Our current understanding of galaxy evolution still has many uncertainties associated with the details of the accretion, processing, and removal of gas across cosmic time. The next generation of radio telescopes will image the neutral hydrogen (H i) in galaxies over large volumes at high redshifts, which will provide key insights into these processes. We are conducting the COSMOS H i Large Extragalactic Survey (CHILES) with the Karl G. Jansky Very Large Array, which is the first survey to simultaneously observe H i from z = 0 to z ∼ 0.5. Here, we report the highest redshift H i 21 cm detection in emission to date of the luminous infrared galaxy COSMOS J100054.83+023126.2 at z = 0.376 with the first 178 hr of CHILES data. The total H i mass is (2.9 ± 1.0) × 10¹⁰ M _⊙ and the spatial distribution is asymmetric and extends beyond the galaxy. While optically the galaxy looks undisturbed, the H i distribution suggests an interaction with a candidate companion. In addition, we present follow-up Large Millimeter Telescope CO observations that show it is rich in molecular hydrogen, with a range of possible masses of (1.8–9.9) × 10¹⁰ M _⊙. This is the first study of the H i and CO in emission for a single galaxy beyond z ∼ 0.2.

The validity of the emission-line luminosity versus ionized gas velocity dispersion (L–σ) correlation for H ii galaxies (HIIGx) and its potential as an accurate distance estimator are assessed. For a sample of 128 local (0.02 ≲ z ≲ 0.2) compact HIIGx with high equivalent widths of their Balmer emission lines, we obtained the ionized gas velocity dispersion from high signal-to-noise ratio (S/N) high-dispersion spectroscopy (Subaru High Dispersion Spectrograph (HDS) and European Southern Observatory (ESO) Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT–UVES)) and integrated Hβ fluxes from low-dispersion wide aperture spectrophotometry. We find that the L(Hβ)–σ relation is strong and stable against restrictions in the sample (mostly based on the emission-line profiles). The ‘Gaussianity’ of the profile is important for reducing the root-mean-square (rms) uncertainty of the distance indicator, but at the expense of substantially reducing the sample. By fitting other physical parameters into the correlation, we are able to decrease the scatter significantly without reducing the sample. The size of the star-forming region is an important second parameter, while adding the emission-line equivalent width or the continuum colour and metallicity produces the solution with the smallest rms scatter=δlog L(Hβ) = 0.233. The derived coefficients in the best L(Hβ)–σ relation are very close to what is expected from virialized ionizing clusters, while the derived sum of the stellar and ionized gas masses is similar to the dynamical mass estimated using the Hubble Space Telescope (HST) corrected Petrosian radius. These results are compatible with gravity being the main mechanism causing the broadening of the emission lines in these very young and massive clusters. The derived masses range from about 2 × 10⁶ M_⊙ to 10⁹ M_⊙ and their ‘corrected’ Petrosian radius ranges from a few tens to a few hundred pc.

The relationship between the integrated H β line luminosity and the velocity dispersion of the ionized gas of H ii galaxies and giant H ii regions represents an exciting standard candle that presently can be used up to redshifts z ∼ 4. Locally it is used to obtain precise measurements of the Hubble constant by combining the slope of the relation obtained from nearby (z ≤ 0.2) H ii galaxies with the zero-point determined from giant H ii regions belonging to an ‘anchor sample’ of galaxies for which accurate redshift-independent distance moduli are available. We present new data for 36 giant H ii regions in 13 galaxies of the anchor sample that includes the megamaser galaxy NGC 4258. Our data are the result of the first 4 yr of observation of our primary sample of 130 giant H ii regions in 73 galaxies with Cepheid determined distances. Our best estimate of the Hubble parameter is 71.0 ± 2.8(random) ± 2.1(systematic) km s^{− 1}Mpc^{− 1}. This result is the product of an independent approach and, although at present less precise than the latest SNIa results, it is amenable to substantial improvement.

We present independent determinations of cosmological parameters using the distance estimator based on the established correlation between the Balmer line luminosity, L(H β), and the velocity dispersion (σ) for H ii galaxies (HIIG). These results are based on new VLT-KMOS high spectral resolution observations of 41 high-z (1.3 ≤ z ≤2.6) HIIG combined with published data for 45 high-z and 107 z ≤0.15 HIIG, while the cosmological analysis is based on the MultiNest Markov Chain Monte Carlo (MCMC) procedure not considering systematic uncertainties. Using only HIIG to constrain the matter density parameter (Ω_m), we find |$\Omega _\mathrm{ m} = 0.244^{+0.040}_{-0.049}$| (stat), an improvement over our best previous cosmological parameter constraints, as indicated by a 37 per cent increase of the figure of merit. The marginalized best-fitting parameter values for the plane {Ω_m; w₀} = |$\lbrace 0.249^{+0.11}_{-0.065}; -1.18^{+0.45}_{-0.41}\rbrace$| (stat) show an improvement of the cosmological parameters constraints by 40 per cent. Combining the HIIG Hubble diagram, the cosmic microwave background (CMB) and the baryon acoustic oscillation (BAO) probes yields Ω_m = 0.298 ± 0.012 and w₀ = −1.005 ± 0.051, which are certainly compatible – although less constraining – than the solution based on the joint analysis of Ia supernovae (SNIa), CMB and BAO measurements. An attempt to constrain the evolution of the dark energy with time (CPL model), using a joint analysis of the HIIG, CMB, and BAO measurements, shows a degenerate 1σ contour of the parameters in the {w₀, w_a} plane.

We report the first results of a programme aimed at studying the properties of high-redshift galaxies with ongoing massive and dominant episodes of star formation (H ii galaxies). We use the L(Hβ)–σ distance estimator based on the correlation between the ionized gas velocity dispersions and Balmer emission line luminosities of H ii galaxies and Giant H ii regions to trace the expansion of the Universe up to z ∼ 2.33. This approach provides an independent constraint on the equation of state of dark energy and its possible evolution with look-back time. Here we present high-dispersion (8000 to 10 000 resolution) spectroscopy of H ii galaxies at redshifts between 0.6 and 2.33, obtained at the Very Large Telescope (VLT) using XShooter. Using six of these H ii galaxies we obtain broad constraints on the plane Ω_m–w₀. The addition of 19 high-z H ii galaxies from the literature improves the constraints and highlights the need for high-quality emission line profiles, fluxes and reddening corrections. The 25 high-z H ii galaxies plus our local compilation of 107 H ii galaxies up to z = 0.16 were used to impose further constraints. Our results are consistent with recent studies, although weaker due to the as yet small sample and low quality of the literature data of high-z H ii galaxies. We show that much better and competitive constraints can be obtained using a larger sample of high-redshift H ii galaxies with high quality data that can be easily obtained with present facilities like K-band Multi Object Spactrograph (KMOS) at the VLT.