Globular clusters (GCs) are dense star clusters found in all massive galaxies. Recent work has established that they follow a tight relation between their internal stellar velocity dispersion σ and luminosity, enabling accurate distance measurements. In this work, we aim to apply this GC velocity dispersion (GCVD) distance method to measure the distance to M 104 (NGC 4594, the Sombrero galaxy). We have measured internal stellar velocity dispersions for 85 globular clusters (GCs) and one ultra-compact dwarf galaxy around M 104 using high-resolution multi-object integrated-light spectroscopy with FLAMES/GIRAFFE on the Very Large Telescope. The measured velocity dispersions range from σ = 4 − 30 km s, with a mean uncertainty of Δ σ = 2.5 km s. For a subset of 77 GCs with V -band magnitudes and reliable velocity dispersion measurements above σ > 4 km s, we constructed the M V - σ relation to measure the distance to M 104, finding D = 9.00 ± 0.29 (stat.) ± 0.26 (sys.) Mpc. The GCs follow the Milky Way and M 31 M V − σ relation closely, with the exception of the luminous ultra-compact dwarf SUCD1, which is nearly one magnitude brighter than the mean relation. 29 GCs in the sample have sizes determined from Hubble Space Telescope imaging which allowed us to determine their masses and V -band dynamical mass-to-light ratios (M/L). We find a mean < M / L V > = 2.6 M ⊙ / L ⊙ for the luminous ( M V < − 8 mag) M 104 GCs, which is higher than the Milky Way GCs, but is reminiscent of the brightest GCs in Centaurus A. With the exception of SUCD1, the GCs of M 104 follow the GCVD relation irrespective of their mass-to-light ratio.

We have employed a novel way to measure the distance to NGC1052-DF2, using the internal stellar velocity dispersions (sigma) of its globular clusters (GCs). We obtained deep (15.1 h), R = 18 200, calcium triplet integrated-light spectra for 10 GCs in NGC1052-DF2 using FLAMES GIRAFFE on VLT. For five GCs, we measured the sigma values, along with precision velocities for the whole sample. We also present a new photometric analysis based on 40 orbits of archival Hubble Space Telescope imaging for 16 spectroscopically confirmed GCs. Assuming that the NGC1052-DF2 GCs obey the M-V - log(sigma) relation followed by the Milky Way and M31 GCs, the NGC1052-DF2 GCs indicate a distance, d = 16.2 +/- 1.3 (stat.) +/- 1.7 (sys.) Mpc. In contrast, adopting a literature distance of d = 21.7 Mpc from forward modelling of the tip of the red giant branch (TRGB), the GCs lie above the Milky Way + M31 relation by similar to 0.6 magnitudes. For a shorter literature distance of 13 Mpc, the GCs fall below the relation by similar to 0.4 mag. At d = 16.2 Mpc, we obtain mean dynamical M/L-V = 1.61 +/- 0.44 M-circle dot/L-circle dot and median half-light radii of r(h) = 3.0 +/- 0.5 pc. This is entirely consistent with Milky Way GCs, with mean M/L-V = 1.77 +/- 0.10 M-circle dot/L-circle dot and median r(h) = 3.2 +/- 0.6 pc. For the further distance of 21.7 Mpc, we obtain systematically lower M/L-V ratios (M/L-V = 1.19 +/- 0.33 M-circle dot/L-circle dot), which could suggest ages of similar to 6 Gyr assuming canonical mass functions. However, such young ages are inconsistent with a MUSE stellar population analysis of the NGC1052-DF2 GCs, which indicates they are similar to 10 Gyr old. For d = 16.2 Mpc, coupled with our new photometry, we find that the properties of the GCs in NGC1052-DF2 appear to be entirely consistent with those in the Milky Way and other Local Group galaxies. To reconcile the further distance with our results, a mass function that is more dwarf-depleted than the Milky Way GCs must be invoked for the GCs of NGC1052-DF2.

As ancient star clusters, globular clusters (GCs) are regarded as powerful tracers of galaxy evolution and assembly. Due to their brightness and compact sizes, GCs are employed to probe the kinematics and stellar population properties of galaxies, from the central regions out into the halo where the underlying stellar light becomes too faint for spectroscopic studies. In this work, we present a comprehensive study of the GC system of M 104 (NGC 4594, also known as the Sombrero galaxy) based on literature spectroscopic catalogues and newly collected data from Very Large Telescope (VLT) MUSE integral-field spectroscopy combined with multi-object spectroscopy from VLT FLAMES and OSIRIS at the Gran Telescopio de Canarias (GTC). We present a new catalogue of 499 GCs with radial velocity measurements that span from the inner disc region out to similar to 70 kpc (24 '). In addition to velocities, we measured metallicities from the MUSE, OSIRIS, and FLAMES spectra of 190 GCs. Together with literature values, we collected a sample of 278 metallicities. We found good agreement between the velocity and metallicity measurements of GCs observed with multiple instruments. Studying GC kinematics with a simple model confirms a decreasing velocity dispersion profile and low rotation velocities. The blue GCs appear to be more dispersion-dominated, while the red GCs follow the kinematics of the stars more closely. We find a large scatter of GC metallicities with distance from the centre, and metal-rich GCs are found over all radii. We discuss how the GC metallicity distribution with a broad metal-poor component likely reflects the complex assembly history of M 104.

Nuclear star clusters (NSCs) are dense, compact stellar systems only a few parsecs across, located at galaxy centers. Their small sizes make them difficult to resolve spatially. NSCs often coexist with massive black holes, and both trace the dynamical state and evolution of their host galaxies. Dense stellar environments such as NSCs are also ideal sites for forming intermediate-mass black holes (IMBHs). To date, spatially resolved NSC properties, crucial for reconstructing dynamical and star-formation histories, have only been obtained for galaxies within 5 Mpc, using the highest-resolution instruments on the current class of very large telescopes. This severely limits spectroscopic studies, and a systematic, unbiased survey has never been accomplished. Because the vast majority of known NSCs are located in the Northern Hemisphere, only a 30-m-class telescope in the North can provide the statistical power needed to study their physical properties and measure the mass of coexisting central black holes. We propose leveraging the capabilities of a 30-m-class Northern telescope to obtain the first comprehensive, spatially resolved survey of NSCs, finally allowing us to unveil their formation pathways and their yet unknown connection with central massive black holes.

The properties of massive and compact early-type galaxies provide important constraints on early galaxy formation processes. Among these, massive relic galaxies, characterized by old stellar populations and minimal late-time accretion, are considered to be preserved compact galaxies from the high-z Universe. In this work, we investigate the properties of compact and massive galaxies (CMGs) using the TNG50 cosmological simulation, applying a uniform selection criterion that matches observational surveys at z = 0, z = 0.3, and z = 0.7. This approach provides a basis for direct comparisons with observed compact galaxies at each evaluated redshift. We classify CMGs according to their stellar mass assembly histories to investigate how compactness relates to dynamical properties and chemical enrichment across cosmic time. Our results show that simulated CMGs consistently follow the observed mass-size relation, with the number of compact galaxies increasing at higher redshifts; this number density follows the trend seen in observational data. In the dynamical context, while observations suggest that relic galaxies are outliers in the stellar mass-velocity dispersion plane, the simulated compacts show relatively uniform velocity dispersions across different accretion histories. Observed relics tend to be more metal-rich than other compact galaxies with extended star formation histories, deviating from the local mass-metallicity relation. In contrast, simulated compact galaxies are, overall, more metal-rich than the quiescent population, regardless of their accretion histories. We also find that the deviation of the simulated CMGs from the mass-metallicity relation decreases with increasing redshift. These findings suggest that the extreme characteristics of the CMGs in TNG50, particularly with regard to metal enrichment and dynamical properties, are less pronounced than those observed in real relic galaxies. However, the results offer a theoretical framework for assessing the properties of such extreme objects from different epochs, highlighting both alignment with and deviations between the models.

We employ a new way to measure the distance to NGC1052-DF2 via internal stellar velocity dispersions (σ) of its globular clusters (GCs). We obtained deep (15.1h), R=18,200, Ca Triplet integrated-light spectra for 10 GCs in NGC1052-DF2 using FLAMES GIRAFFE on VLT. For five GCs we measure σ, along with precision velocities for the whole sample. We also present a new photometric analysis based on 40 orbits of archival Hubble Space Telescope imaging for 16 spectroscopically confirmed GCs. Assuming that the NGC1052-DF2 GCs obey the M_V – log(σ) relation followed by the Milky Way and M31 GCs, the NGC1052-DF2 GCs give a distance, d=16.2±1.3 (stat.) ±1.7 (sys.) Mpc. By contrast, using a literature distance of d=21.7 Mpc from forward modelling of the TRGB, the GCs lie above the Milky Way + M31 relation by ∼0.6 magnitudes. For a shorter literature distance of 13 Mpc, the GCs fall below the relation by ∼0.4 mag. At d = 16.2 Mpc, we obtain mean dynamical M/L_V = 1.61±0.44 M_⊙/L_⊙, and median half-light radii, r_h =3.0±0.5 pc. This is entirely consistent with Milky Way GCs, with mean M/L_V = 1.77±0.10 M_⊙/L_⊙, median r_h =3.2±0.6 pc. For the further distance of 21.7 Mpc, we obtain low M/L_V ratios (M/L_V = 1.19±0.33 M_⊙/L_⊙) which could suggest ages of ∼6 Gyr.. Such young ages are inconsistent with our MUSE stellar population (companion paper, Fahrion et al.) analysis of the NGC1052-DF2 GCs which indicates they are ∼10 Gyr old. For d = 16.2 Mpc, coupled with our new photometry, we find that the properties of the GCs in NGC1052-DF2 appear entirely consistent with those in the Milky Way and other Local Group galaxies. In order to reconcile the further distance with our results, a mass function more dwarf-depleted than the Milky Way GCs must be invoked for the GCs of NGC1052-DF2.

Aims. The goal of this work is to scrutinise the surface brightness fluctuation (SBF) calculation methodology. We analysed the SBF derivation procedure, measured the accuracy of the fitted SBF under controlled conditions, retrieved the uncertainty associated with the variability of a system that is inherently stochastic, and studied the SBF reliability under a wide range of conditions. Additionally, we address the possibility of an SBF gradient detection. We also examine the problems related with biased measurements of the SBF and low luminosity sources. All of this information allows us to put forward guidelines to ensure a valid SBF retrieval. Methods. To perform all the experiments described above, we carried out Monte Carlo simulations of mock galaxies as an ideal laboratory. Knowing its underlying properties, we attempted to retrieve SBFs under different conditions. The uncertainty was evaluated through the accuracy, the precision, and the standard deviation of the fitting. Results. We demonstrate how the usual mathematical approximations taken in the SBF theoretical derivation have a negligible impact on the results and how modelling the instrumental noise reduces the uncertainty. We conducted various studies where we varied the size of the mask applied over the image, the surface and fluctuation brightness of the galaxy, its size and profile, its point spread function, and the sky background. It is worth highlighting that we find a strong correlation between having a high number of pixels within the studied mask and retrieving a low uncertainty result. We address how the standard deviation of the fitting underestimates the actual uncertainty of the measurement. Lastly, we find that, when studying SBF gradients, the result is a pixel-weighted average of all the SBFs present within the studied region. Retrieving an SBF gradient requires high-quality data and a sufficient difference in the fluctuation value through the different radii. We show how the SBF uncertainty can be obtained and we present a collection of qualitative recommendations for a safe SBF retrieval. Conclusions. Our main findings are as follows. It is important to model the instrumental noise, rather than fitting it. The target galaxies must be observed under appropriate observational conditions. In a traditional SBF derivation, one should avoid pixels with fluxes lower than ten times the SBF estimate to prevent biased results. The uncertainty associated with the intrinsic variability of the system can be obtained using sets of Monte Carlo mock galaxy simulations. We offer our computational implementation in the form of a simple code designed to estimate the uncertainty of the SBF measurement. This code can be used to predict the quality of future observations or to evaluate the reliability of those already conducted.

Context. The chemical composition of globular clusters (GCs) across the Local Group provides information on chemical abundance trends. Studying GCs in isolated systems in particular provides us with important initial conditions plausibly unperturbed by mergers and tidal forces from the large Local Group spirals. Aims. We present a detailed chemical abundance analysis of Sextans A GC-1. The host galaxy, Sextans A, is a low-surface-brightness dwarf irregular galaxy located on the edge of the Local Group. We derive the dynamical mass of the GC together with the mass-to-light ratio and the abundances of the α, Fe-peak, and heavy elements. Methods. Abundance ratios were determined from the analysis of an optical integrated-light spectrum of Sextans A GC-1, obtained with UVES on the VLT. We apply non-local thermodynamic equilibrium (NLTE) corrections to Mg, Ca, Ti, Fe, and Ni. Results. The GC appears to be younger and more metal-poor than the majority of the GCs of the Milky Way, with an age of 8.6 ± 2.7 Gyr and [Fe/H] = −2.14 ± 0.04 dex. The calculated dynamical mass is Mdyn = (5.18 ± 1.62)×105 M⊙, which results in an atypically high value of the mass-to-light ratio, 4.35 ± 1.40 M⊙/LV⊙. Sextans A GC-1 has varying α elements – the Mg abundance is extremely low, Ca and Ti are solar-scaled or mildly enhanced, and Si is enhanced. The measured values are [Mg/Fe] = −0.79 ± 0.29, [Ca/Fe] = +0.13 ± 0.07, [Ti/Fe] = +0.27 ± 0.11, and [Si/Fe] = +0.62 ± 0.26, which makes the mean α abundance (excluding Mg) to be enhanced [⟨Si, Ca, Ti⟩/Fe]NLTE = +0.34 ± 0.15. The Fe-peak elements are consistent with scaled-solar or slightly enhanced abundances: [Cr/Fe] = +0.31 ± 0.18, [Mn/Fe] = +0.19 ± 0.32, [Sc/Fe] = +0.22 ± 0.22, and [Ni/Fe] = +0.02 ± 0.12. The heavy elements measured are Ba, Cu, Zn, and Eu. Ba and Cu have sub-solar abundance ratios ([Ba/Fe] = −0.48 ± 0.21 and [Cu/Fe] < −0.343), while Zn and Eu are consistent with their upper limits being solar-scaled and enhanced, [Zn/Fe] < +0.171 and [Eu/Fe] < +0.766. Conclusions. The composition of Sextans A GC-1 resembles the overall pattern and behaviour of GCs in the Local Group. The anomalous values are the mass-to-light ratio and the depleted abundance of Mg. There is no definite explanation for such an extreme abundance value. Variations in the initial mass function or the presence of an intermediate-mass black hole might explain the high mass-to-light ratio value.

Almost Dark Galaxies are objects that have eluded detection by traditional surveys such as the Sloan Digital Sky Survey (SDSS). The low surface brightness of these galaxies ($\mu_r$(0)$>26$ mag/arcsec^2), and hence their low surface stellar mass density (a few solar masses per pc^2 or less), suggests that the energy density released by baryonic feedback mechanisms is inefficient in modifying the distribution of the dark matter halos they inhabit. For this reason, almost dark galaxies are particularly promising for probing the microphysical nature of dark matter. In this paper, we present the serendipitous discovery of Nube, an almost dark galaxy with $<\mu_V>$e~ 26.7 mag/arcsec^2. The galaxy was identified using deep optical imaging from the IAC Stripe82 Legacy Project. Follow-up observations with the 100m Green Bank Telescope strongly suggest that the galaxy is at a distance of 107 Mpc. Ultra-deep multi-band observations with the 10.4m Gran Telescopio Canarias favour an age of ~10 Gyr and a metallicity of [Fe/H]$\sim-1.1$. With a stellar mass of ~4x10^8 Msun and a half-mass radius of Re=6.9 kpc (corresponding to an effective surface density of ~0.9 Msun/pc^2), Nube is the most massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger than typical ultra-diffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local Group have very low mass (~10^5 Msun) and compact structures (effective radius Re<1 kpc). Current cosmological simulations within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube. However, its highly extended and flattened structure is consistent with a scenario where the dark matter particles are ultra-light axions with a mass of m$_B$=($0.8^{+0.4}_{-0.2}$)$\times10^{-23}$ eV.}

The kinematics and chemical composition of stellar populations of different ages provide crucial information about the evolution of a galaxy. We aim to provide such information for IC 1613, an isolated, gas-rich, star-forming dwarf galaxy in the Local Group. We present here the results of a new spectroscopic study performed with MUSE, an integral-field spectrograph on the Very Large Telescope. We extracted from the data cubes more than 2000 sources from which we separated stellar objects for further spectroscopic analysis. The quality of the data set allowed us to obtain accurate classifications and line-of-sight velocities for about 800 stars. Our sample includes not only Red Giant Branch (RGB) and Main Sequence (MS) stars, but also a number of probable Be and C stars. We also obtained reliable metallicities for about 300 RGB stars. The kinematic analysis revealed for the first time the presence of stellar rotation with high significance. We found general agreement with the rotation velocity of the neutral gas component. Examining the kinematics of stars as a function of broad age ranges, we find that the velocity dispersion increases as a function of age, with the behaviour being very clear in the outermost pointings, while the rotation-to-velocity dispersion support decreases. On timescales shorter than a Gyr, the stellar kinematics still follow very closely that of the neutral gas, while the two components decouple on longer timescales. The chemical analysis of the RGB stars revealed average properties comparable to other Local Group dwarf galaxies. We also provide a new estimation of the inclination angle using only independent stellar tracers. Our work provides the largest spectroscopic sample of an isolated LG dwarf galaxy. The results obtained seem to support the scenario in which the stars of a dwarf galaxy are born from a less turbulent gas over time.

ABSTRACT Accurate distances are key to obtaining intrinsic properties of astronomical objects such as luminosity or size. Globular clusters (GCs) follow a well-defined relation between their absolute magnitudes and internal stellar velocity dispersions (σ), offering an independent way to measure distances to their host galaxies via high-resolution spectroscopy. This is reminiscent of the ‘Faber–Jackson’ for elliptical galaxies. However, unlike galaxies, GCs have a very narrow range of mass-to-light ratios and simple star formation histories. Here, we show that the GC MV−log10(σ) relation is linear, whose slope is identical for the Milky Way and M31 GC systems. Based on this, we use 94 Milky Way GCs which have distances from GAIA parallaxes, or proper-motion dispersion profiles to derive a ‘GC velocity dispersion’ distance (GCVD) to M31, obtaining (m − M)0 = 24.51 ± 0.08 (d = 798 ± 28 kpc), in excellent agreement with independent measurements. Combining data for these two galaxies to create a fiducial relation using 296 GCs with high-quality measurements, we obtain a zero-point uncertainty (±0.06 mag) corresponding to a distance uncertainty of $\sim 3~{{\ \rm per\ cent}}$. We then use GCVD to obtain a distance to the giant elliptical galaxy NGC 5128 (Centaurus A), finding (m − M)0 = 27.95 ± 0.09 (d = 3.89 ± 0.16 Mpc). This is in excellent agreement with, and in some cases more precise than, literature estimates from the tip of the red giant branch or surface brightness fluctuations. We apply GCVD to Local Group galaxies with appropriate data and find good agreement with literature values even in cases with only one GC velocity dispersion measurement.

Understanding faint dwarf galaxies is fundamental to the development of a robust theory of galaxy formation on small scales. Since the discovery of a population of ultra diffuse galaxies (UDGs) rich in globular clusters (GCs) in Coma, an increasing number of studies on low surface brightness dwarf galaxies (LSBds) have been published in recent years. The most massive LSBds have been observed predominantly in groups and clusters, with properties displaying dependence on the environment. In this work, we use deep DECam imaging to systematically identify LSBds and their GC populations around the low-density environment of NGC 3115. We carefully analyse the structure and morphology of 24 candidates, 18 of which are reported for the first time. Most candidates exhibit red colours suggesting a connection between their colour and distance to NGC 3115. We followed up with Gemini GMOS imaging 9 LSBds to properly identify their GC populations. We derive lower limits for the number of GCs associated with each galaxy. Our analysis reveals that they occur around of the same loci of Fornax LSB dwarf GC systems. The relationship between the number of GCs and total mass provides a tool in which, by counting the GCs in these galaxies, we estimate an upper limit for the total mass of these LSB dwarfs, obtaining the mean value of similar to 3.3x10(10) M-circle dot. Our results align with expectations for dwarf-sized galaxies, particularly regarding the distribution and specific frequency of their GC systems.

Near-ultraviolet (NUV) spectroscopic studies have suggested that passively evolving massive, early-type galaxies host sub-one per cent fractions of young stars in their innermost regions. We shed light on the origin of these stars by analysing NGC 1277, a widely studied nearby prototypical massive compact relic galaxy. These are rare galaxies that have survived without experiencing significant size evolution via accretion and mergers since their formation at high redshift. We obtain a spectrum in the UV range within the central 1 kpc region of NGC 1277. We compare a carefully selected set of optical and NUV line-strengths to model predictions with star formation histories characteristic of massive galaxies. We find a 0.8 per cent mass fraction of young stars in the centre of NGC 1277, similar to that found in massive early-type galaxies. Given the limited accretion history of NGC 1277, these results favour an intrinsic, in situ, process triggering star formation at later epochs. Our results suggest a general constraint on the amount of young stars in the cores of massive early-type galaxies. This amount should be assumed as an upper limit for the young stellar contribution in massive galaxies, as there might be present other contributions from evolved stars.

ABSTRACT Massive early-type galaxies (ETGs) show several strong CO absorption features in their H- and K-band spectra that cannot be explained by state-of-the-art stellar population models. For many years, the disagreement has been attributed to the presence of intermediate-age stellar components that are dominated by stars in the asymptotic giant branch phase. However, no robust evidence of this scenario has been provided so far. One way to test this claim is by comparison of CO indices for ETGs and for relic galaxies. Lacking the intermediate-age stellar populations, relic galaxies provide us with a unique opportunity to address the origin of strong CO absorptions in ETGs. Here, we utilize the prototype relic galaxy NGC 1277 and compare the CO absorption features of this galaxy with the ones of a representative sample of massive ETGs. We show that the CO lines in both systems have similar strengths, significantly stronger than the predictions of stellar population synthesis models. We conclude that intermediate-age stellar populations in massive ETGs are not the culprit of the strong CO absorptions.

We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultra-diffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii (Re), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, NGC by using sufficiently deep observations that (i) reach the turnover of the GC luminosity function and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that NGC for these galaxies is on average ∼ 20, which implies an average total mass, Mtotal, ∼ 1011 M when applying the relation between NGC and Mtotal. This value of NGC lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GC luminosity function, radial profile and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive (L∗) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models.

The leading method for the determination of relevant stellar population parameters of unresolved extragalactic Globular Clusters is through the study of their integrated spectroscopy, where Balmer line-strength indices are considered to be age sensitive. Previously, a splitting in the highly optimised spectral line-strength index Hβo was observed in a sample of Galactic globular clusters at all metallicities resulting in an apparent ‘upper branch’ and ‘lower branch’ of globular clusters in the Hβo – [MgFe] diagram. This was suggested to be caused by the presence of hot Blue straggler stars (BSSs), resulting in an underestimation of ’spectroscopic’ ages in the upper branch. Over a decade on, we look to re-evaluate these findings. We make use of new, large Galactic Globular Cluster integrated spectroscopy datasets. To produce a large, homogeneously combined sample we have considered a number of factors including the radial dependence of Balmer and metal lines. Using this new sample, in disagreement with previous work, we find the splitting in Hβo only occurs at intermediate to high metallicities ([M/H]>−1), and is not the result of an increased fraction of BSSs, but rather is due to an increased Helium abundance. We explore the possible impact of varying Helium on simple stellar population models to provide a theoretical basis for our hypothesis and then use the relationship between upper branch candidacy and enhanced Helium to predict the Helium content of three M31 clusters. We discuss what this can tell us about their mass and fraction of first generation stars.

We present a detailed chemical abundance analysis of the young massive cluster (YMC) NGC 1569-B. The host galaxy, NGC~1569, is a dwarf irregular starburst galaxy at a distance of 3.36$\pm$0.20 Mpc. We determined the abundance ratios from the analysis of an optical integrated-light spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope. We considered different red-to-blue supergiant ratios, namely: the ratio obtained from a theoretical isochrone, the ratio obtained from a resolved colour-magnitude diagram of the YMC, and the ratio that minimises the $\chi^2$ when comparing our model spectra with the observations. We adopted the latter ratio for our resulting chemical abundances. The derived iron abundance is sub-solar with [Fe/H] = $-0.74\pm0.05$. In relation to the scaled solar composition, we find enhanced $\alpha$-element abundances, $\text{[/Fe]}=+0.25\pm$0.11, with a particularly high Ti abundance of +0.49$\pm$0.05. Other super-solar elements include $\text{[Cr/Fe]}=+0.50\pm$0.11, $\text{[Sc/Fe]}=+0.78\pm$0.20, and $\text{[Ba/Fe]}=+1.28\pm$0.14, while other Fe-peak elements are close to scaled solar abundances: ($\text{[Mn/Fe]}=-0.22\pm$0.12 and $\text{[Ni/Fe]}=+0.13\pm$0.11). The composition of NGC 1569-B resembles the stellar populations of the YMC NGC 1705-1, located in a blue compact dwarf galaxy. The two YMCs agree with regard to $\alpha$-elements and the majority of the Fe-peak elements, except for Sc and Ba, which are extremely super-solar in NGC~1569-B -- and higher than in any YMC studied so far. The blue part of the optical spectrum of a young population is still a very challenging wavelength region to analyse using IL spectroscopic studies. This is due to the uncertain contribution to the light from blue supergiant stars, which can be difficult to disentangle from turn-off stars, even when resolved photometry is available.

We analyse the globular cluster (GC) systems of a sample of 15 massive, compact early-type galaxies (ETGs), 13 of which have already been identified as good relic galaxy candidates on the basis of their compact morphologies, old stellar populations and stellar kinematics. These relic galaxy candidates are likely the nearby counterparts of high redshift red nugget galaxies. Using F814W ( I) and F160W ( H) data from the WFC3 camara onboard the Hubble Space Telescope we determine the total number, luminosity function, specific frequency, colour and spatial distribution of the GC systems. We find lower specific frequencies (SN<2.5 with a median of SN=1) than ETGs of comparable mass. This is consistent with a scenario of rapid, early dissipative formation, with relatively low levels of accretion of low-mass, high-SN satellites. The GC half-number radii are compact, but follow the relations found in normal ETGs. We identify an anticorrelation between the specific angular momentum (lambda_R) of the host galaxy and the (I-H) colour distribution width of their GC systems. Assuming that lambda_R provides a measure of the degree of dissipation in massive ETGs, we suggest that the (I-H) colour distribution width can be used as a proxy for the degree of complexity of the accretion histories in these systems.

ABSTRACT There is a growing consensus that the vast majority of ultradiffuse galaxies (UDGs) are dwarf galaxies. However, there remain a few UDGs that seem to be special in terms of their globular cluster (GC) systems. In particular, according to some authors, certain UDGs exhibit large GC populations when compared to expectations from their stellar (or total) mass. Among these special UDGs, DF44 in the Coma cluster is one of the better-known examples. DF44 has been claimed to have a relatively high number of GCs, $N_{\mathrm{ GC}}=74^{+18}_{-18}$, for a stellar mass of only $3\times 10^8\, \mathrm{ M}_{ \odot}$ which would indicate a much larger dark halo mass than dwarfs of similar stellar mass. In this paper, we revisit this number and, contrary to previous results, find $N_{\mathrm{ GC}}=21^{+7}_{-9}$ assuming that the distribution of the GCs follows the same geometry as the galaxy. If we assume that the GCs around DF44 are distributed in a (projected) circularly symmetric way and, if we use a less strict criterion for the selection of the GCs, we find $N_{\mathrm{ GC}}=18^{+23}_{-12}$. Making use of the MGC–Mhalo relation, this number of GCs suggests a dark matter halo mass of $M_{\mathrm{ halo}}=1.1^{+0.4}_{-0.5} \times 10^{11} \mathrm{ M}_{\odot}$, a value which is consistent with the expected total mass for DF44 based on its velocity dispersion, $\sigma =33^{+3}_{-3}$ km s−1. We conclude that the number of GCs around DF44 is as expected for regular dwarf galaxies of similar stellar mass and DF44 is not extraordinary in this respect.

The aim of this work is to explore the potential of surface brightness fluctuations (SBF) for studying composite stellar populations (CSP). To do so, we have computed the standard (mean) and SBF spectra with E-MILES stellar population synthesis code. We have created a set of models composed by different mass fractions of two single stellar populations, as a first approximation of a CSP scenario. With these models we present an ensemble of SBF colour–colour diagnostic diagrams that reveal different secondary populations depending on the bands used. For this work we focus on those colours capable of unveiling small fractions of metal-poor components in elliptical galaxies, which are dominated by old metal-rich stellar populations. We fit a set of synthetic models and a selection of nearby elliptical galaxies to our CSP models using both mean and SBF colours. We find that the results are highly improved and return small secondary components when mean and SBF values are applied simultaneously, instead of employing them separately or as a constraint. Finally, we explore the possibility of tracking chemical enrichment histories by including in the analysis a variety of SBF colours. For this purpose we present an example where, with two different SBF colour–colour diagrams, we untangle a small contribution of a young solar population and an old metal-poor component from an old solar principal population. The results we have found are promising, but limited by the available data. We highlight the urgent need for new, better, and more consistent SBF observations.