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The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O iii] 4960 and 5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies have stellar masses in the range of log(M */M ⊙) ∼7.6–9.2 and star formation rates of ∼3–50 M ⊙ yr−1, showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [O iii] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with M * ∼ 6 × 109 M ⊙. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.

Understanding how super-massive black holes form and grow in the early Universe has become a major challenge 1 , 2 since it was discovered that luminous quasars existed only 700 million years after the Big Bang 3 , 4 . Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust 5 . Although the last phase has been identified out to a redshift of 7.6 (ref. 6 ), a transitioning quasar has not been found at similar redshifts owing to their faintness at optical and near-infrared wavelengths. Here we report observations of an ultraviolet compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of 7.1899 ± 0.0005. The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 parsec. A red point source in the far-ultraviolet is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, which indicates the emergence of a uniquely ultraviolet compact star-forming region or a Compton-thick super-Eddington black-hole accretion disk at the dusty starburst core. In the latter case, the observed properties are consistent with predictions from cosmological simulations 7 and suggest that GNz7q is an antecedent to unobscured luminous quasars at later epochs. An unusual ultraviolet compact object associated with a dusty starburst has been observed at a redshift of about 7.2, with a luminosity that falls between that of quasars and galaxies, possibly in transition between the two. 

The formation of stars and planets is accompanied not only by the build-up of matter, namely accretion, but also by its expulsion in the form of highly supersonic jets that can stretch for several parsecs 1 , 2 . As accretion and jet activity are correlated and because young stars acquire most of their mass rapidly early on, the most powerful jets are associated with the youngest protostars 3 . This period, however, coincides with the time when the protostar and its surroundings are hidden behind many magnitudes of visual extinction. Millimetre interferometers can probe this stage but only for the coolest components 3 . No information is provided on the hottest (greater than 1,000 K) constituents of the jet, that is, the atomic, ionized and high-temperature molecular gases that are thought to make up the jet’s backbone. Detecting such a spine relies on observing in the infrared that can penetrate through the shroud of dust. Here we report near-infrared observations of Herbig-Haro 211 from the James Webb Space Telescope, an outflow from an analogue of our Sun when it was, at most, a few times 10 4 years old. These observations reveal copious emission from hot molecules, explaining the origin of the ‘green fuzzies’ 4 – 7 discovered nearly two decades ago by the Spitzer Space Telescope 8 . This outflow is found to be propagating slowly in comparison to its more evolved counterparts and, surprisingly, almost no trace of atomic or ionized emission is seen, suggesting its spine is almost purely molecular. Near-infrared imagery and spectroscopy from JWST of the Herbig-Haro 211 system, an analogue of the young Sun, reveals  supersonic jets of hot molecules that can explain the origin of the ‘green fuzzies’ phenomenon.

We investigate the correlation between stellar mass (M⋆) and star formation rate (SFR) across the stellar mass range log10(M⋆/M⊙)≈6-11 . We consider almost 50,000 star-forming galaxies at z ≈ 3–7, leveraging data from COSMOS/SMUVS, JADES/GOODS-S, and MIDIS/XDF. This is the first study spanning such a wide M⋆ range without relying on gravitational lensing effects. We locate our galaxies on the SFR–M⋆ plane to assess how the location of galaxies in the star formation main sequence (MS) and starburst (SB) region evolves with M⋆ and redshift. We find that the two star-forming modes tend to converge at log10(M⋆/M⊙)<7 , with all galaxies found in the SB mode. However, deeper observations will be instrumental for reaching lower SFRs and M⋆ to further validate this scenario. By dissecting our galaxy sample in M⋆ and redshift, we show that the emergence of the star formation MS is M⋆ dependent: while in galaxies with log10(M⋆/M⊙)>9 the MS is already well in place at z = 5–7, for galaxies with log10(M⋆/M⊙)≈7-8 it only becomes significant at z < 4. Overall, our results are in line with previous findings that the SB mode dominates among low stellar-mass galaxies. The earlier emergence of the MS for massive galaxies is consistent with galaxy downsizing.

We investigate the properties of strong (Hβ + [O iii]) emitters before and after the end of the “Epoch of Reionization” from z = 8 to z = 5.5. We make use of ultradeep JWST/NIRCam imaging in the parallel field (P2) of the MIRI Deep Imaging Survey (MIDIS) in the Hubble eXtreme Deep Field (H-XDF), in order to select prominent (Hβ + [O iii]) emitters (with rest-frame equivalent width (EW0) ≳ 100 Å) at z = 5.5–7, based on their flux density enhancement in the F356W band with respect to the spectral energy distribution continuum. We complement our selection with other (Hβ + [O iii]) emitters from the literature at similar and higher (z = 7−8) redshifts. We find (nonindependent) anticorrelations between EW0(Hβ + [O iii]) and both galaxy stellar mass and age, in agreement with previous studies, and a positive correlation with specific star formation rate (sSFR). On the SFR–M ⋆ plane, the (Hβ + [O iii]) emitters populate both the star formation main sequence and the starburst region, which become indistinguishable at low stellar masses ( log10(M⋆)<7.5 ). We find tentative evidence for a nonmonotonic relation between EW0(Hβ + [O iii]) and SFR, such that both parameters correlate with each other at SFR ≳ 1 M ⊙ yr−1, while the correlation flattens out at lower SFRs. This suggests that low metallicities producing high EW0(Hβ + [O iii]) could be important at low SFR values. Interestingly, the properties of the strong emitters and other galaxies (33% and 67% of our z = 5.5–7 sample, respectively) are similar, including, in many cases, high sSFR. Therefore, it is crucial to consider both emitters and nonemitters to obtain a complete picture of the cosmic star formation activity around the Epoch of Reionization.

Star formation at a rate of more than 15 solar masses a year has been observed inside a massive outflow of gas from a nearby galaxy; this could also be happening inside other galactic outflows. Star birth in gas flows Massive, galactic-scale outflows of molecular gas with the physical conditions necessary to form stars have recently been observed and several models predict that star formation could ignite within the outflow itself. Roberto Maiolino et al . report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448 and at an inferred rate exceeding 15 times the mass of the Sun per year. This new mode of star formation might be occurring in other galactic outflows and could have implications for the morphological evolution of galaxies, while contributing to the population of high-velocity stars. Recent observations have revealed massive galactic molecular outflows 1 , 2 , 3 that may have the physical conditions (high gas densities 4 , 5 , 6 ) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself 7 , 8 , 9 , 10 , 11 . This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies 12 , to the evolution in size and velocity dispersion of the spheroidal component of galaxies 11 , 13 , and would contribute to the population of high-velocity stars, which could even escape the galaxy 13 . Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies 9 . Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics 14 , 15 .

Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 au ) regions of protoplanetary disks 1 . Water plays a key role in their formation 2 – 4 , although it is yet unclear whether water molecules are formed in situ or transported from the outer disk 5 , 6 . So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks 7 , similar to PDS 70, the first system with direct confirmation of protoplanet presence 8 , 9 . Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54  au ) planet-carved gap separating an inner and outer disk 10 , 11 . Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H 2 and/or OH, and survival through water self-shielding 5 . This is also supported by the presence of CO 2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir 12 . Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.  Observations with the sensitive mid-infrared spectrometer MIRI on board JWST reveal the presence of a water vapour reservoir in the terrestrial plant-forming zone of the young planetary system PDS 70.

We make use of JWST medium-band and broadband NIRCam imaging, along with ultradeep MIRI 5.6 μm imaging, in the Hubble eXtreme Deep Field to identify prominent line emitters at z ≃ 7–8. Out of a total of 58 galaxies at z ≃ 7–8, we find 18 robust candidates (≃31%) for (Hβ + [O iii]) emitters, based on their enhanced fluxes in the F430M and F444W filters, with EW0(Hβ +[O iii]) ≃87–2100 Å. Among these emitters, 16 lie in the MIRI coverage area and 12 exhibit a clear flux excess at 5.6 μm, indicating the simultaneous presence of a prominent Hα emission line with EW0(Hα) ≃200–3000 Å. This is the first time that Hα emission can be detected in individual galaxies at z > 7. The Hα line, when present, allows us to separate the contributions of Hβ and [O iii] to the (Hβ +[O iii]) complex and derive Hα-based star formation rates (SFRs). We find that in most cases [O iii]/Hβ > 1. Instead, two galaxies have [O iii]/Hβ < 1, indicating that the NIRCam flux excess is mainly driven by Hβ. Most prominent line emitters are very young starbursts or galaxies on their way to/from the starburst cloud. They make for a cosmic SFR density log10(ρSFRHα/(M⊙yr−1Mpc−3))≃−2.35 , which is about a quarter of the total value ( log10(ρSFRtot/(M⊙yr−1Mpc−3))≃−1.76 ) at z ≃ 7–8. Therefore, the strong Hα emitters likely had a significant role in reionization.

MIRI (the Mid-Infrared Instrument for the James Webb Space Telescope [JWST]) operates from 5 to 28.5 μm and combines over this range: (1) unprecedented sensitivity levels; (2) subarcsecond angular resolution; (3) freedom from atmospheric interference; (4) the inherent stability of observing in space; and (5) a suite of versatile capabilities including imaging, low- and medium-resolution spectroscopy (with an integral field unit), and coronagraphy. We illustrate the potential uses of this unique combination of capabilities with various science examples: (1) imaging exoplanets; (2) transit and eclipse spectroscopy of exoplanets; (3) probing the first stages of star and planet formation, including identifying bioactive molecules; (4) determining star formation rates and mass growth as galaxies are assembled; and (5) characterizing the youngest massive galaxies.

By using an ultradeep JWST/MIRI image at 5.6 μm in the Hubble eXtreme Deep Field, we constrain the role of strong Hα emitters (HAEs) during “cosmic reionization” at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = −2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log10(ξion,0/(Hzerg−1))=25.50−0.12+0.10 . We show that ξ ion,0 positively correlates with Hα equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict fesc,LyC=4%−2+3 , which results in log10(ξion/(Hzerg−1))=25.55−0.13+0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( Ṅion ) as Ṅion=1050.53±0.45s−1Mpc−3 . When comparing their Ṅion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization.