Scaling relations and baryonic cycling in local star-forming galaxies: I. The sample

Metallicity and gas content are intimately related in the baryonic exchange cycle of galaxies, and galaxy evolution scenarios can be constrained by quantifying this relation. To this end, we have compiled a sample of ∼400 galaxies in the local Universe, dubbed "MAGMA"(Metallicity And Gas for Mass Assembly), which covers an unprecedented range in parameter space, spanning more than 5 orders of magnitude in stellar mass (Mstar), star-formation rate (SFR), and gas mass (Mgas), and it has a factor of ∼60 in metallicity [Z, 12 + log(O/H)]. Stellar masses and SFRs were recalculated for all of the galaxies using IRAC, WISE, and GALEX photometry, and 12 + log(O/H) was transformed, where necessary, to a common metallicity calibration. To assess the true dimensionality of the data, we applied multidimensional principal component analyses (PCAs) to our sample. We find that even with the vast parameter space covered by MAGMA, the relations between Mstar, SFR, Z, and Mgas (MHI + MH2) require only two dimensions to describe the hypersurface, which confirms the findings of previous work. To accommodate the curvature in the Mstar-Z relation, we applied a piecewise 3D PCA that successfully predicts observed 12 + log(O/H) to an accuracy of ∼0.1 dex. MAGMA is a representative sample of isolated star-forming galaxies in the local Universe, and it can be used as a benchmark for cosmological simulations and to calibrate evolutionary trends with redshift.