Ana Luisa González Morán
We present independent determinations of cosmological parameters using a distance estimator based on the established correlation between the Balmer emission line velocity dispersion and luminosity for HIIG. These were obtained using new high spectral resolution observations of 40 high-z (1.3 < z < 2.6) HIIG with KMOS at the ESO-Very Large Telescope combined with already published data for another 46 high-z and 107 z < 0.15 HIIG. Using only HIIG to constrain the dark matter, we find Ωm = 0.256 +0.042 -0.52 (stat). Constraining the {Ωm, w0} plane, the marginalized best-fit parameter values are Ωm = 0.258 +0.11 -0.066 and w0 = −1.17 +0.46 -0.41 (stat). Combining HIIG, CMB and BAO yields our best estimate: Ωm = 0.299± 0.012 and w0 = −1.00±0.05 which, although less constrained, are certainly compatible with the solution space of SNIa/CMB/BAO. After adding constraints from the CMB and BAO measurements, we provide limits on the evolution of dark energy with time, w0 = −1.03 ± 0.29, wa = 0.06 ± 0.78 for the CPL DE EoS parameterizations which are in agreement with a ΛCDM Cosmology.
Instead, what we can do is to use the General Relativity: specifically the fact that all the different forms of matter and energy affect the spacetime itself, as well as how it changes with time.
The cosmological parameters Ωm and w are obtained combining the low redshift results (z<1.5) for Baryon Acoustic Oscillations (BAO) and Type Ia Supernovae (SNIa) with high redshift results (z∼1000 Planck Cosmic Microwave Background, CMB, fluctuations).
It is important to remark that the maximum difference in cosmological models that include an evolving Dark Energy Equation of State, DE EoS, occurs at redshift between 1 < z < 3.
Our objective is to use H II Galaxies (HIIG) to constrain in an independent manner cosmological parameters on the important range of redshift 1 < z < 3.
What are the HIIG? They are extremely young and massive super stellar clusters (SSC) dominating the emitted luminosity of their host galaxies.
We use the L−σ relation between the emission lines velocity dispersion (σ) and Hβ luminosity, L(Hβ), of HIIG and a Markov Chain Monte Carlo (MCMC) method to find the probability distribution of the solutions of the DE EoS and Ωm. We also combine the HIIG results with those obtained using different probes (SNIa, BAO, CMB).
To reach the objective, we need to observe a large sample of HIIG at high redshift using high resolution spectrographs at 8-10 m class telescopes like MOSFIRE at KECK and KMOS at VLT, in order to measure with great accuracy the flux and the FWHM in the emission lines.
As a result, we show that the L-σ relation is satisfied for high-z HIIG. The physics behind this relation is that as the mass of the young stellar cluster increases, both the number of ionizing photons and the motion of the ionized gas, which is determined by the gravitational potential of the massive stellar cluster and gas complex, also increase. This fact induces the correlation between the luminosity of recombination lines, e.g. L(Hβ), which is proportional to the number of ionizing photons, and the ionized gas velocity dispersion, which can be measured using the emission-line width. Therefore, the L−σ relation can be considered as a distance estimator.
Applying an H0 independent method and the L − σ relation’s intercept and slope to the joint local and high-z sample of 183 HIIG, we find: Ωm = 0.256 +0.042 -0.52 (stat).
Constraining the {Ωm, w0} plane, the marginalized best-fit parameter values are Ωm = 0.258 +0.11 -0.066 and w0 = −1.17 +0.46 -0.41 (stat).
Combining HIIG, CMB and BAO yields our best estimate: Ωm = 0.299± 0.012 and w0 = −1.00±0.05 which, although less constrained, are certainly compatible with the solution space of SNIa/CMB/BAO.
After adding constraints from the CMB and BAO measurements, we provide limits on the evolution of dark energy with time, w0 = −1.03 ± 0.29, wa = 0.06 ± 0.78 for the CPL DE EoS parameterizations which are in agreement with a ΛCDM Cosmology.
It is very encouraging that even with the moderate HIIG sample our analysis of the HII data provides constraints on the cosmological parameters which are in agreement with those of SNIa. This confirms our proposal that the Hubble Diagram for HIIG could provide an efficient tool to understand the mechanism of late cosmic acceleration.