Anna Ferré-Mateu

We introduce and describe the Globular cluster Observations for Luminosity-Dispersion distances (GOLD) project, which has the principal aim of determining independent distances based on the globular cluster (GC) absolute magnitude-velocity dispersion ( M _V − σ ) relation calibrated with Milky Way GCs with Gaia distances. The project comprises observations of GCs in 19 early- and late-type galaxies taken with FLAMES/GIRAFFE on ESO’s Very Large Telescope. So far, 17 galaxies have been observed. The spectra cover the wavelength range 8483−9000 Å, including the calcium triplet region at a spectral resolution of R ∼ 18 000. The spectra provide line-of-sight velocities with typical uncertainties of Δ v = 1 − 2 km s ⁻¹ . Using primarily velocities to separate extragalactic sources from foreground stars, we present here our initial sample of 1062 GCs and 101 ultra-compact dwarf galaxies (UCDs). For more than 650 of these objects we present the first velocity measurement. We discuss the available photometry and size measurements, and show that our velocities are in good agreement with previous studies. Our velocity catalogues are made publicly available. Beyond the principal aim of obtaining precision distances, additional science to be explored with these data includes host galaxy halo dynamics and clustering analysis, mass-to light ratios of GCs and UCDs in the sample, the stellar initial mass function and black hole occupation fraction of the GCs, and chemical abundances from high-dispersion spectra.

We use Keck/KCWI spectroscopy to study one ultra-diffuse galaxy (UDG) and five Nearly UDGs (NUDGEs) in the Perseus cluster, together with an additional UDG in the Coma cluster. As the first paper in a series, we focus on the global and radial stellar population properties of our sample. We find that these galaxies host intermediate-to-old stellar populations, with typical ages of $\sim$7 Gyr, low metallicities ([M/H]$\simeq -$0.9 dex), and enhanced [Mg/Fe] abundances ($\sim$0.3 dex), consistent with previous studies. Six galaxies lie within the scatter of the present-day mass–metallicity relation (MZR), whereas the Coma UDG (DF11) is more consistent with the MZR of high-z galaxies ($z \sim 2$). We find no strong correlation between global stellar population properties and cluster infall parameters, suggesting that any environmental impact is not easily traceable through integrated stellar populations. We go one step further and measure radial gradients for three galaxies. Two show flat age and mildly negative metallicity gradients, similar to classical dwarfs, while one shows a rising metallicity profile as recently found in other UDGs. Comparing with classical dwarfs, we find a continuous correlation between metallicity gradient and globular cluster (GC) richness, where more GC-rich systems tend to show rising profiles. We propose that preferential tidal disruption of GCs in the inner regions of galaxies naturally produces rising metallicity profiles, unlike GC-poor classical dwarfs. This mechanism, potentially coupled with strong stellar feedback from early concentrated star formation, may explain the unusual rising metallicity profiles observed in GC-rich UDGs/NUDGEs.

The gas-phase mass–metallicity relation (MZR) of galaxies shows a noticeable break in slope and an increased scatter at low stellar masses, suggesting that the physical processes governing chemical enrichment differ between dwarf and high-mass systems. Dwarf galaxies, in particular, are highly susceptible to both internal and environmental mechanisms due to their shallow potential wells. The primary aim of this work is to assess whether a single, universal MZR can describe dwarf galaxies across diverse large-scale environments, or whether systematic environmental variations emerge. To probe these, we examine the MZR and star formation rate (SFR) of dwarf galaxies with stellar masses in the range of 8.9 < log(M_⋆/M_⊙),<,9.5. Using optical spectra from the Sloan Digital Sky Survey, we measured the fluxes of key emission lines via the pyPipe3D full spectral fitting pipeline. Aperture-corrected fluxes, along with multiple metallicity indicators and calibrations, were used to derive the MZR and the SFR for 353, 311, and 22 dwarf galaxies located in voids, filaments, and clusters, respectively. We find a systematic variation in the MZR slope, steeper in voids (0.28,±,0.03) and progressively flatter in clusters (0.17,±,0.08), indicating a dependence of the MZR on the large-scale environment in this mass regime. When galaxies are separated by local density, no significant differences are observed between isolated and non-isolated dwarfs in voids. Isolated dwarf galaxies in filaments also exhibit properties similar to those of their counterparts in voids. However, non-isolated filament galaxies exhibit similar MZR slopes comparable to those of cluster dwarfs and flatter slopes than their counterparts in voids. We report both large- and local-scale environmental dependencies in the gas-phase metallicity and in the slope of the MZR for dwarf galaxies. Consistent with the general consensus on the pre-processing of galaxies in filaments, our results indicate that the influence of the local environment becomes increasingly significant within the filamentary regions of the cosmic web, affecting the chemical enrichment and star formation activity of low-mass systems. These findings further suggest that a portion of the scatter commonly observed in the MZR of dwarf galaxies arises from environmental effects.

The formation of massive galaxies remains a fundamental question in astrophysics, with recent JWST observations suggesting that intense star formation occurred earlier than previously expected. We used the prototypical massive relic galaxy NGC,1277 as a fossil record to probe the chemical signatures of early star formation. With a stellar mass of 1.2 =1.05^ and a compact structure (half-light radius of 1.2,kpc), NGC,1277 is representative of massive relic galaxies—systems that formed rapidly at high redshifts (`red nuggets' at z > 2) and have since undergone largely passive evolution, preserving the imprint of their earliest stellar populations. Using deep near-infrared spectroscopy, we identified unusually strong silicon (Si) absorption features in this galaxy. We measure Si/Fe +0.45 _ -0.27 and Mg/Fe =0.36^ +0.27 _ -0.24 , corresponding to a significantly enhanced silicon-to-magnesium ratio ( Si/Mg =0.67^ +0.45 _ -0.27 ), which cannot be reproduced by current stellar population models or typical core-collapse supernova yields. This enhancement suggests a contribution from very massive, metal-poor progenitors during the earliest phases of star formation. Such conditions are consistent with nucleosynthetic yields from pair-instability supernovae or other enrichment channels associated with extremely massive stars, whose chemical signatures are expected to remain less diluted in systems like NGC,1277 due to their rapid formation timescales and minimal late-time accretion. This result provides rare chemical evidence of early massive-star enrichment preserved in a local relic galaxy and opens a new observational window into the chemical evolution of the Universe.

We investigate the synthetic model of globular cluster (GC) systems of 17 compact massive galaxies (CMGs) from the Illustris TNG100 simulation to explore their connection with massive relic galaxies, systems that have undergone little structural evolution across cosmic time. The coevolution of the GC systems and their host galaxies is based on a GC formation and evolution model that assigns clusters to stellar particles according to age and local conditions, providing positional, kinematic, and chemical information for individual GCs. By combining stellar assembly histories, effective radius evolution, and GC properties such as in situ versus ex situ origin, metallicity, and spatial distribution, we identify consistent signatures of early formation and late-time accretion. We find that the GC mass fraction traces the host assembly history more robustly than the GC number fraction, as massive clusters better preserve the imprint of the early accretion history. Three CMGs from TNG100 emerge as strong massive relic analogs, exhibiting high in situ GC fractions, narrow metallicity distributions, and compact spatial distributions. A tight correlation between the host stripped fraction and the extent of the ex situ GC population further reveals the possibility to consider GC spatial profiles as a signature to identify tidal stripping processes. These results indicate that the combined analysis of GC populations and host stellar assembly offers a robust diagnostic for identifying massive relic galaxies and constraining their evolutionary histories.

Local Universe dwarf galaxies can serve as both cosmological and mass assembly probes. Deep surveys have enabled the study of these objects down to the low surface brightness (LSB) regime. In this paper, we estimate Euclid ’s dwarf detection capabilities as well as limits of its MERge processing function (MER pipeline), which is responsible for producing the stacked mosaics and final catalogues. To do this, we injected mock dwarf galaxies in a real Euclid Wide Survey (EWS) field in the VIS band and compared the input catalogue to the final MER catalogue. The mock dwarf galaxies were generated using simple Sérsic models with structural parameters (including size and surface brightness) drawn from observed dwarf galaxy catalogues. These simulations represent an idealised case in the sense they do not account for additional factors such as ellipticity, morphology, or crowding. To characterise the detected dwarfs, we used the mean surface brightness inside the effective radius SB _e (in mag arcsec ⁻² ). The final MER catalogues achieve a completenesses of 91% for SB _e ∈ [21, 24] and 54% for SB _e ∈ [24, 28]. These numbers do not take into account possible contaminants, including confusion with background galaxies at the location of the dwarfs. After taking those effects into account, they respectively became 86% and 38%. The MER pipeline performs a final local background subtraction with a small mesh size, leading to a flux loss for galaxies with R _e > 10″. By using the final MER mosaics and reinjecting this local background, we obtained an image in which we recover reliable photometric properties for objects under the arcminute scale. This background-reinjected product is thus suitable for the study of Local Universe dwarf galaxies. Euclid ’s data reduction pipeline serves as a test bed for other deep surveys, particularly regarding background subtraction methods, a key issue in LSB science.

Context. This paper presents new results from the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). The LEWIS sample consists of low-surface-brightness galaxies (LSBs) and ultra-diffuse galaxies (UDGs) located inside 0.4 R _vir of the Hydra I cluster. Integral-field spectroscopy is acquired for 24 galaxies with the MUSE spectrograph mounted on the Very Large Telescope (VLT). Aims. Our main objectives are to analyse possible correlations between the environment and the integrated stellar population properties of our targets, based on which we infer clues about their formation. Methods. For each galaxy in the sample, we extracted the 1D stacked spectrum in an aperture of one effective radius R _e and adopted previously published stellar kinematics to derive the age, metallicity, and [Mg/Fe] through a full spectral fitting technique. Results. We find that the analysed LEWIS sample has a mean metallicity of ⟨[M/H]⟩= − 0.9 ± 0.2 dex and a mean age of 10 ± 2 Gyr, comparable to previous results of UDGs in other clusters. According to their position in the projected phase space, galaxies can be classified into two groups: very early infaller galaxies, which on average have slightly higher metallicities (⟨[M/H]⟩ _early = −0.8 ± 0.1 dex), and late infaller galaxies, with slightly lower values (⟨[M/H]⟩ _late = −1.0 ± 0.1 dex). According to their properties, late-infallers tend to be rotation-supported systems. Conversely, two types of galaxies are found in the early-infall region. Roughly half have metallicities consistent with the dwarf galaxy mass–metallicity relation. The other half show higher metallicities (with ⟨[M/H]⟩≥ − 1.0 dex) and are located outside the 1 σ scatter of the mass-metallicity relation. The two subgroups of early-infallers also display different timescales for stellar mass assembly. Metal-rich galaxies reached 50% of their stellar mass in less than 1 Gyr and show a prolonged and almost constant star formation over more than 12 Gyr. The other galaxies exhibit a star formation history similar to that found for galaxies in the late-infall region. Both early and late infallers show solar-like α abundances. Conclusions. From the analysis of stellar population properties presented in this work and of stellar kinematics previously obtained from LEWIS, we identified different classes of UDGs within the Hydra I cluster – as shown by metallicities, quenching timescales, and kinematics – which suggest different formation mechanisms. Almost all of the UDGs and LSBs in this cluster are consistent with the puffed-up dwarf formation scenario, having dwarf-like metallicities and being consistent with the mass-metallicity relation for dwarfs. In the innermost regions of the cluster, where more metal-rich UDGs are found, tidal effects or the environment might have influenced their formation and evolution.