F. R. Ditrani

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.

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.

Collisional ring galaxies (RiGs) are the result of the impact between two galaxies, with one of them passing close to the centre of the other, piercing its gaseous and stellar disc. In this framework, the impact generates a shock wave front that propagates within the disc of the target galaxy soon after the encounter, producing a characteristic expanding ring-shaped structure. RiGs represent one of the most extreme environments in which we can study the physical properties of galaxies and the transformations they undergo during collisions. The paradigm RiG is the Cartwheel galaxy atz = 0.03. This galaxy has been the object of both theoretical and observational studies, but the details of the mechanisms that lead to its peculiar morphology of double rings with connecting spokes and to its physical properties are still far from clear. To shed light on the history of the Cartwheel galaxy, we performed a spatially resolved analysis as a function of galactocentric distance, exploiting spectroscopic data from VLT/MUSE observations combined with photometric data covering a large wavelength range, from the UV GALEX to the IR JWST/MIRI. Using full-index fitting of the stellar spectra, an analysis of the nebular emission, and joint full spectral and photometry fitting, we derived stellar ages, gas and stellar metallicities, and star formation histories (SFHs) in four spatially distinct regions of the galaxy. We find that, apart from the peculiar morphology, a large fraction of the Cartwheel galaxy is not affected by the recent impact from the companion bullet, and retains the characteristics of a typical spiral galaxy. On the contrary, the outer ring is strongly affected by the recent impact, and is completely dominated by stars formed not earlier than ∼400 Myr ago. Our picture suggests that the collision shock wave, while moving forward to the external region of the galaxy, drags the already formed stars, sweeping the inner areas outwards, as proposed by recent collision models. At the same time, the ages found in the external ring are older than the predicted timescale of the ring expansion after the collision.