Shuang Zhou

Aims. We present an investigation of the evolutionary pathways of green valley (GV) galaxies, defined as galaxies with a distance to the star-forming main sequence in the range −1.3 < Δ _SFMS < −0.5, drawn from the SDSS-IV/MaNGA survey. Our goal is to examine the connection between the dynamical galaxy structure, specifically, its stellar angular momentum, and its key physical properties, including gas-phase metallicity, star formation history (SFH), and chemical enrichment history (ChEH). By exploring these correlations, we aim to constrain the physical processes that govern the evolution of green valley galaxies. Methods. We divided our sample into fast- and slow-rotating galaxies using a criterion motivated by the bimodal distribution of the stellar spin and compared their integrated stellar and gas-phase metallicities. Additionally, using a simple but comprehensive galaxy chemical evolution model, optimised to fit the gas-phase metallicity estimates and the integrated stellar spectra for each galaxy, we reconstructed the past star formation and chemical enrichment histories of the galaxies. The derived SFHs and ChEHs, along with parameters governing the gas-infall timescale and outflow strengths, offer valuable insights into the physical processes driving the evolution and quenching of our GV sample galaxies. Results. We found that fast-rotating galaxies exhibit systematically higher metallicities in the gas and stellar phases compared to slow-rotating galaxies. However, in the gas phase, the difference is significant only at the low-mass end, while the stellar metallicity offset is observed consistently across the full stellar mass range. Our modelling framework yields simple but physically motivated explanations for these trends. At low stellar masses, the model predicts similar gas-infall and star formation timescales for fast- and slow-rotating galaxies, but the stronger outflows inferred for the slower population substantially reduce their chemical content in the gas and stars. At high masses, slow-rotating galaxies show shorter gas-infall and star formation timescales; the combination of a reduced pristine gas inflow and more efficient gas removal produces gas-phase metallicities that are comparable to those of fast-rotating galaxies, but systematically lower stellar metallicities. Conclusions. The systematic differences in stellar and gas-phase metallicity, as well as in model-inferred gas-accretion and outflow parameters, highlight the contrasting properties of fast- and slow-rotating galaxies in our GV sample. Interpreting these differences within our chemical evolution framework and combining evidence from theoretical studies suggests distinct past evolutions. Slow-rotating galaxies likely experienced more merger events, usually associated with strong gas removal processes, leading to their systematically lower metallicities. At low masses, stronger supernova-driven outflows reduce their chemical content while leaving star formation timescales similar to those of fast-rotating galaxies. At high masses, merger-triggered feedback from active galactic nuclei may rapidly deplete and suppress gas infall, producing the shorter star formation timescales seen in slow-rotating galaxies. Alternative environmental and assembly-driven scenarios are also discussed.

Context. The new generation of optical spectrographs, including WEAVE, 4MOST, DESI, and WST, offers huge multiplexing capabilities and excellent spectral resolution. This is an unprecedented opportunity to statistically unveil the details of the star formation histories (SFHs) of galaxies. However, these observations are not easily comparable with the predictions of cosmological simulations. Aims. Our goal is to build a reference framework for comparing spectroscopic observations with cosmological simulations and to test the currently available tools for deriving the stellar population properties of mock galaxies as well as their SFHs. We focus on the observational strategy of the Stellar Population at intermediate redshift Survey (StePS) carried out with the WEAVE instrument. Methods. We created mock datasets of ∼750 galaxies at redshifts of z = 0.3, 0.5, and 0.7 from the TNG50 cosmological simulation. We performed radiative transfer calculations using SKIRT and analyzed the spectra with the pPXF algorithm, treating them as if they were real observations. Results. This work presents the methodology used to generate the mock datasets, providing an initial exploration of stellar population properties (i.e. mass-weighted ages and metallicities) and SFHs of a test sample of three galaxies at z = 0.7 and their descendants at z = 0.5 and 0.3. We show that there is very good agreement between mock WEAVE-like spectra compared to the intrinsic values in TNG50 (average difference of 0.2 ± 0.3 Gyr). We also report that an overall agreement is seen when retrieving the SFHs of galaxies, especially if they form the bulk of their stars on short timescales and at early epochs. While we did identify a tendency to overestimate the weight of old stellar populations in galaxies with complex SFHs, we were able to properly recover the timescales on which galaxies build up 90% of their mass, with almost no difference in the measured and intrinsic cumulative SFHs over the last 4 Gyr. Conclusions. We have released the datasets concurrently with this publication of this paper, which consist of multi-wavelength imaging and spectroscopic data of ∼750 galaxies at redshift z = 0.3, 0.5, and 0.7. This work provides a fundamental bench-test for forthcoming WEAVE observations, providing the community with realistic mock spectra of galaxies that can be used to test currently available tools for deriving first-order stellar populations parameters (i.e. ages and metallicities) as well as more complex diagnostics, such as mass and SFHs.

The spectrum of a galaxy is a complicated convolution of many properties of the galaxy, such as the star formation history (SFH), initial mass function, and metallicity. Inferring galaxy properties from the observed spectrum via spectral synthesis modeling is thus challenging. In particular, a simple yet flexible model for the SFH is required to obtain unbiased inferences. In this paper, we use SFHs from the IllustrisTNG and EAGLE simulations to test SFH models in terms of their capability of describing the simulated SFHs and the spectra generated from them. In addition to some commonly used SFH models (Γ, τ, and nonparametric), we also examine a model developed from principal component analysis (PCA), trained by a set of SFHs from IllustrisTNG. We find that when using the first five principal components (eigenhistories), the PCA-based models can achieve a good balance between simplicity and accuracy. Among the models tested, the PCA-based model provides high flexibility, by capturing diverse and complex simulated SFHs. To accurately reproduce spectra generated from the simulated SFHs, it is necessary to have a degree of freedom to describe the most recent SFH (e.g., a step function covering the age of 0–0.3 Gyr). Overall, the PCA+step model performs well in capturing the diversity of SFHs and reproducing the associated spectra, suggesting it is a promising and reliable approach for spectral synthesis modeling.

This is the second paper in a series that utilizes integral field spectroscopy from MaNGA, NUV imaging from Swift/UVOT, and NIR imaging from 2MASS to investigate dust attenuation properties on kpc scales in nearby galaxies. We apply the method developed in our previous work to the updated SwiM_v4.2 catalog, and measure the optical attenuation curve and the attenuation in three NUV bands for 2487 spaxels selected from 91 galaxies with S/N> 20 and A _V > 0.25. We classify all spaxels into two subsets: star-forming (SF) regions and non-SF regions. We explore the correlations of optical opacity (A _V ) and the optical and NUV slopes of the attenuation curves (A _B /A _V and A _w2 /A _w1 ) with a broad range of stellar population and emission-line properties, including specific surface brightness of Hα emission (Σ_Hα /Σ_*), stellar age, stellar and gas-phase metallicity, and diagnostics of recent star formation history. Overall, when comparing SF and non-SF regions, we find that A _V and A _B /A _V exhibit similar correlations with all the stellar population and emission-line properties considered, while the NUV slopes in SF regions tend to be flatter than those in non-SF regions. The NUV slope A _w2 /A _w1 exhibits an anti-correlation with Σ_Hα /Σ_*, a trend that is primarily driven by the positive correlation between A _w2 /A _w1 and Σ_*. The NUV slope flattens in SF regions that contain young stellar populations and have experienced recent star formation, but it shows no obvious dependence on stellar or gas-phase metallicity. The spatially resolved dust attenuation properties exhibit no clear correlations with the inclination of host galaxies or the galactocentric distance of the regions. This finding reinforces the conclusion from Paper I that dust attenuation is primarily regulated by local processes on kpc scales or smaller, rather than by global processes at galactic scales.

Aims. We present a study of the evolution of star-forming galaxies within what is known as the Wall structure at z ∼ 0.73 in the field of the COSMOS survey. We use a sample of star-forming galaxies from a comprehensive range of environments and across a wide stellar mass range. We discuss the correlation between the environment and the galaxy’s internal properties, including its metallicity from the present-day gas-phase value and its past evolution as imprinted in its stellar populations. Methods. We measured emission-line fluxes from the stacked spectra of galaxies selected within small stellar mass bins and in different environments. These fluxes were then converted to gas-phase metallicities. In addition, we built a simple yet comprehensive galaxy chemical evolution model, which is constrained by the gas-phase metallicities, stacked spectra, and photometry of galaxies to reach a full description of the galaxies’ past star formation and chemical evolution histories in different environments. Parameters derived from best-fit models provide insights into the physical process behind the evolution. Results. We reproduce the downsizing formation of galaxies in their star formation histories and in their chemical evolution histories at z ∼ 0.73 so that more massive galaxies tend to grow their stellar mass and become enriched in metals earlier than less massive ones. In addition, the current gas-phase metallicity of a galaxy and its past evolution correlate with the environment it inhabits. Galaxies in groups, especially massive groups that have X-ray counterparts, tend to have higher gas-phase metallicities and are enriched in metals earlier than field galaxies of similar stellar mass. Galaxies in the highest stellar mass bin and located in X-ray groups exhibit a more complex and varied chemical composition. Conclusions. The evolution of a galaxy, including its star formation history and chemical enrichment history, exhibits a notable dependence on the environment where the galaxy is located. This dependence is revealed in our sample of star-forming galaxies in the Wall region at a redshift of z ∼ 0.73. Strangulation due to interactions with the group environment, leading to an early cessation of gas supply, may have driven the faster mass growth and chemical enrichment observed in group galaxies. Additionally, the removal of metal-enriched gas could play a key role in the evolution of the most massive galaxies. Alternative mechanisms other than environmental processes are also discussed.

The evolution of quiescent galaxies is driven by numerous physical processes, often considered to be related to their stellar mass and environment over cosmic time. Tracing their stellar populations can provide insight into the processes that transformed these galaxies into their observed quiescent state. In particular, higher-redshift galaxies, being younger, exhibit more pronounced relative age differences. At early stages, even small differences in age remain significant, whereas as galaxies evolve, these differences become less detectable, making it harder to trace the impact of environmental effects in the local Universe. The COSMOS Wall is a structure at z ∼ 0.73 that contains a large variety of environments, from rich and dense clusters down to field-like regions. Thus, this sample offers a great opportunity to study the effect of the environment on the quiescent galaxy population. Leveraging high-quality spectroscopic data from the LEGA-C survey, combined with the extensive photometric coverage of the COSMOS2020 catalogue, we performed a full-index and photometry fitting of 74 massive (log M_⋆/M_⊙ = 10.47) quiescent galaxies, deriving their mass-weighted ages, metallicities, and star formation timescales. We characterised the environment in three subsamples: X-ray- and non-X-ray-detected groups and a lower-density subsample similar to the average field. We find a decreasing trend in mass-weighted age with increasing environmental density, with galaxies groups ≳1 Gyr older than those in the field. Conversely, we do not find any significant difference in stellar metallicity between galaxies in X-ray and non-X-ray groups, while we find galaxies with 0.15 dex higher metallicities in the field. Our results indicate that, at z ∼ 0.7, the environment plays a crucial role in shaping the evolution of massive quiescent galaxies, noticeably affecting both their mass-weighted age and star formation timescale. These results support faster quenching mechanisms, at fixed stellar mass, in the dense X-ray-detected groups compared to the field.

We analyse a sample of massive disc galaxies selected from the fourth-generation Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory survey to investigate how the evolution of these galaxies depends on their stellar and halo masses. We applied a semi-analytic spectral fitting approach to the data from different regions in the galaxies to derive several of their key physical properties. From the best-fitting model results, together with direct observables such as morphology, colour, and the Mgb/〈Fe〉 index ratio measured within 1R_e, we find that for central galaxies both their stellar and halo masses have a significant influence in their evolution. For a given halo mass, galaxies with higher stellar mass accumulate their stellar mass and become chemically enriched earlier than those with smaller stellar mass. Furthermore, at a given stellar mass, galaxies living in more massive haloes have longer star formation time-scales and are delayed in becoming chemically enriched. In contrast, the evolution of massive satellite galaxies is mostly determined by their stellar mass. The results indicate that both the assembled halo mass and the halo assembly history impact the evolution of central galaxies. Our spatially resolved analysis indicates that only the galaxy properties in the central region (0.0–0.5R_e) show the dependencies described above. This fact supports a halo-driven formation scenario since the galaxies’ central regions are more likely to contain old stars formed along with the halo itself, keeping a memory of the halo formation process.