Eppur è piatto? The cosmic chronometer take on spatial curvature and cosmic concordance

Abstract

The question of whether Cosmic Microwave Background (CMB) temperature and polarization data from Planck favor a spatially closed Universe with curvature parameter ${\Omega }_K<0$ has been the subject of recent intense discussions. Attempts to break the geometrical degeneracy combining Planck data with external datasets such as Baryon Acoustic Oscillation (BAO) measurements all point towards a spatially flat Universe, at the cost of significant tensions with Planck, which make the resulting dataset combination problematic. Settling this issue requires identifying a dataset which can break the geometrical degeneracy while not incurring in these tensions. We argue that cosmic chronometers (CC), measurements of the expansion rate $H(z)$ from the relative ages of massive early-type passively evolving galaxies, are the dataset we are after. Furthermore, CC come with the additional advantage of being virtually free of cosmological model assumptions. Combining Planck 2018 CMB temperature and polarization data with the latest CC measurements, we break the geometrical degeneracy and find ${\Omega }_K=-0.0054\pm 0.0055$, consistent with a spatially flat Universe and competitive with the Planck+BAO constraint. Our results are stable against minimal parameter space extensions and CC systematics, and we find no substantial tension between Planck and CC data within a non-flat Universe, making the resulting combination reliable. Our results allow us to assert with confidence that the Universe is spatially flat to the $\mathcal{O}(10^{-2})$ level, a finding which might possibly settle the ongoing spatial curvature debate, and lends even more support to the already very successful inflationary paradigm.

30 pages, 6 figures. The busy reader should skip to Fig. 1 and Tab. 3 for the main results, and to Fig. 5 and Tab. 4 if they are interested in the extended parameter space results. "Piatto" = "flat" in Italian, "Note added" between conclusions and acknowledgements explains our choice of title. v2: abstract shortened, references added, version accepted for publication in ApJ. Comments are welcome

References in corpus (33)

• Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM
• Raising the bar: new constraints on the Hubble parameter with cosmic chronometers at z$\sim$2
• Planck evidence for a closed Universe and a possible crisis for cosmology
• Inflationary Cosmology
• The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints
• Late-time cosmology with 21cm intensity mapping experiments
• Cosmic Microwave Weak lensing data as a test for the dark universe
• Cosmographic bounds on the cosmological deceleration-acceleration transition redshift in $f(\mathcal{R})$ gravity
• The evolution of star formation histories of quiescent galaxies
• HD 140283: A Star in the Solar Neighborhood that Formed Shortly After the Big Bang
• Dynamical Dark Energy or Simply Cosmic Curvature?
• The Assembly Histories of Quiescent Galaxies Since z=0.7 from Absorption Line Spectroscopy
• Holographic dark energy from nonadditive entropy: cosmological perturbations and observational constraints
• New observational constraints on $f(R)$ gravity from cosmic chronometers
• Probing for dynamics of dark energy and curvature of universe with latest cosmological observations
• Interacting Dark Energy in a closed universe
• Three Ancient Halo Subgiants: Precise Parallaxes, Compositions, Ages, and Implications for Globular Clusters
• Dynamical dark energy: scalar fields and running vacuum
• Cosmological discordances II: Hubble constant, Planck and large-scale-structure data sets
• Strong evidence for an accelerating universe
• Constraining cosmic curvature by using age of galaxies and gravitational lenses
• The local and distant Universe: stellar ages and $H_0$
• Soundness of Dark Energy properties
• Connecting early and late epochs by f(z)CDM cosmography
• Inflation in a closed universe
• Model-independent constraints on cosmic curvature: implication from updated Hubble diagram of high-redshift standard candles
• Probing the properties of relic neutrinos using the cosmic microwave background, the Hubble Space Telescope and galaxy clusters
• Tracing the cosmic history by Gauss-Bonnet gravity
• Cosmological discordances III: more on measure properties, Large-Scale-Structure constraints, the Hubble constant and Planck
• Testing the mutual consistency of different supernovae surveys
• Uncertainty on determining the dark energy equation of state due to the spatial curvature
• The Age-Redshift Relationship of Old Passive Galaxies
• Current lookback time-redshift bounds on dark energy

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