We examine the spatial distribution of star clusters in NGC628 using the statistical tool INDICATE to quantify clustering tendencies. Our sample, based on Hubble Space Telescope and James Webb Space Telescope observations, is the most complete to date, spanning ages from 1 to >100 Myr. We find cluster spatial behaviour varies with galactic position, age, and mass. Most emerging young clusters are tightly spatially associated with each other, while fully emerged clusters are in 1.5 times looser spatial associations, irrespective of age. Young Massive Clusters (YMCs ≥ 10⁴ M⁠_⨀) tend to associate with lower-mass clusters but not strongly with other YMCs, implying that intense star formation regions produce a few YMCs alongside many lower-mass clusters rather than multiple YMCs together. Young concentrated clusters show a wide radial distribution in the galactic disc, which narrows with age; with concentrated clusters >100 Myr mostly residing between 2 and 6 kpc. This pattern may reflect either faster dispersal of isolated tight cluster spatial ‘structure’ in a lower gas density outer disc or gradual inside-out growth, with the formation of this structure shifting outwards over time. We also detect distinct spatial behaviours for clusters within 2 kpc, linked to the inner Lindblad resonance (⁠≤1 kpc), nuclear ring (∼⁠0.5–1 kpc), and the start of spiral arms (∼⁠1.25–2 kpc), suggesting these regions exhibit strong radial motions that could hinder clusters from forming and remaining in tight concentrations. Our results highlight how spatially resolved studies of clusters can reveal the influence of galactic dynamics on star formation and cluster evolution.

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.

We present JWST NIRCam observations of the emerging young star clusters (eYSCs) detected in the nearby spiral galaxy M83. The NIRcam mosaic encompasses the nuclear starburst, the bar, and the inner spiral arms. The eYSCs, detected in Paα and Brα maps, have been largely missed in previous optical campaigns of young star clusters (YSCs). We distinguish between eYSCI, if they also have compact 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission associated with them, and eYSCII, if they only appear as compact Paα emitters. We find that the variations in the 3.3 μm PAH feature are consistent with an evolutionary sequence where eYSCI evolve into eYSCII and then optical YSCs. This sequence is clear in the F300M​​​​​​−F335M (tracing the excess in the 3.3 μm PAH feature) and the F115W−F187N (tracing the excess in Paα) colors, which become increasingly bluer as clusters emerge. The central starburst stands out as the region where the most massive eYSCs are currently forming in the galaxy. We estimate that only about 20% of eYSCs will remain detectable as compact YSCs. Combining eYSCs and YSCs (≤10 Myr), we recover an average clearing timescale of 6 Myr in which clusters transition from embedded to fully exposed. We see evidence of shorter emergence timescales (∼5 Myr) for more massive (>5 × 10³ M_⊙) clusters, while star clusters of ∼10³ M_⊙ about 7 Myr. We estimate that eYSCs remain associated with the 3.3 μm PAH emission for 3–4 Myr. Larger samples of eYSC and YSC populations will provide stronger statistics to further test environmental and cluster mass dependencies on the emergence timescale.

We present new JWST/NIRCam observations of the starburst irregular galaxy NGC 4449, obtained in Cycle 1 as part of the Feedback in Emerging extrAgalactic Star clusTers program, which we use to investigate its resolved stellar populations and their spatial distributions. NGC 4449 near-IR color-magnitude diagrams reveal a broad range of stellar populations, spanning different evolutionary phases, from young main sequence stars, to old red giant branch stars and asymptotic giant branch (AGB) stars. The analysis of their spatial distributions shows that younger (≤10 Myr) populations form an S-shaped distribution aligned with the galaxy’s north-south axis, while stars aged 10-60 Myr show shifting concentrations from the north to the south, consistent with the possibility that external interactions or tidal effects may have triggered star formation in spatially distinct bursts. Clusters of comparable ages generally follow these distributions, suggesting that cluster and field stars form at the same pace in each galaxy region. Thanks to the unprecedented high-spatial resolution and sensitivity of the JWST data, we recover a clear gap between oxygen-rich and the carbon star branch of the AGB population, as well as the presence of a massive AGB star “finger.” The analysis of these stars can provide constraints on AGB evolution models and dust production in this galaxy. These results confirm NGC 4449's status as a compelling example of a local dwarf starburst galaxy undergoing complex and possibly externally driven star formation and underscore the power of JWST in probing the full lifecycle of stars in nearby starburst systems.

We combine James Webb Space Telescope images of the nearby galaxy NGC 5194 in the hydrogen recombination line Paα (1.8756 μm) from the Cycle 1 program JWST-FEAST with 21 μm dust continuum images from the Cycle 2 Treasury program JWGT to quantify the difference in the calibration of mid-infrared star formation rates (SFRs) between H II regions and galaxies. We use archival Hubble Space Telescope Hα imaging to correct the Paα emission for the effects of dust attenuation. Our data confirm previous results that the dust-corrected Paα flux is tightly correlated with the 21 μm emission at the scales of H II regions. When combined with published JWST data for the H II regions of the galaxy NGC 628 and Spitzer Space Telescope 24 μm data for whole galaxies and for kiloparsec-size galaxy regions, we show that the L(24)–L(Paα) relation has exponent > 1 across six decades in luminosity. In addition, the hybrid 24 μm + Hα SFR indicator has a scaling constant about 4.4 times higher for H II regions than for whole galaxies, also in agreement with previous results. Models of stellar populations with a range of star formation histories reveal that the observed trends can be entirely ascribed to and quantified with the contribution to the infrared emission by stellar populations older than ∼5–6 Myr. Based on the models’ results, we provide (1) a calibration for the infrared SFR across 6 orders of magnitude in L(24), from H II regions to luminous galaxies, and (2) a prescription for the scaling constant of the hybrid infrared SFR indicators as a function of the star formation timescale.

We present a combined Hubble Space Telescope (HST) and JWST 0.2–to–5 μm analysis of the spectral energy distributions (SED) of emerging young star clusters (eYSCs) in four nearby galaxies from the Feedback in Emerging Extrgalactic Star Clusters survey: M51, M83, NGC 628, and NGC 4449. These clusters, selected for their bright Paα and 3.3 μm polycyclic aromatic hydrocarbon emission, are still associated with their natal gas cloud and have been largely missed in previous HST optical campaigns. We modeled their SEDs using the CIGALE fitting code and identified (i) a systematic flux excess at 1.5–2.5 μm that is not accounted for by current stellar population models and (ii) the preference for a set of dust model parameters that is not aligned with expectations from self-consistent analyses of star-forming regions, suggesting model shortcomings also in the 3–5 μm. The near-infrared excess is most prominent in low-mass (≤3000 M ⊙) and young (≤6 Myr) clusters. Additionally, we see that the SED fitting analysis wrongly assigns ages ≥6 Myr to a fraction of strong Paα emitters with equivalent widths suggestive of significantly younger ages. A parallel analysis with the slug code suggests that stochastic initial mass function (IMF) sampling of pre-main-sequence stars combined with extinction might partially reduce the gap. We conclude that the inclusion of young stellar object SEDs, along with more realistic sampling of the cluster IMF, might be needed to fully account for the stellar population and dust properties of eYSCs.