Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers (1201.3609v4)

Abstract: We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (\sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z \sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a \Lambda CDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z \sim 2.

• The paper uses cosmic chronometers by analyzing 11,000 early-type galaxies to directly measure H(z) up to z~1.1.
• It employs the D4000 spectral break and stellar population synthesis models to robustly calibrate galaxy ages and minimize uncertainties.
• The results strongly support the ΛCDM model, achieving 5%-12% precision and setting a framework for future high-redshift dark energy studies.

Improved Constraints on the Expansion Rate of the Universe

The paper titled "Improved constraints on the expansion rate of the Universe up to \$z\sim1.1\$ from the spectroscopic evolution of cosmic chronometers" contributes to the understanding of the Universe's expansion dynamics utilizing cosmic chronometers. The methodology hinges on employing massive, passive elliptical galaxies (early-type galaxies, ETGs), whose differential evolutionary history in redshift provides a direct measurement of the Hubble parameter $H(z)$ without necessitating assumptions of standard candles or rulers.

Methodology and Data

The authors compiled a robust data selection from numerous spectroscopic surveys, culminating in a sample size of approximately 11,000 ETGs covering a redshift range of $0.15$D4000$) in stellar spectra, a feature predominantly influenced by stellar age and metallicity, employing stellar population synthesis models to calibrate the dependence of age on changes in $D4000$. From this calibration, the function $H(z)$ is derived as:

$H(z) = -\frac{A(Z)}{1+z} \frac{dz}{dD4000_n}$

where $A(Z)$ is the slope relating $D4000_n$ to age for a specific metallicity. Special attention was given to minimizing errors by testing for statistical robustness and considering systematic uncertainties from stellar population models, metallicity, and star formation history.

Results and Interpretation

The research offers eight new $H(z)$ measurements, achieving a precision between 5%–12%, and mapping the redshift up to $z\sim1.1$. This accuracy outstrips previous estimations significantly. Crucially, the measurements align closely with the $\Lambda$CDM cosmological model, asserting the Universe's accelerated expansion and dismissing alternative models like Einstein-de Sitter with high statistical significance. It addresses the critical epochs around $0.5 < z < 0.8$, suggesting future work could discern between competing dark energy models, especially if similar methodologies were expanded to higher redshifts, potentially up to $z \sim 2$, with forthcoming surveys like Euclid.

Conclusion and Implications

This work presents a pivotal advancement in cosmic chronometer usage for $H(z)$ measurements, reducing reliance on traditional distance measurements (e.g., supernovae, BAO). By confirming the $\Lambda$CDM model and highlighting the Universe's accelerated expansion, this paper opens paths for future precision in cosmology, especially concerning quintessence models. The integration of massive datasets, diverse sourcing, and rigorous statistical techniques underscore the robustness of the presented findings, thus anchoring a framework for consequent high-redshift analyses. As astronomical instruments and surveys advance, integrating these techniques will refine the cosmic expansion narrative and better constrain theoretical cosmological models.