Francesca Pozzi

Context. Understanding the interstellar medium (ISM) requires high-resolution, multi-component mapping to capture its complex physical structure. Nearby spiral galaxies, with their abundant and diverse ISM, provide an ideal laboratory for such a comprehensive analysis at sub-galactic scales. Aims. We investigate dust-to-gas and dust-to-metal ratios (DGR and DMR) as functions of the gas-phase metallicity ( Z ) on spatial scales ranging from 0.6 to 2.3 kpc, in a sample of ten nearby spiral galaxies spanning more than an order of magnitude in stellar mass (9.7 ≤ log( M _* / M _⊙ )≤11.0), star formation rate (SFR, ∼0.3–3 M _⊙ yr ⁻¹ ), and metallicity ranging from 8.3 ≲ 12 + log(O/H) ≲ 8.8. We explore how the DGR– Z and DMR– Z relations are shaped by the assumptions behind the CO-to-H ₂ conversion factor ( α _CO ). Methods. We homogeneously combined maps of dust, atomic gas, molecular gas, and metallicity. Motivated by the diversity in L _{CO(1 − 0)} /SFR ratios and metallicity across our sample, we introduced a hybrid α _CO prescription to distinguish between CO-bright and CO-dark regimes. The derived DGR– Z and DMR– Z relations were compared with other global and resolved observational results, and with the predictions of dust and chemical evolution models. Results. Both DGR– Z and DMR– Z relations are dependent on the adopted α _CO prescription, and no single α _CO can reproduce the properties of the entire sample, motivating the use of a hybrid approach. The DGR increases with metallicity, spanning ∼1 dex across the sampled range, while the DMR remains approximately constant at log(DMR) = − 0.53 ± 0.13, implying that ∼30% of metals are locked into dust grains. This flat behaviour indicates an evolved dust phase where efficient ISM grain growth drives a saturation regime balancing dust formation and destruction.

Aims. DustPedia and Local Volume Legacy (LVL) are two samples representative of the local galaxy population, including in total ∼1000 unique objects of all morphological types, with a wide range of stellar masses and star formation activity, and a spectral coverage from the ultraviolet to the far-infrared. The purpose of this work is to show that these samples cover two complementary ranges in stellar mass and galaxy morphology, making them an ideal set for constraining the dominant processes in the evolution of the galactic dust content. Methods. Using the multi-wavelength data provided by the two surveys, we fitted the galaxies’ spectral energy distribution and estimated their physical properties, in particular the stellar mass, M _* , the specific dust mass, sM _dust = M _dust / M _* , and the specific star formation rate, sSFR = SFR/ M _* . Results. By combining DustPedia and LVL, we highlight that the trend of log ₁₀ ( sM _dust ) with log ₁₀ ( M _* ) is not monotonic. Thanks to a large number of objects across a wide range of M _* , we have been able to fit two smoothly joined linear correlations: a positive one for log ₁₀ ( M _* /M _⊙ )≲9.5 (a range populated mostly by LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia, spirals (with early-type galaxies being distinct and more dispersed in the same mass regime). For log ₁₀ ( M _* /M _⊙ ) > 9.5, we confirm a strong correlation between sM _dust and sSFR; dwarf galaxies, instead, lie below this trend, showing a large scatter of sM _dust for −10.5 < log ₁₀ (sSFR/yr ⁻¹ ) < − 9.0. By using chemical evolution models we find that the observed log ₁₀ ( sM _dust )–log ₁₀ ( M _* ) and log ₁₀ ( sM _dust )–log ₁₀ (sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the galaxy ages, respectively. Low-mass Sm-Irr galaxies with low sM _dust and a high sSFR can only be reproduced by the models by assuming a highly efficient photofragmentation rate of large grains, and/or low grain growth in clouds.

We present the stellar mass–metallicity relation (MZR) and mass–metallicity–star formation relation (“fundamental metallicity relation”; FMR) of 18 massive ( log ( M ⋆ / M ⊙ ) = 9.5 − 11 ) main-sequence galaxies at z ∼ 5 from the ALPINE–CRISTAL–JWST sample. This sample complements recent studies by JWST at up to 2 orders of magnitude lower stellar masses. The metallicities are derived using strong optical lines and verified by temperature-based oxygen abundance measurements for five galaxies for which faint auroral lines are detected. We find that the metal abundance evolves, on average, from 40% to 60% solar between z ∼ 5 and cosmic noon ( z ∼ 2) at the massive end of the MZR, suggesting already significant metal enrichment at early times. The FMR at z = 5 exhibits a 5× larger scatter (preferentially to lower metallicities) compared to the local FMR relation. This scatter can be explained by a bursty star formation and the direct buildup of metals in early galaxies, as well as differences in age and outflow efficiencies. Capitalizing on all available samples, we find that the observed MZR and FMR over 3 orders of stellar mass is generally in good agreement with results from cosmological simulations, although some underestimate the metal enrichment at low stellar masses. This may be due to too efficient metal-rich outflows. We show that the ALPINE–CRISTAL–JWST galaxies likely joined the current FMR at z ∼ 10 and will evolve into massive ( log ( M ⋆ / M ⊙ ) ∼ 11.4 ) galaxies with supersolar metallicities by z = 0.

Gaseous halos around galaxies play an important role in galaxy evolution. The exchange of metals from the interstellar medium (ISM) to the circumgalactic medium (CGM) is caused by the formation, feedback, and/or merging history of galaxies. We study the variation in chemical composition between the ISM (≲3 kpc) and CGM (∼5–10 kpc) for a sample of M _⋆ > 10 ^9.5 M _⊙ main-sequence galaxies at 4 < z < 6 with both JWST and Atacama Large Millimeter/submillimeter Array observations. Using JWST/NIRSpec integral field spectroscopy, we derive the optical line ratios from the ISM and the CGM for our sample, focusing on the typical optical lines used for metallicity studies. Our comparison shows that the ISM and the CGM have similar chemical abundances. This indicates that the CGM of these typical 4 < z < 6 galaxies is enriched to the level of their ISM in the early Universe. Using statistical tests, we find that some of the line ratios show marginal differences between the ISM and CGM. Combined with Cloudy modeling, our results suggest that a difference in ionization level (higher for the ISM) is the dominant reason for the observed ratio difference of oxygen line ratios. There is also indication of a deficit in the nitrogen abundance with respect to oxygen in the CGM, which suggests a delay in redistribution of secondary nitrogen. Finally, an enhanced F _{[C II]158 μ m} / F _{H α} ratio is observed in the CGM, suggesting that feedback and/or mergers play a key role in metal mixing.

Quasars at the dawn of cosmic time ( z > 6) are fundamental probes for investigating the early coevolution of supermassive black holes and their host galaxy. Nevertheless, their infrared spectral energy distribution currently remains poorly constrained because the photometric coverage that probes the far-infrared wavelength range in which the dust modified blackbody is expected to peak (∼80 μm) is limited. We studied the high-frequency dust emission via a dedicated ALMA Band 8 (∼400 GHz) campaign targeting 11 quasar host galaxies at 6 < z < 7. Combined with archival observations in other ALMA bands, this program enables a detailed characterization of their infrared emission, which allowed us to derive dust masses ( M _d ), dust emissivity indexes ( β ), dust temperatures ( T _d ), infrared luminosities ( L _IR ), and associated star formation rates (SFRs). Our analysis confirmed that dust temperature is higher in this sample (34−65 K) than in local main-sequence galaxies, and this finding can be linked to the increased star formation efficiency we derived, as also suggested by the [CII] _158 μm deficit. Most remarkably, we note that the average value of T _d of this sample does not differ from the one that is observed in luminous, ultraluminous and hyperluminous infrared galaxies at different redshifts that show no signs of hosting a quasar. Finally, our findings suggest that the presence of a bright AGN does not significantly bias the derived infrared properties, although further high frequency observations with a high spatial resolution might reveal more subtle effects on subkiloparsec scales.

Characterizing dust attenuation is crucial for revealing the intrinsic physical properties of galaxies. We present an analysis of dust attenuation in 18 spectroscopically confirmed star-forming main-sequence galaxies at z = 4.4−5.7 observed with JWST/NIRSpec IFU and NIRCam, selected from the ALPINE and CRISTAL ALMA large programs. We fit the emission-line fluxes from NIRSpec and the broadband photometry from NIRCam with Prospector , using both spatially integrated emission and ∼0.6 kpc pixel-by-pixel measurements. We derive the stellar-to-nebular dust attenuation ratio ( f = E ( B − V ) _star / E ( B − V ) _neb ) from the SED fits and the Balmer decrement with H α and H β . Although individual galaxies show large scatter, the best-fit value is f = 0.5 1 − 0.03 + 0.04 , slightly higher than that measured for local starburst galaxies. We find weak correlations of f with galaxy properties, increasing with higher specific star formation rates, younger stellar ages, and more recent star formation. For the range of E ( B − V ) _star = 0.009−0.15 mag for in our sample, assuming f = 1 (often adopted in high-redshift studies) instead of f = 0.51 leads to the underestimation of line luminosities and ionizing photon production efficiency ξ _ion by ∼3%−36% and ∼4​​​​​​%−46%, respectively. Finally, total stellar masses estimated from spatially integrated SED fits with delayed- τ star formation histories are systematically smaller than the sums of pixel-by-pixel SED fits by a median of ∼0.26 dex, likely because the integrated fits are biased toward luminous young stellar populations.

To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kiloparsec-resolved imaging and spectroscopy from the Hubble Space Telescope, JWST, and Atacama Large Millimeter/submillimeter Array for 18 representative main-sequence galaxies at z = 4–6 and log ( M * / M ⊙ ) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The cospatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1–2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at z ∼ 5, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H α halos. Our targeted galaxies are relatively metal rich (10%–70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission-line ratios. Six show broad H α emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers.

Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this work, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame λ _rest ∼ 3 μm, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most (≳50%) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ( N _H > 3 × 10 ²⁴ cm ⁻² ) gas obscuration is common, and likely confined within the dust sublimation radius ( R _sub ∼ 0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear.