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Melia, Fulvio (8)

Melia, Fulvio (8)

Univ Arizona, Dept Astron (8)

Univ Arizona, Dept Phys, Appl Math Program (4)Univ Arizona, Dept Phys (3)Leaf, Kyle (2)Univ Arizona, Dept Phys, Program Appl Math (2)Zhang, Tong-Jie (2)Cao, Shu-Lei (1)Chen, Yu (1)View MoreTypes
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Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background

Melia, Fulvio; López-Corredoira, M. (EDP SCIENCES S A, 2018-03-09)

Aim. The lack of large-angle correlations in the fluctuations of the cosmic microwave background (CMB) conflicts with predictions of slow-roll inflation. But while probabilities (≲0.24%) for the missing correlations disfavour the conventional picture at ≳3σ, factors not associated with the model itself may be contributing to the tension. Here we aim to show that the absence of large-angle correlations is best explained with the introduction of a non-zero minimum wave number kmin for the fluctuation power spectrum P(k).
Methods. We assumed that quantum fluctuations were generated in the early Universe with a well-defined power spectrum P(k), although with a cut-off kmin ≠ 0. We then re-calculated the angular correlation function of the CMB and compared it with Planck observations.
Results. The Planck 2013 data rule out a zero kmin at a confidence level exceeding 8σ. Whereas purely slow-roll inflation would have stretched all fluctuations beyond the horizon, producing a P(k) with kmin = 0 – and therefore strong correlations at all angles – a kmin ≠ 0 would signal the presence of a maximum wavelength at the time (tdec) of decoupling. This argues against the basic inflationary paradigm, and perhaps even suggests non-inflationary alternatives, for the origin and growth of perturbations in the early Universe. In at least one competing cosmology, the Rh = ct universe, the inferred kmin corresponds to the gravitational radius at tdec.

A comparison of the Rh=ct and Λ CDM cosmologies based on the observed halo mass function

Yennapureddy, Manoj K.; Melia, Fulvio (SPRINGER, 2019-07-08)

The growth of structure may be traced via the redshift-dependent halo mass function. This quantity probes the re-ionization history and quasar abundance in the Universe, constituting an important probe of the cosmological predictions. Halos are not directly observable, however, so their mass and evolution must be inferred indirectly. The most common approach is to presume a relationship with galaxies and halos. Studies based on the assumption of a constant halo to stellar mass ratio Mh/M (extrapolated from z less than or similar to 4) reveal significant tension with Lambda CDM - a failure known as The Impossibly Early Galaxy Problem. But whether this ratio evolves or remains constant through redshift 4 less than or similar to z less than or similar to 10 is still being debated. To eliminate the tension with Lambda CDM, it would have to change by about 0.8 dex over this range, an issue that may be settled by upcoming observations with the James Webb Space Telescope. In this paper, we explore the possibility that this major inconsistency may instead be an indication that the cosmological model is not completely correct. We study this problem in the context of another Friedmann-Lemaitre-Robertson-Walker (FLRW) model known as the Rh=ct universe, and use our previous measurement of sigma 8 from the cosmological growth rate, together with new solutions to the Einstein-Boltzmann equations, to interpret these recent halo measurements. We demonstrate that the predicted mass and redshift dependence of the halo distribution in Rh=ct is consistent with the data, even assuming a constant Mh/M throughout the observed redshift range (4 less than or similar to z less than or similar to 10), contrasting sharply with the tension in Lambda CDM. We conclude that - if Mh/M turns out to be constant - the massive galaxies and their halos must have formed earlier than is possible in Lambda CDM.

Analysing H(z) data using two-point diagnostics

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2017-09)

Measurements of the Hubble constantH(z) are increasingly being used to test the expansion rate predicted by various cosmological models. But the recent application of two-point diagnostics, such as Om(zi, zj) and Omh(2)(zi, zj), has produced considerable tension between Lambda CDM's predictions and several observations, with other models faring even worse. Part of this problem is attributable to the continued mixing of truly model-independent measurements using the cosmic-chronometer approach, and model-dependent data extracted from baryon acoustic oscillations. In this paper, we advance the use of two-point diagnostics beyond their current status, and introduce new variations, which we call Delta h(zi, zj), that are more useful for model comparisons. But we restrict our analysis exclusively to cosmic-chronometer data, which are truly model independent. Even for these measurements, however, we confirm the conclusions drawn by earlier workers that the data have strongly non-Gaussian uncertainties, requiring the use of both 'median' and 'mean' statistical approaches. Our results reveal that previous analyses using two-point diagnostics greatly underestimated the errors, thereby misinterpreting the level of tension between theoretical predictions and H(z) data. Instead, we demonstrate that as of today, only Einstein-de Sitter is ruled out by the two-point diagnostics at a level of significance exceeding similar to 3s. The R-h = ct universe is slightly favoured over the remaining models, including Lambda cold dark matter and Chevalier-Polarski-Linder, though all of them (other than Einstein-de Sitter) are consistent to within 1 sigma with the measured mean of the Delta h(zi, zj) diagnostics.

A two-point diagnostic for the H ii galaxy Hubble diagram

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2018-03)

A previous analysis of starburst-dominated HII galaxies and HII regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the R-h = c(t) universe, over Lambda cold dark matter (Lambda CDM) and its related dark-matter parametrizations. In this paper, we employ a two-point diagnostic with these data to present a complementary statistical comparison of Rh = ct with Planck Lambda CDM. Our two-point diagnostic compares, in a pairwise fashion, the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that Rh = ct is statistically preferred over Planck Lambda CDM. But we also find that the reported errors in the HII measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of HII galaxies and HII regions as standard candles may be improved even further with a better handling of the systematics in these sources.

Unseen Progenitors of Luminous High-z Quasars in the Rh = ct Universe

Fatuzzo, Marco; Melia, Fulvio (IOP PUBLISHING LTD, 2017-09-11)

Quasars at high redshift provide direct information on the mass growth of supermassive black holes (SMBHs) and, in turn, yield important clues about how the universe evolved since the first (Pop III) stars started forming. Yet even basic questions regarding the seeds of these objects and their growth mechanism remain unanswered. The anticipated launch of eROSITA and ATHENA is expected to facilitate observations of high-redshift quasars needed to resolve these issues. In this paper, we compare accretion-based SMBH growth in the concordance Lambda CDM model with that in the alternative Friedmann-Robertson-Walker cosmology known as the R-h = ct universe. Previous work has shown that the timeline predicted by the latter can account for the origin and growth of the greater than or similar to 10(9) M-circle dot highest redshift quasars better than that of the standard model. Here, we significantly advance this comparison by determining the soft X-ray flux that would be observed for Eddington-limited accretion growth as a function of redshift in both cosmologies. Our results indicate that a clear difference emerges between the two in terms of the number of detectable quasars at redshift z greater than or similar to 7, raising the expectation that the next decade will provide the observational data needed to discriminate between these two models based on the number of detected high-redshift quasar progenitors. For example, while the upcoming ATHENA mission is expected to detect similar to 0.16 (i.e., essentially zero) quasars at z similar to 7 in R-h = ct, it should detect similar to 160 in Lambda CDM-a quantitatively compelling difference.

Model selection based on the angular-diameter distance to the compact structure in radio quasars

Melia, Fulvio (IOP PUBLISHING LTD, 2018-09-03)

Of all the distance arid temporal measures in cosmology, the angular-diameter distance, d(A)(z), uniquely reaches a maximum value at some finite redshift z(max )and then decreases to zero towards the Big Bang. This effect has been difficult to observe due to a lack of reliable, standard rulers, though refinements to the identification of the compact structure in radio quasars may have overcome this deficiency. In this letter, we assemble a catalog of 140 such sources with 0 less than or similar to z less than or similar to 3 for model selection and the measurement of z(max). In flat Lambda CDM, we find that Omega(m) = 0.24(-0.09)(+0.1) fully consistent with the Planck optimized value, with z(max) = 1.69. Both of these values are associated with a d(A)(z) indistinguishable from that predicted by the zero active mass condition, rho + 3p = 0, in terms of the total pressure rho and total energy density rho of the cosmic fluid. An expansion driven by this constraint, known as the Rh = ct universe, has z(max )= 1.718, which differs from the Lambda CDM optimized value by less than similar to 1.6%. Indeed, the Bayes Information Criterion favours R-h = ct over flat Lambda CDM with a likelihood of similar to 81% vs. 19%, suggesting that the optimized parameters in Planck Lambda CDM mimic the constraint p = -rho/3.

Testing the Rh=ct universe jointly with the redshift-dependent expansion rate and angular-diameter and luminosity distances

Wan, Hao-Yi; Cao, Shu-Lei; Melia, Fulvio; Zhang, Tong-Jie (ELSEVIER, 2019-12)

We use three different data sets, specifically H(z) measurements from cosmic chronometers, the HII-galaxy Hubble diagram, and reconstructed quasar-core angular-size measurements, to perform a joint analysis of three flat cosmological models: the R-h = ct Universe, Lambda CDM, and wCDM. For R-h = ct, the 1 sigma best-fit value of the Hubble constant H-0 is 62.336 +/- 1.464 km s(-1) Mpc(-1), which matches previous measurements (similar to 63 km s(-1) Mpc(-1)) based on best fits to individual data sets. For Lambda CDM, 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 Omega(m) = 0.347 +/- 0.049 similarly coincides with its Planck value to within 1 sigma. For wCDM, the optimized parameters are H-0 = 64.718 +/- 3.088 km s(-1) Mpc(-1), Omega(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 similar to 97% versus. 3% for the other two cosmologies. (c) 2019 Elsevier B.V. All rights reserved.

Using Spatial Curvature with H II Galaxies and Cosmic Chronometers to Explore the Tension in H 0

Ruan, Cheng-Zong; Melia, Fulvio; Chen, Yu; Zhang, Tong-Jie (IOP PUBLISHING LTD, 2019-08-21)

We present a model-independent measurement of spatial curvature Omega(k) in the Friedmann-Lemaitre-Robertson-Walker universe, based on observations of the Hubble parameter H(z) using cosmic chronometers, and a Gaussian process (GP) reconstruction of the H II galaxy Hubble diagram. We show that the imposition of spatial flatness (i.e., Omega(k) - 0) easily distinguishes between the Hubble constant measured with Planck and that based on the local distance ladder. We find an optimized curvature parameter Omega(k) = -0.120(-0.147)(+0.168) when using the former (i.e., H-0 = 67.66 +/- 0.42 km s(-1) Mpc(-1)), and Omega(k) = -0.298(-0.088)(+0.122) for the latter (H-0 = 73.24 +/- 1.74 km s(-1) Mpc(-1)). The quoted uncertainties are extracted by Monte Carlo sampling, taking into consideration the covariances between the function and its derivative reconstructed by GP. These data therefore reveal that the condition of spatial flatness favors the Planck measurement, while ruling out the locally inferred Hubble constant as a true measure of the large-scale cosmic expansion rate at a confidence level of similar to 3 sigma.

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