arXiv subjects

Wlodzimierz Godlowski

Publications and source records attributed to Wlodzimierz Godlowski.

At least 37 records · Page 2Linked to original sources

arXiv2008

Autocorrelation Function for Radio Galaxies

We discuss the autocorrelation function $/zeta (r)$ for the sample 1157 radio-identified galaxies . The sample of galaxies is based on the Las Campanas Redshift Survey (LCRS) and 1.4 Ghz NRA)-VLA Sky Survey (NVSS) catalog of the radio sources. For separation $2-15h^{-1}$ Mpc autocorrelation function $/zeta (r)$$γ(s)$ can be approximated by the power law with correlation length and slope $-γ(s)=-1.8$. There are no clearly differences for correlation length between AGN and SB galaxies while value $γ$ for both samples are different: $γ=2.4$ for AGN and $γ=1.7$ for SB.

astro-ph↗

arXiv2008

Testing and selection of cosmological models with $(1+z)^6$ corrections

In the paper we check whether the contribution of $(-)(1+z)^6$ type in the Friedmann equation can be tested. We consider some astronomical tests to constrain the density parameters in such models. We describe different interpretations of such an additional term: geometric effects of Loop Quantum Cosmology, effects of braneworld cosmological models, non-standard cosmological models in metric-affine gravity, and models with spinning fluid. Kinematical (or geometrical) tests based on null geodesics are insufficient to separate individual matter components when they behave like perfect fluid and scale in the same way. Still, it is possible to measure their overall effect. We use recent measurements of the coordinate distances from the Fanaroff-Riley type IIb (FRIIb) radio galaxy (RG) data, supernovae type Ia (SNIa) data, baryon oscillation peak and cosmic microwave background radiation (CMBR) observations to obtain stronger bounds for the contribution of the type considered. We demonstrate that, while $ρ^2$ corrections are very small, they can be tested by astronomical observations -- at least in principle. Bayesian criteria of model selection (the Bayesian factor, AIC, and BIC) are used to check if additional parameters are detectable in the present epoch. As it turns out, the $Λ$CDM model is favoured over the bouncing model driven by loop quantum effects. Or, in other words, the bounds obtained from cosmography are very weak, and from the point of view of the present data this model is indistinguishable from the $Λ$CDM one.

gr-qc↗

arXiv2007

Constraining bouncing cosmology caused by Casimir effect

In our paper we constrain Friedman Robertson Walker (FRW) model with ``radiation-like'' contribution to the Friedmann equation against the astronomical data. We analyze the observational limitations on a $(1+z)^4$ term from SNIa data, FRIIb radio galaxy (RG) data, baryon oscillation peak and CMBR observations. We argue that it is not possible to determine the energy densities of individual components scaling like radiation from a kinematic astronomical test. The bounds for density parameter for total radiation-like term can be obtained. We find different interpretations of the presence of scaling like radiation term: FRW universe filled with a massless scalar field in a quantum regime (Casimir effect), Friedmann-Robertson-Walker (FRW) model in a semi-classical approximation of loop quantum gravity, FRW model in the Randall Sundrum scenario with dark radiation or cosmological model with global rotation. In this paper we mainly concentrate on Casimir effect arising from quantum effects of the scalar field. This contribution can describe decaying part of cosmological constant. We discuss the back reaction of gravity on Casimir-type force which is a manifestation of the vacuum fluctuations of the quantum scalar field at low temperature. It is shown that while the Casimir energy gives rise to accelerating Universe, the cosmological constant term is still required. We argue that a small negative contribution of a radiation-like term can reconcile the tension between the observed primordial ${}^4He$ and $D$ abundance. Moreover the presence of such contribution can also remove the disagreement between Hubble parameter $H_0$ values obtained from both SNIa and Wilkinson Microwave Anisotropy Probe (WMAP) satellite data.

astro-ph↗

arXiv2007

Acceleration of the Universe driven by the Casimir force

We investigate an evolutional scenario of the FRW universe with the Casimir energy scaling like $(-)(1+z)^4$. The Casimir effect is used to explain the vacuum energy differences (its value measured from astrophysics is so small compared to value obtained from quantum field theory calculations). The dynamics of the FRW model is represented in terms of a two-dimensional dynamical system to show all evolutional paths of this model in the phase space for all admissible initial conditions. We find also an exact solution for non flat evolutional paths of Universe driven by the Casimir effect. The main difference between the FRW model with the Casimir force and the $Λ$CDM model is that their generic solutions are a set of evolutional paths with a bounce solution and an initial singularity, respectively. The evolutional scenario are tested by using the SNIa data, FRIIb radiogalaxies, baryon oscillation peak and CMB observation. We compare the power of explanation of the model considered and the $Λ$CDM model using the Bayesian information criterion and Bayesian factor. Our investigation of the information criteria of model selection showed the preference of the $Λ$CDM model over the model considered. However the presence of negative like the radiation term can remove a tension between the theoretical and observed primordial ${}^4$He and D abundance.

gr-qc↗

arXiv2006

Towards observational constraints on negative (1+z)^4 type contribution in the Friedmann equation

We discuss certain issues related to the limitations of density parameters for a ``radiation''-like contribution to the Friedmann equation using kinematical or geometrical measurements. We analyse the observational constraint of a negative $(1+z)^4$-type contribution in cosmological models. We argue that it is not possible to determine the energy densities of individual components of matter scaling like radiation from astronomical observations. We find three different interpretations of the presence of the radiation term: 1) the FRW universe filled with a massless scalar field in a quantum regime (the Casimir effect), 2) the Friedmann-Robertson-Walker (FRW) model in the Randall Sundrum scenario with dark radiation, 3) the cosmological model with global rotation. From supernovae type Ia (SNIa) data, Fanaroff-Riley type IIb (FRIIb) radio galaxy (RG) data, baryon oscillation peak and cosmic microwave background radiation (CMBR) observations we obtain bounds for the negative radiation-like term. A small negative contribution of dark radiation can reconcile the tension in nucleosynthesis and remove also the disagreement between $H_0$ values obtained from both SNIa and the Wilkinson Microwave Anisotropy Probe (WMAP) satellite data.

astro-ph↗

arXiv2006

Dark matter and dark energy as a effects of Modified Gravity

We explain the effect of dark matter (flat rotation curve) using modified gravitational dynamics. We investigate in this context a low energy limit of generalized general relativity with a nonlinear Lagrangian ${\cal L}\propto R^n$, where $R$ is the (generalized) Ricci scalar and $n$ is parameter estimated from SNIa data. We estimate parameter $β$ in modified gravitational potential $V(r) \propto -\frac{1}{r}(1+(\frac{r}{r_c})^β)$. Then we compare value of $β$ obtained from SNIa data with $β$ parameter evaluated from the best fitted rotation curve. We find $β\simeq 0.7$ which becomes in good agreement with an observation of spiral galaxies rotation curve. We also find preferred value of $Ω_{m,0}$ from the combined analysis of supernovae data and baryon oscillation peak. We argue that although amount of "dark energy" (of non-substantial origin) is consistent with SNIa data and flat curves of spiral galaxies are reproduces in the framework of modified Einstein's equation we still need substantial dark matter. For comparison predictions of the model with predictions of the $Λ$CDM concordance model we apply the Akaike and Bayesian information criteria of model selection.

astro-ph↗

arXiv2006

Accelerated Cosmological Models in Modified Gravity tested by distant Supernovae SNIa data

Recent supernovae of type Ia measurements and other astronomical observations suggest that our universe is in accelerating phase of evolution at the present epoch. While a dark energy of unknown form is usually proposed as the most feasible mechanism for the acceleration, there are appears some alternative conception that some effects arising from generalization of Einstein equation can mimic dark energy through a modified Friedmann equation. In this work we investigate some observational constraints on modified Friedmann equation obtained from generalized Lagrangian ${\cal L} \propto R^n$ in minimal coupling with matter in Palatini formalism. We mainly concentrate on the constraints of model parameters from distant supernovae but other constraint from baryon oscillation prior is also considered. We obtain the confidence levels on two additional model parameter ($n$,$Ω_{m,0}$). We conclude that the FRW model of First-Order Non-linear gravity survives several observational test like SNIa observation and baryon oscillation peaks. We find preferred value of $Ω_{m,0} \simeq 0.3$ from combined analysis of supernovae data and baryon oscillation peak. For deeper statistical analysis we apply Akaike and Bayesian information criteria of model selection for comparison prediction of the model with prediction of concordance $Λ$CDM model.

astro-ph↗

arXiv2006

Equation of state for Universe from similarity symmetries

In this paper we proposed to use the group of analysis of symmetries of the dynamical system to describe the evolution of the Universe. This methods is used in searching for the unknown equation of state. It is shown that group of symmetries enforce the form of the equation of state for noninteracting scaling multifluids. We showed that symmetries give rise the equation of state in the form $p=-Λ+w_{1}ρ(a)+w_{2}a^β+0$ and energy density $ρ=Λ+ρ_{01}a^{-3(1+w)}+ρ_{02}a^β+ρ_{03}a^{-3}$, which is commonly used in cosmology. The FRW model filled with scaling fluid (called homological) is confronted with the observations of distant type Ia supernovae. We found the class of model parameters admissible by the statistical analysis of SNIa data. We showed that the model with scaling fluid fits well to supernovae data. We found that $Ω_{\text{m},0} \simeq 0.4$ and $n \simeq -1$ ($β= -3n$), which can correspond to (hyper) phantom fluid, and to a high density universe. However if we assume prior that $Ω_{\text{m},0}=0.3$ then the favoured model is close to concordance $Λ$CDM model. Our results predict that in the considered model with scaling fluids distant type Ia supernovae should be brighter than in $Λ$CDM model, while intermediate distant SNIa should be fainter than in $Λ$CDM model. We also investigate whether the model with scaling fluid is actually preferred by data over $Λ$CDM model. As a result we find from the Akaike model selection criterion prefers the model with noninteracting scaling fluid.

astro-ph↗

arXiv2006

Can brane dark energy model be probed observationally by distant supernovae?

The recent astronomical measurements of distant supernovae as well as other observations indicate that our universe is presently accelerating. There are different proposals for the explanation of this acceleration, such as the cosmological constant $Λ$, decaying vacuum energy, an evolving scalar field (quintessence), phantom energy, etc. Most of these proposals require the existence of exotic matter with negative pressure violating the strong energy condition. On the other hand, there have appeared many models which offer dramatically different mechanisms for the current acceleration, in which dark energy emerges from the gravity sector rather than from the matter sector. In this paper, we compare the concordance $Λ$CDM model with the Sahni-Shtanov brane-world models of dark energy by using the Akaike and Bayesian information criteria. We show that new parameters in the brane model are not statistically significant in terms of the information criteria, although the best fit method gives an improved fit to the SNIa data, because of the additional parameters. This is because the information criteria of model selection compensate for this advantage by penalizing models having more free parameters. We conclude that only new future observational data are accurate enough to give an advantage to dark-energy models of the brane origin, i.e., a very high-significance detection is required to justify the presence of new parameters. In our statistical analysis both Riess et al.'s and Astier et al.'s SNIa samples are used. For stringent constraining parameters of the models the baryon oscillation peak (BOP) test is used.

astro-ph↗

arXiv2005

Weak redshift discretisation in the Local Group of Galaxies?

We discuss the distribution of radial velocities of galaxies belonging to the Local Group. Two independent samples of galaxies as well as several methods of reduction from the heliocentric to the galactocentric radial velocities are explored. We applied the power spectrum analysis using the Hann function as a weighting method, together with the jackknife error estimation. We performed a detailed analysis of this approach. The distribution of galaxy redshifts seems to be non-random. An excess of galaxies with radial velocities of $\sim 24 {km} \cdot {s}^{-1}$ and $\sim 36 {km} \cdot {s}^{-1}$ is detected, but the effect is statistically weak. Only one peak for radial velocities of $\sim 24 {km} \cdot {s}^{-1}$ seems to be confirmed at the confidence level of 95%.

astro-ph↗

arXiv2005

Which cosmological models -- with dark energy or modified FRW dynamics?

Recent measurements of distant type Ia supernovae (SNIa) as well as other observations indicate that our universe is in accelerating phase of expansion. In principle there are two alternative explanation for such an acceleration. While in the first approach an unknown form of energy violating the strong energy condition is postulated, in second one some modification of FRW dynamics is postulated. The both approaches are in well agreement with present day observations which is the manifestation of the degeneracy problem appearing in observational cosmology. We use the Akaike (AIC) and Bayesian (BIC) information criteria of model selection to overcome this degeneracy and to determine a model with such a set of parameters which gives the most preferred fit to the SNIa data. We consider five representative evolutional scenarios in each of groups. Among dark energy proposal the $Λ$CDM model, CDM model with phantom field, CDM model with topological defect, model with Chaplygin gas, and the model with the linear dynamical equation of state parameter. As an alternative prototype scenarios we consider: brane world Dvali Gabadadze Porrati scenario, brane models in Randall-Sundrum scenario, Cardassian models with dust matter and radiation, bouncing model with the cosmological constant and metric-affine gravity (MAG) inspired cosmological models. Applying the model selection criteria we show that both AIC and BIC indicates that additional contribution arises from nonstandard FRW dynamics are not necessary to explain SNIa. Adopting the model selection information criteria we show that the AIC indicates the flat phantom model while BIC indicates both flat phantom and flat $Λ$CDM models.

astro-ph↗

arXiv2005

Complementary constraints on non-standard cosmological models from CMB and BBN

We study metric-affine gravity (MAG) inspired cosmological models. Those models were statistically estimated using the SNIa data. We also use the cosmic microwave background observations and the big-bang nucleosynthesis analysis to constrain the density parameter $Ω_{ψ,0}$ which is related to the non-Riemannian structure of the underlying spacetime. We argue that while the models are statistically admissible from the SNIa analysis, complementary stricter limits obtained from the CMB and BBN indicate that the models with density parameters with a $a^{-6}$ scaling behaviour are virtually ruled out. If we assume the validity of the particular MAG based cosmological model throughout all stages of the Universe, the parameter estimates from the CMB and BBN put a stronger limit, in comparison to the SNIa data, on the presence of non-Riemannian structures at low redshifts.

astro-ph↗

arXiv2005

Can the initial singularity be detected by cosmological tests?

In the present paper we raise the question whether initial cosmological singularity can be proved from the cosmological tests. The classical general relativity predict the existence of singularity in the past if only some energy conditions are satisfied. On the other hand the latest quantum gravity applications to cosmology suggest of possibility of avoiding the singularity and replace it with the bounce. The distant type Ia supernovae data are used to constraints on bouncing evolutional scenario where square of the Hubble function $H^2$ is given by formulae $H^2=H^2_0[Ω_{m,0}(1+z)^{m}-Ω_{n,0}(1+z)^{n}]$, where $Ω_{m,0}, Ω_{n,0}>0$ are density parameters and $n>m>0$. We show that the on the base of the SNIa data standard bouncing models can be ruled out on the $4σ$ confidence level. If we add the cosmological constant to the standard bouncing model then we obtain as the best-fit that the parameter $Ω_{n,0}$ is equal zero which means that the SNIa data do not support the bouncing term in the model. The bounce term is statistically insignificant the present epoch. We also demonstrate that BBN offer the possibility of obtaining stringent constraints of the extra term $Ω_{n,0}$. The other observational test methods like CMB and the age of oldest objects in the Universe are used. We also use the Akaike informative criterion to select a model according to the goodness of fit and we conclude that this term should be ruled out by Occam's razor, which makes that the big bang is favored rather then bouncing scenario.

astro-ph↗

arXiv2005

Some remarks on the angular momenta of galaxies, their clusters and superclusters

We discuss the relation between angular momenta and masses of galaxy structures base on the Li model of the universe with global rotation. In our previous paper (Godłowski et al 2002) it was shown that the model predicts the presence of a minimum in this relation. In the present paper we discuss observational evidence allowing us to verify this relation. We find null angular momentum J=0 for the masses corresponding to mass of galaxy grups and non-vanishing angular momenta for other galactic structures. We check these theoretical predictions analysing Tully's galaxy grups. The existing data comparing alignment in different galactic structure are consistent with obtained theoretical relation $J(M)$ if we interpret the groving alignment as the galactic increasing angular momenta in the galactic structure.

astro-ph↗

arXiv2004

Generalized Chaplygin Gas Models tested with SNIa

The so called Generalized Chaplygin Gas (GCG) with the equation of state $p = - \frac{A}{ρ^α}$ was recently proposed as a candidate for dark energy in the Universe. In this paper we confront the GCG with SNIa data. Specifically we have tested the GCG cosmology in three different classes of models with (1) $Ω_m= 0.3$, $Ω_{Ch}= 0.7$; (2) $Ω_m= 0.05$, $Ω_{Ch}= 0.95$ and (3) $Ω_m = 0$, $Ω_{Ch} = 1$, as well as the model withouth any assumption on $Ω_m$. The best fitted models are obtained by minimalizing the $χ^2$ function and $χ^2$ levels in the $(A_0, α)$ plane. We supplemented our analysis with confidence intervals in the $(A_0, α)$ plane, as well as one-dimensional probability distribution functions for models parameter. The general conclusion is that SNIa data strongly support the Chaplygin gas (with $α= 1$). Extending our analysisby relaxing the flat prior lead to the result that even though the best fitted values of $Ω_k$ are formally non-zero, still they are close to flat case. It should be viewed as an advantage of the GCG model since in similar analysisof $Λ$CDM model high negative value of $Ω_{k}$ were found to be bestfitted to the data and independent inspiration from CMBR and extragalactic astronomy has been invoked to fix the curvature problem. Our results show clearly that in Generalized Chaplygin Gas cosmology distant $z >1$ supernovae should be brighter than in $Λ$CDM model.This prediction seems to be confirmed with new Riess high redshift SNIa sample. Moreover, we argue that with the future SNAP data it would be possible to differentiate between models with various value of $α$ parameter and/or discriminated between GCG, Cardassian and $Λ$CDM models

astro-ph↗

arXiv2004

Dynamics of the Universe with global rotation

We analyze dynamics of the FRW models with global rotation in terms of dynamical system methods. We reduce dynamics of these models to the FRW models with some fictitious fluid which scales like radiation matter. This fluid mimics dynamically effects of global rotation. The significance of the global rotation of the Universe for the resolution of the acceleration and horizon problems in cosmology is investigated. It is found that dynamics of the Universe can be reduced to the two-dimensional Hamiltonian dynamical system. Then the construction of the Hamiltonian allows for full classification of evolution paths. On the phase portraits we find the domains of cosmic acceleration for the globally rotating universe as well as the trajectories for which the horizon problem is solved. We show that the FRW models with global rotation are structurally stable. This proves that the universe acceleration is due to the global rotation. It is also shown how global rotation gives a natural explanation of the empirical relation between angular momentum for clusters and superclusters of galaxies. The relation $J \sim M^2$ is obtained as a consequence of self similarity invariance of the dynamics of the FRW model with global rotation. In derivation of this relation we use the Lie group of symmetry analysis of differential equation.

astro-ph↗

arXiv2004

Rotation of the Universe and the angular momenta of celestial bodies

We discuss the equation of motion of the rotating homogenous and isotropic model of the Universe. We show that the model predicts the presence of a minimum in the relation between the mass of an astronomical object and its angular momentum. We show that this relation appears to be universal, and we predict the masses of structures with minimal angular momenta in agreement with observations. In such a manner we suggest the possibility at acquirement of angular momenta of celestial bodies during their formation from the global rotation of the Universe.

astro-ph↗

arXiv2004

Towards an Adequate Method to Isolate Spectroscopic Families of Diffuse Interstell Bands

We divide some of the observed diffuse interstellar bands (DIBs) into families which appear to have spectral structures of single species. Three different methods are applied to separate such families, exploring the best approach for future investigations of this type. Starting with statistical treatment of the data, we found that statistical methods by themselves give insufficient results. Two other methods of data analysis ("Averaging EWs" and "Investigating the figures with arranged spectrograms") were found to be more useful as tools for finding the spectroscopic families of DIBs. On the basis of these methods, we suggest some candidates as "relatives" of 5780 and 5797 bands.

astro-ph↗