l_m= 11.03\pm0.25$ pc, which is the typical radius at which AGN jets become opaque at the observed frequency $ν\sim 2$ GHz. In the framework of flat $Λ$CDM model, we find a high value of the matter density parameter, $Ω_m=0.322^{+0.244}_{-0.141}$, and a low value of the Hubble constant, $H_0=67.6^{+7.8}_{-7.4}\; \rm{kms}^{-1}\rm{Mpc}^{-1}$, which is in excellent agreement with the CMB anisotropy measurements by \textit{Planck}. We obtain ${Ω_m}=0.309^{+0.215}_{-0.151}$, $w=-0.970^{+0.500}_{-1.730}$ at 68.3% CL for the constant $w$ of a dynamical dark-energy model, which demonstrates no significant deviation from the concordance $Λ$CDM model. Consistent fitting results are also obtained for other cosmological models explaining the cosmic acceleration, like Ricci dark energy (RDE) or Dvali-Gabadadze-Porrati (DGP) brane-world scenario. While no significant change in $w$ with redshift is detected, there is still considerable room for evolution in $w$ and the transition redshift at which $w$ departing from -1 is located at $z\sim 2.0$. Our results demonstrate that the method extensively investigated in our work on observational radio quasar data can be used to effectively derive cosmological information. Finally, we find the combination of high-redshift quasars and low-redshift clusters may provide an important source of angular diameter distances, considering the redshift coverage of these two astrophysical probes.

astro-ph.CO↗

arXiv2017

New observational constraints on $f(T)$ cosmology from radio quasars

Using a new recently compiled milliarcsecond compact radio data set of 120 intermediate-luminosity quasars in the redshift range $0.46< z <2.76$, whose statistical linear sizes show negligible dependence on redshifts and intrinsic luminosity and thus represent standard rulers in cosmology, we constrain three viable and most popular $f(T)$ gravity models, where $T$ is the torsion scalar in teleparallel gravity. Our analysis reveals that constraining power of the quasars data (N=120) is comparable to the Union2.1 SN Ia data (N=580) for all three $f(T)$ models. Together with other standard ruler probes such as Cosmic Microwave Background and Baryon Acoustic Oscillation distance measurements, the present value of the matter density parameter $Ω_m$ obtained by quasars is much lager than that derived from other observations. For two of the models considered ($f_1$CDM and $f_2$CDM) a small but noticeable deviation from $Λ$CDM cosmology is present, while in the framework of $f_3$CDM the effective equation of state may cross the phantom divide line at lower redshifts. These results indicate that intermediate-luminosity quasars could provide an effective observational probe comparable to SN Ia at much higher redsifts, and $f(T)$ gravity is a reasonable candidate for the modified gravity theory.

astro-ph.CO↗

arXiv2017

The Dynamics of Inhomogeneous Dark Energy

In this paper, by analyzing the dynamics of the inhomogeneous quintessence dark energy, we find that the gradient energy of dark energy will oscillate and gradually vanish, which indicates the gradient energy of the scalar field present in the early universe does not affect the current dynamics of the universe. Moreover, with the decaying of gradient energy, there exists a possible mutual transformation between kinetic energy and gradient energy. In the framework of interacting dark energy models, we argue that inhomogeneous dark energy may have a significant effect on the evolution of the cosmic background, the investigation of which still requires fully relativistic $N$-body numerical simulations in the future.

astro-ph.CO↗

arXiv2017

Speed of Gravitational Waves from Strongly Lensed Gravitational Waves and Electromagnetic Signals

We propose a new model-independent measurement strategy for the propagation speed of gravitational waves (GWs) based on strongly lensed GWs and their electromagnetic (EM) counterparts. This can be done in two ways: by comparing arrival times of GWs and their EM counterparts and by comparing the time delays between images seen in GWs and their EM counterparts. The lensed GW-EM event is perhaps the best way to identify an EM counterpart. Conceptually, this method does not rely on any specific theory of massive gravitons or modified gravity. Its differential setting (i.e., measuring the difference between time delays in GW and EM domains) makes it robust against lens modeling details (photons and GWs travel in the same lensing potential) and against internal time delays between GW and EM emission acts. It requires, however, that the theory of gravity is metric and predicts gravitational lensing similar to general relativity. We expect that such a test will become possible in the era of third-generation gravitational-wave detectors, when about 10 lensed GW events would be observed each year. The power of this method is mainly limited by the timing accuracy of the EM counterpart, which for kilonovae is around $10^4$ s.Thisuncertaintycanbesuppressedbya factor of $\sim 10^{10}$, if strongly lensed transients of much shorter duration associated with the GW event can be identified. Candidates for such short transients include short gamma-ray burst and fast radio bursts.

gr-qc↗

arXiv2017

Measuring the speed of light with ultra-compact radio quasars

In this paper, based on a 2.29 GHz VLBI all-sky survey of 613 milliarcsecond ultra-compact radio sources with $0.0035<z<3.787$, we describe a method of identifying the sub-sample which can serve as individual standard rulers in cosmology. If the linear size of the compact structure is assumed to depend on source luminosity and redshift as $l_m=l L^β(1+z)^n$, only intermediate-luminosity quasars ($10^{27}$ W/Hz$<L<$ $10^{28}$ W/Hz) show negligible dependence ($|n|\simeq 10^{-3}$, $|β|\simeq 10^{-4}$), and thus represent a population of such rulers with fixed characteristic length $l=11.42$ pc. With a sample of 120 such sources covering the redshift range $0.46<z<2.80$, we confirm the existence of dark energy in the Universe with high significance under the assumption of a flat universe, and obtain stringent constraints on both the matter density $Ω_m=0.323^{+0.245}_{-0.145}$ and the Hubble constant $H_0=66.30^{+7.00}_{-8.50}$ km sec$^{-1}$ Mpc$^{-1}$. Finally, with the angular diameter distances $D_A$ measured for quasars extending to high redshifts ($z\sim 3.0$), we reconstruct the $D_A(z)$ function using the technique of Gaussian processes. This allows us to identify the redshift corresponding to the maximum of the $D_A(z)$ function: $z_m=1.70$ and the corresponding angular diameter distance $D_A(z_m)=1719.01\pm43.46$ Mpc. Similar reconstruction of the expansion rate function $H(z)$ based on the data from cosmic chronometers and BAO gives us $H(z_m)=176.77\pm6.11$ km sec$^{-1}$ Mpc$^{-1}$. These measurements are used to estimate the speed of light: $c=3.039(\pm0.180)\times 10^5$ km/s. This is the first measurement of the speed of light in a cosmological setting referring to the distant past.

astro-ph.CO↗

arXiv2017

Evolutions and Calibrations of Long Gamma-Ray Bursts Luminosity Correlations Revisited

Luminosity correlations of long Gamma-ray bursts (GRB) are extensively proposed as an effective complementarity to trace the Hubble diagram of Universe at high redshifts, which is of great importance to explore properties of dark energy. Recently, several empirical luminosity correlations have been statistically proposed from GRB observations. However, to treat GRB as the distance indicator, there are two key issues: the redshift evolution of luminosity correlations and their calibrations. In this paper, we choose the Amati relation, the correlation between the peak spectra energy and the equivalent isotropic energy of GRBs ($E_{\rm p}-E_{\rm iso}$), as an example, and find that the current GRB dataset implies that there could be a evolution of the luminosity correlation with respect to the redshift. Therefore, we propose an extended Amati relation with two extra redshift-dependent terms to correct the redshift evolution of GRB relation. Secondly, we carefully check the reliability of the calibration method using the low-redshift GRB data. Importantly, we find that the low-redshift calibration method does not take whole correlations between $Ω_{\rm m}$ and coefficients into account. Neglecting these correlation information can break the degeneracies and obtain the biased constraint on $Ω_{\rm m}$ which is very sensitive to values of parameters for the calibration. A small shift of parameters of "calibrated" relation could significantly change the final constraint on $Ω_{\rm m}$ in the low-redshift calibration method. Finally, we simulate several GRB samples with different statistical errors and find that, in order to correctly recover the fiducial value of $Ω_{\rm m}$ using the low-redshift calibration method, we need a large number of GRB samples with high precisions.

astro-ph.HE↗

arXiv2017

Revisiting Studies of the Statistical Property of a Strong Gravitational Lens System and Model-independent Constraint on the Curvature of the Universe

In this paper we use a recently compiled data set, which comprises 118 galactic-scale strong gravitational lensing (SGL) systems to constrain the statistic property of SGL system, as well as the curvature of universe without assuming any fiducial cosmological model. Based on the singular isothermal ellipsoid (SIE) model of SGL system, we obtain that the constrained curvature parameter $Ω_{\rm k}$ is close to zero from the SGL data, which is consistent with the latest result of planck measurement. More interestingly, we find that the parameter $f$ in the SIE model is strongly correlated with the curvature $Ω_{\rm k}$. Neglecting this correlation in the analysis will significantly overestimate the constraining power of SGL data on the curvature. Furthermore, the obtained constraint on $f$ is different from previous results: $f=1.105\pm0.030$ ($68\%$ C.L.), which means that the standard singular isothermal sphere (SIS) model ($f=1$) is disfavored by the current SGL data at more than $3σ$ confidence level. We also divide the whole SGL data into two parts according to the centric stellar velocity dispersion $σ_{\rm c}$ and find that the larger value of $σ_{\rm c}$ the subsample has, the more favored the standard SIS model is. Finally, we extend the SIE model by assuming the power-law density profiles for the total mass density, $ρ=ρ_0(r/r_0)^{-α}$, and luminosity density, $ν=ν_0(r/r_0)^{-δ}$, and obtain the constraints on the power-law indexes: $α=1.95\pm0.04$ and $δ=2.40\pm0.13$ at 68\% confidence level. When assuming the power-law index $α=δ=γ$, this scenario is totally disfavored by the current SGL data, $χ^2_{\rm min,γ} - χ^2_{\rm min,SIE} \simeq 53$.

astro-ph.CO↗

arXiv2017

Test of parametrized post-Newtonian gravity with galaxy-scale strong lensing systems

Based on a mass-selected sample of galaxy-scale strong gravitational lenses from the SLACS, BELLS, LSD and SL2S surveys and using a well-motivated fiducial set of lens-galaxy parameters we tested the weak-field metric on kiloparsec scales and found a constraint on the post-Newtonian parameter $γ= 0.995^{+0.037}_{-0.047}$ under the assumption of a flat $Λ$CDM universe with parameters taken from \textit{Planck} observations. General relativity (GR) predicts exactly $γ=1$. Uncertainties concerning the total mass density profile, anisotropy of the velocity dispersion and the shape of the light-profile combine to systematic uncertainties of $\sim 25\%$. By applying a cosmological model independent method to the simulated future LSST data, we found a significant degeneracy between the PPN $γ$ parameter and spatial curvature of the Universe. Setting a prior on the cosmic curvature parameter $-0.007< Ω_k <0.006$, we obtained the following constraint on the PPN parameter: $γ=1.000^{+0.0023}_{-0.0025}$. We conclude that strong-lensing systems with measured stellar velocity dispersions may serve as another important probe to investigate validity of the GR, if the mass-dynamical structure of the lensing galaxies is accurately constrained in the future lens surveys.

astro-ph.CO↗

arXiv2016

Model-independent estimations for the curvature from standard candles and clocks

Model-independent estimations for the spatial curvature not only provide a test for the fundamental Copernican principle assumption, but also can effectively break the degeneracy between curvature and dark energy properties. In this paper, we propose to achieve model-independent constraints on the spatial curvature from observations of standard candles and standard clocks, without assuming any fiducial cosmology and other priors. We find that, for the popular Union2.1 type Ia supernovae (SNe Ia ) observations, the spatial curvature is constrained to be $Ω_K=-0.045_{-0.172}^{+0.176}$. For the latest joint light-curve analysis (JLA) of SNe Ia observations, we obtain $Ω_K=-0.140_{-0.158}^{+0.161}$. It is suggested that these results are in excellent agreement with the spatially flat Universe. Moreover, compared to other approaches aiming for model-independent estimations of spatial curvature, this method also achieves constraints with competitive precision.

astro-ph.CO↗