arXiv subjects

Zong-Hong Zhu

Publications and source records attributed to Zong-Hong Zhu.

At least 163 records · Page 9Linked to original sources

arXiv2014

Cosmic equation of state from combined angular diameter distances: Does the tension with luminosity distances exist?

Using a relatively complete observational data concerning four angular diameter distance (ADD) measurements and %synthetic combined SN+GRB observations representing current luminosity distance (LD) data, this paper investigates the %tension between compatibility of these two cosmological distances considering three classes of dark energy equation of state (EoS) reconstruction. In particular, we use strongly gravitationally lensed systems from various large systematic gravitational lens surveys and galaxy clusters, which yield the Hubble constant independent ratio between two angular diameter distances $D_{ls}/D_s$ data. Our results demonstrate that, with more general categories of standard ruler data, ADD and LD data are compatible at $1σ$ level. Secondly, we note that consistency between ADD and LD data %are blind is maintained irrespective of the EoS parameterizations: there is a good match between the universally explored CPL model and other formulations of cosmic equation of state. Especially for the truncated GEoS model with $β=-2$, the conclusions obtained with ADD and LD are almost the same. Finally, statistical analysis of generalized dark energy equation of state performed on four classes of ADD data provides stringent constraints on the EoS parameters $w_0$, $w_β$ and $β$, which suggest that dark energy was a subdominant component at early times. Moreover, the GEoS parametrization with $β\simeq 1$ seems to be a more favorable two-parameter model to characterize the cosmic equation of state, because the combined angular diameter distance data (SGL+CBF+BAO+WMAP9) provide the best-fit value $β=0.751^{+0.465}_{-0.480}$.

astro-ph.CO↗

arXiv2014

Strong gravitational lensing of gravitational waves from double compact binaries - perspectives for the Einstein Telescope

Gravitational wave (GW) experiments are entering their advanced stage which should soon open a new observational window on the Universe. Looking into this future, the Einstein Telescope (ET) was designed to have a fantastic sensitivity improving significantly over the advanced GW detectors. One of the most important astrophysical GW sources supposed to be detected by the ET in large numbers are double compact objects (DCO) and some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral DCO events in the ET. This analysis is a significant extension of our previous paper. We are using the intrinsic merger rates of the whole class of DCO (NS-NS,BH-NS,BH-BH)located at different redshifts as calculated by Dominik et al. by using {\tt StarTrack} population synthesis evolutionary code. We discuss in details predictions from each evolutionary scenario. Our general conclusion is that ET would register about $50-100$ strongly lensed inspiral events per year. Only the scenario in which nascent BHs receive strong kick gives the predictions of a few events per year. Such lensed events would be dominated by the BH-BH merging binary systems. Our results suggest that during a few years of successful operation ET will provide a considerable catalog of strongly lensed events.

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arXiv2014

Spatial Ricci scalar dark energy model

Inspired by holographic principle, we suggest that the density of dark energy is proportional to the spatial Ricci scalar curvature (SRDE). Such model is phenomenologically viable. The best fit values of its parameters at 68% confidence level are found to be: $Ω_{\rm m0}=0.259\pm0.016$ and $α=0.261\pm0.0122$, constrained from the Union+CFA3 sample of 397 SNIa and the BAO measurement. We find the equation of state of SRDE crosses -1 at $z\simeq-0.14$. The present values of the deceleration parameter $q(z)$ for SRDE is found to be $q_{z=0}\sim -0.85$. The phase transition from deceleration to acceleration of the Universe for SRDE occurs at the redshift $z_{q=0}\sim 0.4$. After studying on the perturbation of each component of the Universe, we show that the matter power spectra and cosmic microwave background temperature anisotropy is slightly affected by SRDE, compared with $Λ$CDM.

gr-qc↗

arXiv2013

A possible resolution of tension between {\it Planck} and Type Ia supernova observations

There is an apparent tension between cosmological parameters obtained from {\it Planck} cosmic microwave background radiation observations and that derived from the observed magnitude-redshift relation for the type Ia supernova (SNe Ia). Here, we show that the tension can be alleviated, if we first calibrate, with the help of the distance-duality relation, the light-curve fitting parameters in the distance estimation in SNe Ia observations with the angular diameter distance data of the galaxy clusters and then re-estimate the distances for the SNe Ia with the corrected fitting parameters. This was used to explore their cosmological implications in the context of the spatially flat cosmology. We find a higher value for the matter density parameter, $Ω_m$, as compared to that from the original SNLS3, which is in agreement with {\it Planck} observations at $68.3\%$ confidence. Therefore, the tension between {\it Planck} measurements and SNe Ia observations regarding $Ω_m$ can be effectively alleviated without invoking new physics or resorting to extensions for the standard concordance model. Moreover, with the absolute magnitude of a fiducial SNe Ia, $M$, determined first, we obtained a constraint on the Hubble constant with SNLS3 alone, which is also consistent with {\it Planck}.

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arXiv2013

General treatment for dark energy thermodynamics

In this work we discuss a general approach for the dark energy thermodynamics considering a varying equation of state (EoS) parameter of the type $ω(a)=ω_0+F(a)$ and taking into account the role of a non-zero chemical potential $μ$. We derive generalized expressions for the entropy density, chemical potential and dark energy temperature $T$ and use the positiveness of the entropy to impose thermodynamic bounds on the EoS parameter $ω(a)$. In particular, we find that a phantom-like behavior $ω(a)< -1$ is allowed only when the chemical potential assumes negative values ($μ<0$).

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arXiv2013

Strong gravitational lensing of gravitational waves in Einstein Telescope

Gravitational wave experiments have entered a new stage which gets us closer to the opening a new observational window on the Universe. In particular, the Einstein Telescope (ET) is designed to have a fantastic sensitivity that will provide with tens or hundreds of thousand NS-NS inspiral events per year up to the redshift z = 2. Some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral NS-NS events in the Einstein telescope. Being conservative we consider the lens population of elliptical galaxies. It turns out that depending on the local insipral rate ET should detect from one per decade detection in the pessimistic case to a tens of detections per year for the most optimistic case. The detection of gravitationally lensed source in gravitational wave detectors would be an invaluable source of information con- cerning cosmography, complementary to standard ones (like supernovae or BAO) independent of the local cosmic distance ladder calibrations.

astro-ph.CO↗

arXiv2013

A Consistent Test of the Distance-Duality Relation with Galaxy Clusters and Type Ia Supernave

We propose a new consistent method to test of the distance-duality (DD) relation which related angular diameter distances (DA) to the luminosity distances (DL) in a cosmology-independent way. In order to avoid any bias brought by redshift incoincidence between galaxy clusters and Type Ia Supernave (SNe Ia), as well as to ensure the integrity of the galaxy clusters samples, we obtain the luminosity distance of a certain SN Ia point at the same redshift of the corresponding galaxy cluster by interpolating from the nearby SNe Ia. With the observational data at the same redshifts of the angular diameter distances from the complete 38 galaxy cluster sample for the spherical model and the corrected luminosity distances interpolated from the Union2 set, we find that $η\equiv {D_L}{(1+z)}^{-2}/{D_A}=1$ is satisfied within $2σ$ confidence level for various parameterizations of $η(z)$, which are more stringent than previous testing results without considering redshift bias.

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arXiv2013

Probing modified gravity theories with the Sandage-Loeb test

In this paper, we quantify the ability of a future measurement of the Sandage-Loeb test signal from the Cosmic-Dynamic-Experiment-like spectrograph to constrain some popular modified gravity theories including DGP brane-world scenario, $f(R)$ modified gravity and $f(T)$ gravity theory. We find that the Sandage-Loeb test measurements are able to break degeneracies between model parameters markedly and thus greatly improve cosmological constraints for all concerned modified gravity theories when combined with the latest observations of CMB--shift parameter. However, they yield almost the same degeneracy directions between model parameters as that from the distance ratio data derived from the latest observations of the cosmic microwave background and baryonic acoustic oscillations (CMB/BAO). Moreover, for the $f(R)$ modified gravity, the Sandage-Loeb test could provide completely different bounded regions in model parameters space as compared to CMB/BAO and thus supplement strong complementary constraints.

gr-qc↗

arXiv2013

Constraints of relic gravitational waves by Pulsar Timing Array: Forecasts for the FAST and SKA projects

Measurement of the pulsar timing residuals provides a direct way to detect relic gravitational waves at the frequency $f\sim 1/{\rm yr}$. In this paper, we investigate the constraints on the inflationary parameters, the tensor-to-scalar ratio $r$ and the tensor spectral index $n_t$, by the current and future Pulsar Timing Arrays (PTAs). We find that Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China and the planned Square Kilometer Array (SKA) projects have the fairly strong abilities to test the phantom-like inflationary models. If $r=0.1$, FAST could give the constraint on the spectral index $n_t<0.56$, and SKA gives $n_t<0.32$. While an observation with the total time T=20 yr, the pulsar noise level $σ_w=30$ns and the monitored pulsar number $n=200$, could even constrain $n_t<0.07$. These are much tighter than those inferred from the current results of Parkers Pulsar Timing Array (PPTA), European Pulsar Timing Array (EPTA) and North American Nanohertz Observatory for Gravitational waves (NANOGrav). Especially, by studying the effects of various observational factors on the sensitivities of PTAs, we found that compared with $σ_w$ and $n$, the total observation time $T$ has the most significant effect.

astro-ph.CO↗

arXiv2013

Cosmic opacity: cosmological-model-independent tests and their impacts on cosmic acceleration

With assumptions that the violation of the distance-duality (DD) relation entirely arises from non-conservation of the photon number and the absorption is frequency independent in the observed frequency range, we perform cosmological-model-independent tests for the cosmic opacity. The observational data include the largest Union2.1 SN Ia sample, which is taken for observed $D_\mathrm{L}$, and galaxy cluster samples compiled by De Filippis {\it et al.} and Bonamente {\it et al.}, which are responsible for providing observed $D_\mathrm{A}$. Two parameterizations, $τ(z)=2εz$ and $τ(z)=(1+z)^{2ε}-1$ are adopted for the optical depth associated to the cosmic absorption. We find that, an almost transparent universe is favored by Filippis {\it et al.} sample but it is only marginally accommodated by Bonomente {\it et al.} samples at 95.4% confidence level (C. L.) (even at 99.7% C. L. when the $r<100 \mathrm{kpc}$-cut spherical $β$ model is considered). Taking the possible cosmic absorption (in 68.3% C. L. range) constrained from the model-independent tests into consideration, we correct the distance modulus of SNe Ia and then use them to study their cosmological implications. The constraints on the $Λ$CDM show that a decelerating expanding universe with $Ω_Λ=0$ is only allowed at 99.7% C. L. by observations when the Bonamente {\it et al.} sample is considered. Therefore, our analysis suggests that an accelerated cosmic expansion is still needed to account for the dimming of SNe and the standard cosmological scenario remains to be supported by current observations.

astro-ph.CO↗

arXiv2013

On the gravitational wave background from compact binary coalescences in the band of ground-based interferometers

This paper reports a comprehensive study on the gravitational wave (GW) background from compact binary coalescences. We consider in our calculations newly available observation-based neutron star and black hole mass distributions and complete analytical waveforms that include post-Newtonian amplitude corrections. Our results show that: (i) post-Newtonian effects cause a small reduction in the GW background signal; (ii) below 100 Hz the background depends primarily on the local coalescence rate $r_0$ and the average chirp mass and is independent of the chirp mass distribution; (iii) the effects of cosmic star formation rates and delay times between the formation and merger of binaries are linear below 100 Hz and can be represented by a single parameter within a factor of ~ 2; (iv) a simple power law model of the energy density parameter $Ω_{GW}(f) ~ f^{2/3}$ up to 50-100 Hz is sufficient to be used as a search template for ground-based interferometers. In terms of the detection prospects of the background signal, we show that: (i) detection (a signal-to-noise ratio of 3) within one year of observation by the Advanced LIGO detectors (H1-L1) requires a coalescence rate of $r_0 = 3 (0.2) Mpc^{-3} Myr^{-1}$ for binary neutron stars (binary black holes); (ii) this limit on $r_0$ could be reduced 3-fold for two co-located detectors, whereas the currently proposed worldwide network of advanced instruments gives only ~ 30% improvement in detectability; (iii) the improved sensitivity of the planned Einstein Telescope allows not only confident detection of the background but also the high frequency components of the spectrum to be measured. Finally we show that sub-threshold binary neutron star merger events produce a strong foreground, which could be an issue for future terrestrial stochastic searches of primordial GWs.

gr-qc↗

arXiv2013

The effect of different observational data on the constraints of cosmological parameters

The constraints on the $Λ$CDM model from type Ia supernova (SNe Ia) data alone and BAO data alone are similar, so it is worthwhile to compare their constraints on the property of dark energy. We apply the SNLS3 compilation of 472 SNe Ia data, the baryon acoustic oscillation measurement of distance, the cosmic microwave background radiation data from the WMAP7, and the Hubble parameter data to study the effect of their different combinations on the fittings of cosmological parameters in the modified holographic dark energy model and the Chevallier-Polarski-Linder model. Neither BAO nor WMAP7 data alone give good constraint on the equation of state parameter of dark energy, but both WMAP7 data and BAO data help SNe Ia data break the degeneracies among the model parameters, hence tighten the constraint on the variation of equation of state parameter $w_a$, and WMAP7 data do the job a little better. Although BAO and WMAP7 data provide reasonably good constraints on $Ω_m$ and $Ω_k$, they are not able to constrain the dynamics of dark energy. On the other hand, SNe Ia data do not provide good constraints on $Ω_m$ and $Ω_k$, but they provide good constraint on the dynamics of dark energy, especially the variation of the equation of state parameter of dark energy, so we need to combine SNe Ia with BAO and WMAP7 data to probe the property of dark energy. The addition of $H(z)$ data helps better constrain the geometry of the Universe $Ω_k$ and the property of dark energy. For the SNLS SNe Ia data, the nuisance parameters $α$ and $β$ are consistent for all different combinations of the above data, and their impacts on the fittings of cosmological parameters are minimal. By fitting the data to different models, $Λ$CDM model is still consistent with all the observational data.

astro-ph.CO↗

arXiv2012

Testing cosmic opacity from SNe Ia and Hubble parameter through three cosmological-model-independent methods

We use the newly published 28 observational Hubble parameter data ($H(z)$) and current largest SNe Ia samples (Union2.1) to test whether the universe is transparent. Three cosmological-model-independent methods (nearby SNe Ia method, interpolation method and smoothing method) are proposed through comparing opacity-free distance modulus from Hubble parameter data and opacity-dependent distance modulus from SNe Ia . Two parameterizations, $τ(z)=2εz$ and $τ(z)=(1+z)^{2ε}-1$ are adopted for the optical depth associated to the cosmic absorption. We find that the results are not sensitive to the methods and parameterizations. Our results support a transparent universe.

astro-ph.CO↗

arXiv2012

Seven-Year Multi-Color Optical Monitoring of BL Lacertae Object S5 0716+714

We have monitored the BL Lac object S5 0716+714 in five intermediate optical wavebands from 2004 September to 2011 April. Here we present the data that include 8661 measurements which represents one of the largest databases obtained for an object at optical domain. A simple analysis of the data indicates that the object was active in most time, and intraday variability was frequently observed. In total, the object varied by 2.614 magnitudes in the $i$ band. Strong bluer-when-brighter chromatism was observed on long, intermediate, and short timescales.

astro-ph.HE↗

arXiv2012

A unification of RDE model and XCDM model

In this Letter, we propose a new generalized Ricci dark energy (NGR) model to unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE and XCDM by introducing a parameter $β$ called weight factor. When $β=1$, NGR model becomes the usual RDE model. The XCDM model is corresponding to $β=0$. Moreover, NGR model permits the situation where neither $β=1$ nor $β=0$. We then perform a statefinder analysis on NGR model to see how $β$ effects the trajectory on the $r-s$ plane. In order to know the value of $β$, we constrain NGR model with latest observations including type Ia supernovae (SNe Ia) from Union2 set (557 data), baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method, the constraint result is $β$=$0.08_{-0.21}^{+0.30}(1σ)_{-0.28}^{+0.43}(2σ)$, which manifests the observations prefer a XCDM universe rather than RDE model. It seems RDE model is ruled out in NGR scenario within $2σ$ regions. Furthermore, we compare it with some of successful cosmological models using AIC information criterion. NGR model seems to be a good choice for describing the universe.

astro-ph.CO↗

arXiv2012

A multi-wavelength study of the gravitational lens COSMOS J095930+023427

We present a multi-wavelength study of the gravitational lens COSMOS J095930+023427 (z=0.89), together with the associated galaxy group located at $z\sim0.7$ along the line of sight and the lensed background galaxy. The source redshift is currently unknown, but estimated to be at $z_s \sim 2$. The analysis is based on the available public HST, Subaru, Chandra imaging data, and VLT spectroscopy. The lensing system is an early-type galaxy showing a strong [OII] emission line, and produces 4 bright images of the distant background source. It has an Einstein radius of 0.79", about 4 times large than the effective radius. We perform a lensing analysis using both a Singular Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution (PIEMD) for the lensing galaxy, and find that the final results on the total mass, the dark matter (DM) fraction within the Einstein radius and the external shear due to a foreground galaxy group are robust with respect of the choice of the parametric model and the source redshift (yet unknown). We measure the luminous mass from the photometric data, and find the DM fraction within the Einstein radius $f_{\rm DM}$ to be between $0.71\pm 0.13$ and $0.79 \pm 0.15$, depending on the unknown source redshift. Meanwhile, the non-null external shear found in our lensing models supports the presence and structure of a galaxy group at $z\sim0.7$, and an independent measurement of the 0.5-2 keV X-ray luminosity within 20" around the X-ray centroid provides a group mass of $M=(3-10)\times 10^{13}$ M$_{\odot}$, in good agreement with the previous estimate derived through weak lensing analysis.

astro-ph.CO↗

arXiv2012

Testing the interaction model with cosmological data and gamma-ray bursts

We use the new gamma-ray bursts (GRBs) data, combined with the baryon acoustic oscillation(BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release, the newly obtained $A$ parameter at $z=0.6$ from the WiggleZ Dark Energy Survey, the cosmic microwave background (CMB) observations from the 7-Year Wilkinson Microwave Anisotropy Probe (WMAP7) results, and the type Ia supernovae (SNeIa) from Union2 set, to constrain a phenomenological model describing possible interactions between dark energy and dark matter, which was proposed to alleviate the coincidence problem of the standard $Λ$CDM model. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the marginalized $1σ$ constraints $Ω_{m}=0.2886\pm{0.0135}$, $r_m=-0.0047\pm{0.0046}$, and $w_X=-1.0658\pm{0.0564}$. We also consider other combinations of these data for comparison. These results show that: (1) the energy of dark matter is slightly transferring to that of dark energy; (2) even though the GRBs+BAO+CMB data present less stringent constraints than SNe+BAO+CMB data do, the GRBs can help eliminate the degeneracies among parameters.

astro-ph.CO↗

arXiv2012

Observational constraints on new generalized Chaplygin gas model

We use the latest data to investigate observational constraints on the new generalized Chaplygin gas (NGCG) model. Using the Markov Chain Monte Carlo (MCMC) method, we constrain the NGCG model with the type Ia supernovae (SNe Ia) from Union2 set (557 data), the usual baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the newly revised $H(z)$ data, as well as a value of $θ_{BAO} (z=0.55) = (3.90 \pm 0.38)^{\circ}$ for the angular BAO scale. The constraint results for NGCG model are $ω_X = -1.0510_{-0.1685}^{+0.1563}(1σ)_{-0.2398}^{+0.2226}(2σ)$, $η= 1.0117_{-0.0502}^{+0.0469}(1σ)_{-0.0716}^{+0.0693}(2σ)$, and $Ω_X = 0.7297_{-0.0276}^{+0.0229}(1σ)_{-0.0402}^{+0.0329}(2σ)$, which give a rather stringent constraint. From the results, we can see a phantom model is slightly favored and the probability that energy transfers from dark matter to dark energy is a little larger than the inverse.

astro-ph.CO↗