We report the discovery of two galaxy candidates at redshifts between 15.7 < z < 16.4 in James Webb Space Telescope (JWST) observations from the GLIMPSE survey. These robust sources were identified using a combination of Lyman break selection and photometric redshift estimates. The ultradeep NIRCam imaging from GLIMPSE, combined with the strong gravitational lensing of the AS1063 galaxy cluster, allows us to probe an intrinsically fainter population (down to M_UV = −17.0 mag) than previously achievable. These galaxies have absolute magnitudes ranging from M_UV = −17.0 to −17.2 mag, with blue (β ≃ −2.87) ultraviolet (UV) continuum slopes, consistent with young, dust-free stellar populations. The number density of these objects, log₁₀(ϕ/[Mpc⁻³ mag⁻¹]) = −3.47−0.10+0.13 at M_UV = −17, is in clear tension with pre-JWST theoretical predictions, extending the overabundance of galaxies from z ∼ 10 to z ∼ 17. These results, together with the scarcity of brighter galaxies in other public surveys, suggest a steep decline in the bright end of the UV luminosity function at z ∼ 16, implying efficient star formation and possibly a close connection to the halo mass function at these redshifts. Testing a variety of star formation histories suggests that these sources are plausible progenitors of the unusually UV-bright galaxies that JWST now routinely uncovers at z = 10–14. Overall, our results indicate that the luminosity distribution of the earliest star-forming galaxies could be shifting toward fainter luminosities, implying that future surveys of cosmic dawn will need to explore this faint luminosity regime.

We present a detailed JWST/NIRSpec and NIRCam analysis of a gravitationally lensed galaxy (μ = 17 - 21) at a redshift of 6.14 magnified by the Hubble Frontier Field galaxy cluster MACS J0416. The target galaxy is a typical compact and UV-faint (MUV = - 17.8) Lyman-α emitter, yet the large magnification allows the detailed characterization of structures on sub-galactic scales (down to a few parsecs). Prominent optical Hα, Hβ, and [OIII]λλ4959, 5007 lines are spatially resolved with the high-spectral-resolution grating (G395H, R 2700), with large equivalent widths, EW(Hβ+OIII) ≳ 1000 Å, and elevated ionizing photon production efficiencies, log(ξion/erg- 1Hz) = 25.2-25.7. NIRCam deep imaging reveals the presence of compact rest-UV-bright regions along with individual star clusters of Reff = 3 - 8 pc in size and M ~ 2 · 105 - 5 · 106 M⊙ in mass. These clusters are characterized by steep UV slopes, βUV ≲ - 2.5, which in some cases are associated with a dearth of line emission, indicating possible leaking of the ionizing radiation, as also supported by a Lyman-α emission peaking at ~100 km s- 1 from the systemic redshift. While the entire system is characterized by low metallicity, ~0.1 Z⊙, the NIRSpec-IFU map also reveals the presence of a low-luminosity, metal-poor region with Z ≲ 2% Z⊙, which is barely detected in NIRCam imaging; this region is displaced by > 200 pc from one of the brightest structures of the system in UV, and would have been too faint to detect if not for the large magnification of the system.

Deuteration of hydrocarbon material, including polycyclic aromatic hydrocarbons (PAHs), has been proposed to account for the low gas-phase abundances of D in the interstellar medium (ISM). JWST spectra of four star-forming regions in M51 show an emission feature, with central wavelength ∼4.647 μm and FWHM 0.0265 μm, corresponding to the C-D stretching mode in aliphatic hydrocarbons. The emitting aliphatic material is estimated to have (D/H)aliph. ≈0.17 ± 0.02—a factor of ∼104 enrichment relative to the overall ISM. On ∼50 pc scales, deuteration levels toward four H ii regions in M51 are 2-3 times higher than in the Orion Bar photodissociation region (PDR), with implications for the processes responsible for the formation and evolution of hydrocarbon nanoparticles, including PAHs. The deuteration of the aliphatic material is found to anticorrelate with helium ionization in the associated H ii, suggesting that harsh far-UV radiation may act to lower the deuteration of aliphatics in PDRs near massive stars. No evidence is found for deuteration of aromatic material, with (D/H)arom. ≲ 0.016: deuteration of the aliphatic material exceeds that of the aromatic material by at least a factor of 10. The observed levels of deuteration may account for the depletion of D observed in the Galactic ISM. If so, the 4.65 μm feature may be detectable in absorption.

Haro 11 is the closest known Lyman continuum leaking galaxy and serves as an important laboratory for studying the escape of Lyman continuum radiation. The galaxy is a metal-poor, starburst galaxy believed to be undergoing a merger that might help facilitate the escape of radiation. In this study, we carry out a large suite of numerical simulations of a merger between two disc galaxies, to study possible origins of Haro 11 and understand under which conditions various features of the galaxy are formed. By varying galaxy parameters describing the orbital configurations, masses, and their inclination, we perform a total of ~500 simulations. We demonstrate that a two-disc galaxy merger is able to reproduce key, observed features of Haro 11, including its morphology, gas kinematics, star formation history, and stellar population ages and masses. We also find that small parameter variations have minimal impact on the orbits and resulting galaxy properties. In particular, we present a fiducial Haro 11 model that produces the single observed tidal tail, the presence of three stellar knots, and inner gas morphology and kinematics. By performing mock observations, we compare with the results of observational data and discuss possible origins for various features. Furthermore, we present newly gathered observational data that confirms the presence of a stellar tidal tail with similar length and direction as our simulations.

We investigate the nature of star formation in gas-rich galaxies at z > 7 forming in a markedly overdense region, in the vicinity of a massive virialized halo already exceeding 1012 M⊙, through the use of the very-high-resolution cosmological hydrodynamical simulation MassiveBlackPS with a spatial resolution of 2 pc. We find that not only the primary galaxy but also the lower-mass companion galaxies rapidly develop massive self-gravitating compact gas disks, less than 500 pc in size, which undergo fragmentation by gravitational instability into very massive bound clumps. Star formation proceeds fast in the clumps, which quickly turn into compact star clusters with masses in the range 105-108 M⊙ and typical half-mass radii of a few parsec, reaching characteristic densities above 105 M⊙ pc−2. The properties of the clusters in the lowest-mass galaxy bear a striking resemblance to those recently discovered by the James Webb Space Telescope (JWST) in the lensed Cosmic Gems arc system at z = 10.2. We argue that, due to their extremely high stellar densities, intermediate-mass black holes would form rapidly inside the clusters, which would then swiftly sink and merge on their way to the galactic nucleus, easily growing into a 107 M⊙ supermassive black hole (SMBH). Due to the high fractional mass contribution of clusters to the stellar mass of the galaxies, in the range 20%-40%, the central SMBH would comprise more than 10% of the mass of its host galaxy, naturally explaining the overmassive SMBHs discovered by JWST at z > 6.

We report the first detections of [Ne v] λ14.3 μm and [Ne vi] λ7.7 μm at high confidence (S/N ≥ 6) in the nuclear region of the nearby spiral galaxy M83. Emission-line maps of these high-ionization lines show several compact structures. Specifically, the [Ne vi] emission is located at 140 pc from the optical nucleus and appears as a point source of size ≲18 pc (FWHM ≲ 0.″8). We investigate the possible source of this extreme emission through comparison with photoionization models and ancillary data. We find that photoionization models of fast radiative shocks are able to reproduce the observed high-excitation emission-line fluxes only for the lowest preshock density available in the library, n = 0.01 cm⁻³. Additionally, tailored active galactic nucleus (AGN) photoionization models assuming a two-zone structure are compatible with the observed high-ionization fluxes. Our simple AGN model shows that the emission at the location of the [Ne vi] source can be the result of a cloud being ionized by the radiation cone of an AGN. We stress, however, that to definitively confirm an AGN as the main source of the observed emission, more complex modeling accounting for different geometries is required. Previously known as a purely starburst system, these new findings of the nuclear region of M83 will require a reassessment of its nature and of objects similar to it, particularly now that we have access to the unparalleled infrared sensitivity and spatial resolution of the James Webb Space Telescope.

JWST/MIRI images have been used to study the Fourier transform power spectra (PS) of two spiral galaxies, NGC 628 and NGC 5236, and two dwarfs, NGC 4449 and NGC 5068, at distances ranging from 4 to 10 Mpc. The PS slopes on scales larger than 200 pc range from −0.6 at 21µm to −1.2 at 5.6µm. These slopes for one-dimensional PS are consistent with the PS slopes observed elsewhere using HI and dust emission. They are likely related to turbulence, but they may also be viewed as a hierarchical distribution of objects having a size-luminosity relation and size distribution function. There is no evidence for a kink or steepening of the PS at some transition from two-dimensional to three-dimensional turbulence on the scale of the disk thickness. This lack of a kink could be from large positional variations in the PS depending on two opposite effects: local bright sources that make the slope shallower and exponential galaxy profiles that make the slope steeper. The sources could also be confined to a layer of molecular clouds that is thinner than the HI or cool dust layers where PS kinks have been observed before. If the star formation layers observed in the mid-infrared here are too thin, then the PS kink could also be hidden in the broad tail of the JWST point spread function.

Context. The Lyman-α (Lyα) line of hydrogen is a well-known tracer of galaxies at high redshift. However, the connection between Lyα observables and galaxy properties has not been fully established, limiting the use of the line to probe the physics of galaxies. Aims. Here, we derive the global neutral hydrogen gas (Hi) properties of nearby Lyα-emitting galaxies to assess the impact of neutral gas on the Lyα output of galaxies. Methods. We observed the 21 cm line emission using the Karl G. Jansky Very Large Array in D-array configuration (∼5500 resolution, ∼38 kpc) for 37 star-forming galaxies with available Hubble Space Telescope (HST) Lyα imaging from the Lyman Alpha Reference Samples. Results. We detected 21 cm emission for 33 out of the 37 galaxies observed. We found no significant correlation of global Hi properties (including Hi mass, column density, gas fraction, depletion time, line width, or velocity shift between Hi and Lyα), with the Lyα luminosity, escape fractions, or equivalent widths (EW) derived with HST photometry. Additionally, both Lyα-emitters and weak or non-emitters are distributed evenly along the Hi parameter space of optically selected z = 0 galaxies. Around 74% of the sample is undergoing galaxy interaction, this fraction is higher for Lyα-emitters (83% for galaxies with EW ≥ 20 Å) than for weak or non-emitters (70%). Nevertheless, galaxies identified as interacting have Lyα and Hi properties statistically consistent with those of non-interacting galaxies. Conclusions. Our results show that global Hi properties (on scales >30kpc) have little direct impact on the Lyα output from galaxies. Instead, Hi likely regulates Lyα emission on small scales: statistical comparisons of Lyα and high angular resolution 21 cm observations are required to fully assess the role of Hi in Lyα radiative transfer. While our study indicates that major and minor galaxy mergers could play a role in the emission of Lyα photons in the Local Universe, especially for galaxies with high Hi fractions, the line of sight that a system is observed through ultimately determines the Lyα observables.

We present a sample of 1956 individual stellar clumps at redshift 0.7<z<10⁠, detected with JWST/NIRCam in 476 galaxies lensed by the galaxy cluster Abell2744. The lensed clumps present magnifications ranging between μ = 1.8 and μ = 300. We perform simultaneous size-photometry estimates in 20 JWST/NIRCam median and broad-band filters from 0.7 to 5 μm. Spectral energy distribution (SED) fitting analyses enable us to recover the physical properties of the clumps. The majority of the clumps are spatially resolved and have effective radii in the range R_eff=10−700 pc⁠. We restrict this first study to the 1751 post-reionization era clumps with redshift <5.5⁠. We find a significant evolution of the average clump ages, star formation rates (SFRs), SFR surface densities, and metallicity with increasing redshift, while median stellar mass and stellar mass surface densities are similar in the probed redshift range. We observe a strong correlation between the clump properties and the properties of their host galaxies, with more massive galaxies hosting more massive and older clumps. We find that clumps closer to their host galactic centre are on average more massive, while their ages do not show clear sign of migration. We find that clumps at cosmic noon sample the upper-mass end of the mass function to higher masses than at z>3⁠, reflecting the rapid increase towards the peak of the cosmic star formation history. We conclude that the results achieved over the studied redshift range are in agreement with expectation of in situ clump formation scenario from large-scale disc fragmentation.

We present a comparative study of the molecular gas in two galaxies from the Legacy ExtraGalactic UV Survey (LEGUS) sample: barred spiral NGC 1313 and flocculent spiral NGC 7793. These two galaxies have similar masses, metallicities, and star formation rates, but NGC 1313 is forming significantly more massive star clusters than NGC 7793, especially young massive clusters (<10 Myr, >10⁴M_⊙). Using Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) observations of the two galaxies with the same sensitivity and resolution (13 pc), we directly compare the molecular gas in these two similar galaxies to determine the physical conditions responsible for their large disparity in cluster formation. By fitting size–line width relations for the clouds in each galaxy, we find that NGC 1313 has a higher intercept than NGC 7793, implying that its clouds have higher kinetic energies at a given size scale. NGC 1313 also has more clouds near virial equilibrium than NGC 7793, which may be connected to its higher rate of massive cluster formation. However, these virially bound clouds do not show a stronger correlation with young clusters than with the general cloud population. We find surprisingly small differences between the distributions of molecular cloud populations in the two galaxies, though the largest of those differences is that NGC 1313 has higher surface densities and lower freefall times.