Abstract
We continue to build support for the proposal to use HII galaxies (HIIGx) and giant extragalactic HII regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission-line luminosity and ionized-gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model $\Lambda$CDM and the $R_{\rm h}=ct$ Universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat $\Lambda$CDM model, the best fit is obtained with $\Omega_{\rm m}= 0.40_{-0.09}^{+0.09}$. However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favor $R_{\rm h}=ct$ over the standard model with a likelihood of $\approx 94.8\%-98.8\%$ versus only $\approx 1.2\%-5.2\%$. For $w$CDM (the version of $\Lambda$CDM with a dark-energy equation of state $w_{\rm de}\equiv p_{\rm de}/\rho_{\rm de}$ rather than $w_{\rm de}=w_{\Lambda}=-1$), a statistically acceptable fit is realized with $\Omega_{\rm m}=0.22_{-0.14}^{+0.16}$ and $w_{\rm de}= -0.51_{-0.25}^{+0.15}$ which, however, are not fully consistent with their concordance values. In this case, $w$CDM has two more free parameters than $R_{\rm h}=ct$, and is penalized more heavily by these criteria. We find that $R_{\rm h}=ct$ is strongly favored over $w$CDM with a likelihood of $\approx 92.9\%-99.6\%$ versus only $0.4\%-7.1\%$. The current HIIGx sample is already large enough for the BIC to rule out $\Lambda$CDM/$w$CDM in favor of $R_{\rm h}=ct$ at a confidence level approaching $3\sigma$.
Highlights
H II galaxies (HIIGx) are massive and compact aggregates of star formation
To facilitate a direct comparison between CDM and Rh = ct, we show in Fig. 4 the Hubble diagrams for the combined 25 high-z H II galaxies and the 131 local sample (107 H II galaxies and 24 Giant Extragalactic H II Regions)
HIIGx and Giant extragalactic H II regions (GEHR) have been proposed as useful standard candles due to the correlation between their velocity dispersion and the luminosity of their H β emission line
Summary
H II galaxies (HIIGx) are massive and compact aggregates of star formation. The total luminosity of an HIIGx is almost completely dominated by the starburst. Melnick, Terlevich & Terlevich 2000; Siegel et al 2005) is the fact that as the mass of the starburst component increases, both the number of ionizing photons and the turbulent velocity of the gas, which is dominated by gravitational potential of the star and gas, increase This naturally induces a correlation between the luminosity L(H β) in H β and the ionized gas velocity dispersion σ (Terlevich & Melnick 1981). Inserra & Smart 2014; Wei, Wu & Melia 2015b), and the age measurements of passively evolving galaxies (e.g. Alcaniz & Lima 1999; Lima & Alcaniz 2000; Wei et al 2015c) In all such one-on-one comparisons completed far, model selection tools show that the data favour Rh = ct over CDM
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