The COSMOS-Wall at <i>z</i> ∼ 0.73: Star-forming galaxies and their evolution in different environments

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.