Population Gradients Research Articles

Bioclimatic variables affect seed mass and seedling traits of four Gymnocalycium (Cactaceae) species along elevational gradients

Differences in climatic factors associated with elevation can lead to natural selection for local adaptation in species with a wide distribution range, with some regenerative characteristics changing along the gradient. Most Cactaceae species occur in heterogeneous environments, mainly in mountains. The increasing severity of environmental conditions along elevational gradients could affect seed size, influencing seedling growth. The main aims of the study were to analyse whether seed mass, and seedling size and shape are related to elevational gradients in different populations of four species of the genus Gymnocalycium and to evaluate the relationship between seed mass and bioclimatic variables. Populations of four species of Gymnocalycium (G. andreae, G. erinaceum, G. monvillei and G. mostii) were sampled; the populations were located along three different elevation gradients, with each population corresponding to an elevational class (extremes and intermediate sites). At each elevational site, mature fruits were collected and seed mass and seedling traits were measured. A shape index was calculated by dividing height by width. A value of 1 represents 'globose' seedlings, while increasing values indicate that the seedlings become 'columnar'. The Pearson correlation coefficient was calculated to analyse the relationship between seed mass and seedling size variables. Linear models were used to analyse seed size and seedling shape. First, with elevation as a predictor and then for seed mass, the 19 bioclimatic variables were extracted from WorldClim. The results show that seed mass was positively correlated with seedling shape index, and with seedling height and width. Differences in seed mass among populations were explained by the species and the gradient where they lived, as well as by the environmental variables mean temperature of the coldest quarter, precipitation of the wettest month, and precipitation of the driest month. In conclusion, the intraspecific analyses of the four Gymnocalycium species revealed that the seedling shape patterns were similar across all species in relation to elevation. However, seed mass varied with elevation differently for each species. These findings suggest that each species possesses unique characteristics that enable them to thrive in varying climatic conditions along elevational gradients.

JADES Ultrared Flattened Objects: Morphologies and Spatial Gradients in Color and Stellar Populations

One of the more surprising findings after the first year of JWST observations is the large number of spatially extended galaxies (ultrared flattened objects, or UFOs) among the optically faint galaxy (OFG) population otherwise thought to be compact. Leveraging the depth and survey area of the JWST Advanced Deep Extragalactic Survey, we extend observations of the OFG population to an additional 112 objects, 56 of which are well-resolved in F444W with effective sizes, R e > 0.″25, more than tripling previous UFO counts. These galaxies have redshifts around 2 < z < 4, high stellar masses ( log(M*/M⊙)∼10–11 ), and star formation rates around ∼100–1000 M ⊙ yr−1. Surprisingly, UFOs are red across their entire extents, which spatially resolved analysis of their stellar populations shows is due to large values of dust attenuation (typically A V > 2 mag even at large radii). Morphologically, the majority of our UFO sample tends to have low Sérsic indices (n ∼ 1) suggesting that these large, massive, OFGs have little contribution from a bulge in F444W. Further, a majority have axis ratios between 0.2 < q < 0.4, which Bayesian modeling suggests that their intrinsic shapes are consistent with being a mixture of inclined disks and prolate objects with little to no contribution from spheroids. While kinematic constraints will be needed to determine the true intrinsic shapes of UFOs, it is clear that an unexpected population of large, disky or prolate objects contributes significantly to the population of OFGs.

A Timeline of the M81 Group: Properties of the Extended Structures of M82 and NGC 3077

Mergers of and interactions between galaxies imprint a wide diversity of morphological, dynamical, and chemical characteristics in stellar halos and tidal streams. Measuring these characteristics elucidates aspects of the progenitors of the galaxies we observe today. The M81 group is the perfect galaxy group to understand the past, present, and future of a group of galaxies in the process of merging. Here, we measure the end of star formation (t 90) and metallicity ([M/H]) of the stellar halo of M82 and the eastern tidal stream of NGC 3077 to: (1) test the idea that M82 possesses a genuine stellar halo, formed before any interaction with M81; (2) determine if NGC 3077's tidal disruption is related to the star formation history in its tails; and (3) create a timeline of the assembly history of the central trio in the M81 group. We argue that M82 possesses a genuine, metal-poor ([M/H] ∼ −1.62 dex) stellar halo, formed from the merger of a small satellite galaxy roughly 6.6 Gyr ago. We also find that the stars present in NGC 3077's tails formed before tidal disruption with M81, and possess a roughly uniform metallicity as shown in S. Okamoto et al., implying that NGC 3077's progenitor had significant population gradients. Finally, we present a timeline of the central trio’s merger/interaction history.

Age and metal gradients in massive quiescent galaxies at 0.6 ≲ z ≲ 1.0: implications for quenching and assembly histories

ABSTRACT We present spatially resolved, simple stellar population equivalent ages, stellar metallicities, and abundance ratios for 456 massive ($10.3\lesssim \log (\mathrm{M}_*/\mathrm{M}_\odot)\lesssim 11.8$) quiescent galaxies at $0.6\lesssim z\lesssim 1.0$ from the Large Early Galaxy Astrophysics Census, derived using full-spectrum models. Typically, we find flat age and [Mg/Fe] gradients, and negative [Fe/H] gradients, implying iron-rich cores. We also estimate intrinsic [Fe/H] gradients via forward modelling. We examine the observed gradients in three age bins. Younger quiescent galaxies typically have negative [Fe/H] gradients and positive age gradients, possibly indicating a recent central starburst. Additionally, this finding suggests that photometrically measured flat colour gradients in young quiescent galaxies are the result of the positive age and negative metallicity gradients cancelling each other. For older quiescent galaxies, the age gradients become flat and [Fe/H] gradients weaken, though remain negative. Thus, negative colour gradients at older ages are likely driven by metallicity gradients. The diminishing age gradient may result from the starburst fading. Furthermore, the persistence of the [Fe/H] gradients may suggest that the outskirts are simultaneously built up by mergers with lower metallicity satellites. On the other hand, the gradients could be inherited from the star-forming phase, in which case mergers may not be needed to explain our findings. This work illustrates the need for resolved spectroscopy, instead of just photometry, to measure stellar population gradients. Extending these measurements to higher redshift is imperative for understanding how stellar populations in quiescent galaxies are assembled over cosmic time.

When does a parasite become a disease? eDNA unravels complex host-pathogen dynamics across environmental stress gradients in wild salmonid populations

Infectious diseases stem from disrupted interactions among hosts, parasites, and the environment. Both abiotic and biotic factors can influence infection outcomes by shaping the abundance of a parasite's infective stages, as well as the host's ability to fight infection. However, disentangling these mechanisms within natural ecosystems remains challenging. Here, combining environmental DNA analysis and niche modelling at a regional scale, we uncovered the biotic and abiotic drivers of an infectious disease of salmonid fish, triggered by the parasite Tetracapsuloides bryosalmonae. We found that the occurrence and abundance of the parasite in the water—i.e., the propagule pressure— were mainly correlated to the abundances of its two primary hosts, the bryozoan Fredericella sultana and the fish Salmo trutta, but poorly to local abiotic environmental stressors. In contrast, the occurrence and abundance of parasites within fish hosts—i.e., proxies for disease emergence—were closely linked to environmental stressors (water temperature, agricultural activities, dams), and to a lesser extent to parasite propagule pressure. These results suggest that pathogen distribution alone cannot predict the risk of disease in wildlife, and that local anthropogenic stressors may play a pivotal role in disease emergence among wild host populations, likely by modulating the hosts' immune response. Our study sheds light on the intricate interplay between biotic and abiotic factors in shaping pathogen distribution and raises concerns about the effects of global change on pathogen emergence.

Surface currents shape protist community structure across the Indo-Pacific.

Biogeographic structure in marine protist communities is shaped by a combination of dispersal potential and environmental selection. High-throughput sequencing and global sampling efforts have helped better resolve the composition and functions of these communities in the world's oceans using both molecular and visual methods. However, molecular barcoding data are critically lacking across the Indo-Pacific, a region widely considered the epicenter of marine biodiversity. To fill this gap, we characterized protist communities in four sampling regions across Indonesia that represent the latitudinal, longitudinal, and human population gradients of the region: Lombok, Wakatobi, Misool, and Waigeo. We show high spatial structuring in marine protist communities across Indonesia, and biotic factors appear to play little role in driving this observed structure. Our results appear to be driven by abiotic factors linked to surface current patterns across the Indo-Pacific as a result of: (1) a choke point in circulation at the Indonesian Throughflow leading to low diatom diversity in Lombok, Wakatobi, and Misool; (2) an increase in nutrient availability at the edge of the Halmahera Eddy in Waigeo, leading to an increase in diatom diversity; and/or (3) seasonal variations in protist communities in line with shifts in velocity of the Indonesian Throughflow. Overall, our results highlight the importance of abiotic factors in shaping protist communities on broad geographic scales over biotic, top-down pressures, such as grazing from higher trophic levels.

Stellar Metallicities and Gradients in the Isolated, Quenched Low-mass Galaxy Tucana

We measure the metallicities of 374 red giant branch (RGB) stars in the isolated, quenched dwarf galaxy Tucana using Hubble Space Telescope narrowband (F395N) calcium H and K imaging. Our sample is a factor of ∼7 larger than what is available from previous studies. Our main findings are as follows. (i) A global metallicity distribution function (MDF) with 〈[Fe/H]〉=−1.55−0.04+0.04 and σ[Fe/H]=0.54−0.03+0.03 . (ii) A metallicity gradient of −0.54 ± 0.07 dex Re−1 (−2.1 ± 0.3 dex kpc−1) over the extent of our imaging (∼2.5 R e ), which is steeper than literature measurements. Our finding is consistent with predicted gradients from the publicly available FIRE-2 simulations, in which bursty star formation creates stellar population gradients and dark matter cores. (iii) Tucana’s bifurcated RGB has distinct metallicities: a blue RGB with 〈[Fe/H]〉=−1.78−0.06+0.06 and σ[Fe/H]=0.44−0.06+0.07 and a red RGB with 〈[Fe/H]〉=−1.08−0.07+0.07 and σ[Fe/H]=0.42−0.06+0.06 . (iv) At fixed stellar mass, Tucana is more metal-rich than Milky Way satellites by ∼0.4 dex, but its blue RGB is chemically comparable to the satellites. Tucana’s MDF appears consistent with star-forming isolated dwarfs, though MDFs of the latter are not as well populated. (v) About 2% of Tucana’s stars have [Fe/H] < −3% and 20% have [Fe/H] > −1. We provide a catalog for community spectroscopic follow-up.

The TNG50-SKIRT Atlas: Wavelength dependence of the effective radius

Galaxy sizes correlate with many other important properties of galaxies, and the cosmic evolution of galaxy sizes is an important observational diagnostic for constraining galaxy evolution models. The effective radius is probably the most widely used indicator of galaxy size. We used the TNG50-SKIRT Atlas to investigate the wavelength dependence of the effective radius of galaxies at optical and near-infrared (NIR) wavelengths. We find that, on average, the effective radius in every band exceeds the stellar mass effective radius, and that this excess systematically decreases with increasing wavelength. The optical g-band (NIR Ks-band) effective radius is on average 58% (13%) larger than the stellar mass effective radius. Effective radii measured from dust-obscured images are systematically larger than those measured from dust-free images, although the effect is limited (8.7% in the g-band, 2.1% in the Ks-band). We find that stellar population gradients are the dominant factor (about 80%) in driving the wavelength dependence of the effective radius, and that differential dust attenuation is a secondary factor (20%). Comparing our results to recent observational data, we find offsets in the absolute values of the median effective radii, up to 50% for the population of blue galaxies. We find better agreement in the slope of the wavelength dependence of the effective radius, with red galaxies having a slightly steeper slope than green–blue galaxies. Comparing our effective radii with those of galaxies from the Siena Galaxy Atlas in separate bins in z-band absolute magnitude and g − z colour, we find excellent agreement for the reddest galaxies, but again significant offsets for the blue populations: up to 70% for galaxies around Mz = −21.5. This difference in median effective radius for the bluer galaxies is most probably due to intrinsic differences in the morphological structure of observed and TNG50 simulated galaxies. Finally, we find that the median effective radius in any broadband filter increases systematically with decreasing u − r colour and with increasing galaxy stellar mass, total SFR, sSFR, and dust-to-stellar-mass ratio. For the slope of the wavelength dependence of Re, however, there does not seem to be a systematic, monotonic correlation with any of these global properties.

The history of star-forming regions in the tails of six GASP jellyfish galaxies observed with the Hubble Space Telescope

Aims. In this work, we aim to characterize the stellar populations of star-forming regions detached from the stellar disks of galaxies undergoing ram-pressure stripping. Methods. Using images collected with the WFC3 camera on board of the Hubble Space Telescope, we detected stellar clumps in continuum-subtracted Hα and the ultraviolet (F275W filter); such clumps are often embedded in larger regions (star-forming complexes) detected in the optical (F606W filter). Our sample includes 347 Hα clumps, 851 F275W clumps, and 296 star-forming complexes. We modeled the photometry of these objects in five bands using BAGPIPES to obtain their stellar population parameters. Results. The median mass-weighted stellar ages are 27 Myr for Hα clumps and 39 Myr for F275W clumps and star-forming complexes, but the oldest stars in the complexes can be older than ∼300 Myr which indicates that star formation is sustained for long periods of time. Stellar masses vary from 103.5 to 107.1 M⊙, with star-forming complexes being more massive objects in the sample. Clumps and complexes found further away from the host galaxy are on average younger, less massive, and less obscured by dust. We interpret these trends as due to the effect of ram pressure in different phases of the interstellar medium. Hα clumps form a well-defined sequence in the stellar mass–SFR plane with a slope of 0.73. Some F275W clumps and star-forming complexes follow the same sequence while others stray away from it and passively age. The difference in mean stellar age between a complex and its youngest embedded clump scales with the distance between the clump and the center of the optical emission of the complex, with the most displaced clumps being hosted by the most elongated complexes. This is consistent with a fireball-like morphology, where star formation proceeds in a small portion of the complex while older stars are left behind producing a linear stellar population gradient. The stellar masses of star-forming complexes are consistent with the ones of globular clusters, but their stellar mass surface densities are lower by 2 dex, and their properties are more consistent with the population of dwarf galaxies in clusters.

Living Tool Diversity (LTD) along Environmental and Population Gradients in Shinan-gun, South Korea

To measure influences of environmental factors and population on Living Tool Diversity (LTD) in 10 islands of Shinan-gun, the number of living tools was determined. Correlation analysis, simple linear regression analysis, and principal component analysis (PCA) were performed. Results showed that coastline length and population were positively related to LTD and thus, island size and human dynamics. PCA results showed that living tools could be classified into four groups and that islands could be classified into three groups. Living tool-environmental biplot showed that: 1) the first group composed of AG tools was related to human dynamics as PO, CL, and IA; 2) the second group composed of FI tools was related to island biogeography as DM and PS; 3) the third group composed of FP tools was related to geographical coordinates as LA and LO; 4) the fourth group composed of TA, CO, BR, FS, PM, and CT had weaker correlations than other groups. Island-environmental biplot showed that: 1) the first group composed of R7 and R9 was related to AG and FP tools; 2) the second group composed of R2 was related to FI tools; and 3) the third group composed of R3, R6, R8, and R10 was related to TA, CO, BR, FS, PM, and CT tools. Regression and PCA models accounted for most of the variation of LTD by population and environmental factors across Shinan-gun islands of South Korea.

Simulating supermassive black hole mass measurements for a sample of ultramassive galaxies using ELT/HARMONI high-spatial-resolution integral-field stellar kinematics

ABSTRACT As the earliest relics of star formation episodes of the Universe, the most massive galaxies are the key to our understanding of the stellar population, cosmic structure, and supermassive black hole (SMBH) evolution. However, the details of their formation histories remain uncertain. We address these problems by planning a large survey sample of 101 ultramassive galaxies (z ≤ 0.3, |δ + 24°| &amp;lt; 45°, |b| &amp;gt; 8°), including 76 per cent ellipticals, 17 per cent lenticulars, and 7 per cent spirals brighter than MK ≤ −27 mag (stellar mass 2 × 1012 ≲ M⋆ ≲ 5 × 1012 M⊙) with ELT/HARMONI. Our sample comprises diverse galaxy environments ranging from isolated to dense-cluster galaxies. The primary goals of the project are to (1) explore the stellar dynamics inside galaxy nuclei and weigh SMBHs, (2) constrain the black hole scaling relations at the highest mass, and (3) probe the late-time assembly of these most massive galaxies through the stellar population and kinematical gradients. We describe the survey, discuss the distinct demographics and environmental properties of the sample, and simulate their HARMONI Iz-, Iz + J-, and H + K-band observations by combining the inferred stellar-mass models from Pan-STARRS observations, an assumed synthetic spectrum of stars, and SMBHs with masses estimated based on different black hole scaling relations. Our simulations produce excellent state-of-the-art integral field spectrography and stellar kinematics (ΔVrms ≲ 1.5 per cent) in a relatively short exposure time. We use these stellar kinematics in combination with the Jeans anisotropic model to reconstruct the SMBH mass and its error using a Markov chain Monte Carlo simulation. Thus, these simulations and modellings can be benchmarks to evaluate the instrument models and pipelines dedicated to HARMONI to exploit the unprecedented capabilities of ELT.

The structure and growth of ethnic neighborhoods

We introduce a new statistical definition of an immigrant ethnic neighborhood based on a choice model and using the location distribution of natives as a benchmark. We then examine the characteristics of ethnic neighborhoods in the United States using decadal census tract data from 1970 to 2010. We estimate that 43% of the foreign-born population lived in ethnic neighborhoods in 1970, increasing to 67% by 2010. Ethnic neighborhoods have lower average incomes and housing values, and a higher percentage of residents living in rental housing and commuting without a car, than other locations in the city where the same group lives. Neighborhoods vary greatly in size and the population distribution across neighborhoods within a group follows a power law. Most neighborhoods disappear within one or two decades but larger neighborhoods persist longer. Large neighborhoods have a well-defined spatial structure with negative population gradients from the center of the neighborhood and grow primarily through spatial expansion into adjacent locations.

Interpopulation variation in seed traits of five Polygonaceae

Interpopulation variability in seed traits may drive the regeneration capacity of a species to colonize different environments. In the present study, we evaluated the variation in seed physical traits (mass / size, water imbibition, shape index) and physiological traits (germination) of five Polygonaceae species. Seeds of Polygonum lapathifolium var. salicifolium, P. lapathifolium, Reynoutria japonica, Rumex trisetifer, and R. obtusifolius were collected from two or three populations in Jiujiang, China. Physical seed traits were measured before germination tests conducted under different combinations of light and temperatures. Most species had a significant variation in seed physical and physiological traits, although populations are geographically close. Interpopulation variation in seed traits appeared to be species-specific, with the highest variation for R. japonica and lowest for R. trisetifer seeds. Germination response to temperature and light conditions also varied among species and populations, being mostly inhibited in the dark treatments. The light dependence of germination can be related to the small seed size, except for the round-seeded Rumex, depending on the temperature regime. Optimal temperature ranges mainly varied from 10/20°C to 25/35°C, with significant decreases in germination percentage at both coolest and warmest extremes. Germination requirements seem to be related to altitudinal gradients in populations of P. lapathifolium and R. japonica seeds.

Wild ungulate density data generated by camera trapping in 37 European areas: first output of the European Observatory of Wildlife (EOW)

The European Observatory of Wildlife (EOW) as part of the ENETWILD project, aims to improve the European capacity for monitoring wildlife populations, implementing international standards for data collection, providing guidance on wildlife density estimation, and finally, to promote collaborative, open data networks to develop wildlife monitoring, initially focusing on terrestrial wild mammals. This report presents density estimates for species that are widely distributed (wild boar (Sus scrofa), European roe deer (Capreolus capreolus), red deer (Cervus elaphus)) by following a standardised camera trapping (CT) protocol, in 48 areas from 28 different countries in Europe, during 2022. Density values are provided for 37 areas from 20 countries, while an additional 9 locations from 8 countries are currently completing the data analysis. The EOW involved different stakeholders over most European countries, which resulted for the first time in a number of reliable (known precision) wild ungulate density estimates, from areas representing different European bioregions. These estimates are the result of a collaborative effort from the network to apply practical systematic and rigorous protocols. The results presented from the first pilot campaign of the EOW cannot be used to accurately describe wildlife population gradients and trends at European level but can be used as first baseline data for future trend analyses. Our results show data gaps, but also provide relevant insights into some of the main drivers of demographic evolution of wild ungulate populations in Europe. We will expand and improve the EOW in the future to include more representative sites. The Agouti app, including photogrammetry methods to estimate CT detection zone size and animal speed of movement using a computer vision process proved useful to reduce the workload and to improve objectivity of measurements for REM method. We discuss the results obtained by the 2022 campaign in relation to the specific objectives of the EOW and propose the next steps.

Trends in Phenolic Profiles of Achillea millefolium from Different Geographical Gradients.

The traditional widely used raw material of Achillea millefolium is currently mainly derived from wild populations, leading to diversification and uncertainty in its quality. The aim of the study was to determine the accumulation differences of phenolic compounds between geographically distant populations of Achillea millefolium from northern and southern gradients. Plant material was collected from Gaziantep and Nevşehir provinces in Turkey and from wild populations in Lithuania. A complex of nine hydroxycinnamic acids and eleven flavonoids was identified and quantified in the methanolic extracts of inflorescences, leaves, and stems using the HPLC-PDA method. Caffeoylquinic acids predominated in leaves, while inflorescences tended to prevail in flavonoids. The PCA score plot model represented the quantitative distribution pattern of phenolic compounds along a geographical gradient of populations. The content of phenolic compounds in plant materials from northern latitudes was more than twice that of plants from southern latitudes. A significant correlation of individual phenolic compounds with latitude/longitude corresponded to their differences between two countries. Differences in accumulation of caffeoylquinic acids and flavonoids revealed several intraspecific groups within A. millefolium. Our findings suggest that spatial geographical data on the distribution of phenolic compounds in A. millefolium populations could be used as a tool to find potential collection sites for high-quality raw materials.

Impact of Urban Form on CO₂ Emissions Using a STIRPAT Model: Focusing on 15 cities in South, Southeast and West Asia

The United Nations (UN) estimates that an additional 2.5 billion people will reside in urban areas by 2050. Due to rapid economic development and urbanization, urban areas are responsible for more than 70% of global greenhouse gas (GHG) emissions from final energy use. Rapid urbanization will predominantly occur in emerging nations, particularly in Asia, where more than four billion people reside, accounting for around 55% of the world’s population. However, the temporal and spatial characteristics of urban structure in emerging cities and their correlations with GHG emissions are hardly understood, despite the fact that urban form is an important determinant of urban sustainability. Given this context, the study aims to evaluate the dynamics of urban form using three key measurements—population density, Moran’s index, and population gradient coefficient—in the capital cities of South, Southeast, and West Asia and investigate how urban form affects CO₂ emissions. The study employs a modified STRIPAT (Stochastic Impacts by Regression on Population, Affluence, and Technology) model as its major framework, using panel data from 2000 to 2019 with a five-year gap. The results indicate that the evolution of urban form varies from city to city while the population density continues to increase with slight variations in Moran’s and population gradient coefficients. Considering the changes in the three indicators over time in the cities under study, it can be concluded that urbanization in the researched areas is generally getting more compact. Moran’s index is a statistically significant factor concerning CO₂ emissions, indicating that CO₂ emissions could be lowered in cities with more clustered forms. The findings of this research have major implications for urban policy-makers seeking to explain the dynamics of urban form, how it evolves in developing countries, and how CO₂ emissions are affected.

Bateman gradients reflect variation in sexual selection in a species with dynamic sex roles.

Bateman gradients, the slope of the regression of reproductive success on mating success, are among the most commonly reported measures of sexual selection. They are particularly insightful in species with reversed sex roles, where females are expected to be under sexual selection. We measured Bateman gradients in replicate experimental populations of the spermatophore gift‐giving bushcricket Kawanaphila nartee (Orthoptera: Tettigoniidae). In this species, the operational sex ratio (OSR) and thus the sex competing for mates varies depending on the availability of pollen food resources: under pollen‐limited regimens females are more competitive, whereas under pollen‐rich regimens males are more competitive. We maintained populations in enclosures with either limited or supplemented pollen and calculated Bateman gradients for males and females under both conditions. Bateman gradients were significantly positive in males, and the slope was steeper in pollen‐supplemented populations where the OSR was more male‐biased. Bateman gradients for females were shallow and nonsignificant regardless of pollen availability. Our results show that the strength of sexual selection on males can depend on environmental context. The lack of significant gradients among females may reflect experimental limitations on our ability to estimate Bateman gradients in female K nartee.

The Next Generation Virgo Cluster Survey. XXXIII. Stellar Population Gradients in the Virgo Cluster Core Globular Cluster System

We present a study of the stellar populations of globular clusters (GCs) in the Virgo Cluster core with a homogeneous spectroscopic catalog of 692 GCs within a major-axis distance R maj = 840 kpc from M87. We investigate radial and azimuthal variations in the mean age, total metallicity, [Fe/H], and α-element abundance of blue (metal-poor) and red (metal-rich) GCs using their co-added spectra. We find that the blue GCs have a steep radial gradient in [Z/H] within R maj = 165 kpc, with roughly equal contributions from [Fe/H] and [α/Fe], and flat gradients beyond. By contrast, the red GCs show a much shallower gradient in [Z/H], which is entirely driven by [Fe/H]. We use GC-tagged Illustris simulations to demonstrate an accretion scenario where more massive satellites (with more metal- and α-rich GCs) sink further into the central galaxy than less massive ones, and where the gradient flattening occurs because of the low GC occupation fraction of low-mass dwarfs disrupted at larger distances. The dense environment around M87 may also cause the steep [α/Fe] gradient of the blue GCs, mirroring what is seen in the dwarf galaxy population. The progenitors of red GCs have a narrower mass range than those of blue GCs, which makes their gradients shallower. We also explore spatial inhomogeneity in GC abundances, finding that the red GCs to the northwest of M87 are slightly more metal-rich. Future observations of GC stellar population gradients will be useful diagnostics of halo merger histories.

Stellar population gradients at cosmic noon as a constraint to the evolution of passive galaxies

Context. The radial variations of the stellar populations properties within passive galaxies at high redshift contain information about their assembly mechanisms, based on which galaxy formation and evolution scenarios may be distinguished. Aims. The aim of this work is to give constraints on massive galaxy formation scenarios through one of the first analyses of age and metallicity gradients of the stellar populations in a sample of passive galaxies at z &gt; 1.6 based on spectroscopic data from the Hubble Space Telescope. Methods. We combined G141 deep slitless spectroscopic data and F160W photometric data of the spectroscopically passive galaxies at 1.6 &lt; z &lt; 2.4 with H160 &lt; 22.0 in the field of view of the cluster JKCS 041. We extracted spectra from different zones of the galaxies, and we analysed them by fitting them with a library of synthetic templates of stellar population models to obtain estimates of the age and metallicity gradients. Results. We obtained reliable measurements of age and metallicity parameters in different spatial zones of four galaxies. We performed spatially resolved measurements in individual high-redshift galaxies without the need of peculiar situations (i.e. gravitational lensing) for the first time. All four galaxies exhibit negative metallicity gradients. Their amplitude, similar to that measured in galaxies in the local Universe, suggests that the stellar populations of passive galaxies from z ∼ 2 to z = 0 are not redistributed. Conclusions. Although the sample we analysed is small, the results we obtained suggest that the main mechanism that determines the spatial distribution of the stellar population properties within passive galaxies is constrained in the first 3 Gyr of the Universe. This is consistent with the revised monolithic scenario.

Transmission of SARS-CoV-2 in the Population Living in High- and Low-Density Gradient Areas in Dhaka, Bangladesh.

Community transmission of SARS-CoV-2 in densely populated countries has been a topic of concern from the beginning of the pandemic. Evidence of community transmission of SARS-CoV-2 according to population density gradient and socio-economic status (SES) is limited. In June–September 2020, we conducted a descriptive longitudinal study to determine the community transmission of SARS-CoV-2 in high- and low-density areas in Dhaka city. The Secondary Attack Rate (SAR) was 10% in high-density areas compared to 20% in low-density areas. People with high SES had a significantly higher level of SARS-CoV-2-specific Immunoglobulin G (IgG) antibodies on study days 1 (p = 0.01) and 28 (p = 0.03) compared to those with low SES in high-density areas. In contrast, the levels of seropositivity of SARS-CoV-2-specific Immunoglobulin M (IgM) were comparable (p > 0.05) in people with high and low SES on both study days 1 and 28 in both high- and low-density areas. Due to the similar household size, no differences in the seropositivity rates depending on the population gradient were observed. However, people with high SES showed higher seroconversion rates compared to people with low SES. As no difference was observed based on population density, the SES might play a role in SARS-CoV-2 transmission, an issue that calls for further in-depth studies to better understand the community transmission of SARS-CoV-2.