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JournalMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY (4)ASTRONOMY & ASTROPHYSICS (3)AMERICAN JOURNAL OF PHYSICS (2)The Astrophysical Journal (2)ASTROPHYSICAL JOURNAL (1)EPL (1)EPL (Europhysics Letters) (1)EUROPEAN PHYSICAL JOURNAL C (1)INTERNATIONAL JOURNAL OF MODERN PHYSICS A (1)PHYSICAL REVIEW D (1)View MoreAuthors

Univ Arizona, Dept Astron (18)

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Melia, Fulvio (17)Melia, Fulvio (4) Univ Arizona, Dept Phys (4)Leaf, Kyle (2)Ruan, Cheng-Zong (2)Yennapureddy, Manoj K. (2)Zhang, Tong-Jie (2)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.

Model selection with strong-lensing systems

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2018-05-24)

In this paper, we use an unprecedentedly large sample (158) of confirmed strong lens systems for model selection, comparing five well-studied Friedmann–Robertson–Walker cosmologies: ΛCDM, wCDM (the standard model with a variable dark-energy equation of state), the Rh = ct universe, the (empty) Milne cosmology, and the classical Einstein-de Sitter (matter-dominated) universe. We first use these sources to optimize the parameters in the standard model and show that they are consistent with Planck, though the quality of the best fit is not satisfactory. We demonstrate that this is likely due to underreported errors, or to errors yet to be included in this kind of analysis. We suggest that the missing dispersion may be due to scatter about a pure single isothermal sphere (SIS) model that is often assumed for the mass distribution in these lenses. We then use the Bayes information criterion, with the inclusion of a suggested SIS dispersion, to calculate the relative likelihoods and ranking of these models, showing that Milne and Einstein-de Sitter are completely ruled out, while Rh = ct is preferred over ΛCDM/wCDM with a relative probability of ∼73percent versus ∼24percent. The recently reported sample of new strong lens candidates by the Dark Energy Survey, if confirmed, may be able to demonstrate which of these two models is favoured over the other at a level exceeding 3σ.

The apparent (gravitational) horizon in cosmology

Melia, Fulvio (AMER ASSOC PHYSICS TEACHERS, 2018-08)

In general relativity, a gravitational horizon (more commonly known as the "apparent horizon") an imaginary surface beyond which all null geodesics recede from the observer. The Universe has an apparent (gravitational) horizon, but unlike its counterpart in the Schwarzschild and Kerr metrics, it is not static. It may eventually turn into an event horizon-an asymptotically defined membrane that forever separates causally connected events from those that are not-depending on the equation of state of the cosmic fluid. In this paper, we examine how and why an apparent (gravitational) horizon is manifested in the Friedmann-Robertson-Walker metric, and why it is becoming so pivotal to our correct interpretation of the cosmological data. We discuss its observational signature and demonstrate how it alone defines the proper size of our visible Universe. In so doing, we affirm its physical reality and its impact on cosmological models. (C) 2018 American Association of Physics Teachers.

J1342+0928 supports the timeline in the = cosmology

Melia, Fulvio (EDP SCIENCES S A, 2018-07-24)

Aims. The discovery of quasar J1342+0928 (z = 7.54) reinforces the time compression problem associated with the premature formation of structure in A cold dark matter (ACDM). Adopting the Planck parameters, we see this quasar barely 690 Myr after the big bang, no more than several hundred Myr after the transition from Pop III to Pop II star formation. Yet conventional astrophysics would tell us that a 10 M-circle dot seed, created by a Pop II/III supernova, should have taken at least 820 Myr to grow via Eddington-limited accretion. This failure by ACDM constitutes one of its most serious challenges, requiring exotic "fixes", such as anomalously high accretion rates, or the creation of enormously massive (similar to 10(5) M-circle dot) seeds, neither of which is ever seen in the local Universe, or anywhere else for that matter. Indeed, to emphasize this point, J1342+0928 is seen to be accreting at about the Eddington rate, negating any attempt at explaining its unusually high mass due to such exotic means. In this paper, we aim to demonstrate that the discovery of this quasar instead strongly confirms the cosmological timeline predicted by the R-h = Ct Universe. Methods. We assume conventional Eddington-limited accretion and the time versus redshift relation in this model to calculate when a seed needed to start growing as a function of its mass in order to reach the observed mass of J1342+0928 at z = 7.54. Results. Contrary to the tension created in the standard model by the appearance of this massive quasar so early in its history, we find that in the R-h = Ct cosmology, a 10 M-circle dot seed at z similar to 15 (the start of the Epoch of Reionization at t similar to 878 Myr) would have easily grown into an 8 x 10(8) M-circle dot black hole at z = 7.54 (t similar to 1.65 Gyr) via conventional Eddington-limited accretion.

The apparent (gravitational) horizon in cosmology

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

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2017-12-01)

A previous analysis of starburst-dominated H II galaxies and H II regions has demonstrated
a statistically significant preference for the Friedmann–Robertson–Walker cosmology with
zero active mass, known as the Rh = ct universe, over cold dark matter (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 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 CDM. But we also find that the reported errors in the
H II measurements may not be purely Gaussian, perhaps due to a partial contamination by
non-Gaussian systematic effects. The use of H II galaxies and H II regions as standard candles
may be improved even further with a better handling of the systematics in these sources.

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.

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.

A cosmological solution to the Impossibly Early Galaxy Problem

Yennapureddy, Manoj K.; Melia, Fulvio (ELSEVIER SCIENCE BV, 2018-03-26)

To understand the formation and evolution of galaxies at redshifts 0 less than or similar to z less than or similar to 10, one must invariably introduce specific models (e.g., for the star formation) in order to fully interpret the data. Unfortunately, this tends to render the analysis compliant to the theory and its assumptions, so consensus is still some-what elusive. Nonetheless, the surprisingly early appearance of massive galaxies challenges the standard model, and the halo mass function estimated from galaxy surveys at z greater than or similar to 4 appears to be inconsistent with the predictions of Lambda CDM, giving rise to what has been termed "The Impossibly Early Galaxy Problem" by some workers in the field. A simple resolution to this question may not be forthcoming. The situation with the halos themselves, however, is more straightforward and, in this paper, we use linear perturbation theory to derive the halo mass function over the redshift range 0 less than or similar to z less than or similar to 10 for the R-h = ct universe. We use this predicted halo distribution to demonstrate that both its dependence on mass and its very weak dependence on redshift are compatible with the data. The difficulties with Lambda CDM may eventually be overcome with refinements to the underlying theory of star formation and galaxy evolution within the halos. For now, however, we demonstrate that the unexpected early formation of structure may also simply be due to an incorrect choice of the cosmology, rather than to yet unknown astrophysical issues associated with the condensation of mass fluctuations and subsequent galaxy formation.

J1342+0928 supports the timeline in the R-h = ct cosmology

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