Cygnus A and other 3CR sources in cosmological tests

The Astrophysical Journal, 2000

A sample of 20 powerful extended radio galaxies with redshifts between zero and 2 were used to deter-mine constraints on global cosmological parameters. Data for six radio sources were obtained from the VLA archive, analyzed, and combined with the sample of ...

The Astrophysical Journal, 1998

The multipole moments of the power spectrum of large scale structure, observed in redshift space, are calculated for a finite sample volume including the effects of both the linear velocity field and geometry. A variance calculation is also performed including the effects of shot noise. The sensitivity with which a survey with the depth and geometry of the Sloan Digital Sky Survey (SDSS) can measure cosmological parameters Ω 0 and b 0 (the bias) or λ 0 (the cosmological constant) and b 0 is derived through fitting power spectrum moments to the large scale structure in the linear regime in a way which is independent of the evolution of the galaxy number density. A fiducial model is assumed and the region of parameter space which can then be excluded to a given confidence limit is determined. In the absence of geometric and evolutionary effects, the ratios of multipole moments (in particular the zeroth and second), are degenerate for models of constant β ≈ Ω 0.6 /b 0. However, this degeneracy is broken by the Hubble expansion, so that in principle Ω 0 and b 0 may be measured separately by a deep enough galaxy redshift survey (Nakamura, Matsubara, & Suto (1997)). We find that for surveys of the approximate depth of the SDSS no restrictions can be placed on Ω 0 at the 99% confidence limit when a fiducial open, Ω 0 = 0.3 model is assumed and bias is unconstrained. At the 95% limit, Ω 0 < .85 is ruled out. Furthermore, for this fiducial model, both flat (cosmological constant) and open models are expected to reasonably fit the data. For flat, cosmological constant models with a fiducial Ω 0 = 0.3, we find that models with Ω 0 > 0.48 are ruled out at the 95% confidence limit regardless of the choice of the bias parameter, and open models cannot fit the data even at the 99% confidence limit. We also find significant deviations in β from the naive estimate for both fiducial models. Thus, we conclude for the SDSS that linear evolution-free statistics alone can strongly distinguish between Ω 0 = 1 and low matter density models only in the case of the fiducial cosmological constant model. For the open model, Ω 0 = 1 is only at best only nominally excluded unless Ω 0 < 0.3.

Monthly Notices of The Royal Astronomical Society, 2010

The clustering of galaxies observed in future redshift surveys will provide a wealth of cosmological information. Matching the signal at different redshifts constrains the dark energy driving the acceleration of the expansion of the Universe. In tandem with these geometrical constraints, redshift-space distortions (RSD) depend on the build up of large-scale structure. As pointed out by many authors measurements of these effects are intrinsically coupled. We investigate this link, and argue that it strongly depends on the cosmological assumptions adopted when analysing data. Using representative assumptions for the parameters of the Euclid survey in order to provide a baseline future experiment, we show how the derived constraints change due to different model assumptions. We argue that even the assumption of a Friedman-Robertson-Walker (FRW) space-time is sufficient to reduce the importance of the coupling to a significant degree. Taking this idea further, we consider how the data would actually be analysed and argue that we should not expect to be able to simultaneously constrain multiple deviations from the standard $\Lambda$CDM model. We therefore consider different possible ways in which the Universe could deviate from the $\Lambda$CDM model, and show how the coupling between geometrical constraints and structure growth affects the measurement of such deviations.

In this paper we explore the impact of including redshift information on cosmological applications with the forthcoming generation of large-scale, deep radio continuum surveys. By cross-matching these radio surveys with shallow optical to near-infrared surveys we can essentially separate the source distribution into a low redshift sample and the high-z tail of the radio sources that are unidentified, thus providing a constraint on the evolution of cosmological parameters such as those of dark energy. We examine two radio surveys, the Evolutionary Map of the Universe (EMU) and the Westerbork Observations of the Deep APERTIF Northern sky (WODAN). A crucial advantage is their combined potential to provide a deep, full-sky survey. The surveys used for the cross-identifications are SkyMapper and SDSS, for the southern and northern skies, respectively. We concentrate on the galaxy clustering angular power spectrum as our benchmark observable and find that the possibility of including this low redshift information yields major improvements in the results. With this approach, we are able to put strict constraints on the dark energy parameters, i.e. w_0=-0.9+/-0.065(0.087) and w_a=-0.24+/-0.19(0.26) with(without) priors from Planck; this corresponds to a Figure of Merit (FoM) of circa 400(>200), which is two to three orders of magnitude times better than the case without any redshift information and more than three times better than what obtained by using only the cross-identified sources.

Physics of the Dark Universe

We use three different data sets, specifically H(z) measurements from cosmic chronometers, the HII-galaxy Hubble diagram, and reconstructed quasarcore angular-size measurements, to perform a joint analysis of three flat cosmological models: the R h = ct Universe, ΛCDM, and wCDM. For R h = ct, the 1σ best-fit value of the Hubble constant H 0 is 62.336±1.464 km s −1 Mpc −1 , which matches previous measurements (∼ 63 km s −1 Mpc −1) based on best fits to individual data sets. For ΛCDM, our inferred value of the Hubble constant, H 0 = 67.013 ± 2.578 km s −1 Mpc −1 , is more consistent with the Planck optimization than the locally measured value using Cepheid variables, and the matter density Ω m = 0.347 ± 0.049 similarly coincides with its Planck value to within 1σ. For wCDM, the optimized parameters are H 0 = 64.718 ± 3.088 km s −1 Mpc −1 , Ω m = 0.247 ± 0.108 and w = −0.693 ± 0.276, also consistent with Planck. A direct comparison of these three models using the Bayesian Information Criterion shows that the R h = ct universe is favored by the joint analysis with a likelihood of ∼ 97% versus 3% for the other two cosmologies.

2001

We describe a new estimate of the radio galaxy 1.4GHz luminosity function and its evolution at intermediate redshifts (z ∼ 0.4). Photometric redshifts and color selection have been used to select B J < 23.5 early-type galaxies from the Panoramic Deep Fields, a multicolor survey of two 252 • fields. Approximately 230 radio galaxies have then been selected by matching early-type galaxies with NVSS radio sources brighter than 5mJy. Estimates of the 1.4GHz luminosity function of radio galaxies measure significant evolution over the observed redshift range. For an Ω M = 1 cosmology the evolution of the radio power is consistent with luminosity evolution where P (z) ∼ P (0)(1 + z) k L and 3 < k L < 5. The observed evolution is similar to that observed for U V X and X-ray selected AGN and is consistent with the same physical process being responsible for the optical and radio luminosity evolution of AGN.

Physical Review D, 2006

We measure the large-scale real-space power spectrum P (k) using luminous red galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS) and use this measurement to sharpen constraints on cosmological parameters from the Wilkinson Microwave Anisotropy Probe (WMAP). We employ a matrix-based power spectrum estimation method using Pseudo-Karhunen-Loève eigenmodes, producing uncorrelated minimum-variance measurements in 20 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.01 h/Mpc < k < 0.2 h/Mpc. Results from the LRG and main galaxy samples are consistent, with the former providing higher signal-to-noise. Our results are robust to omitting angular and radial density fluctuations and are consistent between different parts of the sky. They provide a striking confirmation of the predicted large-scale ΛCDM power spectrum. Combining only SDSS LRG and WMAP data places robust constraints on many cosmological parameters that complement prior analyses of multiple data sets. The LRGs provide independent cross-checks on Ωm and the baryon fraction in good agreement with WMAP. Within the context of flat ΛCDM models, our LRG measurements complement WMAP by sharpening the constraints on the matter density, the neutrino density and the tensor amplitude by about a factor of two, giving Ωm = 0.24±0.02 (1σ), mν ∼ < 0.9 eV (95%) and r < 0.3 (95%). Baryon oscillations are clearly detected and provide a robust measurement of the comoving distance to the median survey redshift z = 0.35 independent of curvature and dark energy properties. Within the ΛCDM framework, our power spectrum measurement improves the evidence for spatial flatness, sharpening the curvature constraint Ωtot = 1.05±0.05 from WMAP alone to Ωtot = 1.003 ± 0.010. Assuming Ωtot = 1, the equation of state parameter is constrained to w = −0.94 ± 0.09, indicating the potential for more ambitious future LRG measurements to provide precision tests of the nature of dark energy. All these constraints are essentially independent of scales k > 0.1h/Mpc and associated nonlinear complications, yet agree well with more aggressive published analyses where nonlinear modeling is crucial.

The Astrophysical Journal, 2007

Constraints on cosmological parameters from upcoming measurements with the Mileura Widefield Array-Low Frequency Demonstrator (MWA-LFD) of the redshifted 21 cm power spectrum are forecast assuming a flat ΛCDM cosmology and that the reionization of neutral hydrogen in the intergalactic medium occurs below a redshift of z = 8. We find that observations with the MWA-LFD cannot constrain the underlying cosmology in this scenario. In principle, a similar experiment with a 10-fold increase in collecting area could provide useful constraints on the slope of the inflationary power spectrum, n s , and the running of the spectral index, α s , but these constraints are subject to the caveat that even a small reionization contribution could be confused with the cosmological signal. In addition to the redshifted 21 cm signal, we include two nuisance components in our analysis related to the systematics and astrophysical foregrounds present in low-frequency radio observations. These components are found to be well separated from the signal and contribute little uncertainty (<30%) to the measured values of the cosmological model parameters.

2010

The low frequency tail of the CMB spectrum, down along the radio range (~1 GHz), may carry weak spectral distortions which are fingerprints of processes occurred during different epochs of the thermal history of the Universe, from z~3\times 10^6 to reionization. TRIS and ARCADE2 are the most recent experiments dedicated to the exploration of this chapter of CMB cosmology. The level of instrumental accuracy they reached in the determination of the absolute sky temperature is such that the removal of galactic and extra-galactic contamination is the true bottleneck towards the recovery of the cosmological signal. This will be certainly the case also for future experiments in the radio domain. Here we present an update of a study originally done to recognize the contribution of unresolved extra-galactic radio sources to the sky brightness measured by TRIS. Despite the specific context which originated our analysis, this is a study of general interest, improved by the inclusion of all th...

The Astrophysical Journal, 2009

Physical sizes of extended radio galaxies can be employed as a cosmological "standard ruler," using a previously developed method. Eleven new radio galaxies are added to our previous sample of 19 sources, forming a sample of 30 objects with redshifts between 0 and 1.8. This sample of radio galaxies are used to obtain the best-fit cosmological parameters in a quintessence model in a spatially flat universe, a cosmological constant model that allows for nonzero space curvature, and a rolling scalar field model in a spatially flat universe. Results obtained with radio galaxies are compared with those obtained with different supernova samples, and with combined radio galaxy and supernova samples. Results obtained with different samples are consistent, suggesting that neither method is seriously affected by systematic errors. Best-fit radio galaxy and supernovae model parameters determined in the different cosmological models are nearly identical, and are used to determine dimensionless coordinate distances to supernovae and radio galaxies, and distance moduli to the radio galaxies. The distance moduli to the radio galaxies can be combined with supernovae samples to increase the number of sources, particularly highredshift sources, in the samples. The constraints obtained here with the combined radio galaxy plus supernovae dataset in the rolling scalar field model are quite strong. The best-fit parameter values suggest that Ω m is less than about 0.35, and the model parameter α is close to zero; that is, a cosmological constant provides a good description of the data. We also obtain new constraints on the physics of engines that power the large-scale radio emission. The equation that describes the predicted size of each radio source is controlled by one model parameter, β, which parameterizes the extraction of energy from the black hole. Joint fits of radio galaxy and supernova samples indicate a best-fit value of β that is very close to a special value for which the relationship between the braking magnetic field strength and the properties of the spinning black hole is greatly simplified, and the braking magnetic field strength depends only upon the spin angular momentum per unit mass and the gravitational radius of the black hole. The best-fit value of β of 1.5 indicates that the beam power L j and the initial spin energy of the black hole E are related by L j ∝ E 2 , and that the relationship that might naively be expected for an Eddington limited system, L j ∝ E, is quite clearly ruled out for the jets in these systems.