Gravitational Lenses as Standard Rulers in Cosmology

The accelerating expansion of the Universe is a great challenge for both physics and cosmology. From the observational point of view, it is crucial to have various methods to assess cosmic expansion history, which can be alternative to standard candles (SNIa in cosmological context). Strongly gravitationally lensed systems create such a new opportunity by combining stellar kinematics with lensing geometry. Using strong gravitational lenses as probes of cosmic expansion is becoming attractive in light of ongoing surveys like SLACS based on different protocols than older searches focused on potential sources. In this approach, pursued recently by the authors, strongly lensed systems with known central velocity dispersions act as “standard rulers” — Einstein radius being standardized by stellar kinematics

Distance Duality in Different Cosmological Models

At cosmological scales, one can actually measure two types of distances: luminosity distance dL and angular diameter distance dA. Within General Relativity, providing there are no processes eliminating photons from the beam, these two distances are related by the so-called distance duality relation. In this paper we used the measurements of the angular diameter distance of 38 cluster of galaxies by Bonamente et al. together with our own fits on the latest Union2 compilation of supernovae to test the distance duality relation in different cosmological models invoked to explain accelerating expansion of the Universe. Our results demonstrate that distance duality violation parameter (z) does not depend on the cosmological model assumed, but considerably depends on assumptions about mass density distribution profile of the cluster. Maximum likelihood estimates of might be interpreted as the distance duality violation. However, this effect is more pronounced for isothermal models of clusters than for the models based on hydrostatic equilibrium. This suggests that more sophisticated and accurate modeling of clusters mass density profiles is needed before the X-ray + SZ technique becomes competitive to other methods of measuring distances

Constraints on Cosmic Equation of State from Joint Analysis of Standard Rulers and Standard Candles

A key issue of contemporary cosmology is the problem of currently accelerating expansion of the Universe. The nature of this phenomenon is one of the most outstanding problems of physics and astronomy today. Its origin may be attributed to either unknown exotic material component with negative pressure — so-called Dark Energy (DE), to infra red modification of gravity at cosmological scale or requires to relax the assumption of homogeneity of the Universe. The strength of modern cosmology lies in consistency across independent pieces of evidence (like e.g. CMB anisotropies, the large-scale distribution of galaxies, the observed abundances of light elements, etc.) rather than in single one, crucial experiment. In this spirit we performed a joint analysis of two dark energy models using five different tests. These tests will be called diagnostics and include the data coming from supernovae, Gamma Ray Bursts, CMB acoustic peaks, Baryon Acoustic Oscillations and strong lensing systems. Part of the diagnostics makes use of the angular diameter distance, and part of them uses the luminosity distance splitting these probes into two categories: Standard Rules and Standard Candles. It was shown that combined analysis of them had higher restrictive power in the parameter space. The best fits we obtained for the model parameters in joint analysis turned out to prefer cases effectively equivalent to CDM model. Our findings are in agreement with paralel studies performed by other authors on different sets of diagnostic probes

On the Complementarity of Different Cosmological Probes with SLACS, BELLS and SL2S Strong Gravitational Lensing Data

Accelerating expansion of the Universe is now an indisputable observational fact and became one of the most important issues of both physics and cosmology today, known as dark energy (DE) problem. The nature of this phenomenon is still unknown and from observational point of view the only way to put some light on cosmic expansion history is to combine different methods which are alternative to each other. In this light, we explore the idea that strong gravitational lensing systems offer new opportunity to constrain DE parameters in a way complementary to other cosmological probes. It turns out that the angle of the confidence contour major axis for strong lensing measurements depends on the redshift of the sample what may help to break the degeneracy in the w0–wa parameters plane in the Chevalier–Polarski–Linder parametrization of DE equation of state

Cosmology with Strong Lensing Systems

In this paper, we assemble a catalog of 118 strong gravitational lensing systems from SLACS, BELLS, LSD and SL2S surveys and use them to constrain the cosmic equation of state. In particular we consider two cases of dark energy phenomenology: $XCDM$ model where dark energy is modeled by a fluid with constant $w$ equation of state parameter and in Chevalier - Polarski - Linder (CPL) parametrization where $w$ is allowed to evolve with redshift: $w(z) = w_0 + w_1 \frac{z}{1+z}$. We assume spherically symmetric mass distribution in lensing galaxies, but relax the rigid assumption of SIS model in favor to more general power-law index $\gamma$, also allowing it to evolve with redshifts $\gamma(z)$. Our results for the $XCDM$ cosmology show the agreement with values (concerning both $w$ and $\gamma$ parameters) obtained by other authors. We go further and constrain the CPL parameters jointly with $\gamma(z)$. The resulting confidence regions for the parameters are much better than those obtained with a similar method in the past. They are also showing a trend of being complementary to the supernova Ia data. Our analysis demonstrates that strong gravitational lensing systems can be used to probe cosmological parameters like the cosmic equation of state for dark energy. Moreover, they have a potential to judge whether the cosmic equation of state evolved with time or not.Comment: 7 figures, 2 table

New perspectives for multifrequency GW astronomy : strong gravitational lensing of GW

Direct detection of gravitational waves was for a long time the holy grail of observational astronomy. The situation changed in 2015 with the first registration of a gravitational wave signal (GW150914) by laboratory interferometers on Earth. Now, successful operating runs of LIGO/Virgo gravitational wave detectors, resulting in numerous observations of gravitational wave signals from coalescing double compact objects (mainly binary black hole mergers) with the first evidence of a coalescing binary neutron star system, has elevated multimessenger astronomy to an unprecedented stage. Double compact objects (binary black hole systems, mixed black hole–neutron star systems, and double neutron star systems) are the main targets of future ground-based and space-borne gravitational wave detectors, opening the possibility for multifrequency gravitational wave studies and yielding very rich statistics of such sources. This, in turn, makes it possible that certain, non-negligible amounts of double compact objects will have a chance of being strongly lensed. In this paper, we will discuss new perspectives for future detections of gravitational wave signals in the case of strong gravitational lensing. First, the expected rates of lensed gravitational wave signals will be presented. Multifrequency detections of lensed gravitational wave events will demand different treatments at different frequencies, i.e., wave approach vs. geometric optics approach. New possibilities emerging from such multifrequency detections will also be discussed

Graviton mass in the era of multi-messenger astronomy

The idea of massive graviton plays a fundamental role in modern physics as a landmark of most scenarios related to modified gravity theories. Limits on graviton mass can be obtained through different methods, using all the capabilities of multi-messenger astronomy available today. In this paper, we consider some emerging opportunities. In particular, modified relativistic dispersion relations of massive gravitons may lead to changes in the travel time of gravitational waves (GWs) emitted from distant astrophysical objects. Strong gravitational lensing of signals from a carefully selected class of extra-galactic sources such as compact object binaries (actually, binary neutron stars) is predicted to play an important role in this context. Comparing time delays between images of the lensed GW signal and its electromagnetic (EM) counterpart may be a new model-independent strategy (proposed by us in X.-L. Fan et al, 2017), which is especially promising in light of the fruitful observing runs of interferometric GW detectors, resulting in numerous GW signals. In addition to this direct, kinematic method, one can use an indirect, static method. In this approach, the non-zero graviton mass would modify estimates of the total cluster mass via a Yukawa term, influencing the Newtonian potential. In A. Piórkowska-Kurpas et al, 2022, using the X-COP galaxy cluster sample, we obtained mg < (4.99 6.79) 1029 eV (at 95% C.L.), which is one of the best available constraints

Clusters of galaxies as a tool in cosmology

Using the data comprising measurements of the gas mass fraction fgas for 42 hot and dynamically relaxed galaxy clusters with redshift spanning the range of 0:05 < z < 1:1, collected and analysed by Allen (2008) from the Chandra X-ray observations, we obtained constraints on the matter density parameter m and baryonic matter density parameter b. In our calculations, we took into account two most popular cosmological scenarios: quintessence model in which dark energy equation of state is constant and the model in which cosmic equation of state evolves with redshift according to Chevalier–Polarski–Linder (CPL) parametrization. Our results for quintessence model: m = 0:301 0:086, b = 0:042 0:011 as well as for time-varying CPL scenario: m = 0:268 0:094, b = 0:038 0:012 are in a very good agreement with the latest Planck results. This demonstrates that galaxy clusters can be an excellent tool to constrain the values of relevant cosmological parameters

Galaxy clusters for cosmology

Using the gas mass fraction fgas measurements obtained on the basis of X-ray data for two samples of hot and dynamically relaxed galaxy clusters: 42 clusters with redshifts in the range of 0:05 < z < 1:1 collected and analysed by Allen et al. (2008) and 35 clusters at redshifts 0:15 < z < 0:30 selected and analysed by Landry et al. (2013), we obtained constraints on main cosmological parameters in two popular cases: wCDM model in which dark energy equation of state is constant in time and the model in which dark energy equation of state evolves with redshift according to the Chevalier–Polarski–Linder (CPL) parametrization. [...] This shows that galaxy clusters can be used as a good tool in cosmology. Moreover, we investigate the recent (i.e. at low redshift) expansion history of the Universe finding no evidence that the cosmic acceleration is now slowing down