Main Progenitor Research Articles

Loss of ATG5 in KRT14+ cells leads to accumulated functional impairments of salivary glands via pyroptosis.

Macroautophagy/autophagy is critically involved in the process of salivary gland (SG) diseases such as xerostomia, which has a serious impact on quality of life. KRT14+ progenitor cells are found to be the main progenitors for maintaining the ductal homeostasis of the submandibular SGs. In this study, we investigated the role of ATG5 in SG KRT14+ cells in mice and humans. Human labial salivary glands (LSG) from primary Sjogren's syndrome (pSS) and non-pSS patients (normal), and submandibular glands (SMG) from Atg5flox/flox ; Krt14-Cre (cKO) mice were used. ATG5+ KRT14+ and p62+ KRT14+ cells were detected by immunofluorescence staining in LSG. TUNEL, immunofluorescence, immunohistochemistry, and western blot were performed to detect cell death in SMG. Saliva was collected in 12-week-old (12 W) and 32-week-old (32 W) mice, then the concentration of calcium and buffering capacity were detected to analyze the function of SG. We found that LSG from pSS patients showed increased p62 and decreased ATG5 in KRT14+ cells. We further revealed that in 32 W, (1) the function of salivary glands was significantly impaired in cKO mice, (2) cell death increased in cKO mice, but cl-Caspase 3 was not significantly changed, and (3) cleaved gasdermin D increased and was highly expressed in KRT14+ cells of cKO mice. After applying a pyroptosis inhibitor to 32 W mice, the reduced saliva flow rate was rescued. In addition, pyroptosis was also found in KRT14+ cells of pSS patients. Collectively, our results indicate that Atg5 deficiency would induce pyroptosis in mice SG, which could lead to functional impairments of SG.

Star formation quenching in the infall region around galaxy clusters

ABSTRACT We analyse the connection between the star formation quenching of galaxies and their location in the outskirts of clusters in the redshift range z = [0, 2] by estimating the fraction of red galaxies. More specifically, we focus on galaxies that infall isotropically from those that are infalling alongside filaments. We use a sample of galaxies obtained from the semi-analytical model of galaxy formation sag applied to the MultiDark simulation, mdpl2. In agreement with observational results, we find that the infall regions show levels of star formation that are intermediate between those of galaxies in clusters and in the field. Moreover, we show that, in the redshift range [0–0.85], the quenching of the star formation is stronger in the filamentary region than in the isotropic infall region. We also study the fraction of red galaxies as a function of the normalized distance to the cluster centre and find that, for radii R/R200 > 3, the fraction of red galaxies in the filamentary region is considerably larger than in the isotropic infall region. From the analysis of properties of the main progenitors of galaxies identified at z = 0, we find that they have different evolutionary behaviours depending on the stellar mass and environment. Our results confirm the observational findings that suggest that the infall regions of clusters play an important role in the pre-processing of galaxies along most of the evolutionary history of galaxies.

Milky Way's Eccentric Constituents with Gaia, APOGEE, and GALAH

We report the results of an unsupervised decomposition of the local stellar halo in the chemodynamical space spanned by the abundance measurements from APOGEE DR17 and GALAH DR3. In our Gaussian mixture model, only four independent components dominate the halo in the solar neighborhood, three previously known, Aurora, Splash, and Gaia-Sausage/Enceladus (GS/E), and one new, Eos. Only one of these four is of accreted origin, namely, the GS/E, thus supporting the earlier claims that the GS/E is the main progenitor of the Galactic stellar halo. We show that Aurora is entirely consistent with the chemical properties of the so-called Heracles merger. In our analysis in which no predefined chemical selection cuts are applied, Aurora spans a wide range of [Al/Fe] with a metallicity correlation indicative of a fast chemical enrichment in a massive galaxy, the young Milky Way. The new halo component dubbed Eos is classified as in situ given its high mean [Al/Fe]. Eos shows strong evolution as a function of [Fe/H], where it changes from being the closest to GS/E at its lowest [Fe/H] to being indistinguishable from the Galactic low-α population at its highest [Fe/H]. We surmise that at least some of the outer thin disk of the Galaxy started its evolution in the gas polluted by the GS/E, and Eos is evidence of this process.

Detection and genetic variation analysis of apple chlorotic leaf spot virus and apple stem grooving virus in wild apple (Malus sieversii) from Xinjiang, China

AbstractHere, we produced nucleotide and amino acid sequences of the movement protein (MP) and the coat protein (CP) genes of apple chlorotic leaf spot virus (ACLSV) and apple stem grooving virus (ASGV) from wild apple of Xinjiang, the main progenitor of the domesticated apple. Genetic variation and phylogenetics were assessed using these and previously reported sequences. Phylogenetic analysis of ACLSV nucleotide and amino acid data sets assigned some ACLSV variants to known groups and others to novel clades. In an MP‐based phylogenetic tree, ASGV sequences downloaded from GenBank and those of wild apple isolates were assigned to separate groups. A recombinant sequence was identified in a ACLSV variant (MS‐GL‐1‐c‐3) of wild apple, and both parents of the recombinant had been isolated from the same plant (GL). Two potential recombination events of ASGV (MS‐GL‐2‐g‐3 and MS‐NF‐1‐g‐3) were identified in this study. These findings may constitute a valuable basis for future studies on variability of virus genetics and pathogenicity.

Observing EAGLE galaxies with JWST: predictions for Milky Way progenitors and their building blocks

ABSTRACT We present predictions, derived from the EAGLE ΛCDM cosmological hydrodynamical simulations, for the abundance and properties of galaxies expected to be detected at high redshift by the James Webb Space Telescope (JWST). We consider the galaxy population as a whole and focus on the sub-population of progenitors of Milky Way (MW) analogues, defined to be galaxies with accretion histories similar to the MW’s, that is, galaxies that underwent a merger resembling the Gaia-Enceladus-Sausage (GES) event and that contain an analogue of the Large Magellanic Cloud (LMC) satellite today. We derive the luminosity function of all EAGLE galaxies in JWST/NIRCam passbands, in the redshift range z = 2 − 8, taking into account dust obscuration and different exposure times. For an exposure time of T = 105s, average MW progenitors are observable as far back as z ∼ 6 in most bands, and this changes to z ∼ 5 and z ∼ 4 for the GES and LMC progenitors, respectively. The progenitors of GES and LMC analogues are, on average, ∼2 and ∼1 mag fainter than the MW progenitors at most redshifts. They lie, on average, within ∼60 and 30 arcsec, respectively, of their future MW host at all times, and thus will appear within the field of view of JWST/NIRCam. We conclude that galaxies resembling the main progenitor of the MW and its major accreted components should be observable with JWST beyond redshift 2, providing a new and unique window in studying the formation history of our own galaxy.

The Unmixed Debris of Gaia-Sausage/Enceladus in the Form of a Pair of Halo Stellar Overdensities

In the first billion years after its formation, the Galaxy underwent several mergers with dwarf satellites of various masses. The debris of Gaia-Sausage/Enceladus (GSE), the galaxy responsible for the last significant merger of the Milky Way, dominates the inner halo and has been suggested to be the progenitor of both the Hercules-Aquila Cloud (HAC) and Virgo Overdensity (VOD). We combine SEGUE, APOGEE, Gaia, and StarHorse distances to characterize the chemodynamical properties and verify the link between HAC, VOD, and GSE. We find that the orbital eccentricity distributions of the stellar overdensities and GSE are comparable. We also find that they have similar, strongly peaked, metallicity distribution functions, reinforcing the hypothesis of common origin. Furthermore, we show that HAC and VOD are indistinguishable from the prototypical GSE population within all chemical-abundance spaces analyzed. All these evidences combined provide a clear demonstration that the GSE merger is the main progenitor of the stellar populations found within these halo overdensities.

#DictatorErdogan: How Social Media Bans Trigger Backlash

ABSTRACT Can authorities effectively shut down widely used social media platforms? This article theorizes that banning social media platforms with existing user bases triggers the psychological mechanism of reactance. Reactance motivates citizens to circumvent bans and ultimately results in intensified criticism of the censoring authorities on banned platforms. Reactance dynamics in response to social media bans are particularly relevant in countries with hybrid regimes – that is, regimes with both democratic and autocratic characteristics. Authorities in these countries generally allow widespread adoption of social media platforms. At the same time, they engage in temporary platform bans, usually to limit antiregime discourse at crucial political junctures such as elections. This combination of large user bases and temporary bans creates a “reactance equilibrium” in which there is high demand among citizens to access the restricted platforms. Unlike with censorship of traditional media such as television and print news outlets, the costs for citizens to circumvent social media bans are relatively low, which allows citizens to act on their reactance states. Drawing on a dataset of 15 million geolocated tweets, this article presents evidence of a censorship backlash to Turkey’s March 2014 Twitter ban, which is considered among the first attempts to block a widely adopted social media platform. A synthetic control model and descriptive statistics reveal widespread circumvention of the ban. Furthermore, sentiment analysis shows that, in the wake of the ban, Twitter discourse became increasingly negative, especially toward the ban’s main progenitor then-Prime Minister Recep Tayyip Erdogan.

Phylogeography and conservation gaps of Musa balbisiana Colla genetic diversity revealed by microsatellite markers

Collection and storage of crop wild relative (CWR) germplasm is crucial for preserving species genetic diversity and crop improvement. Nevertheless, much of the genetic variation of CWRs is absent in ex situ collections and detailed passport data are often lacking. Here, we focussed on Musa balbisiana, one of the two main progenitor species of many banana cultivars. We investigated the genetic structure of M. balbisiana across its distribution range using microsatellite markers. Accessions stored at the International Musa Germplasm Transit Centre (ITC) ex situ collection were compared with plant material collected from multiple countries and home gardens from Vietnam. Genetic structure analyses revealed that accessions could be divided into three main clusters. Vietnamese and Chinese populations were assigned to a first and second cluster respectively. A third cluster consisted of ITC and home garden accessions. Samples from Papua New Guinea were allocated to the cluster with Chinese populations but were assigned to a separate fourth cluster if the number of allowed clusters was set higher. Only one ITC accession grouped with native M. balbisiana populations and one group of ITC accessions was nearly genetically identical to home garden samples. This questioned their wild status, including accessions used as reference for wild M. balbisiana. Moreover, most ITC accessions and home garden samples were genetically distinct from wild populations. Our results highlight that additional germplasm should be collected from the native distribution range, especially from Northeast India, Myanmar, China, and the Philippines and stored for ex situ conservation at the ITC. The lack of passport data for many M. balbisiana accessions also complicates the interpretation of genetic information in relation to cultivation and historical dispersal routes.

Type 2 Diabetes Mellitus Facilitates Shift of Adipose-Derived Stem Cells Ex Vivo Differentiation toward Osteogenesis among Patients with Obesity.

Objective: Sedentary behavior with overnutrition provokes the development of obesity, insulin resistance, and type 2 diabetes mellitus (T2DM). The main progenitor cells of adipose tissue are adipose-derived stem cells (ADSCs) which can change differentiation, metabolic, and secretory phenotypes under obesity conditions. The purpose of this study was to evaluate ADSC osteogenesis activity among patients with obesity in normal glucose tolerance (NGT) and T2DM conditions. Methods: In the study, ADSCs from donors with obesity were used. After clinical characterization, all patients underwent bariatric surgery and ADSCs were isolated from subcutaneous fat biopsies. ADSCs were subjected to osteogenic differentiation, stained with Alizarin Red S, and harvested for real-time PCR and Western blotting. Cell senescence was evaluated with a β-galactosidase-activity-based assay. Results: Our results demonstrated the significantly increased calcification of ADSC on day 28 of osteogenesis in the T2DM group. These data were confirmed by the statistically significant enhancement of RUNX2 gene expression, which is a master regulator of osteogenesis. Protein expression analysis showed the increased expression of syndecan 1 and collagen I before and during osteogenesis, respectively. Moreover, T2DM ADSCs demonstrated an increased level of cellular senescence. Conclusion: We suggest that T2DM-associated cellular senescence can cause ADSC differentiation to shift toward osteogenesis, the impaired formation of new fat depots in adipose tissue, and the development of insulin resistance. The balance between ADSC adipo- and osteogenesis commitment is crucial for the determination of the metabolic fate of patients and their adipose tissue.

The eROSITA view of the Abell 3391/95 field: Case study from the Magneticum cosmological simulation

Context.Clusters of galaxies reside at the nodes of the cosmic web, interconnected by filamentary structures that contain tenuous diffuse gas, especially in the warm-hot phase. Galaxy clusters grow by mergers of smaller objects and gas that are mainly accreted through these large-scale filaments. For the first time, the large-scale cosmic structure and a long gas-emission filament have been captured by eROSITA on board the Spectrum-Roentgen-Gamma mission in a direct X-ray observation of the A3391/95 field.Aims.We investigate the assembly history of an A3391/95-like system of clusters and the thermo-chemical properties of the diffuse gas in it by connecting simulation predictions to the eROSITA observations with the aim to constrain the origin and nature of the gas in the pair-interconnecting bridge.Methods.We analysed the properties of a system resembling A3391/95, extracted from the (352h−1cMpc)3volume of the Magneticum Pathfinder cosmological simulations atz= 0.07. We tracked the main progenitors of the pair clusters and of surrounding groups back in time to study the assembly history of the system and its evolution.Results.Similarly to the observed A3391/95 system, the simulated cluster pair is embedded in a complex network of gas filaments, with structures aligned over more than 20 projected Mpc, and the whole region collapses towards the central overdense node. The spheres of influence (3 ×R200) of the two main clusters already overlap atz= 0.07, but their virial boundaries are still physically separated. The diffuse gas located in the interconnecting bridge closely reflects the warm-hot intergalactic medium, with a typical temperature of ~1 keV and an overdensityδ ~100 with respect to the mean baryon density of the Universe, and a lower enrichment level compared to the intra-cluster medium in clusters. We find that most of the bridge gas collapsed from directions roughly orthogonal to the intra-cluster gas accretion directions, and its origin is mostly unrelated to the two cluster progenitors. We find clear signatures in the surrounding groups of infall motion towards the pair, such as significant radial velocities and a slowdown of gas compared to dark matter. These findings further support the hypothesis that the Northern Clump (MCXC J0621.7-5242) cluster infalls along a cosmic gas filament towards Abell 3391 and might be merging with it.Conclusions.We conclude that in this configuration, the pair clusters of the A3391/95-like system are in a pre-merger phase and have not yet interacted. The diffuse gas in the interconnecting bridge is mostly warm filament gas and not tidally stripped cluster gas.

Newcomers and suburbanites can drive the evolution of the size–stellar mass relation of early-type galaxies in galaxy clusters

ABSTRACT At fixed stellar mass M*, the effective radius Re of massive satellite early-type galaxies (ETGs) in galaxy clusters is, on average, larger at lower redshift. We study theoretically this size evolution using the state-of-the-art cosmological simulation IllustrisTNG100: we sampled 75 simulated satellite ETGs at redshift z = 0 with M* ≥ 1010.4M⊙ belonging to the two most massive (≈1014.6M⊙) haloes of the simulation. We traced back in time the two clusters’ main progenitors and we selected their satellite ETGs at z > 0 with the same criterion adopted at z = 0. The Re–M* relation of the simulated cluster satellite ETGs, which is robustly measured out to z = 0.85, evolves similarly to the observed relation over the redshift range 0 ≲ z ≲ 0.85. In the simulation the main drivers of this evolution are the acquisition of new galaxies (‘newcomers') by the clusters and the transformation of member galaxies located at large cluster-centric distance (‘suburbanites’) at z = 0.85, which end up being massive satellite ETGs at z = 0. Though several physical processes contribute to change the population of satellite ETGs in the considered redshift interval, the shape of the stellar mass function of the simulated cluster ETGs is not significantly different at z = 0.85 and at z = 0, consistent with observations.

Mass of the dynamically hot inner stellar halo predicts the ancient accreted stellar mass

Galactic dynamical structures are fossil records of the assembly histories of galaxies. By analyzing the cosmological hydrodynamical simulation TNG50, we find that a dynamical structure that we call the “hot inner stellar halo”, defined by stars on dynamically hot orbits with circularity λz < 0.5 at 3.5 kpc < r ≲ 2 Re, is a strong indicator of the mass of accreted satellite galaxies. We find a strong correlation between the mass of this hot inner stellar halo and the total ex situ stellar mass. There is a similarly strong correlation with the stellar mass of the most massive secondary galaxy ever merged. These TNG50 correlations are compatible with those predicted by other simulations, for example by TNG100 across the whole mass range under study (galaxy stellar masses, M*, in the 1010.3 − 11.6 M⊙ range) and by EAGLE for M* ≳ 1010.6 M⊙ galaxies. This shows that our predictions are robust across different galaxy formation and feedback models and hold across a wide range of numerical resolution. The hot inner stellar halo is a product of massive and typically ancient mergers, with inner-halo stars exhibiting three main physical origins: accreted and stripped from massive satellites, dynamically heated by mergers from the bulge and/or disk in the main progenitor, and formed from star formation triggered during mergers. The mass of the hot inner stellar halo defined in this paper is a quantity that can be robustly obtained for real galaxies by applying a population-orbit superposition method to integral-field-unit spectroscopy data, out to a distance of ∼2 Re, which is possible with current observations. Hence, this paper shows that integral-field-unit observations and dynamical models of the inner regions of galaxies provide a way to quantitatively determine the mass of ancient accreted satellites.

The Metallicity Distribution Function in Outer Halo Fields of Simulated Elliptical Galaxies Compared to Observations of NGC 5128

Stellar metallicity distribution functions (MDFs) have been measured for resolved stellar populations in the outer halos of many galaxies in nearby groups. Among them, the MDF of NGC 5128, the central giant elliptical in the Centaurus group, provides essential constraints for theories of massive galaxy formation and hierarchical assembly. To investigate the formation and chemical evolution history of the outer halo of giant elliptical galaxies, we examine the chemical properties of three zoom-in high-resolution cosmological hydrodynamical simulations of an NGC 5128–like giant elliptical galaxy and compare their outer halo MDFs to the observed one of NGC 5128. Even though the simulated galaxies have different merging histories and age distributions, all predicted MDFs are in good qualitative agreement with the observed one. The median metallicity of the simulated galaxies is, on average, [M/H] = −0.41 ± 0.06 compared to the observed value of [M/H] = −0.38 ± 0.02 for NGC 5128, and the dispersion in metallicity is ∼0.77 dex for both observed and simulated galaxies. We investigate the origin of the stars ending up in the outer halo field of simulated galaxies and show that most have an “accreted” origin, formed in other small galaxies and later accreted in mergers. Only ∼15% of the stars are formed in situ within the main progenitor of the galaxy and radially migrate outward. We show that the contribution of metal-rich in situ stars is subdominant in the outer halos of our simulated galaxies but can be prominent in the inner regions.

The three hundred project: galaxy cluster mergers and their impact on the stellar component of brightest cluster galaxies

ABSTRACT Using the data set of the three hundred project, i.e. a suite of 324 hydrodynamical resimulations of cluster-sized haloes, we study galaxy cluster mergers and their effect on colour and luminosity changes of their brightest cluster galaxies (BCG). We track the main progenitor of each halo at z = 0 and search for merger situations based on its mass accretion history, defining mergers as very rapid increases in the halo mass. Based upon the evolution of the dynamical state of the cluster we define a pre- and post-merger phase. We create a list of all these events and statistically study their mass ratio and time-scales, with the former verifying that all instances are in fact major mergers. By comparing to a control sample of clusters without mergers, we study the effect mergers have on the stellar component of the BCG. Analysing the mass, age, and metallicity of the BCG stellar particles, we find that the stellar content of BCGs grows significantly during mergers and, even though the main growth mechanism is the accretion of older stars, there is even a burst in star formation induced by the merger. In our simulations, BCGs in mergers form in median around 70 per cent more stars than those normally growing, although this depends on the radius considered for defining the BCG. Regarding observable properties, we see an increase in SDSS-u luminosity of 20 per cent during mergers, accompanied by a slightly slower increase of the galaxy g − r colour as compared to the control sample.

The weak dependence of velocity dispersion on disc fractions, mass-to-light ratio, and redshift: implications for galaxy and black hole evolution

ABSTRACT Velocity dispersion (σ) is a key driver for galaxy structure and evolution. We here present a comprehensive semi-empirical approach to compute σ via detailed Jeans modelling assuming both a constant and scale-dependent mass-to-light ratio M*/L. We compare with a large sample of local galaxies from MaNGA and find that both models can reproduce the Faber–Jackson (FJ) relation and the weak dependence of σ on bulge-to-total (B/T) ratio (for B/T ≳ 0.25). The dynamical-to-stellar mass ratio within R ≲ Re can be fully accounted for by a gradient in M*/L. We then build velocity dispersion evolutionary tracks σap[M*, z] (within an aperture) along the main progenitor dark matter haloes assigning stellar masses, effective radii, and Sérsic indices via a variety of abundance matching and empirically motivated relations. We find: (1) clear evidence for downsizing in σap[M*, z] along the progenitor tracks; (2) at fixed stellar mass σ ∝ (1 + z)0.2−0.3 depending on the presence or not of a gradient in M*/L. We extract σap[M*, z] from the TNG50 hydrodynamic simulation and find very similar results to our models with constant M*/L. The increasing dark matter fraction within Re tends to flatten the σap[M*, z] along the progenitors at z ≳ 1 in constant M*/L models, while σap[M*, z] have a steeper evolution in the presence of a stellar gradient. We then show that a combination of mergers and gas accretion is likely responsible for the constant or increasing σap[M*, z] with time. Finally, our σap[M*, z] are consistent with a nearly constant and steep Mbh − σ relation at z ≲ 2, with black hole masses derived from the LX − M* relation.

Halo merger tree comparison: impact on galaxy formation models

ABSTRACT We examine the effect of using different halo finders and merger tree building algorithms on galaxy properties predicted using the galform semi-analytical model run on a high resolution, large volume dark matter simulation. The halo finders/tree builders hbt, rockstar, subfind, and VELOCI raptor differ in their definitions of halo mass, on whether only spatial or phase-space information is used, and in how they distinguish satellite and main haloes; all of these features have some impact on the model galaxies, even after the trees are post-processed and homogenized by galform. The stellar mass function is insensitive to the halo and merger tree finder adopted. However, we find that the number of central and satellite galaxies in galform does depend slightly on the halo finder/tree builder. The number of galaxies without resolved subhaloes depends strongly on the tree builder, with VELOCIraptor, a phase-space finder, showing the largest population of such galaxies. The distributions of stellar masses, cold and hot gas masses, and star formation rates agree well between different halo finders/tree builders. However, because VELOCIraptor has more early progenitor haloes, with these trees galform produces slightly higher star formation rate densities at high redshift, smaller galaxy sizes, and larger stellar masses for the spheroid component. Since in all cases these differences are small we conclude that, when all of the trees are processed so that the main progenitor mass increases monotonically, the predicted galform galaxy populations are stable and consistent for these four halo finders/tree builders.

The changing pattern of European country groups: Economic, financial, and health indicators, 2000–2015

Abstract This study compares the European country groups using economic, financial and health indicators in 2000 and 2015. The “Core” European Union (EU) countries, which are the main progenitors of the deterioration processes within the EU, have changed their cluster memberships from higher-order clusters to lower-order ones. Deposits in banks (assets) to GDP (%) and inflation at consumer prices (annual %) have played a leading role in the formation of EU country groups for 2000 and 2015. The study emphasized the importance of political cohesion and financial stance to mitigate European countries’ financial risks and welfare states.

Dancing in the void: hydrodynamical N-body simulations of the extremely metal-poor galaxy DDO 68

ABSTRACT Using hydrodynamical N-body simulations, we show that the observed structure and kinematics of the extremely metal-poor dwarf irregular galaxy DDO 68 is compatible with a merger event with at least two smaller satellite galaxies. We were able to obtain a self-consistent model that simultaneously reproduces several of its observed features, including the very asymmetric and disturbed shape of the stellar component, the overall ${\rm H\, \small {\rm I}}$ distribution and its velocity field, the arc-like stellar structure to the west, and the low surface brightness stellar stream to the north. The model implies the interaction of the main progenitor of DDO 68 with two systems with dynamical masses $7\times 10^8\, \mathrm{ M}_{\odot }$ and almost $10^8\, \mathrm{ M}_{\odot }$ – 1/20 and 1/150 times the dynamical mass of DDO 68, respectively. We show that the merger between DDO 68 and the most massive of its satellites offers a route to explain the large offset of DDO 68 from the mass–metallicity relation. Assuming that the interacting galaxies have metallicities prior to the merger compatible with those of galaxies with similar stellar masses, we provide quantitative evidence that gas mixing alone does not suffice at diluting the gas of the two components; according to our simulations, the ${\rm H\, \small {\rm II}}$ regions observed along the cometary tail trace the low metallicity of the accreted satellite rather than that of DDO 68’s main body. In this case, the mass corresponding to the low metallicity is that of the secondary body and DDO 68 becomes consistent with the mass–metallicity relation.

Hidden in the haystack: low-luminosity globular clusters towards the Milky Way bulge

ABSTRACT Recent wide-area surveys have enabled us to study the Milky Way with unprecedented detail. Its inner regions, hidden behind dust and gas, have been partially unveiled with the arrival of near-infrared (IR) photometric and spectroscopic data sets. Among recent discoveries, there is a population of low-mass globular clusters, known to be missing, especially towards the Galactic bulge. In this work, five new low-luminosity globular clusters located towards the bulge area are presented. They were discovered by searching for groups in the multidimensional space of coordinates, colours, and proper motions from the Gaia EDR3 catalogue and later confirmed with deeper VVV survey near-IR photometry. The clusters show well-defined red giant branches and, in some cases, horizontal branches with their members forming a dynamically coherent structure in proper motion space. Four of them were confirmed by spectroscopic follow-up with the MUSE instrument on the ESO VLT. Photometric parameters were derived, and when available, metallicities, radial velocities, and orbits were determined. The new clusters Gran 1 and 5 are bulge globular clusters, while Gran 2, 3 and 4 present halo-like properties. Preliminary orbits indicate that Gran 1 might be related to the Main Progenitor, or the so-called ‘low-energy’ group, while Gran 2, 3 and 5 appears to follow the Gaia-Enceladus/Sausage structure. This study demonstrates that the Gaia proper motions, combined with the spectroscopic follow-up and colour–magnitude diagrams, are required to confirm the nature of cluster candidates towards the inner Galaxy. High stellar crowding and differential extinction may hide other low-luminosity clusters.

A sparse regression approach to modelling the relation between galaxy stellar masses and their host haloes

ABSTRACT Sparse regression algorithms have been proposed as the appropriate framework to model the governing equations of a system from data, without needing prior knowledge of the underlying physics. In this work, we use sparse regression to build an accurate and explainable model of the stellar mass of central galaxies given properties of their host dark matter (DM) halo. Our data set comprises 9521 central galaxies from the EAGLE hydrodynamic simulation. By matching the host haloes to a DM-only simulation, we collect the halo mass and specific angular momentum at present time and for their main progenitors in 10 redshift bins from z = 0 to z = 4. The principal component of our governing equation is a third-order polynomial of the host halo mass, which models the stellar-mass–halo-mass relation. The scatter about this relation is driven by the halo mass evolution and is captured by second- and third-order correlations of the halo mass evolution with the present halo mass. An advantage of sparse regression approaches is that unnecessary terms are removed. Although we include information on halo specific angular momentum, these parameters are discarded by our methodology. This suggests that halo angular momentum has little connection to galaxy formation efficiency. Our model has a root mean square error (RMSE) of 0.167log10(M*/M⊙), and accurately reproduces both the stellar mass function and central galaxy correlation function of EAGLE. The methodology appears to be an encouraging approach for populating the haloes of DM-only simulations with galaxies, and we discuss the next steps that are required.