Ilse De Looze

We present a resolved far-infrared/sub-millimetre study of dust in the nearby spiral galaxy M 81 using Herschel PACS/SPIRE and JCMT SCUBA-2 observations from 70 to 850 μm. We model the dust emission using both single-temperature modified blackbody (SMBB) fits and point process mapping (PPMAP), comparing pixel-by-pixel SED-fitting with image cubes of dust surface density as a function of position and temperature. For fixed β = 1.9 and a dust opacity of κ350μm = 1.92 cm2 g−1, SMBB gives an integrated dust mass of (1.77 ± 0.09) × 107M⊙, while PPMAP gives (2.65 ± 0.13) × 107M⊙. The higher PPMAP mass is expected because real lines of sight contain dust over a range of temperatures, whereas SMBB assumes a single effective temperature and can underestimate the dust mass. Both methods show enhanced dust surface densities along the spiral arms and a radially declining dust temperature, with the warmest dust in the central region. Variable-β fits indicate only moderate spatial variation in β for well-constrained pixels, but the strong T–β degeneracy motivates a fixed emissivity index for the main analysis. Combining the dust maps with H i data, we find a positive radial gas-to-dust ratio gradient, with dlog10(GDR)/dR = 0.065 dex kpc−1. Comparison with M 81’s metallicity gradient implies a declining dust-to-metals ratio, potentially consistent with more efficient grain growth in the inner disc. The star formation rate is modest, ~0.27 M⊙ yr−1, and is strongly concentrated along the spiral arms. These results suggest that the dust, gas, and star-forming structures of M 81 are strongly shaped by its spiral arms, while the central region hosts the warmest dust in the disc.

Context. JWST observations of Cassiopeia A have revealed a pockmarked region of shocked circumstellar medium (CSM) featuring circular holes surrounded by bright rings, known as the Green Monster (GM). The physical origin of these structures is an active topic of debate, with plausible explanations ranging from post-shock sculpting by ejecta fingers or pre-shock puncturing by fast-moving knots (FMKs). Aims. We carried out a quantitative test of the physical viability of the FMK-driven scenario against observed GM morphologies and kinematics. We determined the observational diagnostics required to distinguish among the competing formation mechanisms. Methods. We performed 3D hydrodynamic simulations of isolated FMKs interacting with a dense circumstellar shell, followed by the passage of the supernova remnant’s forward shock. A range of FMK properties and shell densities was explored, comparing the resulting hole–ring systems directly with JWST observational constraints. Results. In the FMK-driven scenario, holes and rings are formed by bow shocks that precede the knots, which stands in contrast to the post-shock scenario, where cavities result from ejecta displacing material that has already been processed by the forward shock. While primary FMKs can reproduce qualitative GM-like features, they generally produce hole–ring systems that are significantly larger than the 1″–3″ (i.e., ∼0.016–0.048 pc at a distance of ≈ 3.4 kpc of Cas A) features observed by JWST—unless the knots are slow (≲8000 km s ⁻¹ ) and the shell is dense ( n _sh ≳ 200 cm ⁻³ ). Furthermore, these structures are transient, typically distorting within 30–60 yr following the forward-shock passage. Conclusions. The GM’s diverse hole–ring systems and complex kinematics cannot be attributed to a single idealized scenario. Instead, these features can be explained by the simultaneous action of three different mechanisms operating within a structured, heterogeneous CSM. While large cavity relics are carved by early-stage primary FMKs, compact pristine rings are produced by recent "first contact" punctures of secondary knots from fragmented ejecta fingers and older structures are continuously sculpted by long-term post-shock interactions with large-scale ejecta fingers.

We present JWST/MIRI observations of the Type I superluminous supernova (SLSN) 2017gci obtained over 2000 rest-frame days after the supernova (SN) exploded, which represent the latest phase images taken of any known SLSN to date. We find that archival Wide-field Infrared Survey Explorer (WISE) detections of SN 2017gci taken 70–200 days after explosion are most likely explained by an IR dust echo from a ∼10 ⁻⁴ M _⊙ shell of preexisting dust, as opposed to freshly formed dust. New JWST observations reveal mid-infrared emission at the position of SN 2017gci; however, the flux level and spatial offset indicate that this emission is most likely dominated by the host galaxy. We therefore derive upper limits from these observations to constrain dust emission at late times. Radiative transfer modeling of carbonaceous dust shows that warm optically thin dust masses up to 0.18 M _⊙ are excluded at the 3 σ confidence level. However, substantially larger dust masses cannot be ruled out if the dust is optically thick. Infrared detections of other SLSNe have suggested that SLSNe may be highly efficient dust producers. While our constraints are insufficient to determine the total dust yield of SN 2017gci, they indicate that any late-time dust emission must either be modest compared to the most dust-rich SNe or arise from dust that is optically thick. A larger sample of deep infrared observations will be required to determine whether SLSNe are significant contributors to cosmic dust production.

Using JWST/MIRI imaging of M51 in eight broadband filters, we investigate correlations of mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs) and dust continuum with molecular, atomic, and ionized gas traced by ¹² CO (1–0), H i , and Pa α , respectively. In molecular-gas-dominated regions, PAH-dominated filters (F560W, F770W, F1130W, F1280W) exhibit near-linear correlations with ¹² CO (1–0) at ∼40 pc scale, indicating that PAHs are well mixed with gas and experience relatively constant radiation field intensities. The F1500W, F1800W, and F2100W dust-continuum-dominated filters show shallower slopes, with ¹² CO (1–0) reflecting contributions from star-forming regions with high radiation field intensities. This is reinforced by the near-linear scaling between F2100W and Pa α . PAH-dominated bands do not show this linear trend with Pa α , likely due to their destruction in ionized regions. F1000W behaves similarly to PAH bands in its correlations with ¹² CO (1–0) and Pa α . Modeling mid-infrared emission with an empirical decomposition into gas- and star-formation-associated components shows that PAH-dominated filters receive comparable contributions from both, while the relative contribution associated with the Pa α template increases toward longer wavelengths, reaching ∼75% in F2100W. These results demonstrate that mid-infrared simultaneously traces the gas column and star formation, but with a systematic wavelength-dependent shift in what drives the correlations—PAHs being more gas-tracing and dust continuum reflecting star formation. Lastly, considering both H i and H ₂ at ∼440 pc resolution, we find a tight, approximately linear relation between Σ HI + H 2 and PAH-dominated filters. Although most of our coverage is in H ₂ -dominated regions, we note similar observations with H i , suggesting that PAHs are also well mixed with atomic gas.

We present results of new observations of [O i ] 145 μ m and [N ii ] 205 μ m emission lines from four star-forming galaxies at redshifts between z = 6.58 and 7.68 that have previous detections of [C ii ] 158 μ m and dust continua. Using the Atacama Large Millimeter/submillimeter Array, we successfully detect [O i ] 145 μ m emission from all targets at >4 σ significance. However, [N ii ] 205 μ m emission is undetected in all galaxies (signal-to-noise ratio < 3.5 σ ) except for a tentative detection from A1689-zD1. From the observed high [C ii ]/[N ii ] emission line ratios (≳20−80), we find that most of the [C ii ] 158 μ m emission arises from neutral gas regions (3 σ lower limits of ≳74%−96%). From [O i ] 145 μ m, [C ii ] 158 μ m lines, and IR luminosities, we estimate the neutral gas densities of n _H = 10 ^3.5 –10 ⁶ cm ⁻³ and the far-UV (FUV) radiation strengths of G ₀ ∼ 10 ^2.5 –10 ³ . While the neutral gas densities are similar to those of high-redshift starburst galaxies, the FUV strengths are lower compared to both local and high-redshift starbursts. Finally, we estimate atomic hydrogen masses using [O i ] 145 μ m emission lines and the oxygen abundances measured from recent JWST observations. We find gas mass ratios of f _gas ∼ 0.3–0.8, which are similar to earlier studies using [C ii ] 158 μ m. Starting from this pilot observation, future large [O i ] 145 μ m emission line surveys will provide us with currently little-known neutral gas properties of star-forming galaxies in the early Universe.

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.

We present JWST MIRI and NIRCam imaging of the inner ∼5 kpc of the M82 superwind at ∼ 0 . ″ 05 − 0 . ″ 375 (∼0.9–6.5 pc) resolution. Targeted filters probe emission from polycyclic aromatic hydrocarbons (PAHs; F335M, F360M , F770W, F1130W) and continuum (F250M, F360M) The images reveal a network of cool wind filaments traced by PAHs. PAH surface brightness declines with the inverse square of distance to the midplane, suggesting that the incident radiation field from the starburst drives the observed PAH intensity out to ±2.5 kpc. The 3.3/11.3 and 3.3/7.7 μ m band ratios show uniformity with distance from the starburst, though comparisons with mid-IR dust emission models indicate a modest shift toward larger PAHs. Outside the disk, 11.3/7.7 μ m increases moderately, reflecting that PAHs become more neutral with distance from the starburst as they are exposed to a declining radiation field and ionization parameter. Overall, PAHs in the wind are consistent with standard-to-large sizes and standard-to-high ionization states. Including Spitzer and Herschel data, PAH abundance ( q _PAH ) is set at ∼1% in the starburst and remains unchanging out to ±5 kpc off the disk. This flat q _PAH profile suggests that PAHs are shielded from the hot wind, perhaps residing in the surface layers of cool clouds, with possible replenishment from cloud interiors and enrichment of the halo from previous bursts. In this picture, clouds are not dense enough to promote PAH growth, and they likely undergo radiative cooling and mixing with the hot phase to survive the gauntlet for at least ∼20 Myr.

We report the discovery of strongly absorbed [O I ] 63 μm in a sample of 12 dusty star-forming galaxies (DSFGs) at 4.2 < z < 5.8. This is the first systematic survey of the [O I ] 63 μm fine-structure line at z > 4, targeting a sub-sample of gravitationally lensed DSFGs selected from the South Pole Telescope survey. Using ALMA Bands 9 and 10, we obtained spatially and spectrally resolved observations that probe the interstellar medium on sub-kiloparsec scales. Despite reaching sensitivities one to two orders of magnitude deeper than most previous studies, we detect [O I ] 63 μm in emission in only two sources at low significance, with the remaining galaxies yielding stringent non-detections over the full velocity range covered by robust detections of other far-infrared lines, including [C II ] 158 μm and [N II ] 205 μm. We identify several compact (0.05–0.2″) regions with [O I ] 63 μm absorption against the far-infrared dust continuum, some of which are possibly reaching below rest-frame cosmic-microwave-background (CMB) radiation level. This suggests the presence of low-excitation-temperature (Tex ≤ T _CMB ( z )), low-density gas along those lines of sight. We also detect narrow, spatially localised [O I ] 63 μm emission ’escape channels’ preferentially detected in regions with weak or absent dust continuum emission. We also predict that similar absorption effects may appear in the [C II ] 158 μm line, particularly when concentrating on the regions with the densest foreground material along the line of sight. The [O I ] 63 μm line appears to be strongly affected by the influence of extended star forming regions, with a mix of compact, high-optical-depth [O I ] 63 μm -emitting regions and sub-thermally excited, oxygen-rich molecular clouds dispersed throughout high-redshift starbursts that are capable of absorbing the ground-state line emission. Combined with a comparison to cosmological radiation hydrodynamical simulations, this supports the interpretation that regions with higher gas and dust column densities may lead to weakening an intrinsically strong [O I ] 63 μm line emission. We argue that the high [O I ] 63 μm optical depth is the dominant effect causing the strong absorption, limiting the diagnostic power of this line to trace regions of massive star formation in high-redshift DSFGs.

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.

We present Keck/MOSFIRE H -band spectroscopic measurements covering the [C iii ] λ 1907, C iii ] λ 1909 doublet for a sample of eight z ∼ 7 spectroscopically confirmed star-forming galaxies drawn from the Reionization Era Bright Emission Line Survey (REBELS). This REBELS–MOSFIRE sample is notable for its bright median UV luminosity ( M UV = −22.5 AB) and large median stellar mass ( log M * / M ⊙ = 9.2 ). Although three sources show tentative evidence of a C iii ] detection, we obtain no confident detections for any of the eight REBELS–MOSFIRE sources. The median [C iii ] λ 1907+C iii ] λ 1909 3 σ upper limit in equivalent width (EW) for the REBELS–MOSFIRE sample is 6.5 Å, and a stack of their H -band MOSFIRE spectra yields a nondetection with an associated 3 σ upper limit of 2.6 Å. These upper limits fall significantly below the C iii ] EW measured in a composite spectrum of representative z ∼ 7 star-forming galaxies, as well as those measured for notable early star-forming galaxies such as GN-z11, GHZ2, GS-z12, and RXCJ2248-ID. The lack of strong C iii ] emission can be understood within the context of the stellar populations of the REBELS galaxies, as well as the ionization conditions and gas-phase metallicity implied by rest-frame optical spectroscopic properties ([O iii ]+H β EWs, and [O iii ] λ 5007/[O ii ] λ 3727 and [Ne iii ] λ 3869/[O ii ] λ 3727 line ratios). The REBELS–MOSFIRE sample represents the higher-mass, higher-metallicity, lower-excitation tail of the z ∼ 7 galaxy population, whose ionizing properties must be fully characterized to constrain the role of star-forming galaxies during cosmic reionization.