Abundance analysis of 84 type-2 AGNs finds oversolar He and subsolar O at z>2.8, including one object at z=6.26 with record He abundance of 12+log(He/H)=11.64, plus marginal trends of declining He/H and rising O/H toward z=0.
Measurement of the primordial helium abundance from the intergalactic medium
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abstract
Almost every helium atom in the Universe was created just a few minutes after the Big Bang through a process commonly referred to as Big Bang Nucleosynthesis. The amount of helium that was made during Big Bang Nucleosynthesis is determined by the combination of particle physics and cosmology. The current leading measures of the primordial helium abundance (Y_P) are based on the relative strengths of H I and He I emission lines emanating from star-forming regions in local metal-poor galaxies. As the statistical errors on these measurements improve, it is essential to test for systematics by developing independent techniques. Here we report the first determination of the primordial helium abundance based on a near-pristine intergalactic gas cloud that is seen in absorption against the light of a background quasar. This gas cloud, observed when the Universe was just one-third of its present age (z_abs = 1.724), has a metal content ~100 times less than the Sun, and ~30 per cent less metals than the most metal-poor H II region currently known where a determination of the primordial helium abundance is afforded. We conclude that the helium abundance of this intergalactic gas cloud is Y = 0.250^{+0.033}_{-0.025}, which agrees with the Standard Model primordial value, Y_P = 0.24672 +/- 0.00017. Our determination of the primordial helium abundance is not yet as precise as that derived using metal-poor galaxies, but our method has the potential to offer a competitive test of physics beyond the Standard Model during Big Bang Nucleosynthesis.
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A statistical reanalysis of 143 Y_p determinations from 1960s-2022 reveals long-term convergence with change points in the mid-2000s and early 2010s, plus significant non-independence among many extragalactic H II region measurements.
New constraints on dark radiation parameters from recent cosmological datasets show the model alleviates the Hubble tension with SH0ES inclusion while remaining consistent with standard expectations without it.
Interacting k-essence dark energy and non-pressureless dark matter models with two interaction forms are shown to reproduce major cosmological epochs and fit observations comparably to LambdaCDM while admitting late-time de Sitter attractors.
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Cosmic evolution of the helium and oxygen abundances in type 2 Active Galactic Nuclei: Helium-loud AGNs
Abundance analysis of 84 type-2 AGNs finds oversolar He and subsolar O at z>2.8, including one object at z=6.26 with record He abundance of 12+log(He/H)=11.64, plus marginal trends of declining He/H and rising O/H toward z=0.
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Fifty years of primordial helium abundances: A statistical reanalysis
A statistical reanalysis of 143 Y_p determinations from 1960s-2022 reveals long-term convergence with change points in the mid-2000s and early 2010s, plus significant non-independence among many extragalactic H II region measurements.
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Exploring the Dark Sector: Interacting Radiation in Light of Modern Cosmological Probes
New constraints on dark radiation parameters from recent cosmological datasets show the model alleviates the Hubble tension with SH0ES inclusion while remaining consistent with standard expectations without it.
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Interacting $k$-essence field with non-pressureless Dark Matter: Cosmological Dynamics and Observational Constraints
Interacting k-essence dark energy and non-pressureless dark matter models with two interaction forms are shown to reproduce major cosmological epochs and fit observations comparably to LambdaCDM while admitting late-time de Sitter attractors.