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.
The H II galaxy Hubble diagram strongly favours R-h = ct over Lambda CDMWei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio; Univ Arizona, Dept Phys; Univ Arizona, Dept Astron (OXFORD UNIV PRESS, 2016-12-01)We continue to build support for the proposal to use H II galaxies (HIIGx) and giant extragalactic H II regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission -line luminosity and ionized -gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model Lambda CDM and the R-h = ct universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat Lambda CDM model, the best fit is obtained with Omega(m) = 0.40(-0.09)(+0.09). However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favour R-h = Ct over the standard model with a likelihood of approximate to 94.8-98.8 per cent versus only per cent. For wCDM (the version of ACDM with a dark -energy equation of state wde = Pde/Pde rather than was t WA = 1), a statistically acceptable fit is realized with Omega(m) = 0.221(-0.14)(+0.16) and wde = 0.511'0'21-5" which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than R-h = Ct, and is penalized more heavily by these criteria. We find that R-h = Ct is strongly favoured over wCDM with a likelihood of approximate to 92.9-99.6 per cent versus only 0.4-7.1 per cent. The current HIIGx sample is already large enough for the BIC to rule out ACDM/wCDM in favour of R-h = Ct at a confidence level approaching 3 sigma.
A cosmological solution to the Impossibly Early Galaxy ProblemYennapureddy, Manoj K.; Melia, Fulvio; Univ Arizona, Dept Phys; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (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.