In this paper, we use a set of observational $H(z)$ data (OHD) to constrain the $Λ$CDM cosmology. This data set can be derived from the differential ages of the passively evolving galaxies. Meanwhile, the $\mathcal {A}$-parameter, which describes the Baryonic Acoustic Oscillation (BAO) peak, and the newly measured value of the Cosmic Microwave Background (CMB) shift parameter $\mathcal {R}$ are used to present combinational constraints on the same cosmology. The combinational constraints favor an accelerating flat universe while the flat $Λ$CDM cosmology is also analyzed in the same way. We obtain a result compatible with that by many other independent cosmological observations. We find that the observational $H(z)$ data set is a complementarity to other cosmological probes.
We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia suprenovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter, thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a co…
We use the Simon, Verde, & Jimenez (2005) determination of the redshift dependence of the Hubble parameter to constrain cosmological parameters in three dark energy cosmological models. We consider the standard $Λ$CDM model, the XCDM parameterization of the dark energy equation of state, and a slowly rolling dark energy scalar field with an inverse power-law potential. The constraints are restrictive, consistent with those derived from Type Ia supernova redshift-magnitude data, and complement those from galaxy cluster gas mass fraction versus redshift data.
The problem of the physical nature of the Hubble flow in the Local Volume ($D < 10$ Mpc) stated by Sandage(1986, 1999) is studied. New observational data on galaxy motions and matter distribution around the Local Group and nearby similar systems are described. Dynamical models are discussed on the basis of the recent data on cosmic vacuum or dark energy.
A spherical cosmological model with a local void on scales of $\sim 200$ Mpc and with an inhomogeneous Hubble constant was proposed in recent two papers. This model explains consistently the observed properties of the cosmic bulk flow, the accelerating behavior of type Ia supernovae and the CMB dipole anisotropy without invoking a cosmological constant. As we are in a position deviated from the center in the model, the anisotropy of the Hubble constant appears owing to the directional difference of the distance from the observer to the boundary of the void region. It is found that the anisotro…
The dependence of luminosity distance on observed resdhift and the cosmological parameters H and q is derived for a contracting Friedmann universe with no cosmological constant. The result is consistent with recent supernovae observations.
The age of the Universe depends on both the present-day Hubble Constant and on the history of cosmic expansion. For decelerating cosmologies such as Omega_m= 1, the dimensionless product H_0,t_0<1 and modestly high values of the Hubble constant H_0 > 70 would be inconsistent with a cosmic age t_0 larger than 12 Gyr. But if Omega_Lambda > 0, then H_0,t_0 can take on a range of values. Evidence from the Hubble diagram for high redshift Type Ia supernovae favors Omega_Lambda~0.7 and H_0,t_0 ~ 1. Then, if H_0 lies in the range 65--73, the age of the Universe, t_0, is 14+/-1.6 Gyr.
We performed a systematic and comprehensive estimate of the Hubble constant $H_0$ via the Sunyaev-Zel'dovich temperature decrement and the X-ray measurements for clusters up to the redshift $z=0.541$, with particular attention to its dependence on the density parameter $Ω_0$, and the cosmological constant $λ_0$. The resulting values of $H_0$ are largely consistent with that derived from the Cepheid distance for nearby galaxies. We discuss how the angular diameter distance $d_A$ vs. $z$ diagram from the accurate SZ measurements of high-$z$ clusters can distinguish the values of $Ω_0$ and $λ_0$.
We generalise the procedure for joint estimation of cosmological parameters to allow freedom in the relative weights of various probes. This is done by including in the joint Likelihood function a set of 'Hyper-Parameters', which are dealt with using Bayesian considerations. The resulting algorithm is simple to implement. We illustrate the method by estimating the Hubble constant H_0 from the recent Cosmic Microwave Background experiments Boomerang and Maxima. For an assumed flat Lambda-CDM model with fixed parameters (n=1, Omega_m = 1-lambda = 0.3, Omega_b h^2 = 0.03, Qrms = 18 mu K) we solve…
The possibility of having an extension of the cosmological standard model with a Hubble expansion rate $H$ constrained to a finite interval is considered. Two periods of accelerated expansion arise naturally when the Hubble expansion rate approaches to the two limiting values. The new description of the history of the universe is confronted with cosmological data and with several theoretical ideas going beyond the standard cosmological model.
We explore the cosmological model in which a late-time mild inflation is realized after the star formation epoch. Non-vanishing curvature coupling of a classical boson field yields this mild inflation without a cosmological constant. Accordingly the lifetime of the present Universe is remarkably increased in our model. Thus we show that the present observed high value of the Hubble parameter $H_0 \approx 70-80{\rm km/sec/Mpc}$ is compatible with the age of the oldest stars $14{\rm Gyr}$ without introducing the cosmological constant or the open Universe model. Moreover in our model, the local H…
The existence of cosmological perturbations of wavelength larger than the Hubble radius is a generic prediction of the inflationary paradigm. We provide the derivation beyond perturbation theory of a conserved quantity which generalizes the linear comoving curvature perturbation. As a by-product, we show that super-Hubble-radius (super-Hubble) perturbations have no physical influence on local observables e.g., the local expansion rate) if cosmological perturbations are of the adiabatic type.
We present observations of the Type Ia supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshift z~0.5. They were discovered in early 1999 with the 4.0~m Blanco telescope at Cerro Tololo Inter-American Observatory by the High-z Supernova Search Team (HZT) and subsequently followed with many ground-based telescopes. SNe 1999Q and 1999U were also observed with the Hubble Space Telescope. We computed luminosity distances to the new SNe using two methods, and added them to the high-z Hubble diagram that the HZT has been constructing since 1995. The new distance moduli confirm the results…
Deep and high resolution radio observations of the Hubble Deep Field and flanking fields have shown the presence of two distant edge-darkened FR I radio galaxies, allowing for the first time an estimate of their high redshift space density. If it is assumed that the space density of FR I radio galaxies at z>1 is similar to that found in the local universe, then the chance of finding two FR I radio galaxies at these high radio powers in such a small area of sky is <1%. This suggests that these objects were significantly more abundant at z>1 than at present, effectively ruling out the possibilit…
We combine magnitude and photometric redshift data on galaxies in the Hubble Deep Fields with morphological classifications in order to separate out the distributions for early type galaxies. The updated morphological galaxy number counts down to I = 25 and the corresponding redshift distributions are used as joint constraints on cosmological models, in particular on the values of the density parameter Omega_{0} and normalised cosmological constant Lambda_{0}. We find that an Einstein - de Sitter universe with simple passive evolution gives an excellent fit to the counts and redshift data at a…
Galaxy cluster gas mass fraction versus redshift data and Hubble parameter versus redshift data are used to jointly constrain dark energy models. These constraints favor the Einstein cosmological constant limit of dark energy but do not strongly rule out slowly-evolving dark energy.
The acceleration of the cosmic expansion has been discovered as a consequence of redshift Supernovae data. In the usual way, this cosmic acceleration is explained by the presence of a positive cosmological constant or quantum vacuum energy, in the background of standard Friedmann models. Recently, looking for an alternative explanation, I have considered an inhomogeneous barotropic spherically symmetric spacetime. Obviously, in this inhomogeneous model the philosophical cosmological principle is not verified. Within this framework, the kinematical acceleration of the cosmic fluid or, equivalen…
We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based upon five events at redshift up to z~0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption line spectroscopy from the Keck observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto (2002) and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II 516.9 nm P-Cygni feature observed during the plateau …
The cosmological vacuum, which is perfectly uniform, dominates by density over all the forms of cosmic matter. It makes the Universe be actually more uniform than it could be seen from the visible picture of the highly non-uniform matter distribution, especially inside the observed cell of uniformity (100-150 Mpc). This uniformity reveals itself in the structure of the Hubble matter flow which extends over a giant range of cosmic space scales -- from few Mpc to a thousand Mpc, -- preserving its kinematical identity. According to Sandage (1999), this flow is mysteriously regular and quiet even …
Basing on the increasing evidence for the cosmological relevance of the local Hubble flow, we consider a simple analytical cosmological model for the Local Universe. This is a non-Friedmann model with a non-uniform static space-time. The major dynamical factor controlling the local expansion is the antigravity produced by the omnipresent and permanent dark energy of the cosmic vacuum (or the cosmological constant). The antigravity dominates at distances larger than 1-2 Mpc from the center of the Local Group. The model gives a natural explanation of the two key quantitative characteristics of t…
The last decade has seen increasing efforts to circumscribe and bound the cosmological Hubble flow in terms of model-independent constraints on the cosmological fluid - such as, for instance, the classical energy conditions of general relativity. Quite a bit can certainly be said in this regard, but much more refined bounds can be obtained by placing more precise constraints (either theoretical or observational) on the cosmological fluid. In particular, the use of the w-parameter (w=p/rho) has become increasingly common as a surrogate for trying to say something about the cosmological equation…
General relativistic kinematics and the cosmological principle alone imply a monotonicity constraint in the Hubble diagram, which we confront to present-day supernova data. We use the running gradient method of statistical inference by Hall & Heckman (2000). We find no significant departure from monotonicity. The method seems well adapted and we recommend its use with future data.
The hypothesis of quantum nonequilibrium at the big bang is shown to have observable consequences. For a scalar field on expanding space, we show that relaxation to quantum equilibrium (in de Broglie-Bohm theory) is suppressed for field modes whose quantum time evolution satisfies a certain inequality, resulting in a 'freezing' of early quantum nonequilibrium for these particular modes. For an early radiation-dominated expansion, the inequality implies a corresponding physical wavelength that is larger than the (instantaneous) Hubble radius. These results make it possible, for the first time, …
Gamma-Ray Bursts (GRBs) offer a potential way to extend the Hubble diagram to very high redshifts and to constrain the nature of dark energy in a way complementary to distant type Ia supernovae. However, gravitational lensing systematically brightens distant GRBs through the magnification bias, in addition to increasing the dispersions of distance measurements. We investigate how the magnification bias limits the cosmological usage of GRBs. We perform Monte-Carlo simulations of Swift GRBs assuming a cosmological constant dominated universe and then constrain the dark energy equation of state n…
We present and constrain a cosmological model where the only component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a bulk viscosity coefficient proportional to the Hubble parameter. The model is constrained using the SNe Ia Gold 2006 sample, the Cosmic Microwave Background (CMB) shift parameter R, the Baryon Acoustic Oscillation (BAO) peak A and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the mod…
The idea of the global gravitational effect as the source of cosmological redshift was considered by de Sitter (1916, 1917), Eddington (1923), Tolman (1929) and Bondi (1947). Also Hubble (1929) called the discovered distance-redshift relation as "De Sitter effect". For homogeneous matter distribution cosmological gravitational redshift is proportional to square of distance: z_grav ~ r^2. However for a fractal matter distribution having the fractal dimension D=2 the global gravitational redshift is the linear function of distance: z_grav ~ r, which gives possibility for interpretation of the Hu…
Modified $f(R)$ gravity in the Palatini approach has been presently applied to Cosmology as a realistic alternative to dark energy. In this concern, a number of authors have searched for observational constraints on several $f(R)$ gravity functional forms using mainly data of type Ia supenovae (SNe Ia), Cosmic Microwave Background ({\rm CMB}) radiation and Large Scale Structure ({\rm LSS}). In this paper, by considering a homogeneous and isotropic flat universe, we use determinations of the Hubble function $H(z)$, which are based on differential age method, to place bounds on the free paramete…
