The N/O-O/H relation across different large-scale environments

The large-scale structure (LSS) of the Universe shapes galaxy evolution through its intricate web-like morphology, yet its specific influence on gas-phase chemical abundances remains uncertain. Particularly, a homogeneous comparison of the N/O-O/H relation, a tracer of the mass assembly and baryonic cycle, across distinct LSS environments has, until now, been lacking. In this study, we analyze a local SDSS galaxy sample curated within the framework of the CAVITY project—dedicated to studying void galaxies—in which galaxies are classified by their LSS environment into three groups: clusters, voids, and non-cluster/non-void (NCNV) environments (historically referred to as filaments). We extract spectroscopic emission line fluxes from the central SDSS spectra and analyze how different galaxy properties affect the scatter in the N/O-O/H relation. For that, we subtract the main N/O-O/H relation from the data and study the dependence of the resulting residuals (ξ_N/O) on a set of parameters, including stellar mass (M_∗), g-r colour, and star formation rate (SFR). We find that M_∗-related variables are the best predictors of the scatter in the N/O-O/H relation, with little influence of the recent star formation history of the galaxy. Regarding the LSS comparison, no statistically significant differences are found for void and NCNV galaxies. Cluster galaxies, however, present a N/O-O/H relation systematically lower (with ξ_N/O ~ -0.02). Consistent with this shift and with M_∗ as a good predictor of N/O-O/H deviations, we find that environmental dependences are also reflected in fundamental scaling relations: both the MZR and N/O-M_∗ relations are different for cluster galaxies. These combined results point to mechanisms in the dense intracluster medium (such as strangulation or re-accretion of metal-enriched gas) as the primary drivers of these chemical offsets for galaxies in cluster environments.

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