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

## TL;DR

This study compiles a comprehensive local galaxy sample to analyze the relationships between metallicity, gas content, stellar mass, and star formation rate, revealing that these parameters are primarily governed by two underlying dimensions.

## Contribution

The paper introduces the MAGMA sample, covering extensive parameter space, and demonstrates that galaxy properties can be effectively described by a two-dimensional hypersurface using PCA.

## Key findings

- Galaxy relations are primarily two-dimensional.
- A piecewise 3D PCA predicts metallicity with ~0.1 dex accuracy.
- MAGMA serves as a benchmark for galaxy evolution models.

## Abstract

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 a factor of ~60 in metallicity [Z, 12+log(O/H)]. Stellar masses and SFRs have been recalculated for all the galaxies using IRAC, WISE and GALEX photometry, and 12+log(O/H) has been transformed, where necessary, to a common metallicity calibration. To assess the true dimensionality of the data, we have applied multi-dimensional principal component analyses (PCAs) to our sample. In confirmation of previous work, 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. To accommodate the curvature in the Mstar-Z relation, we have applied a piecewise 3D PCA that successfully predicts observed 12+log(O/H) to an accuracy of ~0.1dex. MAGMA is a representative sample of isolated star-forming galaxies in the Local Universe, and can be used as a benchmark for cosmological simulations and to calibrate evolutionary trends with redshift.