Magda Arnaboldi

Context. This paper presents a detailed analysis of a gas-rich star-forming ultra-diffuse galaxy (UDG) as part of the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). Among the UDGs in the LEWIS sample, UDG 6 is the only galaxy that hosts a significant amount of ionised gas with evidence of emission lines, suggesting recent star-forming activity. Aims. The main goal of this work is to constrain the formation history of this UDG by comparing its properties with the main formation scenarios proposed for this extreme class of galaxies. Methods. We adopted integral field spectroscopy from MUSE to derive the morphology and the structural properties of the stellar and gas components of UDG 6. We applied spectral fitting and Voronoi tessellation algorithms to the MUSE data-cube to derive the kinematics and properties of the gas and stellar component, explore gas dynamics, and characterise emission lines. Moreover, we derived the properties of the globular cluster (GC) populations by applying a multi-band spectrophotometric analysis. Results. We confirmed that UDG 6 is a member of the Hydra I cluster and that it has a systemic velocity of V _sys, * ∼ 3580 km s ⁻¹ . It is characterised by a regular and elongated shape and contains a significant dust content ( A _V = 1.2 ± 0.5 mag), a metal-poor (12 + log ₁₀ (O/H) = 7.7 ± 0.2 dex) ionised gas fraction ( f _gas = 0.24 ± 0.08), and an underlying old-to-intermediate (≳3 Gyr) stellar component. Evidence of local and clumpy star-forming activity has been revealed through the analysis of emission line ratios, and an arc-like tidal feature was discovered from unsharp masking analysis. The number counts of GCs in UDG 6 is N _GC = 0.2 ± 5.4. Conclusions. Similar to the other UDGs in LEWIS, UDG 6 might originate from a “puffed-up dwarf” whose stellar content has been stretched out to larger radii, passively evolving into a more diffuse galaxy. Since UDG 6 is located in a dynamically active region of the cluster characterised by tidal features and stripping phenomena, we suggest that the environmental processes have played a role in shaping its properties. A tidal interaction with a nearby galaxy might have triggered recent star-formation activity without dramatically altering the coherent gas rotation in UDG 6.

We present the analysis of the stellar and interstellar medium (ISM) properties of MARTA-4327, a star-forming galaxy at z = 2.223 observed by means of deep JWST/NIRSpec spectroscopy in both medium- and high-resolution gratings as part of the “Measuring Abundances at high Redshift with the Te Approach” (MARTA) program. We report one of the highest-redshift detections of the Wolf–Rayet (WR) blue and red bumps in a non-lensed system. The broad He II λ 4686 feature is consistent with a young (∼5−6 Myr) burst dominated by WN stars, although both stellar population synthesis models and empirical templates struggle to reproduce nitrogen stellar features at ≈4640 Å. Based on the relative strength of the available optical stellar features, we disfavor the presence of very massive stars (VMS) in this system. Elemental abundance ratios such as Ne/O, N/O, and Ar/O align with observations of local star-forming galaxies (including WR galaxies), suggesting that any impact of the WR population on the chemical enrichment of the ISM is strongly localized. However, the gas-phase Fe/O ratio appears enhanced compared to local galaxies of similar metallicity, which we interpret as evidence for reduced Fe depletion onto dust grains, possibly linked to localized destruction in WR-driven wind environments. In addition, we detect a broad (∼445 km s ⁻¹ ) and blueshifted (∼70 km s ⁻¹ ) H α component, suggesting the presence of an ionized outflow with a mass loading factor η ∼ 0.2. Finally, we report the robust detection of O I λ 8446 emission (among the firsts at high redshift), which we interpret as originating from Ly β fluorescence and/or collisional excitation in dense clumps. Overall, MARTA-4327 represents a unique system for studying the role of massive stars in shaping the ISM properties of galaxies at Cosmic Noon.

Introduction: We present the results from the observations of the galaxy NGC 628 with the Planetary Nebulae Spectrograph (PN.S) equipped with the Hα arm. With the third PN.S arm, the Hα arm, we measure the Hα fluxes, in addition to fluxes and line-of-sight velocities (LOSV) of monochromatic, spatially unresolved [OIII] 5007Å sources, in the nearly face-on disc of NGC 628. Methods: The narrow band color ([OIII] 5007Å–Hα) vs m ₅₀₀₇ magnitude diagram does separate planetary nebulae (PNe) from single compact ionized HII regions and supernovae remnants (SNRs), which also emit in [OIII]5007 Å. The goals are to detect bona fide PNe in the face-on spiral galaxy NGC 628 (M74) so that we can measure the velocity dispersion of the stars perpendicular to the main plane of the disc. By associating the velocity dispersion orthogonal to the disc of the evolved stars whose scale height is measured for edge-on discs in the near-infrared wavelengths, we can measure the surface mass density directly and break the disc-halo degeneracy. Results: This study motivates and validates the empirical selection criteria for PNe with the PN.S in star forming discs, while the modelling of the disc dynamics, based on the selected PN samples, is done in companion papers. We classified 442 PNe and 251 spatially isolated, unresolved HII regions: the PN.S with the Hα arm increased the number of known PNe in NGC 628 by a factor 4. In this study, we find evidence for two kinematically distinct PN populations in the NGC 628 disc. The kinematically ‘cold’ PN population dominates the PN luminosity function (LF) close to the bright cut-off magnitude, indicating that the PN massive, short-lived progenitors dominate the PNLF bright cut-off in NGC 628. The ‘warmer’ PN component increasingly dominates at fainter magnitudes. The velocity dispersion orthogonal to the disc plane of these two populations are σ _z,cold = 8.8 km ^–1 and σ _z,warm = 26.1 km ^–1 respectively, over a range of radii 80’’ to 425’’. Discussion: The cold and warmer components contribute to the total sample of the PN population in NGC 628 with the ratio 46% (cold) and 54% (warm). Once the velocity dispersion of the old component is matched with the population’s scale height, the decomposition of the rotation curve for NGC 628 leads to a maximal disc, with the rotation of the baryonic component accounting for 78% of the total rotational velocity in NGC 628.

We present a comprehensive analysis of the nitrogen-to-oxygen (N/O) abundance ratio in a sample of ∼660 star-forming galaxies at redshift z ∼ 1 − 6, with a median redshift of ⟨ z ⟩ = 3.0, using deep JWST/NIRSpec spectroscopy. Leveraging detections of faint auroral emission lines in 92 galaxies at z > 1 from both the MARTA survey and a large compilation of high-redshift literature objects, we derived direct electron-temperature-based abundances for nitrogen and oxygen using rest-frame optical lines. We establish the first high-redshift calibrations of strong-line N/O diagnostics based on ‘direct’ abundance measurements, finding a mild evolution for the N2O2 = log([N II ] λ 6585/[O II ] λλ 3727,3729) diagnostic and no clear evolution for the N2S2 = log([N II ] λ 6585/[S II ] λλ 6717,6731) diagnostic compared to local realisations. We then investigated the N/O–O/H relation across cosmic time using both ‘direct’ abundances and strong-line-based measurements (additional 535 galaxies). We find evidence of mild but systematic nitrogen enhancement at high redshift: galaxies at z > 1 exhibit N/O ratios elevated by ∼0.18 dex (median offset) at fixed O/H compared to local trends, with a more pronounced enhancement at low metallicity (i.e. 12 + log(O/H)≲8.1), where the offset reaches up to ∼0.4−0.5 dex. We considered several scenarios to explain the observed trends, including bursty star formation, differential metal loading, and inflows of pristine gas. Our results provide the most extensive confirmation of elevated N/O ratios at high-redshift to date based on rest-optical diagnostics and within a self-consistent frame.

In galaxy clusters, the hierarchical model of galaxy assembly predicts the formation of stellar substructures and intracluster light (ICL), a diffuse component consisting of stars that are not gravitationally bound to any single galaxy but instead follow the global gravitational potential of the cluster. These features encode the details of the cluster’s assembly history. However, observations are challenging due to their faint surface brightness, so independent tracers such as intracluster planetary nebulae and globular clusters (GCs) can provide valuable insight. For this work, we used deep VLT/FORS V - and I -band imaging to study the GC population in the Hydra I galaxy cluster, a rich environment of galaxies that is located at a distance of 45.7 Mpc. Our photometric sample of GC candidates was constructed from the VI colour-magnitude diagram, where point sources with a similar colour as confirmed GCs were selected. Dividing our GC sample in two colour groups, we show a striking difference between the two populations: while red GCs tend to be clustered around Hydra’s massive galaxies (mainly NGC 3311 and NGC 3309), blue GCs are more extended and spatially coincide with the peak of the cluster’s X-ray emitting gas. The GCs around the central galaxies also have different spatial distributions according to their stellar population properties. Young metal-rich GCs are more extended and may be associated with ram-pressure tails, whereas old metal-poor GCs are more concentrated and could be related to disrupted dwarfs. The red, old, and metal-rich GCs are likely associated with the central massive galaxies. Comparing the GC number density profiles to the surface brightness profile of NGC 3311, we find that the red GCs closely follow the galaxy’s light, while the blue population significantly deviates from it and traces the global gravitational potential of the cluster. This result is also evidenced by the specific frequency of blue GCs, which is ∼5 times larger in the ICL-dominated outskirts when compared to the inner parts of the cluster and to the red population. Finally, we introduce a novel method to constrain the evolution of the galaxy luminosity function of the cluster from GC specific frequencies and colour distributions. This method results in a past Schechter slope of α = −1.81 ^+0.16 _−0.16 for the faint end compared to α = −1.41 ^+0.08 _−0.05 in the present day, which is consistent with measurements at high redshift and with cosmological simulations.

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.

Context. As some of the oldest stellar systems in the Universe, globular clusters (GCs) are key fossil tracers of galaxy formation and interaction histories. This paper is part of the LEWIS project, which provides the first homogeneous MUSE integral-field spectroscopic survey of a complete sample of ultra-diffuse galaxies (UDGs) in the Hydra I cluster. Aims. We use MUSE spectroscopy and new VIRCAM H -band imaging data to study the GC populations and dark matter content in four dwarf galaxies from the LEWIS sample, which were found to host several GC candidates based on previous photometric studies. Methods. We retrieved line-of-sight velocities (LOSVs) for all the sources in the observed MUSE fields and classified them based on their spectral features and LOSVs. Because the spectroscopic measurements are limited to relatively bright sources ( m _H ≲ 23.5 AB mag), we developed a multi-band photometric procedure to identify additional GC candidates that are too faint for spectroscopic confirmation. GC candidates were selected based on a combination of photometric properties (colors, magnitudes) and morphometric criteria (shape and size). The same selection criteria were applied to empty fields to estimate a statistical background correction for the number of identified GC candidates. Additionally, H -band observations were used to constrain the stellar masses of the studied galaxies. Results. Based on the spectroscopic classification, we confirm one GC in UDG 3, two in UDG 7, and four in UDG 11, while UDG 9 has no spectroscopically confirmed bright GCs. We identify four intracluster GCs in the vicinity of UDG 3 and UDG 11, and one ultra-compact dwarf (UCD) with a radial velocity only −85 ± 10 km/s different from that of UDG 7 and thus possibly bound to it. Considering the completeness correction and accounting for possible contamination by unresolved background galaxies, from the photometry we estimate that the number of GCs ranges between 0 and ∼40 for the investigated UDGs. Their specific frequencies suggest that three out of four UDGs are either GC rich, similar to those in the Coma cluster, or belong to an intermediate population, as seen in the Perseus cluster. Dark matter content estimates, inferred from GC counts and stellar mass, indicate that these galaxies are dark matter dominated, with dynamical-to-stellar mass ratios ranging from ∼10 − 1000.

Aims. Distance measurements using the planetary nebula luminosity function (PNLF) rely on the bright-end cutoff magnitude ( M ^* ), which is defined by a number of the [O III ] λ 5007-brightest planetary nebulae (PNe). In early-type galaxies (ETGs), the formation of these PNe is enigmatic; the population is typically too old to form the expected M ^* PNe from single star evolution. We aim to provide a viable solution to this problem. Methods. We selected five ETGs with known MUSE-PNLF distances. The MUSE instrument allows us to calculate the PNLF and consistently investigate the underlying stellar populations. Using stellar population synthesis, we derived the population age, star formation history, metallicity, and alpha abundance. We compared these parameters to the PNLF variables: the absolute magnitude of the bright cutoff ( M ^* ) and luminosity-specific PN number at the top 0.5 mag of the PNLF ( α _0.5 ). We also compare our results with PNe In Cosmological Simulations (PICS) model applied to Magneticum Pathfinder analogue galaxies. Results. The average mass-weighted ages and metallicities of the stellar populations in our datasets are typically old (9 < Age < 13.5 Gyr) and rather metal rich (−0.4 < [M/H] < +0.2). We find the value of M ^* to be independent of age and metallicity in these ages and metallicity intervals. We observed a positive correlation between α _0.5 values and the mass fraction of stellar population ages of 2–10 Gyr, implying that most of the PNe originate from stars with intermediate ages. Similar trends are also found in the PICS analogue galaxies. Conclusions. We show that when ∼2% of the stellar mass present is younger than 10 Gyr, it is sufficient to form the M ^* PNe in ETGs. We also present observing requirements for an ideal PNLF distance determination in ETGs.

We present the first results from MARTA (Measuring Abundances at high Redshift with the T _e Approach), a programme that leverages ultra-deep, medium-resolution JWST/NIRSpec spectroscopy to probe the interstellar medium of star-forming galaxies at z ∼ 2 − 3. We report detections of one or more auroral lines, including [O III ] λ 4363, [O II ] λλ 7320, 7330, [S II ] λ 4068, and [S III ] λ 6312, for 16 galaxies in the sample, providing measurements of multiple ionic temperatures. We tested the validity of the T [O II ]– T [O III ] relation at high redshifts considering a total sample of 21 objects, including literature data, and obtained a shallower slope than in the low- z literature. However, such a slope is consistent with low-redshift data when ultra-low-metallicity objects are considered. We assessed the correlation of the T [O II ]– T [O III ] relationship and its scatter on different physical parameters, finding a mild correlation with the ionisation parameter and radiation field hardness, and no significant correlation with gas density. The location of high-redshift data is also consistent with the low- z literature in the T [O II ]– T [S II ] and T [S III ]– T [O III ] relations, although this conclusion is limited due to low-number statistics. Finally, we leveraged our sample together with a comprehensive compilation of galaxies with [O III ] λ 4363 detections from the literature to recalibrate classical strong-line diagnostics at high redshifts. MARTA represents a key addition in this space because it provides direct metallicities at moderately high oxygen abundances (12 + log(O/H) ∼ 8.0−8.4).

Context. The nearest giant spiral, the Andromeda galaxy (M31), exhibits a kinematically hot stellar disc, a global star formation episode ∼2–4 Gyr ago, and conspicuous substructures in its stellar halo that are suggestive of a recent accretion event. Aims. Recent chemodynamical measurements in the M31 disc and inner halo can be used as additional constraints for N-body hydrodynamical simulations that successfully reproduce the disc age-velocity dispersion relation and star formation history as well as the morphology of the inner halo substructures. Methods. We combined an available N-body hydrodynamical simulation of a major merger (mass ratio 1:4) with a well-motivated chemical model to predict abundance distributions and gradients in the merger remnant at z = 0. We computed the projected phase space and the [M/H] distributions for the substructures in the M31 inner halo, namely, the Giant Stellar Stream (GSS) and the North-East (NE) and Western (W) shelves. We compared the chemodynamical properties of the simulated M31 remnant with recent measurements for the M31 stars in the inner halo substructures. Results. This major merger model predicts (i) multiple distinct components within each of the substructures; (ii) a high mean metallicity and large spread in the GSS and NE and W shelves, which explain various photometric and spectroscopic metallicity measurements; (iii) simulated phase space diagrams that qualitatively reproduce various features identified in the projected phase space of the substructures in published data from the Dark Energy Spectroscopic Instrument (DESI); (iv) a large distance spread in the GSS, as suggested by previous tip of the red giant branch measurements; and (v) phase space ridges caused by several wraps of the secondary as well as up-scattered main M31 disc stars that also have plausible counterparts in the observed phase spaces. Conclusions. These results provide further strong and independent arguments for a major satellite merger in M31 ∼3 Gyr ago and a coherent explanation for many of the observational results that make M31 appear so different from the Milky Way.