JWST has enabled the detection of galaxies in the earliest stages of cosmic history. We compare the ultraviolet luminosity functions (UVLFs) at redshifts z=7-15 predicted by the new cosmological hydrodynamics simulations, COLIBRE with observations, including those from JWST. The UV luminosities of COLIBRE galaxies are derived using the radiative transfer code SKIRT, which tracks stellar emission and its processing through the multi-phase interstellar medium and dust distribution predicted by COLIBRE. We find that although COLIBRE is consistent with the observed evolution of the stellar mass function up to z=12, its dust-attenuated UVLFs fall systematically below the observations at the bright end: at the number density of 10^-6 Mpc^-3 mag^-1, the brightest galaxies are underluminous by ≈ 1 mag at z=7, increasing to ≈ 2.5 mag at z=15. Accounting for observational uncertainties brings the COLIBRE UVLFs closer to the observational data, but does not fully resolve the discrepancy. Ignoring dust attenuation allows COLIBRE to produce sufficiently bright galaxies at 7≲ z ≲ 12, while at z=15, COLIBRE still underpredicts the luminosities of the brightest galaxies, indicating the need for additional physical mechanisms to boost the UV luminosities at the earliest cosmic epochs, such as a ”top-heavy” stellar initial mass function. We fit the COLIBRE UVLFs with Schechter functions and calculate the evolution of the best-fit parameters. We find that the galaxy number density decreases, the characteristic luminosity becomes fainter and the faint-end slope becomes steeper towards higher redshifts. The UV luminosity density decreases by a factor of ≈ 300 from z = 7 to z = 15.

The background galaxies in Euclid Early Release Observation images of the Perseus cluster make up a remarkable sample for the combination of a 0.57 deg2 area, 25.3 and 23.2 AB mag depth, and angular resolutions in the optical and near-infrared bands of 0⋅′′1 and 0⋅′′3, respectively. As part of the effort towards characterising the history of the Hubble sequence, we performed a morphological analysis of 2445 and 12 786 galaxies with IE ≤ 21 and IE ≤ 23, respectively. We used single-Sérsic profiles and the sums of a Sérsic bulge and an exponential disc to model these galaxies with SourceXtractor++ and analysed their positional, structural, and flux parameters in order to assess their similarities and differences. The fitted galaxies to IE ≤ 21 span the various Hubble types with ubiquitous bulge and disc components and a bulge-to-total light ratio (B/T) that takes all values from 0 to 1. The effective radius of the single-Sérsic profile is an intermediate estimate of galaxy size (between the bulge and disc effective radii) depending on B/T. The axis ratio of the single-Sérsic profile is higher than the disc axis ratio, and this difference increases with B/T. The choice of model impacts the photometry with −0.08 to 0.01 mag median systematic IE offsets between single-Sérsic and bulge-disc total magnitudes and a 0.05–0.15 mag dispersion from low to high B/T. We measured a median 0.3 mag bulge-disc colour difference in rest-frame Mg − Mi that originates from the disc-dominated galaxies, whereas bulge-dominated galaxies have median colours similar to those of their components. Remarkably, we also measured redder inside disc colour gradients based on 5 to 10% systematic variations of disc effective radii between the optical and near-infrared bands. This analysis demonstrates the usefulness and limitations of single-Sérsic profile modelling and the power of bulge-disc decomposition for characterising the morphology of lenticulars and spirals in Euclid images. We make available the catalogues of best-fit parameters for the morphological and SED fits.

Untargeted neutral hydrogen (HI) surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE HI XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE HI detections to find 29 LSBGs, and 26 of these meet the size requirement (R_eff > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted HI spectra at the location of all optically identified galaxies, placing upper limits on the HI-to-stellar mass ratio in these systems. While the HI-identified population overall tends toward bluer colors, the HI-identified and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the HI-identified LSBGs were missed in optical searches, this work highlights the utility of HI surveys in finding these faint systems. The HI-identified LSBGs are gas rich compared to the general HI-selected population. Furthermore, three out of four HI-selected UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of HI observations for finding and characterizing the low surface brightness Universe.

We present predictions from the recent COLIBRE cosmological hydrodynamical simulations of galaxy formation for the present-day galaxy luminosity functions (LFs) at wavelengths ranging from the far-ultraviolet (FUV) to the submillimetre. The simulations are post-processed with the radiative transfer code SKIRT, accounting for dust attenuation and emission using the distribution and properties of dust grains predicted directly by COLIBRE. Results from simulations varying in mass resolution by a factor of ∼ 10^2 (∼ 10^5 - 10^7 M_⊙) show very good convergence over most luminosity ranges. The COLIBRE-SKIRT LFs match the data remarkably well from the FUV to the near-infrared (3.4 μm) and also in the far-infrared and submillimetre wavelength range (70-850 μm). In the mid-infrared (MIR; 8-24 μm), COLIBRE-SKIRT matches the data well at low luminosities but significantly underpredicts the luminosities of MIR-bright galaxies, with the discrepancy increasing towards longer wavelengths. The total infrared LF, obtained by integrating the spectral energy distributions over 8-1000 μm, also matches observations well at the faint end but underpredicts the number of very bright galaxies. The unprecedented agreement at all other wavelengths indicates that COLIBRE, coupled with this calibration-free SKIRT post-processing framework, successfully predicts the properties of stellar populations at the present day and the amount and distribution of interstellar dust.

Many stellar systems exhibit a finite spatial extent, yet constructing self-consistent spherical models with a prescribed outer boundary is non-trivial because sharp density cutoffs introduce discontinuities that lead to inconsistencies in the associated distribution function. In this paper we show that these difficulties arise from the abruptness of the truncation rather than from the finite extent itself. We introduce a general and infinitely differentiable radial truncation scheme that can be applied to any density profile, and illustrate its behaviour using the Hernquist model. We find that softly truncated models are dynamically consistent provided that the truncation is sufficiently gradual, and we determine the corresponding critical truncation sharpness. Their distribution functions display a characteristic bump-dip feature near the truncation energy that signals the transition between consistent and inconsistent cases. In contrast to sharply truncated models, softly truncated systems can support an extensive family of Osipkov-Merritt orbital structures, including moderately radial ones. Soft truncations therefore offer a general and physically motivated route to constructing finite-extent dynamical models with well-controlled outer-edge behaviour.

Aims. We investigate the impacts of the evolution of dust mass and grain size distribution on the evolution of global attenuation curves, with a focus on the optical-ultraviolet (UV) slope and the 2175 Å bump, within a Milky Way-like (MW-like) galaxy simulation. In addition, we discuss the contributions of the star-dust geometry, scattering, and dust properties to the attenuation curves. Methods. We performed the post-processing dust radiative transfer using the SKIRT code based on a MW-like galaxy simulation. The hydrodynamic simulation was carried out with the GADGET4-OSAKA code, which models the evolution of grain size distributions. Results. For lower inclination angles (i.e., closer to face-on), the attenuation curve flattens over time up to t = 1 Gyr and becomes progressively steeper. The steeper slope of the attenuation curve is caused by the interplay between scattering and the dust disk becoming more extended over time (i.e., changes in the star-dust geometry). At higher inclination angles, the effect of scattering is suppressed and the attenuation curves steepen slightly over time due to the formation of small grains and the bias of observed UV emission toward old stars. The 2175 Å bump becomes stronger on a timescale of ∼250 Myr due to the formation of small carbonaceous grains. However, the bump strength is affected not only by the abundance of small grains, but also by star-dust geometry. At higher AV, or at higher inclination angles, the bump strengths become weaker. These results may help interpret flatter attenuation curves and less prominent bumps in high-redshift galaxies. Furthermore, we find that variations in the star-dust geometry alter the amount of scattered photons escaping the galaxy, thereby driving the anti-correlation between the slope and V-band attenuation, AV. The scatter in this relation arises from differences in dust optical depth along and perpendicular to the line of sight, reflecting differences in the inclination and star-dust geometry. Additional contributions to the scatter come from variations in the grain size distribution and the fraction of obscured young stars.

The core–Sérsic model is the standard tool for describing partially depleted stellar cores in massive early-type galaxies, yet its physical admissibility has rarely been examined. Using numerical deprojections, we show that many formally allowed parameter combinations cannot represent realistic stellar systems: sharp transitions between the inner power-law core and the outer Sérsic profile (large α) always generate non-monotonic intrinsic density profiles. We identify, for each set of structural parameters (γ, m, Re/Rb), a critical transition parameter, αcrit, above which monotonicity is violated. This threshold systematically depends on the core slope and Sérsic index, implying that a fraction of the commonly used parameter space, including the widely adopted sharp-transition limit α → ∞, is physically ruled out. These constraints have important consequences for measuring core sizes and mass deficits in massive ellipticals, for constructing dynamical models, and for comparing observations with simulations of supermassive black hole binary evolution.

The relationship between the already formed stellar mass in a galaxy and the gas reservoir of neutral atomic hydrogen, is a key element in our understanding of how gas is turned into stars in galaxy haloes. In this paper, we measure the M_ HI-M_⋆ relation based on a stellar-mass selected sample at 0.25 < z < 0.5 and the MIGHTEE-HI DR1 spectral data. Using a powerful Bayesian stacking technique, for the first time we are also able to measure the underlying bivariate distribution of HI mass and stellar mass of galaxies with M_⋆ > 10^9.5 M_⊙, finding that an asymmetric underlying HI distribution is strongly preferred by our complete samples. We define the concepts of the average of the logarithmic HI mass, ⟨log_10(M_ HI)⟩, and the logarithmic average of the HI mass, log_10(⟨ M_ HI⟩), and find that the difference between ⟨log_10(M_ HI)⟩ and log_10(⟨ M_ HI⟩) can be as large as ∼0.5 dex for the preferred asymmetric HI distribution. We observe shallow slopes in the underlying M_ HI-M_⋆ scaling relations, suggesting the presence of an upper HI mass limit beyond which a galaxy can no longer retain further HI gas. From our bivariate distribution we also infer the HI mass function at this redshift and find tentative evidence for a decrease of 2-10 times in the co-moving space density of the most HI massive galaxies up to z∼ 0.5.

The Euclid Early Release Observations (ERO) showcase Euclid's capabilities in advance of its main mission by targeting 17 astronomical objects, including galaxy clusters, nearby galaxies, globular clusters, and star-forming regions. A total of 24 hours of observing time was allocated in the early months of operation, and the scientific community was engaged through an early public data release. We describe the development of the ERO pipeline to create visually compelling images while simultaneously meeting the scientific demands within months of launch by leveraging a pragmatic data-driven development strategy. The pipeline's key requirements are to preserve the image quality and to provide flux calibration and photometry for compact and extended sources. The pipeline's five pillars are removal of instrumental signatures, astrometric calibration, photometric calibration, image stacking, and the production of science-ready catalogues for both the VIS and NISP instruments. We report a point spread function (PSF) with a full width at half maximum of 0.'' 16 in the optical I-E-band and 0.'' 49 in the near-infrared (NIR) bands Y-E, J(E), and H-E. Our VIS mean absolute flux calibration is accurate to about 1%, and the accuracy is 10% for NISP due to a limited calibration set; both instruments have considerable colour terms for individual sources. The median depth is 25.3 and 23.2 AB mag with a signal-to-noise ratio (S/N) of ten for galaxies, while it is 27.1 and 24.5 AB mag at an S/N of five for point sources for VIS and NISP, respectively. Euclid's ability to observe diffuse emission is exceptional due to its extended PSF nearly matching a pure diffraction halo, the best ever achieved by a wide-field high-resolution imaging telescope. Euclid offers unparalleled capabilities for exploring the low-surface brightness (LSB) Universe across all scales, providing high precision within a wide field of view (FoV), and opening a new observational window in the NIR. Median surface-brightness levels of 29.5 and 27.9, AB mag arcsec(-2) are achieved for VIS and NISP, respectively, for detecting a 10 '' x 10 '' extended feature at the 1 sigma level.

The properties of interstellar dust grains are being scrutinized more than ever before, with the advent of large facilities. Infrared emission from dust grains is a powerful asset that can help constrain their physical and chemical properties. Among these, the relative ratio of carbon-rich to silicate-rich grains remains one that has not yet been investigated thoroughly due to the lack of dedicated instruments and modeling limitations. We quantify the modeling degeneracies inherent to constraining the far-infrared (far-IR) slope of the dust emission spectral energy distribution. Used as a proxy for the silicate-to-carbon ratio, we find that recovering the far-IR slope is affected by the estimate of the local radiation field and the input abundances of different grain species. We show that PRIMA's hyperspectral imaging will lead to better constrained local radiation fields, which will aid-together with PRIMA's polarization capabilities-to better constrain the silicate-to-carbon ratio in M31, and how it spatially varies within the galaxy. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JATIS.11.3.031623]

Several models of nuclear dust in active galactic nuclei (AGNs) have been proposed to determine its physical and geometrical properties, usually assuming the dust density distribution as the main aspect producing differences in the mid-infrared (MIR) emission of AGNs. We present a study of the MIR emission of nearby AGNs by exploring the effects of dust distribution and chemical composition on the spectral energy distributions (SEDs) using radiative transfer simulations. Our model grid includes smooth, clumpy, and two-phase dust distributions, combined with two dust compositions: the interstellar medium (ISM) dust composition including large grains (up to 10 mu m ), and the oxide/silicate-based composition obtained in our previous work. A synthetic SED library was generated and analysed both on a model-to-model basis and with observed MIR spectra from 68 AGNs. We found that both dust distribution and composition significantly influence the spectral shape and silicate features at 10 and 18 mu m, especially at edge-on orientations. Smooth distribution produces stronger and broader absorption features, while clumpy distribution enhances silicate emission. Two-phase distributions exhibit intermediate characteristics depending on clumpiness (f(cl)) and filling factor (f(fill)). The ISM composition with large grains better reproduces observations, particularly with Type-2 SEDs, independently of dust distribution. The oxide/silicate-based composition provides more good fits with Type-1 SEDs for f(cl)<= 0.5, and with Type-2 SEDs for f(cl)>= 0.9. This work shows that none of the considered combinations of dust distribution and composition reproduces all observed spectra.

We develop a few science cases, using the PRIMA far-infrared (FIR) probe, aimed at achieving several breakthroughs in our understanding of the dust properties and their evolution. We argue that the specific observational capabilities of PRIMA, namely, its unprecedented sensitivity over the whole FIR range and the possibility to obtain continuous spectra between lambda=24 and 235 mu m, are essential to progress in our understanding of the physics of the interstellar medium (ISM) and galaxy evolution. Our science cases revolve around observations of nearby galaxies. We discuss the importance of detecting the IR emission of the diffuse ISM of these galaxies, including very low-metallicity systems. We also discuss the opportunity of detecting various solid-state features to understand the mineralogy of interstellar grains. Finally, we stress the unique opportunity brought by the possible simultaneous measures of both the dust continuum and the FIR fine-structure gas lines. These science cases could be distributed in a few large programs. (c) 2025 Society of Photo-Optical Instrumentation Engineers (SPIE)

We present an analysis of Euclid observations of a 0.5 deg$^2$ field in the central region of the Fornax galaxy cluster that were acquired during the performance verification phase. With these data, we investigate the potential of Euclid for identifying GCs at 20 Mpc, and validate the search methods using artificial GCs and known GCs within the field from the literature. Our analysis of artificial GCs injected into the data shows that Euclid's data in $I_{\rm E}$ band is 80% complete at about $I_{\rm E} \sim 26.0$ mag ($M_{V\rm } \sim -5.0$ mag), and resolves GCs as small as $r_{\rm h} = 2.5$ pc. In the $I_{\rm E}$ band, we detect more than 95% of the known GCs from previous spectroscopic surveys and GC candidates of the ACS Fornax Cluster Survey, of which more than 80% are resolved. We identify more than 5000 new GC candidates within the field of view down to $I_{\rm E}$ mag, about 1.5 mag fainter than the typical GC luminosity function turn-over magnitude, and investigate their spatial distribution within the intracluster field. We then focus on the GC candidates around dwarf galaxies and investigate their numbers, stacked luminosity distribution and stacked radial distribution. While the overall GC properties are consistent with those in the literature, an interesting over-representation of relatively bright candidates is found within a small number of relatively GC-rich dwarf galaxies. Our work confirms the capabilities of Euclid data in detecting GCs and separating them from foreground and background contaminants at a distance of 20 Mpc, particularly for low-GC count systems such as dwarf galaxies.

Context. As a major cooling line of interstellar gas, the far-infrared 158 mu m line from singly ionised carbon [C II] is an important tracer of various components of the interstellar medium in galaxies across all spatial and morphological scales. Yet, there is still not a strong constraint on the origins of [C II] emission. Aims. In this work, we derive the resolved [C II] star formation rate relation and aim to unravel the complexity of the origin of [C II]. Methods. We used the Field-Imaging Far-Infrared Line Spectrometer on board the Stratospheric Observatory for Infrared Astronomy to map [C II] in three nearby star-forming galaxies at sub-kiloparsec scales, namely, NGC 3627, NGC 4321, and NGC 6946, and we compared these [C II] observations to the galactic properties derived from complementary data from the literature. Results. We find that the relationship between the [C II] fine structure line and star formation rate shows variations between the galaxies as well as between different environments within each galaxy. Conclusions. Our results show that the use of [C II] as a tracer for star formation is much more tangled than has previously been suggested within the extragalactic literature, which typically focuses on small regions of galaxies and/or uses large-aperture sampling of many different physical environments. As found within resolved observations of the Milky Way, the picture obtained from [C II] observations is complicated by its local interstellar medium conditions. Future studies will require a larger sample and additional observational tracers, obtained on spatial scales within galaxies, in order to accurately disentangle the origin of [C II] and calibrate its use as a star formation tracer.

Extragalactic globular clusters (EGCs) are an abundant and powerful tracer of galaxy dynamics and formation, and their own formation and evolution is also a matter of extensive debate. The compact nature of globular clusters means that they are hard to spatially resolve and thus study outside the Local Group. In this work we have examined how well EGCs will be detectable in images from the Euclid telescope, using both simulated pre-launch images and the first early-release observations of the Fornax galaxy cluster. The Euclid Wide Survey will provide high-spatial resolution VIS imaging in the broad IE band as well as near-infrared photometry (YE, JE, and HE). We estimate that the galaxies within 100 Mpc in the footprint of the Euclid survey host around 830 000 EGCs of which about 350 000 are within the survey's detection limits. For about half of these EGCs, three infrared colours will be available as well. For any galaxy within 50Mpc the brighter half of its GC luminosity function will be detectable by the Euclid Wide Survey. The detectability of EGCs is mainly driven by the residual surface brightness of their host galaxy. We find that an automated machine-learning EGC-classification method based on real Euclid data of the Fornax galaxy cluster provides an efficient method to generate high purity and high completeness GC candidate catalogues. We confirm that EGCs are spatially resolved compared to pure point sources in VIS images of Fornax. Our analysis of both simulated and first on-sky data show that Euclid will increase the number of GCs accessible with high-resolution imaging substantially compared to previous surveys, and will permit the study of GCs in the outskirts of their hosts. Euclid is unique in enabling systematic studies of EGCs in a spatially unbiased and homogeneous manner and is primed to improve our understanding of many understudied aspects of GC astrophysics.

Context. Galaxy mergers are an important and complex phase during the evolution of galaxies. They may trigger nuclear activity and/or strong star forming episodes in galaxy centres that potentially alter the evolution of the system. Aims. As part of the guaranteed time observations program Mid-Infrared Characterization Of Nearby Iconic galaxy Centers (MICONIC), we used the medium-resolution spectrometer (MRS) of the Mid-Infrared Instrument on board the James Webb Space Telescope (JWST) to study NGC 6240. We aim to characterise the dual active galactic nuclei (AGN), the ionised gas outflows, and the main properties of the interstellar medium over a mapped area of 6.6 '' x 7.7 ''. Aims. We obtained integral field spectroscopic mid-infrared data (wavelength from 4.9 to 28 mu m) of NGC 6240. We modelled the emission lines through a kinematic decomposition that accounts for the possible existence of various components. Methods. We have resolved both nuclei of NGC 6240 for the first time in the full 5-28 mu m spectral range. The fine structure lines in the southern (S) nucleus are broader than for the northern (N) nucleus (full width at half maximum of >= 1500 versus similar to 700 km s(-1) on average, respectively). High excitation lines, such as [Ne V], [Ne VI], and [Mg V], are clearly detected in the N nucleus. In the S nucleus, the same lines can be detected but only after a decomposition of the polycyclic aromatic hydrocarbon features in the integrated spectrum, due to a combination of a strong mid-IR continuum, broad emission lines, and intense star formation (SF). The SF is distributed all over the mapped field of view of 3.5 kpc x 4.1 kpc (projected), with the maximum located around the S nucleus. Both nuclear regions appear to be connected by a bridge region that is detected with all the emission lines. Based on the observed MRS line ratios and the high velocity dispersion (sigma similar to 600 km s(-1)), shocks also dominate the emission in this system. We detected the presence of outflows as a bubble north-west from the N nucleus and at the S nucleus. We estimated an ionised mass outflow rate of 1.4 +/- 0.3 M-circle dot yr(-1) and 1.8 +/- 0.2 M-circle dot yr(-1), respectively. Given the derived kinetic power of these outflows, both the AGN and the starburst could have triggered them.

The Euclid mission is generating a vast amount of imaging data in four broadband filters at a high angular resolution. This data will allow for the detailed study of mass, metallicity, and stellar populations across galaxies that will constrain their formation and evolutionary pathways. Transforming the Euclid imaging for large samples of galaxies into maps of physical parameters in an efficient and reliable manner is an outstanding challenge. Here, we investigate the power and reliability of machine learning techniques to extract the distribution of physical parameters within well-resolved galaxies. We focus on estimating stellar mass surface density, mass-averaged stellar metallicity, and age. We generated noise-free synthetic high-resolution (100 pcx100 pc) imaging data in the Euclid photometric bands for a set of 1154 galaxies from the TNG50 cosmological simulation. The images were generated with the SKIRT radiative transfer code, taking into account the complex 3D distribution of stellar populations and interstellar dust attenuation. We used a machine learning framework to map the idealised mock observational data to the physical parameters on a pixel-by-pixel basis. We find that stellar mass surface density can be accurately recovered with a <= 0.130 dex scatter. Conversely, stellar metallicity and age estimates are, as expected, less robust, but they still contain significant information that originates from underlying correlations at a sub-kiloparsec scales between stellar mass surface density and stellar population properties. As a corollary, we show that TNG50 follows a spatially resolved mass-metallicity relation that is consistent with observations. Due to its relatively low computational and time requirements, which has a time-frame of minutes without dedicated high performance computing infrastructure once it has been trained, our method allows for fast and robust estimates of the stellar mass surface density distributions of nearby galaxies from four-filter Euclid imaging data. Equivalent estimates of stellar population properties (stellar metallicity and age) are less robust but still hold value as first-order approximations across large samples.

Context. The Tully-Fisher relation (TFR) is one of the most important and widely used empirical correlations in extragalactic astronomy. Apart from its importance as a secondary distance indicator, the TFR relation serves as a test for galaxy evolution models, because it connects the baryonic and dark matter components of galaxies. Aims. We aimed at simulating the multi-wavelength TFR relation from UV to mid-infrared (MIR) wavelengths for the TNG50 cosmological simulation at z = 0, and at comparing the results with observational TFR studies. Our goal was to compare the wavelength dependence of the slope and scatter with the observed values, and to search for secondary parameters that reduce the scatter in the TFR. Methods. We selected a large sample of simulated late-type, disc-dominated galaxies from the TNG50 simulation. For each galaxy, we used the SKIRT radiative transfer code to generate realistic synthetic global fluxes in 12 UV to MIR broadbands and synthetic integrated H I line profiles. We used bivariate linear regression to determine the TFR in each band, and we searched for a second TFR parameter by correlating the residuals with different physical parameters. Results. Our TNG50 TFR reproduces the characteristic behaviour of the observed TFR in many studies: the TFR becomes steeper and tighter as we move from UV/optical to infrared wavelengths. The slope changes from -7.46 +/- 0.14 mag dex-1 in the NUV band to -9.66 +/- 0.09 mag dex-1 in the IRAC [4.5] band. Quantitatively, our slopes are well within the spread of different observational results. The u - r colour or the sSFR can significantly reduce the scatter in the UV and optical bands. Using u - r colour as second parameter, the modified TFR has a roughly constant intrinsic tightness of over the entire UV to MIR range. Conclusions. The combination of the TNG50 cosmological simulation and the SKIRT radiative transfer postprocessing is capable of broadly reproducing the multi-wavelength TFR. A better matched sample selection, the use of different characteristic velocity scales, and more advanced internal dust attenuation correction are steps towards a more stringent comparison of the simulated and observed multi-wavelength TFR.

Close companions influence stellar evolution through tidal interactions, mass transfer and mass-loss effects. While such companions are detected around young stellar objects, main-sequence stars, red giants and compact objects, direct observational evidence of close-in companions around asymptotic giant branch (AGB) stars has remained elusive. Here we present (sub)millimetre time-domain imaging spectroscopy revealing the Keplerian motion of a close-in companion around the AGB star pi 1 Gruis. The companion, slightly more massive than the AGB star, is likely a main-sequence star. Unlike more evolved stars with companions at comparable distances, the companion of pi 1 Gruis follows a circular orbit, suggesting an eccentricity-generating mechanism during the late- or post-AGB phase. Our analysis suggests that model-predicted circularization rates may be underestimated. Our results highlight the potential of multi-epoch (sub)millimetre interferometry in detecting the Keplerian motion of close companions to giant stars and open avenues for our understanding of tidal interaction physics and binary evolution.

We present the redshift evolution of radial color gradients (in rest-frame U - V and V - J) for galaxies in the range 0.5< z <2.5 and investigate their origin and dependence on stellar mass. We select ∼ 10,200 galaxies with stellar masses M_⋆>10^9.5 M_⊙ from publicly available JWST/NIRCam-selected catalogs. Using 2D Sérsic profile fits to account for PSF broadening, we perform spatially resolved SED fitting on HST and JWST/NIRCam photometry retrieving accurate rest-frame U - V and V - J color gradients within 2R_e, F444W. Star-forming galaxies generally exhibit negative V - J color gradients that are strongly mass and redshift dependent. For massive star-forming galaxies (M_⋆>10^10.5 M_⊙) at z>1.5 V - J colors are ≈ 0.5 mag redder within the effective radius than outside, on average. We find that, at all redshifts and across the entire stellar mass range, V - J gradients strongly correlate with global attenuation (A_V), suggesting that they predominantly trace dust attenuation gradients. Edge-on galaxies are redder and have stronger gradients at all z, although the correlation weakens at higher z. The U - V and V - J color gradients in the quiescent galaxy population, in contrast, are weakly negative (from ≈ -0.1 to ≈- 0.2 mag), though significant, and show little or no dependence on stellar mass, redshift or axis ratio. The implication is that quiescent galaxies must be largely transparent, with low A_V, and color gradients mostly attributable to stellar population gradients.