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Impact of young stellar components on quiescent galaxies: deconstructing cosmic chronometers
Cosmology and Nongalactic Astrophysics · Submitted 26 Feb 2018
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Consequently, the measurements of the absolute value of the age or the differential age between different redshifts are incorrect and make the previous calculations of H(z) very inaccurate.
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The abstract, sentence by sentence
Cosmic chronometers may be used to measure the age difference between passively evolving galaxy populations to calculate the Hubble parameter H(z). The age estimator emerges from the relationship between the amplitude of the rest frame Balmer break at 4000 angstroms and the age of a galaxy, assuming that there is one single stellar population within each galaxy. However, recent literature has shown possible contamination (up to 2.4% of the stellar mass in a high redshift sample) of a young component embedded within the predominantly old population of the quiescent galaxy. We compared the data with the predictions of each model, using a new approach of distinguishing between systematic and statistical errors (in previous works, these had incorrectly been added in quadrature) and evaluating the effects of contamination by a young stellar component. The ages inferred using cosmic chronometers represent a galaxy-wide average rather than a characteristic of the oldest population alone. The average contribution from the young component to the rest luminosity at 4000 angstroms may constitute a third of the luminosity in some samples, which means that this is far from negligible. This ratio is significantly dependent on stellar mass, proportional to M^{-0.7}. Consequently, the measurements of the absolute value of the age or the differential age between different redshifts are incorrect and make the previous calculations of H(z) very inaccurate. Some cosmological models, such as the Einstein-de Sitter model or quasi-steady state cosmology, which are rejected under the assumption of a purely old population, can be made compatible with the predicted ages of the Universe as a function of redshift if we take this contamination into account. However, the static Universe models are rejected by these H(z) measurements, even when this contamination is taken into account.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Cosmic chronometers may be used to measure the age difference between passively evolving galaxy populations to calculate the Hubble parameter H(z). | background 0.99 | 0.06 | 0.03 | hedged possibility 0.99 |
| s1 | The age estimator emerges from the relationship between the amplitude of the rest frame Balmer break at 4000 angstroms and the age of a galaxy, assuming that there is one single stellar population within each galaxy. | background 0.93 | 0.07 | 0.03 | asserted 0.99 |
| s2 | However, recent literature has shown possible contamination (up to 2.4% of the stellar mass in a high redshift sample) of a young component embedded within the predominantly old population of the quiescent galaxy. | background 0.85 | 0.06 | 0.06 | hedged possibility 0.88 |
| s3 | We compared the data with the predictions of each model, using a new approach of distinguishing between systematic and statistical errors (in previous works, these had incorrectly been added in quadrature) and evaluating the effects of contamination by a young stellar component. | method 0.88 | 0.93 | 0.05 | asserted 0.97 |
| s4 | The ages inferred using cosmic chronometers represent a galaxy-wide average rather than a characteristic of the oldest population alone. | result 0.67 | 0.56 | 0.20 | asserted 1.00 |
| s5 | The average contribution from the young component to the rest luminosity at 4000 angstroms may constitute a third of the luminosity in some samples, which means that this is far from negligible. | result 0.92 | 0.70 | 0.12 | hedged possibility 0.99 |
| s6 | This ratio is significantly dependent on stellar mass, proportional to M^{-0.7}. | result 1.00 | 0.70 | 0.05 | asserted 1.00 |
| s7 | Consequently, the measurements of the absolute value of the age or the differential age between different redshifts are incorrect and make the previous calculations of H(z) very inaccurate. | interpretation 0.72 | 0.65 | 0.64 | asserted 1.00 |
| s8 | Some cosmological models, such as the Einstein-de Sitter model or quasi-steady state cosmology, which are rejected under the assumption of a purely old population, can be made compatible with the predicted ages of the Universe as a function of redshift if we take this contamination into account. | interpretation 0.85 | 0.49 | 0.18 | hedged possibility 0.86 |
| s9 | However, the static Universe models are rejected by these H(z) measurements, even when this contamination is taken into account. | result 0.68 | 0.70 | 0.32 | asserted 1.00 |
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Original abstract
Cosmic chronometers may be used to measure the age difference between passively evolving galaxy populations to calculate the Hubble parameter H(z). The age estimator emerges from the relationship between the amplitude of the rest frame Balmer break at 4000 angstroms and the age of a galaxy, assuming that there is one single stellar population within each galaxy. However, recent literature has shown possible contamination (up to 2.4% of the stellar mass in a high redshift sample) of a young component embedded within the predominantly old population of the quiescent galaxy. We compared the data with the predictions of each model, using a new approach of distinguishing between systematic and statistical errors (in previous works, these had incorrectly been added in quadrature) and evaluating the effects of contamination by a young stellar component. The ages inferred using cosmic chronometers represent a galaxy-wide average rather than a characteristic of the oldest population alone. The average contribution from the young component to the rest luminosity at 4000 angstroms may constitute a third of the luminosity in some samples, which means that this is far from negligible. This ratio is significantly dependent on stellar mass, proportional to M^{-0.7}. Consequently, the measurements of the absolute value of the age or the differential age between different redshifts are incorrect and make the previous calculations of H(z) very inaccurate. Some cosmological models, such as the Einstein-de Sitter model or quasi-steady state cosmology, which are rejected under the assumption of a purely old population, can be made compatible with the predicted ages of the Universe as a function of redshift if we take this contamination into account. However, the static Universe models are rejected by these H(z) measurements, even when this contamination is taken into account.
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How the literature uses it
11 arXiv papers cite this in 12 sentences
Papers whose main result relates to this one's
States a conflicting result 1 paper
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We show that for our previous measurements of the Hubble parameter, the possible bias induced by the presence of a younger component is well below the current errors.
Papers citing it · 10 sentences without a confident label
Uses its data or values 1 paper
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Our adopted CC data points were compiled from Refs. [ref] , which are independent of the Cepheid distance scale and from any cosmological model, although they are dependent on the modelling of stellar ages, which is based on robust stellar population synthesis techniques (see, for instance, Refs. [ref] for analyses related to CC systematics).
Impact of $H_0$ priors on $f(T)$ late time cosmology · Observational Data · 0.87
Cites it as background 1 paper
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These measurements do not rely on any particular cosmological model, although are subject to other sources of systematic uncertainties, as to the ones associated with the modeling of stellar ages, see e.g. [ref] , which is carried out through the so-called stellar population synthesis (SPS) techniques, and also with a possible contamination due to the presence of young stellar components in quiescent galaxies [ref] .
Measuring the sound horizon and absolute magnitude of SNIa by maximizing the consistency between low-redshift data sets · Cosmic chronometers · 0.80
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