A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang. The abundance of star-forming galaxies is known to decline from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD1 , a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.

The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium.

We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at z 3 phot ~-6. Their infrared luminosities and star formation rates (SFRs) are L IR ~2-6 10 12 ´L and ∼200-600 M  yr −1 , respectively. The sizes of these SMGs range from 0″. 10 to 0″. 38, with a median of 0″. 20 0. 05to that seen in local merger-driven (U)LIRGs rather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in z 3  SMGs strongly supports a massive galaxy formation scenario wherein z 3 ~-6 SMGs evolve into the compact stellar components of z 2 ~cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local universe, mostly via dry mergers. Our results thus suggest that z 3  SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing ∼90% of the age of the universe.

We present the Atacama Large Millimeter/submillimeter Array (ALMA) detection of the [O iii] 88 µm line and rest-frame 90 µm dust continuum emission in a Y -dropout Lyman break galaxy (LBG), MACS0416 Y1, lying behind the Frontier Field cluster MACS J0416.1−2403. This [O iii] detection confirms the LBG with a spectroscopic redshift of z = 8.3118 ± 0.0003, making this object one of the furthest galaxies ever identified spectroscopically. The observed 850 µm flux density of 137 ± 26 µJy corresponds to a de-lensed total infrared (IR) luminosity of L IR = (1.7±0.3)×10 11 L if assuming a dust temperature of T dust = 50 K and an emissivity index of β = 1.5, yielding a large dust mass of 4×10 6 M . The ultraviolet-to-far IR spectral energy distribution modeling where the [O iii] emissivity model is incorporated suggests the presence of a young (τ age ≈ 4 Myr), star-forming (SFR ≈ 60 M yr −1 ), moderately metal-polluted (Z ≈ 0.2Z ) stellar component with a mass of M star = 3 × 10 8 M . An analytic dust mass evolution model with a single episode of star-formation does not reproduce the metallicity and dust mass in τ age ≈ 4 Myr, suggesting a pre-existing evolved stellar component with M star ∼ 3 × 10 9 M and τ age ∼ 0.3 Gyr as the origin of the dust mass.

We present a 0.72 deg2 contiguous 1.1‐mm survey in the central area of the Cosmological Evolution Survey field carried out to a 1σ≈ 1.26 mJy beam−1 depth with the AzTEC camera mounted on the 10‐m Atacama Submillimeter Telescope Experiment. We have uncovered 189 candidate sources at a signal‐to‐noise ratio (S/N) ≥ 3.5, out of which 129, with S/N ≥ 4, can be considered to have little chance of being spurious (≲2 per cent). We present the number counts derived with this survey, which show a significant excess of sources when compared to the number counts derived from the ∼0.5 deg2 area sampled at similar depths in the Submillimetre Common‐User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES). They are, however, consistent with those derived from fields that were considered too small to characterize the overall blank‐field population. We identify differences to be more significant in the S1.1mm≳ 5 mJy regime, and demonstrate that these excesses in number counts are related to the areas where galaxies at redshifts z≲ 1.1 are more densely clustered. The positions of optical–infrared galaxies in the redshift interval 0.6 ≲z≲ 0.75 are the ones that show the strongest correlation with the positions of the 1.1‐mm bright population (S1.1mm≳ 5 mJy), a result which does not depend exclusively on the presence of rich clusters within the survey sampled area. The most likely explanation for the observed excess in number counts at 1.1‐mm is galaxy–galaxy and galaxy–group lensing at moderate amplification levels, which increases in amplitude as one samples larger and larger flux densities. This effect should also be detectable in other high‐redshift populations.