AffiliationUniv Arizona, Dept Astron
Univ Arizona, Dept Phys, Appl Math Program
Keywordsquasars: supermassive black holes
cosmology: distance scale
MetadataShow full item record
PublisherOXFORD UNIV PRESS
CitationFulvio Melia, Cosmological test using the Hubble diagram of high-z quasars, Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 1, October 2019, Pages 517–523, https://doi.org/10.1093/mnras/stz2120
RightsCopyright © 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
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AbstractIt has been known for over three decades that the monochromatic X-ray and UV luminosities in quasars are correlated, though non-linearly. This offers the possibility of using high-z quasars as standard candles for cosmological testing. In this paper, we use a recently assembled, high-quality catalogue of 1598 quasars extending all the way to redshift similar to 6, to compare the predictions of the R-h = ct and Lambda cold dark matter (Lambda CDM) cosmologies. In so doing, we affirm that the parameters characterizing the correlation depend only weakly on the chosen cosmology, and that both models account very well for the data. Unlike Lambda CDM, however, the R-h = ct model has no free parameters for this work, so the Bayesian Information Criterion favours it over Lambda CDM with a relative likelihood of similar to 88 per cent versus similar to 10 per cent. This result is consistent with the outcome of other comparative tests, many of which have shown that R-h = ct is favoured over the standard model based on a diverse range of observations.
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The linear growth of structure in the Rh = ct universeMelia, Fulvio; Univ Arizona, Dept Phys, Program Appl Math; Univ Arizona, Dept Astron (OXFORD UNIV PRESS, 2017-01-11)We use recently published redshift space distortion measurements of the cosmological growth rate, f sigma(8)(z), to examine whether the linear evolution of perturbations in the R-h = ct cosmology is consistent with the observed development of large-scale structure. We find that these observations favour R-h = ct over the version of Lambda cold dark matter (Lambda CDM) optimized with the joint analysis of Planck and linear growth rate data, particularly in the redshift range 0 < z < 1, where a significant curvature in the functional form of f sigma(8)(z) predicted by the standard model-but not by R-h = ct-is absent in the data. When Lambda CDM is optimized using solely the growth rate measurements; however, the two models fit the observations equally well though, in this case, the low-redshift measurements find a lower value for the fluctuation amplitude than is expected in Planck Lambda CDM. Our results strongly affirm the need for more precise measurements of f sigma(8)(z) at all redshifts, but especially at z < 1.
Testing the Rh=ct universe jointly with the redshift-dependent expansion rate and angular-diameter and luminosity distancesWan, Hao-Yi; Cao, Shu-Lei; Melia, Fulvio; Zhang, Tong-Jie; Univ Arizona, Appl Math Program, Dept Phys; Univ Arizona, Dept Astron (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.
The maximum angular-diameter distance in cosmologyMelia, Fulvio; Yennapureddy, Manoj K.; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (OXFORD UNIV PRESS, 2018-07-23)Unlike other observational signatures in cosmology, the angular-diameter distance dA(z) uniquely reaches a maximum (at zmax) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, we estimate and use zmax inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing dA(z) using Gaussian processes, and (3) comparing the predictions of seven different cosmologies and showing that the measured value of zmax can effectively discriminate between them. We find that zmax = 1.70 ± 0.20 – an important new probe of the Universe’s geometry. The most strongly favoured model is Rh = ct, followed by PlanckΛCDM. Several others, including Milne, Einstein-de Sitter, and Static tired light are strongly rejected. According to these results, the Rh = ct universe, which predicts zmax = 1.718, has a ∼92.8 per cent probability of being the correct cosmology. For consistency, we also carry out model selection based on dA(z) itself. This test confirms that Rh = ct and PlanckΛCDM are among the few models that account for angular-size data better than those that are disfavoured by zmax. The dA(z) comparison, however, is less discerning than that with zmax, due to the additional free parameter, H0. We find that H0 = 63.4 ± 1.2 km s−1 Mpc−1 for Rh = ct, and 69.9 ± 1.5 km s−1 Mpc−1 for ΛCDM. Both are consistent with previously measured values in each model, though they differ from each other by over 4σ. In contrast, model selection based on zmax is independent of H0.