Mederic Boquien

Aims . The increasing discovery of high-redshift active galactic nuclei (AGNs) in recent years imposes more stringent requirements on spectral analysis tools for deriving the properties of AGNs and their host galaxies from emission-line diagnostics. To address this need, we have developed a new module for the popular spectral energy distribution (SED) fitting tool Code Investigating GALaxy Emission (CIGALE), namely the [nebular_AGN] module, which enables the efficient and flexible simulation and fitting of emission lines originating from the broad-line regions (BLRs) and narrow-line regions (NLRs) of AGNs and allows for the estimation of the physical properties of these regions. Methods . We used the spectral synthesis code Cloudy to construct the database for the new module. Based on the X-ray and accretion disk continua implemented in CIGALE, we generated the incident radiation fields of the models. We then adopted the AGN geometry and dust settings implemented in CIGALE to define a flexible set of physical parameters for the gas clouds, thereby producing a comprehensive database for the [nebular_AGN] module. Results . We benchmarked the [nebular_AGN] module using a quasar composite spectrum, an empirical metallicity calibration, and observational data from X-ray-selected AGNs. Our module can approximately reproduce the majority of quasar emission-line features, cover the key emission-line ratios observed in AGN samples, and provide an assessment of their physical properties. For specific combinations of parameters, the metallicity derived by our module is consistent with the empirical formula. We further compared our models with other photoionization models used to simulate AGN NLR emission, and we performed a line-sensitivity study to identify the most effective diagnostic lines for each parameter in our module. Finally, we find that the dust attenuation law plays an important role in the SED fitting.

We present the largest study to date of star cluster mass and age distributions in nearby galaxies. The analysis is based on a uniformly selected catalog of over 15,000 (36,000) human- (machine-) classified compact clusters across 38 spiral galaxies in the PHANGS-Hubble Space Telescope survey, with improved photometric SED age dating that mitigates key degeneracies with reddening and metallicity. The galaxies span a factor of ∼100 in star formation rate (SFR) and in their surface density of star formation and molecular gas (Σ _SFR , Σ H 2 ), and cover a broad range of morphologies. We find that cluster mass functions are well described by a power law, dN / dM ∝ M ^β , with β = −1.9 ± 0.2, and that this shape is remarkably similar across all galaxies in our sample and eight composite groups of galaxies with similar SFRs, with no significant dependence on SFR, Σ _SFR , or Σ H 2 . Cluster age distributions decline steeply and can be described by dN / dτ ∝ τ ^γ with γ = −0.83 ± 0.24, again with little dependence on host-galaxy properties or cluster mass. The independence of the mass and age distributions implies a separable joint distribution, g ( M , τ ) ∝ M ^β τ ^γ , and suggests that cluster populations in spiral disks are dominated by strong, mass-independent dissolution over their first approximately gigayear. These results establish a benchmark for interpreting cluster demographics across diverse galactic environments and provide context for studies of young cluster populations at high redshift.

We present 50–100 pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity ( U ) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band ratios remain fairly constant in the diffuse ISM of star-forming disks. However, they show stark variations in extreme environments: highly star-forming central molecular zones (CMZs) and star formation deserts/quiescent bulges. In CMZs, PAH-to-continuum (3.3/21, 7.7/21, and 11.3/21 μ m) and the 10/21 μ m continuum colors are 0.2–0.4 dex lower than in normal disks. We attribute this to higher U based on the far-infrared dust colors and the high 21 μ m/Σ _Mol , which we suggest to be a good tracer of U outside star-forming regions. Meanwhile, star formation deserts show low 7.7 μ m PAH emission, resulting in low 7.7/21 μ m and 7.7/11.3 μ m, while all other mid-IR colors remain typical. This suggests the presence of more neutral PAHs in star formation deserts, where low 7.7 μ m likely reflects ISM conditions similar to early-type and elliptical galaxies. All environments form part of a continuous trend in 7.7/11.3 μ m versus specific star formation rate.

We present gas-phase radial metallicity profiles for 20 main-sequence galaxies at 4 < z < 6 primarily based on JWST NIRSpec IFU observations obtained as part of the JWST-ALPINE-CRISTAL programme. Our study aims to connect the metallicity gradients of these galaxies with their kinematic properties from [C II ] 158 μm ALMA observations. We mapped the radial profiles of oxygen abundance using the strong-line method, leveraging the rich set of rest-frame optical emission lines. Linear fits to the annular-binned radial profiles show that, on average, the metallicity gradients are slightly positive with a median of +0.039 ± 0.010 dex kpc ⁻¹ . However, only three galaxies show a gradient > 0.05 dex kpc ⁻¹ at 1 σ , and none have a significant negative gradient. There are no substantial systematic offsets in gradients when using different line diagnostics. We investigated the correlation between the metallicity gradients and the intrinsic gas velocity dispersion σ ₀ as well as the V _rot / σ ₀ ratio of the disks. Combining our sample with mass-matched literature samples at 3 ≲ z ≲ 7, we found a negative shallow correlation between V _rot / σ ₀ and the metallicity gradients, but no strong relationships with σ ₀ . As V _rot / σ ₀ increases towards later cosmic times, the observed negative trend with V _rot / σ ₀ is consistent with the overall cosmic evolution of metallicity gradients from high to low redshifts. This suggests that disk maturity plays a crucial role in shaping the radial metallicity gradients. We do not find the metallicity gradients of disk galaxies to be significantly different from non-disk galaxies, which could be attributed to the frequent accretion events that took place in these gas-rich systems. Additionally, we find no strong dependence of metallicity gradients on stellar mass and only a marginal positive dependence on specific star-formation rate. Our study extends the efforts to connect the internal kinematics of galaxies with their gas-phase chemical enrichment at kiloparsec scales from cosmic noon to z > 4.

High-resolution JWST-MIRI images allow us to resolve the multi-scale nature of the emission in nearby star-forming galaxies in great detail, from compact star-forming regions to large-scale diffuse emission, providing new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7--21 ) wavelengths take place and whether we can disentangle emission from dense regions from the one linked to a more diffuse component. We use and enhance the Constrained Diffusion Decomposition algorithm (CDD), an alternative to wavelet transform decomposition, to disentangle the emission from compact regions from the emission originating from diffuse sources. This allows us to quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. We find a transition scale for Polycyclic Aromatic Hydrocarbons (PAH) emission around 300 pc, with a weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in regions. We also show variations in the PAH fraction in different morphological environments, with a lower fraction in bright and star-forming environments. By studying and comparing the probability distribution functions (PDFs) of regions and of diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal distribution for the diffuse ISM. We infer the destruction of PAHs in nebular environments and the existence of a transition scale between stellar feedback in nebular regions and heating in the diffuse ISM. We also show that the CDD enables future applications to study the physical scales of emission.

We used narrow-band Hα+ ∋i imaging data gathered during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) survey, a blind survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope, to identify $ erg s$^ regions in 385 galaxies showing ionised gas emission. After excluding objects where the emission is not associated with star formation and edge-on systems, we identified 76,645 regions in 322 star-forming galaxies and studied their physical properties for those above the completeness limit of the survey (L(Hα) ≥ 10 37 -1 , 34,358 regions). The present work is focused on perturbed cluster galaxies, identified as those having a reduced amount of atomic hydrogen when compared to similar objects in the field. We derived composite luminosity functions, diameter and electron density distributions, and several scaling relations, and we compare them to those already derived for unperturbed gas-rich systems identified during the VESTIGE survey. Our analysis shows that the statistical and physical properties of gas-deficient cluster galaxies are different from those of unperturbed systems, with perturbed objects having a steeper faint-end slope and a brighter characteristic Hα luminosity than gas-rich galaxies. The difference in the two distributions comes principally from the outer disc (outside the effective radius). Perturbed and unperturbed systems share a similar size distribution, while gas-poor objects host higher electron density regions than systems. The analysis of the scaling relations indicates that perturbed objects have, on average, a lower number of regions per unit stellar mass and disc surface than unperturbed systems, with differences increasing with the parameter, principally in the outer disc where regions are less present in gas-poor systems. This systematic difference is also observed in the Hα luminosity of the first ranked and first three ranked regions, which is reduced in systems with respect to gas-rich objects. All of these differences can be explained in the framework of galaxy evolution in rich environments, where their hydrodynamic interaction with the surrounding intracluster medium (ram pressure) removes the gas from the outside in, quenching the star formation activity in the outer disc once the atomic hydrogen is removed.

The James Webb Space Telescope (JWST) has revealed an unexpected excess of UV-bright galaxies at z > 10, unaccounted for by extrapolations from pre-JWST observations and theoretical models. Understanding the physical properties and star formation histories (SFHs) of high-redshift systems is key to distinguishing between the different proposed scenarios and assessing their implications for the galaxy formation and evolution picture. We identified and analysed a sample of 2420 robust candidates at z ∼ 7 − 14 drawn from the ASTRODEEP-JWST dataset over ∼0.2 deg ² , and modelled their properties with non-parametric SFHs to derive the specific star formation rate (sSFR) and stellar population properties. We find that the median sSFR and M/L remain roughly constant across the probed redshift range. We show that this result is robust against potential systematics unless a hidden population of dust-enshrouded starbursts, undetectable in the current data, exists at these redshifts. In any case, the absence of observed high-sSFR systems at the highest redshifts suggests that any dust-free starburst phase must be short-lived. The observed sSFR evolution is in tension with most (though not all) theoretical models, making it a key quantity for discriminating among competing scenarios. The sample shows a wide range of physical conditions and galaxy classes, including systems with low sSFRs and high mass-to-light ratios (M/L) up to z ∼ 10, indicative of already-evolved galaxies only a few hundred megayears after the Big Bang, and different degrees of dust attenuation. We finally reconstructed the assembly histories of two sub-samples, namely the highest-M/L galaxies at z ∼ 7 − 8, which appear to have formed the bulk of their stars at least 500 Myr before observation, implying progenitors observable as UV-bright sources at z > 20, and the full sample of z > 11 galaxies, which formed through stochastic SFHs, remaining UV-faint for most of their early evolution, before undergoing recent (∼50 Myr old) episodes of major growth.

Multiple mechanisms are proposed for the formation of giant molecular clouds (GMCs) – from gravitational free-fall caused by self-gravity, to stellar feedback-driven gas compression. Both the galactic environment and galaxy conditions could play an additional role in enhancing the formation via their gas surface density and star formation activity. In this paper, we make use of a catalog of 108 466 GMCs identified by F770W PHANGS-JWST imaging across 66 galaxies at a homogenized resolution of 30 pc. We measure the mass spectra in various galactic regions, whose power-law slopes vary from −1.2 to −2.0. We then estimate the formation time of each cloud using a model in which GMCs form by multiple feedback compression, and find that clouds with masses ≤10 ⁵ M _⊙ form in 20 Myr on average, and more massive clouds (∼10 ^6 − 7 M _⊙ ) take up to 100 Myr. We also find that cloud formation proceeds most rapidly in the central regions of galaxies, with formation timescales that are typically shorter by ∼5 − 10 Myr compared to galactic disks. This effect is most pronounced in central molecular zones with enhanced star formation. This highlights the role of intense massive star formation, high molecular gas surface densities, and strong supersonic compressions in accelerating cloud formation. However, star formation is generally inefficient as the cloud lifetime is ∼1% of the molecular depletion time. The formation time of clouds is ∼0.1 dex longer than the free-fall time. This hints that magnetic fields, stellar feedback, or other mechanisms may prolong their formation instead of immediate free-fall collapse. This indicates a longevity of massive GMCs. The GMC ages also show only limited variation with galactocentric radius in both spiral and disk galaxies, suggesting that cloud formation proceeds similarly in these galaxy types.

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.